Dissociation between the effects of damage to perirhinal cortex and area TE

Novelty preference assessed by eye tracking: A sensitive measure of impaired recognition memory in epilepsy

OBJECTIVE

Epilepsy patients often report memory deficits despite normal objective testing, suggesting that available measures are insensitive or that non-mnemonic factors are involved. The Visual Paired Comparison Task (VPCT) assesses novelty preference, the tendency to fixate on novel images rather than previously viewed items, requiring recognition memory for the "old" images. As novelty preference is a sensitive measure of hippocampal-dependent memory function, we predicted impaired VPCT performance in epilepsy patients compared to healthy controls.

METHODS

We assessed 26 healthy adult controls and 31 epilepsy patients (16 focal-onset, 13 generalized-onset, 2 unknown-onset) with the VPCT using delays of 2 or 30 s between encoding and recognition. Fifteen healthy controls and 17 epilepsy patients (10 focal-onset, 5 generalized-onset, 2 unknown-onset) completed the task at 2-, 5-, and 30-minute delays. Subjects also performed standard memory measures, including the Medical College of Georgia (MCG) Paragraph Test, California Verbal Learning Test-Second Edition (CVLT-II), and Brief Visual Memory Test-Revised (BVMT-R).

RESULTS

The epilepsy group was high functioning, with greater estimated IQ (p = 0.041), greater years of education (p = 0.034), and higher BVMT-R scores (p = 0.024) compared to controls. Both the control group and epilepsy cohort, as well as focal- and generalized-onset subgroups, had intact novelty preference at the 2- and 30-second delays (p-values ≤ 0.001) and declined at 30 min (p-values > 0.05). Only the epilepsy patients had early declines at 2- and 5-minute delays (controls with intact novelty preference at p = 0.003 and p ≤ 0.001, respectively; epilepsy groups' p-values > 0.05).

CONCLUSIONS

Memory for the "old" items decayed more rapidly in overall, focal-onset, and generalized-onset epilepsy groups. The VPCT detected deficits while standard memory measures were largely intact, suggesting that the VPCT may be a more sensitive measure of temporal lobe memory function than standard neuropsychological batteries.

Hippocampal versus cortical deletion of cholinergic receptor muscarinic 1 in mice differentially affects post-translational modifications and supramolecular assembly of respiratory chain-associated proteins, mitochondrial ultrastructure, and respiration: implications in Alzheimer's disease

Introduction: In a previous retrospective study using postmortem human brain tissues, we demonstrated that loss of Cholinergic Receptor Muscarinic 1 (CHRM1) in the temporal cortex of a subset of Alzheimer's patients was associated with poor survival, whereas similar loss in the hippocampus showed no such association. Mitochondrial dysfunction underlies Alzheimer's pathogenesis. Therefore, to investigate the mechanistic basis of our findings, we evaluated cortical mitochondrial phenotypes in Chrm1 knockout (Chrm1^-/-) mice. Cortical Chrm1 loss resulted in reduced respiration, reduced supramolecular assembly of respiratory protein complexes, and caused mitochondrial ultrastructural abnormalities. These mouse-based findings mechanistically linked cortical CHRM1 loss with poor survival of Alzheimer's patients. However, evaluation of the effect of Chrm1 loss on mouse hippocampal mitochondrial characteristics is necessary to fully understand our retrospective human tissue-based observations. This is the objective of this study. Methods: Enriched hippocampal and cortical mitochondrial fractions (EHMFs/ECMFs, respectively) derived from wild-type and Chrm1^-/- mice were used to measure respiration by quantifying real-time oxygen consumption, supramolecular assembly of oxidative phosphorylation (OXPHOS)-associated proteins by blue native polyacrylamide gel electrophoresis, post-translational modifications (PTMs) by isoelectric focusing (IEF), and mitochondrial ultrastructure by electron microscopy. Results: In contrast to our previous observations in Chrm1^-/- ECMFs, EHMFs of Chrm1^-/- mice significantly increased respiration with a concomitant increase in the supramolecular assembly of OXPHOS-associated proteins, specifically Atp5a and Uqcrc2, with no mitochondrial ultrastructural alterations. IEF of ECMFs and EHMFs from Chrm1^-/- mice showed a decrease and an increase, respectively in a negatively charged (pH∼3) fraction of Atp5a relative to the wild-type mice, with a corresponding decrease or increase in the supramolecular assembly of Atp5a and respiration indicating a tissue-specific signaling effect. Discussion: Our findings indicate that loss of Chrm1 in the cortex causes structural, and physiological alterations to mitochondria that compromise neuronal function, whereas Chrm1 loss in the hippocampus may benefit neuronal function by enhancing mitochondrial function. This brain region-specific differential effect of Chrm1 deletion on mitochondrial function supports our human brain region-based findings and Chrm1^-/- mouse behavioral phenotypes. Furthermore, our study indicates that Chrm1-mediated brain region-specific differential PTMs of Atp5a may alter complex-V supramolecular assembly which in turn regulates mitochondrial structure-function.

Visual recognition in rhesus monkeys requires area TE but not TEO

The primate visual system is often described as a hierarchical feature-conjunction pathway, whereby each level represents an increasingly complex combination of image elements, culminating in the representation of whole coherent images in anterior inferior temporal cortex. Although many models of the ventral visual stream emphasize serial feedforward processing ((Poggio T, Mutch J, Leibo J, Rosasco L, Tacchetti A. The computationalmagic of the ventral stream: sketch of a theory (and why some deep architectures work). TechRep MIT-CSAIL-TR-2012-035. MIT CSAIL, Cambridge, MA. 2012); (Yamins DLK, DiCarlo JJ. Eight open questions in the computational modeling of higher sensory cortex. Curr Opin Neurobiol. 2016:37:114-120.)), anatomical studies show connections that bypass intermediate areas and that feedback to preceding areas ((Distler C, Boussaoud D, Desimone R, Ungerleider LG. Cortical connections of inferior temporal area TEO in macaque monkeys. J Comp Neurol. 1993:334(1):125-150.); (Kravitz DJ, Saleem KS, Baker CI, Mishkin M. A new neural framework for visuospatial processing. Nat Rev Neurosci. 2011:12(4):217-230.)). Prior studies on visual discrimination and object transforms also provide evidence against a strictly feed-forward serial transfer of information between adjacent areas ((Kikuchi R, Iwai E. The locus of the posterior subdivision of the inferotemporal visual learning area in the monkey. Brain Res. 1980:198(2):347-360.); (Weiskrantz L, Saunders RC. Impairments of visual object transforms in monkeys. Brain. 1984:107(4):1033-1072.); (Kar K, DiCarlo JJ. Fast recurrent processing via ventrolateral prefrontal cortex is needed by the primate ventral stream for robust Core visual object recognition. Neuron. 2021:109(1):164-176.e5.)). Thus, we sought to investigate whether behaviorally relevant propagation of visual information is as strictly sequential as sometimes supposed. We compared the accuracy of visual recognition after selective removal of specific subregions of inferior temporal cortex-area TEO, area TE, or both areas combined. Removal of TEO alone had no detectable effect on recognition memory, whereas removal of TE alone produced a large and significant impairment. Combined removal of both areas created no additional deficit relative to removal of TE alone. Thus, area TE is critical for rapid visual object recognition, and detailed image-level visual information can reach area TE via a route other than through TEO.

