Limbic lesions and the problem of stimulus--reinforcement associations

Aspiration removal of orbitofrontal cortex disrupts cholinergic fibers of passage to anterior cingulate cortex in rhesus macaques

The study of anthropoid nonhuman primates has provided valuable insights into frontal cortex function in humans, as these primates share similar frontal anatomical subdivisions (Murray et al. 2011). Causal manipulation studies have been instrumental in advancing our understanding of this area. One puzzling finding is that macaques with bilateral aspiration removals of orbitofrontal cortex (OFC) are impaired on tests of cognitive flexibility and emotion regulation, whereas those with bilateral excitotoxic lesions of OFC are not (Rudebeck et al. 2013). This discrepancy is attributed to the inadvertent disruption of fibers of passage by aspiration lesions but not by excitotoxic lesions. Which fibers of passage are responsible for the impairments observed? One candidate is cholinergic fibers originating in the nucleus basalis magnocellularis (NBM) and passing nearby or through OFC on their way to other frontal cortex regions (Kitt et al. 1987). To investigate this possibility, we performed unilateral aspiration lesions of OFC in three macaques, and then compared cholinergic innervation of the anterior cingulate cortex (ACC) between hemispheres. Histological assessment revealed diminished cholinergic innervation in the ACC of hemispheres with OFC lesions relative to intact hemispheres. This finding indicates that aspiration lesions of the OFC disrupt cholinergic fibers of passage, and suggests the possibility that loss of cholinergic inputs to ACC contributes to the impairments in cognitive flexibility and emotion regulation observed after aspiration but not excitotoxic lesions of OFC.

5-HT 2A and 5-HT 2C receptor antagonism differentially modulate reinforcement learning and cognitive flexibility: behavioural and computational evidence

RATIONALE

Cognitive flexibility, the ability to adapt behaviour in response to a changing environment, is disrupted in several neuropsychiatric disorders, including obsessive-compulsive disorder and major depressive disorder. Evidence suggests that flexibility, which can be operationalised using reversal learning tasks, is modulated by serotonergic transmission. However, how exactly flexible behaviour and associated reinforcement learning (RL) processes are modulated by 5-HT action on specific receptors is unknown.

OBJECTIVES

We investigated the effects of 5-HT2A receptor (5-HT2AR) and 5-HT2C receptor (5-HT2CR) antagonism on flexibility and underlying RL mechanisms.

METHODS

Thirty-six male Lister hooded rats were trained on a touchscreen visual discrimination and reversal task. We evaluated the effects of systemic treatments with the 5-HT2AR and 5-HT2CR antagonists M100907 and SB-242084, respectively, on reversal learning and performance on probe trials where correct and incorrect stimuli were presented with a third, probabilistically rewarded, stimulus. Computational models were fitted to task choice data to extract RL parameters, including a novel model designed specifically for this task.

RESULTS

5-HT2AR antagonism impaired reversal learning only after an initial perseverative phase, during a period of random choice and then new learning. 5-HT2CR antagonism, on the other hand, impaired learning from positive feedback. RL models further differentiated these effects. 5-HT2AR antagonism decreased punishment learning rate (i.e. negative feedback) at high and low doses. The low dose also decreased reinforcement sensitivity (beta) and increased stimulus and side stickiness (i.e., the tendency to repeat a choice regardless of outcome). 5-HT2CR antagonism also decreased beta, but reduced side stickiness.

CONCLUSIONS

These data indicate that 5-HT2A and 5-HT2CRs both modulate different aspects of flexibility, with 5-HT2ARs modulating learning from negative feedback as measured using RL parameters and 5-HT2CRs for learning from positive feedback assessed through conventional measures.

Event-specific and persistent representations for contextual states in orbitofrontal neurons

Flexible and context-dependent behaviors require animals, including humans, to identify their current contextual state for proper rules to apply, especially when information that defines these states is partially observable. Depending on behavioral needs, contextual states usually persist for prolonged periods and across other events, including sensory stimuli, actions, and rewards, highlighting prominent challenges of holding a reliable state representation. The orbitofrontal cortex (OFC) is crucial in behaviors requiring the identification of the current context (e.g., reversal learning); however, how single units in the OFC accomplish this function has not been assessed. Do they maintain such information persistently, in separate populations from those responding phasically to events within a task, or is contextual information dynamic and embedded in these phasic responses? Here, we investigated this question by recording single units from OFC in rats performing a task that required them to identify the current contextual state related to estimated proximity to future reward with distracting olfactory cues. We found that while some OFC neurons encode contextual states, most change their selectivity upon the transition of task events. Nevertheless, despite dynamic activities in single neurons, the neural populations maintain persistent representations regarding current contextual states within particular neural subspaces.