DREADD-inactivation of dorsal CA1 pyramidal neurons in mice impairs retrieval of object and spatial memories

The hippocampus, a medial temporal lobe brain region, is critical for the consolidation of information from short-term memory into long-term episodic memory and for spatial memory that enables navigation. Hippocampal damage in humans has been linked to amnesia and memory loss, characteristic of Alzheimer's disease and other dementias. Numerous studies indicate that the rodent hippocampus contributes significantly to long-term memory for spatial and nonspatial information. For example, muscimol-induced depression of CA1 neuronal activity in the dorsal hippocampus impairs the encoding, consolidation, and retrieval of nonspatial object memory in mice. Here, a chemogenetic designer receptor exclusively activated by designer drugs (DREADDs) approach was used to test the selective involvement of CA1 pyramidal neurons in memory retrieval for objects and for spatial location in a cohort of male C57BL/6J mice. Activation of the inhibitory (hM4Di) DREADDs receptor expressed in CA1 neurons significantly impaired the retrieval of object memory in the spontaneous object recognition task and of spatial memory in the Morris water maze. Silencing of CA1 neuronal activity in hM4Di-expressing mice was confirmed by comparing Fos expression in vehicle- and clozapine-N-oxide-treated mice after exploration of a novel environment. Histological analyses revealed that expression of the hM4Di receptor was limited to CA1 neurons of the dorsal hippocampus. These results suggest that a common subset of CA1 neurons (i.e., those expressing hM4Di receptors) in mouse hippocampus contributed to the retrieval of long-term memory for nonspatial and spatial information. Our findings support the view that the contribution of the rodent hippocampus is like that of the primate hippocampus, specifically essential for global memory. Our results further validate mice as a suitable model system to study the neurobiological mechanisms of human episodic memory, but also in developing treatments and understanding the underlying causes of diseases affecting long-term memory, such as Alzheimer's disease.

Neuronal circuitry for recognition memory of object and place in rodent models

Rats and mice are used for studying neuronal circuits underlying recognition memory due to their ability to spontaneously remember the occurrence of an object, its place and an association of the object and place in a particular environment. A joint employment of lesions, pharmacological interventions, optogenetics and chemogenetics is constantly expanding our knowledge of the neural basis for recognition memory of object, place, and their association. In this review, we summarize current studies on recognition memory in rodents with a focus on the novel object preference, novel location preference and object-in-place paradigms. The evidence suggests that the medial prefrontal cortex- and hippocampus-connected circuits contribute to recognition memory for object and place. Under certain conditions, the striatum, medial septum, amygdala, locus coeruleus and cerebellum are also involved. We propose that the neuronal circuitry for recognition memory of object and place is hierarchically connected and constructed by different cortical (perirhinal, entorhinal and retrosplenial cortices), thalamic (nucleus reuniens, mediodorsal and anterior thalamic nuclei) and primeval (hypothalamus and interpeduncular nucleus) modules interacting with the medial prefrontal cortex and hippocampus.

Reduced left lateralized functional connectivity of the thalamic subregions between short-term and chronic insomnia disorder

The purpose of the study was to systematically investigate the structural and functional abnormalities in the subregions of the thalamus and to examine their clinical relevance in patients with short-term and chronic insomnia disorder (ID). Thirty-four patients with short-term ID, 41 patients with chronic ID, and 46 healthy controls (HCs) were recruited. Grey matter volume and seed-based resting-state functional connectivity (RSFC) were compared for each thalamic subregion (bilateral cTtha, lPFtha, mPFtha, mPMtha, Otha, Pptha, rTtha, and Stha) between the three groups. Spearman's correlation was used to estimate the associations between thalamic alterations and clinical variables. Compared with the HCs and chronic ID group, the short-term ID group exhibited lower RSFC of the left cTtha, lPFtha, Otha and Pptha with the bilateral caudate. In addition, the short-term ID group exhibited lower RSFC between the left mPFtha and left caudate in comparison with the other two groups. Convergent RSFC alterations were found in the left cTtha and Otha with the right parahippocampal gyrus in both ID groups. Moreover, a positive correlation was found for the left Otha-caudate RSFC with the Epworth sleepiness scale scores (r = 0.340, P = 0.040). Our findings suggest shared and unique RSFC alterations of certain thalamic subregions with paralimbic regions between short-term and chronic ID. These findings have implications for understanding common and specific pathophysiology of different types of ID.

Entorhinal Subfield Vulnerability to Neurofibrillary Tangles in Aging and the Preclinical Stage of Alzheimer's Disease

BACKGROUND

Neurofibrillary tangle (NFT) accumulation in the entorhinal cortex (EC) precedes the transformation from cognitive controls to mild cognitive impairment and Alzheimer's disease (AD). While tauopathy has been described in the EC before, the order and degree to which the individual subfields within the EC are engulfed by NFTs in aging and the preclinical AD stage is unknown.

OBJECTIVE

We aimed to investigate substructures within the EC to map the populations of cortical neurons most vulnerable to tau pathology in aging and the preclinical AD stage.

METHODS

We characterized phosphorylated tau (CP13) in 10 cases at eight well-defined anterior-posterior levels and assessed NFT density within the eight entorhinal subfields (described by Insausti and colleagues) at the preclinical stages of AD. We validated with immunohistochemistry and labeled the NFT density ratings on ex vivo MRIs. We measured subfield cortical thickness and reconstructed the labels as three-dimensional isosurfaces, resulting in anatomically comprehensive, histopathologically validated tau "heat maps."

RESULTS

We found the lateral EC subfields ELc, ECL, and ECs (lateral portion) to have the highest tau density in semi-quantitative scores and quantitative measurements. We observed significant stepwise higher tau from anterior to posterior levels (p < 0.001). We report an age-dependent anatomically-specific vulnerability, with all cases showing posterior tau pathology, yet older individuals displaying an additional anterior tau burden. Finally, cortical thickness of each subfield negatively correlated with respective tau scores (p < 0.05).

CONCLUSION

Our findings indicate that posterior-lateral subfields within the EC are the most vulnerable to early NFTs and atrophy in aging and preclinical AD.

Reunification of Object and View-Center Background Information in the Primate Medial Temporal Lobe

Recent work has shown that the medial temporal lobe (MTL), including the hippocampus (HPC) and its surrounding limbic cortices, plays a role in scene perception in addition to episodic memory. The two basic factors of scene perception are the object (“what”) and location (“where”). In this review, we first summarize the anatomical knowledge related to visual inputs to the MTL and physiological studies examining object-related information processed along the ventral pathway briefly. Thereafter, we discuss the space-related information, the processing of which was unclear, presumably because of its multiple aspects and a lack of appropriate task paradigm in contrast to object-related information. Based on recent electrophysiological studies using non-human primates and the existing literature, we proposed the “reunification theory,” which explains brain mechanisms which construct object-location signals at each gaze. In this reunification theory, the ventral pathway signals a large-scale background image of the retina at each gaze position. This view-center background signal reflects the first person’s perspective and specifies the allocentric location in the environment by similarity matching between images. The spatially invariant object signal and view-center background signal, both of which are derived from the same retinal image, are integrated again (i.e., reunification) along the ventral pathway-MTL stream, particularly in the perirhinal cortex. The conjunctive signal, which represents a particular object at a particular location, may play a role in scene perception in the HPC as a key constituent element of an entire scene.

Contributions of the Monkey Inferior Temporal Areas TE and TEO to Visual Categorization

The ability to categorize images is thought to depend on neural processing within the ventral visual stream. Recently, we reported that after removal of architectonic area TE, the terminal region of the ventral stream, monkeys were still able to categorize images as cats or dogs moderately well. Here, we investigate the contribution of TEO, the architectonically defined region located one step earlier than area TE in the ventral stream. Bilateral removal of TEO caused only a mild impairment in categorization. However, combined TE + TEO removal was followed by a severe, long-lasting impairment in categorization. All of the monkeys tested, including those with combined TE + TEO removals, had normal low-level visual functions, such as visual acuity. These results support the conclusion that categorization based on visual similarity is processed in parallel in TE and TEO.

When the ventral visual stream is not enough: A deep learning account of medial temporal lobe involvement in perception

The medial temporal lobe (MTL) supports a constellation of memory-related behaviors. Its involvement in perceptual processing, however, has been subject to enduring debate. This debate centers on perirhinal cortex (PRC), an MTL structure at the apex of the ventral visual stream (VVS). Here we leverage a deep learning framework that approximates visual behaviors supported by the VVS (i.e., lacking PRC). We first apply this approach retroactively, modeling 30 published visual discrimination experiments: excluding non-diagnostic stimulus sets, there is a striking correspondence between VVS-modeled and PRC-lesioned behavior, while each is outperformed by PRC-intact participants. We corroborate and extend these results with a novel experiment, directly comparing PRC-intact human performance to electrophysiological recordings from the macaque VVS: PRC-intact participants outperform a linear readout of high-level visual cortex. By situating lesion, electrophysiological, and behavioral results within a shared computational framework, this work resolves decades of seemingly inconsistent findings surrounding PRC involvement in perception.

Reconciling the object and spatial processing views of the perirhinal cortex through task-relevant unitization

The perirhinal cortex is situated on the border between sensory association cortex and the hippocampal formation. It serves an important function as a transition area between the sensory neocortex and the medial temporal lobe. While the perirhinal cortex has traditionally been associated with object coding and the "what" pathway of the temporal lobe, current evidence suggests a broader function of the perirhinal cortex in solving feature ambiguity and processing complex stimuli. Besides fulfilling functions in object coding, recent neurophysiological findings in freely moving rodents indicate that the perirhinal cortex also contributes to spatial and contextual processing beyond individual sensory modalities. Here, we address how these two opposing views on perirhinal cortex-the object-centered and spatial-contextual processing hypotheses-may be reconciled. The perirhinal cortex is consistently recruited when different features can be merged perceptually or conceptually into a single entity. Features that are unitized in these entities include object information from multiple sensory domains, reward associations, semantic features and spatial/contextual associations. We propose that the same perirhinal network circuits can be flexibly deployed for multiple cognitive functions, such that the perirhinal cortex performs similar unitization operations on different types of information, depending on behavioral demands and ranging from the object-related domain to spatial, contextual and semantic information.

Perirhinal cortex area 35 controls the functional link between the perirhinal and entorhinal-hippocampal circuitry: D-type potassium channel-mediated gating of neural propagation from the perirhinal cortex to the entorhinal-hippocampal circuitry

In several experimental conditions, neuronal excitation at the perirhinal cortex (PC) does not propagate to the entorhinal cortex (EC) due to a "wall" of inhibition, which may help to create functional coupling and un-coupling of the PC and EC in the medial temporal lobe. However, little is known regarding the coupling control process. Herein, we propose that the deep layer of area 35 in the PC plays a pivotal role in opening the gate for coupling, thus allowing the activity in the PC to propagate to the EC. Using voltage-sensitive dye imaging for the brain slices of rodents, we show that a slowly inactivating potassium conductance in this area is essential to induce excitation overtaking the inhibitory control. This coupling between the distinct neural circuits persists for at least 1 h. We elucidate further implications of this network-level plastic behavior and its mechanism.

Object Recognition Memory: Distinct Yet Complementary Roles of the Mouse CA1 and Perirhinal Cortex

While the essential contribution of the hippocampus to spatial memory is well established, object recognition memory has been traditionally attributed to the perirhinal cortex (PRh). However, the results of several studies indicate that under specific procedural conditions, temporary or permanent lesions of the hippocampus affect object memory processes as measured in the Spontaneous Object Recognition (SOR) task. The PRh and hippocampus are considered to contribute distinctly to object recognition memory based on memory strength. Allowing mice more, or less, exploration of novel objects during the encoding phase of the task (i.e., sample session), yields stronger, or weaker, object memory, respectively. The current studies employed temporary local inactivation and immunohistochemistry to determine the differential contributions of neuronal activity in PRh and the CA1 region of the hippocampus to strong and weak object memory. Temporary inactivation of the CA1 immediately after the SOR sample session impaired strong object memory but spared weak object memory; while temporary inactivation of PRh post-sample impaired weak object memory but spared strong object memory. Furthermore, mRNA transcription and de novo protein synthesis are required for the consolidation of episodic memory, and activation patterns of immediate early genes (IEGs), such as c-Fos and Arc, are linked to behaviorally triggered neuronal activation and synaptic plasticity. Analyses of c-Fos and Arc protein expression in PRh and CA1 neurons by immunohistochemistry, and of Arc mRNA by qPCR after distinct stages of SOR, provide additional support that strong object memory is dependent on CA1 neuronal activity, while weak object memory is dependent on PRh neuronal activity. Taken together, the results support the view that both PRh and CA1 are required for object memory under distinct conditions. Specifically, our results are consistent with a model that as the mouse begins to explore a novel object, information about it accumulates within PRh, and a weak memory of the object is encoded. If object exploration continues beyond some threshold, strong memory for the event of object exploration is encoded; the consolidation of which is CA1-dependent. These data serve to reconcile the dissension in the literature by demonstrating functional and complementary roles for CA1 and PRh neurons in rodent object memory.

Anatomy and Function of the Primate Entorhinal Cortex

The entorhinal cortex (EC) is a critical element of the hippocampal formation located within the medial temporal lobe (MTL) in primates. The EC has historically received attention for being the primary mediator of cortical information going into and coming from the hippocampus proper. In this review, we highlight the significance of the EC as a major player in memory processing, along with other associated structures in the primate MTL. The complex, convergent topographies of cortical and subcortical input to the EC, combined with short-range intrinsic connectivity and the selective targeting of EC efferents to the hippocampus, provide evidence for subregional specialization and integration of information beyond what would be expected if this structure were a simple conduit of information for the hippocampus. Lesion studies of the EC provide evidence implicating this region as critical for memory and the flexible use of complex relational associations between experienced events. The physiology of this structure's constituent principal cells mirrors the complexity of its anatomy. EC neurons respond preferentially to aspects of memory-dependent paradigms including object, place, and time. EC neurons also show striking spatial representations as primates explore visual space, similar to those identified in rodents navigating physical space. In this review, we highlight the great strides that have been made toward furthering our understanding of the primate EC, and we identify paths forward for future experiments to provide additional insight into the role of this structure in learning and memory.

Explicit memory and cognition in monkeys

Taxonomies of human memory, influenced heavily by Endel Tulving, make a fundamental distinction between explicit and implicit memory. Humans are aware of explicit memories, whereas implicit memories control behavior even though we are not aware of them. Efforts to understand the evolution of memory, and to use nonhuman animals to model human memory, will be facilitated by better understanding the extent to which this critical distinction exists in nonhuman animals. Work with metacognition paradigms in the past 20 years has produced a strong case for the existence of explicit memory in nonhuman primates and possibly other nonhuman animals. Clear dissociations of explicit and implicit memory by metacognition have yet to be demonstrated in nonhumans, although dissociations between memory systems by other behavioral techniques, and by brain manipulations, suggest that the explicit-implicit distinction applies to nonhumans. Neurobehavioral studies of metamemory are beginning to identify neural substrates for memory monitoring in the frontal cortex of monkeys. We have strong evidence that at least some memory systems are explicit in rhesus monkeys, but we need to learn more about the distribution of explicit processes across cognitive systems within monkeys, and across species.

Perirhinal circuits for memory processing

The perirhinal cortex (PRC) serves as the gateway to the hippocampus for episodic memory formation and plays a part in retrieval through its backward connectivity to various neocortical areas. First, I present the evidence suggesting that PRC neurons encode both experientially acquired object features and their associative relations. Recent studies have revealed circuit mechanisms in the PRC for the retrieval of cue-associated information, and have demonstrated that, in monkeys, PRC neuron-encoded information can be behaviourally read out. These studies, among others, support the theory that the PRC converts visual representations of an object into those of its associated features and initiates backward-propagating, interareal signalling for retrieval of nested associations of object features that, combined, extensionally represent the object meaning. I propose that the PRC works as the ventromedial hub of a 'two-hub model' at an apex of the hierarchy of a distributed memory network and integrates signals encoded in other downstream cortical areas that support diverse aspects of knowledge about an object.

Network Plasticity Involved in the Spread of Neural Activity Within the Rhinal Cortices as Revealed by Voltage-Sensitive Dye Imaging in Mouse Brain Slices

The rhinal cortices, such as the perirhinal cortex (PC) and the entorhinal cortex (EC), are located within the bidirectional pathway between the neocortex and the hippocampus. Physiological studies indicate that the perirhinal transmission of neocortical inputs to the EC occurs at an extremely low probability, though many anatomical studies indicated strong connections exist in the pathway. Our previous study in rat brain slices indicated that an increase in excitability in deep layers of the PC/EC border initiated the neural activity transfer from the PC to the EC. In the present study, we hypothesized that such changes in network dynamics are not incidental observations but rather due to the plastic features of the perirhinal network, which links with the EC. To confirm this idea, we analyzed the network properties of neural transmission throughout the rhinal cortices and the plastic behavior of the network by performing a single-photon wide-field optical recording technique with a voltage-sensitive dye (VSD) in mouse brain slices of the PC, the EC, and the hippocampus. The low concentration of 4-aminopyridine (4-AP; 40 μM) enhanced neural activity in the PC, which eventually propagated to the EC via the deep layers of the PC/EC border. Interestingly, washout of 4-AP was unable to reverse entorhinal activation to the previous state. This change in the network property persisted for more than 1 h. This observation was not limited to the application of 4-AP. Burst stimulation to neurons in the perirhinal deep layers also induced the same change of network property. These results indicate the long-lasting modification of physiological connection between the PC and the EC, suggesting the existence of plasticity in the perirhinal-entorhinal network.

Neonatal hippocampal lesions facilitate biconditional contextual discrimination learning in monkeys

This study examined whether selective neonatal hippocampal lesions in monkeys (Macaca mulatta), which left the surrounding cortical areas (parahippocampal cortex) intact, affect contextual learning and memory compared with controls. Monkeys were tested with an automated touch-screen apparatus so that stimuli and contextual cues could be manipulated independently of one another. The data suggest that animals with neonatal hippocampal lesions have sparing of function with regard to contextual learning and memory when (a) contextual information is irrelevant or (b) relevant for good discrimination performance, and (c) when transferring a contextual rule to new discriminations. These findings are at odds with studies examining contextual learning and memory in monkeys with selective adult-onset hippocampal lesions, and those with nonselective neonatal hippocampal lesions, which have demonstrated impairment in contextual learning and memory. Therefore, the sparing of function seen in this study may be attributable to the early nature of the damage and the plastic nature of the infant brain, as well as the intact medial temporal lobe cortical areas as a result of the lesion methodology. Specifically, by removing the hippocampus early in life, before it has begun to function, the parahippocampal (TH/TF) and perirhinal cortices and its interactions with the lateral prefrontal cortex may be able to support context processing throughout life. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Perceptual processing in the ventral visual stream requires area TE but not rhinal cortex

There is an on-going debate over whether area TE, or the anatomically adjacent rhinal cortex, is the final stage of visual object processing. Both regions have been implicated in visual perception, but their involvement in non-perceptual functions, such as short-term memory, hinders clear-cut interpretation. Here, using a two-interval forced choice task without a short-term memory demand, we find that after bilateral removal of area TE, monkeys trained to categorize images based on perceptual similarity (morphs between dogs and cats), are, on the initial viewing, badly impaired when given a new set of images. They improve markedly with a small amount of practice but nonetheless remain moderately impaired indefinitely. The monkeys with bilateral removal of rhinal cortex are, under all conditions, indistinguishable from unoperated controls. We conclude that the final stage of the integration of visual perceptual information into object percepts in the ventral visual stream occurs in area TE.

Methods matter: A primer on permanent and reversible interference techniques in animals for investigators of human neuropsychology

The study of patients with brain lesions has contributed greatly to our understanding of the biological bases of human cognition, but this approach also has several unavoidable limitations. Research that uses animal models complements and extends human neuropsychology by addressing many of these limitations. In this review, we provide an overview of permanent and reversible animal lesion techniques for researchers of human neuropsychology, with the aim of highlighting how these methods provide a valuable adjunct to behavioural, neuroimaging, physiological, and clinical investigations in humans. Research in animals has provided important lessons about how the limitations of one or more techniques, or differences in their mechanism of action, has impacted upon the understanding of brain organisation and function. These cautionary tales highlight the importance of striving for a thorough understanding of how any intereference technique works (whether in animal or human), and for how to best use animal research to clarify the precise mechanisms underlying temporary lesion methods in humans.

Manipulating memory efficacy affects the behavioral and neural profiles of deterministic learning and decision-making

When making a decision, we have to identify, collect, and evaluate relevant bits of information to ensure an optimal outcome. How we approach a given choice can be influenced by prior experience. Contextual factors and structural elements of these past decisions can cause a shift in how information is encoded and can in turn influence later decision-making. In this two-experiment study, we sought to manipulate declarative memory efficacy and decision-making in a concurrent discrimination learning task by altering the amount of information to be learned. Subjects learned correct responses to pairs of items across several repetitions of a 50- or 100-pair set and were tested for memory retention. In one experiment, this memory test interrupted learning after an initial encoding experience in order to test for early encoding differences and associate those differences with changes in decision-making. In a second experiment, we used fMRI to probe neural differences between the two list-length groups related to decision-making across learning and assessed subsequent memory retention. We found that a striatum-based system was associated with decision-making patterns when learning a longer list of items, while a medial cortical network was associated with patterns when learning a shorter list. Additionally, the hippocampus was exclusively active for the shorter list group. Altogether, these behavioral, computational, and imaging results provide evidence that multiple types of mnemonic representations contribute to experienced-based decision-making. Moreover, contextual and structural factors of the task and of prior decisions can influence what types of evidence are drawn upon during decision-making.

Different macaque models of cognitive aging exhibit task-dependent behavioral disparities

Deficits in cognitive functions that rely on the integrity of the frontal and temporal lobes are characteristic of normative human aging. Due to similar aging phenotypes and homologous cortical organization between nonhuman primates and humans, several species of macaque monkeys are used as models to explore brain senescence. These macaque species are typically regarded as equivalent models of cognitive aging, yet no direct comparisons have been made to support this assumption. Here we used adult and aged rhesus and bonnet macaques (Macaca mulatta and Macaca radiata) to characterize the effect of age on acquisition and retention of information across delays in a battery of behavioral tasks that rely on prefrontal cortex and medial temporal lobe networks. The cognitive functions that were tested include visuospatial short-term memory, object recognition memory, and object-reward association memory. In general, bonnet macaques at all ages outperformed rhesus macaques on tasks thought to rely primarily on the prefrontal cortex, and were more resilient to age-related deficits in these behaviors. On the other hand, both species were comparably impaired by age on tasks thought to preferentially engage the medial temporal lobe. Together, these results suggest that rhesus and bonnet macaques are not equivalent models of cognitive aging and highlight the value of cross-species comparisons. These observations should enable improved design and interpretation of future experiments aimed at understanding changes in cognition across the lifespan.

Current Topics Regarding the Function of the Medial Temporal Lobe Memory System

The first clear insight that the medial temporal lobe of the human brain was in fact a system of anatomically connected structures that were organized into a memory system came in 1957 from the observations by Brenda Milner of the noted amnesic patient H.M. Subsequent work in humans, monkeys, and rodents has identified all of the components of the medial temporal lobe (MTL) that formed the memory system. Currently, work is ongoing to identify the specific contributions each structure in the medial temporal lobe makes towards the formation and storage of long-term declarative memory. The historical background of this work is described including what insights the study of noted neurologic patients H.M. and E.P. provided for understanding the function of the medial temporal lobe. The development of an animal model of medial temporal lobe function is described. Additionally, the insights that lead to the understanding that the brain contains multiple, anatomically discrete, memory systems are described. Finally, three current topics of debate are addressed: First, does the perirhinal cortex exclusively support memory, or does it support both memory and higher order visual perception? Second, is there an anatomical separation between recollection and familiarity ? Third, is the organization of spatial memory different between humans and rats, or perhaps the difference is between the working memory capacities of the two species?

The Perceptual-Mnemonic/Feature Conjunction Model of Perirhinal Cortex Function

The perirhinal cortex was once thought to be “silent cortex”, virtually ignored by researchers interested in the neurobiology of learning and memory. Following studies of brain damage associated with cases of amnesia, perirhinal cortex is now widely regarded as part of a “medial temporal lobe (MTL) memory system”. This system is thought to be more or less functionally homogeneous, having a special role in declarative memory, and making little or no contribution to other functions such as perception. In the present article, we summarize an alternative view. First, we propose that components of the putative MTL system such as the hippocampus and perirhinal cortex have distinct and dissociable functions. Second, we provide evidence that the perirhinal cortex has a role in visual discrimination. In addition, we propose a specific role for perirhinal cortex in visual discrimination: the contribution of complex conjunctive representations to the solution of visual discrimination problems with a high degree of “feature ambiguity”. These proposals constitute a new view of perirhinal cortex function, one that does not assume strict modularity of function in the occipito-temporal visual stream, but replaces this idea with the notion of a hierarchical representational continuum.

Current Topics Regarding the Function of the Medial Temporal Lobe Memory System

The first clear insight that the medial temporal lobe of the human brain was in fact a system of anatomically connected structures that were organized into a memory system came in 1957 from the observations by Brenda Milner of the noted amnesic patient H.M. Subsequent work in humans, monkeys, and rodents has identified all of the components of the medial temporal lobe (MTL) that formed the memory system. Currently, work is ongoing to identify the specific contributions each structure in the medial temporal lobe makes towards the formation and storage of long-term declarative memory. The historical background of this work is described including what insights the study of noted neurologic patients H.M. and E.P. provided for understanding the function of the medial temporal lobe. The development of an animal model of medial temporal lobe function is described. Additionally, the insights that lead to the understanding that the brain contains multiple, anatomically discrete, memory systems are described. Finally, three current topics of debate are addressed: First, does the perirhinal cortex exclusively support memory, or does it support both memory and higher order visual perception? Second, is there an anatomical separation between recollection and familiarity? Third, is the organization of spatial memory different between humans and rats, or perhaps the difference is between the working memory capacities of the two species?

The Role of the Perirhinal Cortex and Hippocampus in Learning, Memory, and Perception

One traditional and long-held view of medial temporal lobe (MTL) function is that it contains a system of structures that are exclusively involved in memory, and that the extent of memory loss following MTL damage is simply related to the amount of MTL damage sustained. Indeed, human patients with extensive MTL damage are typically profoundly amnesic whereas patients with less extensive brain lesions centred upon the hippocampus typically exhibit only moderately severe anterograde amnesia. Accordingly, the latter observations have elevated the hippocampus to a particularly prominent position within the purported MTL memory system. This article reviews recent lesion studies in macaque monkeys in which the behavioural effects of more highly circumscribed lesions (than those observed to occur in human patients with MTL lesions) to different subregions of the MTL have been examined. These studies have reported new findings that contradict this concept of a MTL memory system. First, the MTL is not exclusively involved in mnemonic processes; some MTL structures, most notably the perirhinal cortex, also contribute to perception. Second, there are some forms of memory, including recognition memory, that are not always affected by selective hippocampal lesions. Third, the data support the idea that regional functional specializations exist within the MTL. For example, the macaque perirhinal cortex appears to be specialized for processing object identity whereas the hippocampus may be specialized for processing spatial and temporal relationships.

Monkey Perirhinal Cortex is Critical for Visual Memory, but not for Visual Perception: Reexamination of the Behavioural Evidence from Monkeys

Overdependence on discrimination learning paradigms to assess the function of perirhinal cortex has complicated understanding of the cognitive role of this structure. Impairments in discrimination learning can result from at least two distinct causes: (a) failure to accurately apprehend and represent the relevant stimuli, or (b) failure to form and remember associations between stimulus representations and reward. Thus, the results of discrimination learning experiments do not readily differentiate deficits in perception from deficits in learning and memory. Here I describe studies that do dissociate learning and memory from perception and show that perirhinal cortex damage impairs learning and/or memory, but not perception. Reanalysis and reconsideration of other published data call into further question the hypothesis that the monkey perirhinal cortex plays a critical role in visual perception.

Attenuated Activity across Multiple Cell Types and Reduced Monosynaptic Connectivity in the Aged Perirhinal Cortex

The perirhinal cortex (PER), which is critical for associative memory and stimulus discrimination, has been described as a wall of inhibition between the neocortex and hippocampus. With advanced age, rats show deficits on PER-dependent behavioral tasks and fewer PER principal neurons are activated by stimuli, but the role of PER interneurons in these altered circuit properties in old age has not been characterized. In the present study, PER neurons were recorded while rats traversed a circular track bidirectionally in which the track was either empty or contained eight novel objects evenly spaced around the track. Putative interneurons were discriminated from principal cells based on the autocorrelogram, waveform parameters, and firing rate. While object modulation of interneuron firing was observed in both young and aged rats, PER interneurons recorded from old animals had lower firing rates compared with those from young animals. This difference could not be accounted for by differences in running speed, as the firing rates of PER interneurons did not show significant velocity modulation. Finally, in the aged rats, relative to young rats, there was a significant reduction in detected excitatory and inhibitory monosynaptic connections. Together these data suggest that with advanced age there may be reduced afferent drive from excitatory cells onto interneurons that may compromise the wall of inhibition between the hippocampus and cortex. This circuit dysfunction could erode the function of temporal lobe networks and ultimately contribute to cognitive aging.SIGNIFICANCE STATEMENT We report that lower firing rates observed in aged perirhinal cortical principal cells are associated with weaker interneuron activity and reduced monosynaptic coupling between excitatory and inhibitory cells. This is likely to affect feedforward inhibition from the perirhinal to the entorhinal cortex that gates the flow of information to the hippocampus. This is significant because cognitive dysfunction in normative and pathological aging has been linked to hyperexcitability in the aged CA3 subregion of the hippocampus in rats, monkeys, and humans. The reduced inhibition in the perirhinal cortex reported here could contribute to this circuit imbalance, and may be a key point to consider for therapeutic interventions aimed at restoring network function to optimize cognition.

Interaction between age and perceptual similarity in olfactory discrimination learning in F344 rats: relationships with spatial learning

Emerging evidence suggests that aging is associated with a reduced ability to distinguish perceptually similar stimuli in one's environment. As the ability to accurately perceive and encode sensory information is foundational for explicit memory, understanding the neurobiological underpinnings of discrimination impairments that emerge with advancing age could help elucidate the mechanisms of mnemonic decline. To this end, there is a need for preclinical approaches that robustly and reliably model age-associated perceptual discrimination deficits. Taking advantage of rodents' exceptional olfactory abilities, the present study applied rigorous psychophysical techniques to the evaluation of discrimination learning in young and aged F344 rats. Aging did not influence odor detection thresholds or the ability to discriminate between perceptually distinct odorants. In contrast, aged rats were disproportionately impaired relative to young on problems that required discriminations between perceptually similar olfactory stimuli. Importantly, these disproportionate impairments in discrimination learning did not simply reflect a global learning impairment in aged rats, as they performed other types of difficult discriminations on par with young rats. Among aged rats, discrimination deficits were strongly associated with spatial learning deficits. These findings reveal a new, sensitive behavioral approach for elucidating the neural mechanisms of cognitive decline associated with normal aging.

Neural signatures of experience-based improvements in deterministic decision-making

Feedback about our choices is a crucial part of how we gather information and learn from our environment. It provides key information about decision experiences that can be used to optimize future choices. However, our understanding of the processes through which feedback translates into improved decision-making is lacking. Using neuroimaging (fMRI) and cognitive models of decision-making and learning, we examined the influence of feedback on multiple aspects of decision processes across learning. Subjects learned correct choices to a set of 50 word pairs across eight repetitions of a concurrent discrimination task. Behavioral measures were then analyzed with both a drift-diffusion model and a reinforcement learning model. Parameter values from each were then used as fMRI regressors to identify regions whose activity fluctuates with specific cognitive processes described by the models. The patterns of intersecting neural effects across models support two main inferences about the influence of feedback on decision-making. First, frontal, anterior insular, fusiform, and caudate nucleus regions behave like performance monitors, reflecting errors in performance predictions that signal the need for changes in control over decision-making. Second, temporoparietal, supplementary motor, and putamen regions behave like mnemonic storage sites, reflecting differences in learned item values that inform optimal decision choices. As information about optimal choices is accrued, these neural systems dynamically adjust, likely shifting the burden of decision processing from controlled performance monitoring to bottom-up, stimulus-driven choice selection. Collectively, the results provide a detailed perspective on the fundamental ability to use past experiences to improve future decisions.

Medial prefrontal-perirhinal cortical communication is necessary for flexible response selection

The ability to use information from the physical world to update behavioral strategies is critical for survival across species. The prefrontal cortex (PFC) supports behavioral flexibility; however, exactly how this brain structure interacts with sensory association cortical areas to facilitate the adaptation of response selection remains unknown. Given the role of the perirhinal cortex (PER) in higher-order perception and associative memory, the current study evaluated whether PFC-PER circuits are critical for the ability to perform biconditional object discriminations when the rule for selecting the rewarded object shifted depending on the animal's spatial location in a 2-arm maze. Following acquisition to criterion performance on an object-place paired association task, pharmacological blockade of communication between the PFC and PER significantly disrupted performance. Specifically, the PFC-PER disconnection caused rats to regress to a response bias of selecting an object on a particular side regardless of its identity. Importantly, the PFC-PER disconnection did not interfere with the capacity to perform object-only or location-only discriminations, which do not require the animal to update a response rule across trials. These findings are consistent with a critical role for PFC-PER circuits in rule shifting and the effective updating of a response rule across spatial locations.

Getting directions from the hippocampus: The neural connection between looking and memory

Investigations into the neural basis of memory in human and non-human primates have focused on the hippocampus and associated medial temporal lobe (MTL) structures. However, how memory signals from the hippocampus affect motor actions is unknown. We propose that approaching this question through eye movement, especially by assessing the changes in looking behavior that occur with experience, is a promising method for exposing neural computations within the hippocampus. Here, we review how looking behavior is guided by memory in several ways, some of which have been shown to depend on the hippocampus, and how hippocampal neural signals are modulated by eye movements. Taken together, these findings highlight the need for future research on how MTL structures interact with the oculomotor system. Probing how the hippocampus reflects and impacts motor output during looking behavior renders a practical path to advance our understanding of the hippocampal memory system.

True alignment of preclinical and clinical research to enhance success in CNS drug development: a review of the current evidence

Central nervous system pharmacological research and development has reached a critical turning point. Patients suffering from disorders afflicting the central nervous system are numerous and command significant attention from the pharmaceutical industry. However, given the numerous failures of promising drugs, many companies are no longer investing in or, indeed, are divesting from this therapeutic area. Central nervous system drug development must change in order to develop effective therapies to treat these patients. Preclinical research is a cornerstone of drug development; however, it is frequently criticised for its lack of predictive validity. Animal models and assays can be shown to be more predictive than reported and, on many occasions, the lack of thorough preclinical testing is potentially to blame for some of the clinical failures. Important factors such as translational aspects, nature of animal models, variances in acute versus chronic dosing, development of add-on therapies and understanding of the full dose-response relationship are too often neglected. Reducing the attrition rate in central nervous system drug development could be achieved by addressing these important questions before novel compounds enter the clinical phase. This review illustrates the relevance of employing these criteria to translational central nervous system research, better to ensure success in developing new drugs in this therapeutic area.

Monkey׳s short-term auditory memory nearly abolished by combined removal of the rostral superior temporal gyrus and rhinal cortices

While monkeys easily acquire the rules for performing visual and tactile delayed matching-to-sample, a method for testing recognition memory, they have extraordinary difficulty acquiring a similar rule in audition. Another striking difference between the modalities is that whereas bilateral ablation of the rhinal cortex (RhC) leads to profound impairment in visual and tactile recognition, the same lesion has no detectable effect on auditory recognition memory (Fritz et al., 2005). In our previous study, a mild impairment in auditory memory was obtained following bilateral ablation of the entire medial temporal lobe (MTL), including the RhC, and an equally mild effect was observed after bilateral ablation of the auditory cortical areas in the rostral superior temporal gyrus (rSTG). In order to test the hypothesis that each of these mild impairments was due to partial disconnection of acoustic input to a common target (e.g., the ventromedial prefrontal cortex), in the current study we examined the effects of a more complete auditory disconnection of this common target by combining the removals of both the rSTG and the MTL. We found that the combined lesion led to forgetting thresholds (performance at 75% accuracy) that fell precipitously from the normal retention duration of ~30 to 40s to a duration of ~1 to 2s, thus nearly abolishing auditory recognition memory, and leaving behind only a residual echoic memory. This article is part of a Special Issue entitled SI: Auditory working memory.

Mild Perceptual Categorization Deficits Follow Bilateral Removal of Anterior Inferior Temporal Cortex in Rhesus Monkeys

In primates, visual recognition of complex objects depends on the inferior temporal lobe. By extension, categorizing visual stimuli based on similarity ought to depend on the integrity of the same area. We tested three monkeys before and after bilateral anterior inferior temporal cortex (area TE) removal. Although mildly impaired after the removals, they retained the ability to assign stimuli to previously learned categories, e.g., cats versus dogs, and human versus monkey faces, even with trial-unique exemplars. After the TE removals, they learned in one session to classify members from a new pair of categories, cars versus trucks, as quickly as they had learned the cats versus dogs before the removals. As with the dogs and cats, they generalized across trial-unique exemplars of cars and trucks. However, as seen in earlier studies, these monkeys with TE removals had difficulty learning to discriminate between two simple black and white stimuli. These results raise the possibility that TE is needed for memory of simple conjunctions of basic features, but that it plays only a small role in generalizing overall configural similarity across a large set of stimuli, such as would be needed for perceptual categorical assignment.

SIGNIFICANCE STATEMENT

The process of seeing and recognizing objects is attributed to a set of sequentially connected brain regions stretching forward from the primary visual cortex through the temporal lobe to the anterior inferior temporal cortex, a region designated area TE. Area TE is considered the final stage for recognizing complex visual objects, e.g., faces. It has been assumed, but not tested directly, that this area would be critical for visual generalization, i.e., the ability to place objects such as cats and dogs into their correct categories. Here, we demonstrate that monkeys rapidly and seemingly effortlessly categorize large sets of complex images (cats vs dogs, cars vs trucks), surprisingly, even after removal of area TE, leaving a puzzle about how this generalization is done.

Neural representation for object recognition in inferotemporal cortex

We suggest that population representation of objects in inferotemporal cortex lie on a continuum between a purely structural, parts-based description and a purely holistic description. The intrinsic dimensionality of object representation is estimated to be around 100, perhaps with lower dimensionalities for object representations more toward the holistic end of the spectrum. Cognitive knowledge in the form of semantic information and task information feed back to inferotemporal cortex from perirhinal and prefrontal cortex respectively, providing high-level multimodal-based expectations that assist in the interpretation of object stimuli. Integration of object information across eye movements may also contribute to object recognition through a process of active vision.

Object and spatial memory after neonatal perirhinal lesions in monkeys

The contribution of the perirhinal cortex (PRh) to recognition memory is well characterized in adults, yet the same lesions have limited effect on recognition of spatial locations. Here, we assessed whether the same outcomes will follow when perirhinal lesions are performed in infancy. Monkeys with neonatal perirhinal (Neo-PRh) lesions and control animals were tested in three operant recognition tasks as they reached adulthood: Delayed Nonmatching-to-Sample (DNMS) and Object Memory Span (OMS), measuring object recognition, and Spatial Memory Span (SMS), measuring recognition of spatial locations. Although Neo-PRh lesions did not impact acquisition of the DNMS rule, they did impair performance when the delays were extended from 30s to 600s. In contrast, the same neonatal lesions had no impact on either the object or spatial memory span tasks, suggesting that the lesions impacted the maintenance of information across longer delays and not memory capacity. Finally, the magnitude of recognition memory impairment after the Neo-PRh lesions was similar to that previously observed after adult-onset perirhinal lesions, indicating minimal, or no, functional compensation after the early PRh lesions. Overall, the results indicate that the PRh is a cortical structure that is important for the normal development of mechanisms supporting object recognition memory. Its contribution may be relevant to the memory impairment observed with human cases of temporal lobe epilepsy without hippocampal sclerosis, but not to the memory impairment found in developmental amnesia cases.

Brain Imaging, Cognitive Processes, and Brain Networks

The recent, rapid expansion of the application of neuroimaging techniques to a broad variety of questions about the structure and function of mind and brain has led to much necessary and often critical introspection about what these techniques can actually tell us about cognitive processes. In this article, we attempt to place neuroimaging within the broader context of the cognitive neuroscience approach, which emphasizes the benefits of converging methodologies for understanding cognition and how it is supported by the functioning of the brain. Our arguments for what neuroimaging has to offer are supported by two specific examples from research on memory that, we believe, show how neuroimaging data have provided unique insights not only into brain organization, but also into the organization of the mind.

The development of hippocampal-dependent memory functions: Theoretical comments on Jabès and Nelson review (2015)

Studies investigating the development of memory processes and their neural substrates have flourished over the last two decades. The review by Jabès and Nelson (2015) adds an important piece to our understanding of the maturation of different elements and circuits within the hippocampal system and their association with the progressive development of hippocampal-dependent memory processes in humans. In this accompanying commentary, we explore some additional connections between the nonhuman primate work and the human data, and take the opportunity to highlight some common and additional interpretations of the results. This commentary makes three points: (1) the recognition processes present in the first few days of life may be linked to the early maturation of the medial temporal cortical areas instead of, or in addition to, the early maturation of the subiculum; (2) recent findings on the differential protracted maturation of spatial relational memory processes in monkeys further support the notion proposed by Jabès and Nelson that this protracted development may reflect progressive maturation of the CA1 field of the hippocampus followed by further maturation of CA3/dentate gyrus; (3) finally, further considerations of the differential maturation of the longitudinal hippocampal axis and of the diencephalon are proposed as additional contributors to the refinement of episodic memory functions during development.

Blockade of glutamatergic transmission in perirhinal cortex impairs object recognition memory in macaques

The perirhinal cortex (PRc) is essential for visual recognition memory, as shown by electrophysiological recordings and lesion studies in a variety of species. However, relatively little is known about the functional contributions of perirhinal subregions. Here we used a systematic mapping approach to identify the critical subregions of PRc through transient, focal blockade of glutamate receptors by intracerebral infusion of kynurenic acid. Nine macaques were tested for visual recognition memory using the delayed nonmatch-to-sample task. We found that inactivation of medial PRc (consisting of Area 35 together with the medial portion of Area 36), but not lateral PRc (the lateral portion of Area 36), resulted in a significant delay-dependent impairment. Significant impairment was observed with 30 and 60 s delays but not with 10 s delays. The magnitude of impairment fell within the range previously reported after PRc lesions. Furthermore, we identified a restricted area located within the most anterior part of medial PRc as critical for this effect. Moreover, we found that focal blockade of either NMDA receptors by the receptor-specific antagonist AP-7 or AMPA receptors by the receptor-specific antagonist NBQX was sufficient to disrupt object recognition memory. The present study expands the knowledge of the role of PRc in recognition memory by identifying a subregion within this area that is critical for this function. Our results also indicate that, like in the rodent, both NMDA and AMPA-mediated transmission contributes to object recognition memory.

The recognition of a novel-object in a novel context leads to hippocampal and parahippocampal c-Fos involvement

Contextual memory implies recognition based on the association between past and present events experienced. It is important for daily functioning and dysfunctional in many neuropsychological disturbances. The network related to this memory is still open for debate, even though it has been associated with medial temporal lobe regions, including the perirhinal, entorhinal and temporal association cortices, as well as the hippocampus and prefrontal cortex. Our work tries to elucidate whether a change in the context, such as differences in the amount of stimuli presented on the walls and floor of an open field during object exploration, affects the recognition of an object that has been experienced before, and whether this context manipulation could be linked to changes in c-Fos expression. For this purpose, we used a one-trial novel-object recognition task. The animals were divided into two different experimental conditions; in the OR-NORMAL group, the sample and probe test were performed in the same context. However, in the OR-CONTEXT group, the probe test was performed in a different context. Our results showed that the OR-NORMAL group presented a greater exploration of objects than the OR-CONTEXT group. However, both groups presented significant exploration of the novel object. To label the brain regions involved in novel-object recognition under these conditions, we marked the expression of c-Fos protein. Results suggest that a neural circuit that includes the hippocampus, entorhinal and temporal association cortices is involved in the recognition of the novel-object in a novel context.

Hippocampus, perirhinal cortex, and complex visual discriminations in rats and humans

Structures in the medial temporal lobe, including the hippocampus and perirhinal cortex, are known to be essential for the formation of long-term memory. Recent animal and human studies have investigated whether perirhinal cortex might also be important for visual perception. In our study, using a simultaneous oddity discrimination task, rats with perirhinal lesions were impaired and did not exhibit the normal preference for exploring the odd object. Notably, rats with hippocampal lesions exhibited the same impairment. Thus, the deficit is unlikely to illuminate functions attributed specifically to perirhinal cortex. Both lesion groups were able to acquire visual discriminations involving the same objects used in the oddity task. Patients with hippocampal damage or larger medial temporal lobe lesions were intact in a similar oddity task that allowed participants to explore objects quickly using eye movements. We suggest that humans were able to rely on an intact working memory capacity to perform this task, whereas rats (who moved slowly among the objects) needed to rely on long-term memory.

In search of a recognition memory engram

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The role of the perirhinal cortex in familiarity discrimination is reviewed.

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Behavioural, pharmacological and electrophysiological evidence is considered.

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The cortex is found to be essential for memory acquisition, retrieval and storage.

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The evidence indicates that perirhinal synaptic weakening is critically involved.

A large body of data from human and animal studies using psychological, recording, imaging, and lesion techniques indicates that recognition memory involves at least two separable processes: familiarity discrimination and recollection. Familiarity discrimination for individual visual stimuli seems to be effected by a system centred on the perirhinal cortex of the temporal lobe. The fundamental change that encodes prior occurrence within the perirhinal cortex is a reduction in the responses of neurones when a stimulus is repeated. Neuronal network modelling indicates that a system based on such a change in responsiveness is potentially highly efficient in information theoretic terms. A review is given of findings indicating that perirhinal cortex acts as a storage site for recognition memory of objects and that such storage depends upon processes producing synaptic weakening.

Effects of Separate or Combined Neonatal Damage to the Orbital Frontal Cortex and the Inferior Convexity on Object Recognition in Monkeys

Unlike adult damage, neonatal damage to the inferior prefrontal convexity (IC) in monkeys spares learning and performance on the delayed nonmatching-to-sample (DNMS) task ( Málková et al. 2000). We investigated whether this sparing was due to compensation by undamaged orbital frontal cortex (O), an area also critical for DNMS, by comparing combined IC and O damage (Neo-ICO) with damage to O alone (Neo-O). Group Neo-ICO was impaired on DNMS learning at 3 months and 2 years of age. In contrast, Group Neo-O was impaired at 3 months, but recovered this function by 2 years, compared with Neo-IC and controls (N). We propose that the intact IC assumed the function of learning the DNMS rule for Group Neo-O. The persistent impairment after Neo-ICO lesions suggests that whereas O may likely support the rule acquisition in the absence of IC, no compensatory mechanisms are available after the combined damage. For the memory of lists of items, all groups were impaired at 3 months. At 2 years, the performance of Groups N and Neo-IC dramatically improved, whereas that of groups with O damage (Neo-O and Neo-ICO) remained impaired, indicating a critical role for O in recognition memory that cannot be substituted by another area.

The neural representation of 3-dimensional objects in rodent memory circuits

Three-dimensional objects are common stimuli that rodents and other animals encounter in the natural world that contribute to the associations that are the hallmark of explicit memory. Thus, the use of 3-dimensional objects for investigating the circuits that support associative and episodic memories has a long history. In rodents, the neural representation of these types of stimuli is a polymodal process and lesion data suggest that the perirhinal cortex, an area of the medial temporal lobe that receives afferent input from all sensory modalities, is particularly important for integrating sensory information across modalities to support object recognition. Not surprisingly, recent data from in vivo electrophysiological recordings have shown that principal cells within the perirhinal cortex are activated at locations of an environment that contain 3-dimensional objects. Interestingly, it appears that neural activity patterns related to object stimuli are ubiquitous across memory circuits and have now been observed in many medial temporal lobe structures as well as in the anterior cingulate cortex. This review summarizes behavioral and neurophysiological data that examine the representation of 3-dimensional objects across brain regions that are involved in memory.

The development of object recognition memory in rhesus macaques with neonatal lesions of the perirhinal cortex

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Assessed recognition memory in infant monkeys with neonatal perirhinal lesions using the visual paired comparison task.

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Performance was assessed at 4 developmental ages.

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Novelty preference deteriorated with age after neonatal perirhinal lesions.

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Presence of functional sparing.

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Memory deficits after perirhinal lesions occurred earlier than after hippocampal lesions.

To investigate the role of the perirhinal cortex on the development of recognition measured by the visual paired-comparison (VPC) task, infant monkeys with neonatal perirhinal lesions and sham-operated controls were tested at 1.5, 6, 18, and 48 months of age on the VPC task with color stimuli and intermixed delays of 10 s, 30 s, 60 s, and 120 s. Monkeys with neonatal perirhinal lesions showed an increase in novelty preference between 1.5 and 6 months of age similar to controls, although at these two ages, performance remained significantly poorer than that of control animals. With age, performance in animals with neonatal perirhinal lesions deteriorated as compared to that of controls. In contrast to the lack of novelty preference in monkeys with perirhinal lesions acquired in adulthood, novelty preference in the neonatally operated animals remained above chance at all delays and all ages. The data suggest that, although incidental recognition memory processes can be supported by the perirhinal cortex in early infancy, other temporal cortical areas may support these processes in the absence of a functional perirhinal cortex early in development. The neural substrates mediating incidental recognition memory processes appear to be more widespread in early infancy than in adulthood.

Annual research review: The neurobehavioral development of multiple memory systems--implications for childhood and adolescent psychiatric disorders

Extensive evidence indicates that mammalian memory is organized into multiple brains systems, including a 'cognitive' memory system that depends on the hippocampus and a stimulus-response 'habit' memory system that depends on the dorsolateral striatum. Dorsal striatal-dependent habit memory may in part influence the development and expression of some human psychopathologies, particularly those characterized by strong habit-like behavioral features. The present review considers this hypothesis as it pertains to psychopathologies that typically emerge during childhood and adolescence. These disorders include Tourette syndrome, attention-deficit/hyperactivity disorder, obsessive-compulsive disorder, eating disorders, and autism spectrum disorders. Human and nonhuman animal research shows that the typical development of memory systems comprises the early maturation of striatal-dependent habit memory and the relatively late maturation of hippocampal-dependent cognitive memory. We speculate that the differing rates of development of these memory systems may in part contribute to the early emergence of habit-like symptoms in childhood and adolescence. In addition, abnormalities in hippocampal and striatal brain regions have been observed consistently in youth with these disorders, suggesting that the aberrant development of memory systems may also contribute to the emergence of habit-like symptoms as core pathological features of these illnesses. Considering these disorders within the context of multiple memory systems may help elucidate the pathogenesis of habit-like symptoms in childhood and adolescence, and lead to novel treatments that lessen the habit-like behavioral features of these disorders.

Effects of brief time delays on matching-to-sample abilities in capuchin monkeys (Sapajus spp.)

Traditionally, studies of delayed matching-to-sample (DMTS) tasks in nonhuman species have focused on the assessment of the limits of the retrieval of information stored in short- and long-term memory systems. However, it is still unclear if visual recognition in these tasks is affected by very brief delay intervals, which are typically used to study rapidly decaying types of visual memory. This study aimed at evaluating if tufted capuchin monkeys' ability to recognise visual stimuli in a DMTS task is affected by (i) the disappearance of the sample stimulus and (ii) the introduction of delay intervals (0.5, 1.0, 2.0 and 3.0s) between the disappearance of the sample and the presentation of the comparison stimuli. The results demonstrated that the simple disappearance of the sample and the introduction of a delay of 0.5s did not affect capuchins' performance either in terms of accuracy or response time. A delay interval of 1.0s produced a significant increase in response time but still did not affect recognition accuracy. By contrast, delays of 2.0 and 3.0s determined a significant increase in response time and a reduction in recognition accuracy. These findings indicate the existence in capuchin monkeys of processes enabling a very accurate retention of stimulus features within time frames comparable to those reported for humans' sensory memory (0.5-1.0s). The extent to which such processes can be considered analogous to the sensory memory processes observed in human visual cognition is discussed.

Achilles' ear? Inferior human short-term and recognition memory in the auditory modality

Studies of the memory capabilities of nonhuman primates have consistently revealed a relative weakness for auditory compared to visual or tactile stimuli: extensive training is required to learn auditory memory tasks, and subjects are only capable of retaining acoustic information for a brief period of time. Whether a parallel deficit exists in human auditory memory remains an outstanding question. In the current study, a short-term memory paradigm was used to test human subjects' retention of simple auditory, visual, and tactile stimuli that were carefully equated in terms of discriminability, stimulus exposure time, and temporal dynamics. Mean accuracy did not differ significantly among sensory modalities at very short retention intervals (1-4 s). However, at longer retention intervals (8-32 s), accuracy for auditory stimuli fell substantially below that observed for visual and tactile stimuli. In the interest of extending the ecological validity of these findings, a second experiment tested recognition memory for complex, naturalistic stimuli that would likely be encountered in everyday life. Subjects were able to identify all stimuli when retention was not required, however, recognition accuracy following a delay period was again inferior for auditory compared to visual and tactile stimuli. Thus, the outcomes of both experiments provide a human parallel to the pattern of results observed in nonhuman primates. The results are interpreted in light of neuropsychological data from nonhuman primates, which suggest a difference in the degree to which auditory, visual, and tactile memory are mediated by the perirhinal and entorhinal cortices.