Silencing dentate newborn neurons alters excitatory/inhibitory balance and impairs behavioral inhibition and flexibility

Adult neurogenesis confers the hippocampus with unparalleled neural plasticity, essential for intricate cognitive functions. The specific influence of sparse newborn neurons (NBNs) in modulating neural activities and subsequently steering behavior, however, remains obscure. Using an engineered NBN-tetanus toxin mouse model (NBN-TeTX), we noninvasively silenced NBNs, elucidating their crucial role in impulse inhibition and cognitive flexibility as evidenced through Morris water maze reversal learning and Go/Nogo task in operant learning. Task-based functional MRI (tb-fMRI) paired with operant learning revealed dorsal hippocampal hyperactivation during the Nogo task in male NBN-TeTX mice, suggesting that hippocampal hyperexcitability might underlie the observed behavioral deficits. Additionally, resting-state fMRI (rs-fMRI) exhibited enhanced functional connectivity between the dorsal and ventral dentate gyrus following NBN silencing. Further investigations into the activities of PV+ interneurons and mossy cells highlighted the indispensability of NBNs in maintaining the hippocampal excitation/inhibition balance. Our findings emphasize that the neural plasticity driven by NBNs extensively modulates the hippocampus, sculpting inhibitory control and cognitive flexibility.

Dissociable Contributions of Basolateral Amygdala and Ventrolateral Orbitofrontal Cortex to Flexible Learning Under Uncertainty

Reversal learning measures the ability to form flexible associations between choice outcomes with stimuli and actions that precede them. This type of learning is thought to rely on several cortical and subcortical areas, including the highly interconnected orbitofrontal cortex (OFC) and basolateral amygdala (BLA), and is often impaired in various neuropsychiatric and substance use disorders. However, the unique contributions of these regions to stimulus- and action-based reversal learning have not been systematically compared using a chemogenetic approach particularly before and after the first reversal that introduces new uncertainty. Here, we examined the roles of ventrolateral OFC (vlOFC) and BLA during reversal learning. Male and female rats were prepared with inhibitory designer receptors exclusively activated by designer drugs targeting projection neurons in these regions and tested on a series of deterministic and probabilistic reversals during which they learned about stimulus identity or side (left or right) associated with different reward probabilities. Using a counterbalanced within-subject design, we inhibited these regions prior to reversal sessions. We assessed initial and pre-/post-reversal changes in performance to measure learning and adjustments to reversals, respectively. We found that inhibition of the ventrolateral orbitofrontal cortex (vlOFC), but not BLA, eliminated adjustments to stimulus-based reversals. Inhibition of BLA, but not vlOFC, selectively impaired action-based probabilistic reversal learning, leaving deterministic reversal learning intact. vlOFC exhibited a sex-dependent role in early adjustment to action-based reversals, but not in overall learning. These results reveal dissociable roles for BLA and vlOFC in flexible learning and highlight a more crucial role for BLA in learning meaningful changes in the reward environment.

Pharmacogenetic activation of parvalbumin interneurons in the prefrontal cortex rescues cognitive deficits induced by adolescent MK801 administration

The cognitive symptoms of schizophrenia (SZ) present a significant clinical burden. They are treatment resistant and are the primary predictor of functional outcomes. Although the neural mechanisms underlying these deficits remain unclear, pathological GABAergic signaling likely plays an essential role. Perturbations with parvalbumin (PV)-expressing fast-spiking (FS) interneurons in the prefrontal cortex (PFC) are consistently found in post-mortem studies of patients with SZ, as well as in animal models. Our studies have shown decreased prefrontal synaptic inhibition and PV immunostaining, along with working memory and cognitive flexibility deficits in the MK801 model. To test the hypothesized association between PV cell perturbations and impaired cognition in SZ, we activated prefrontal PV cells by using an excitatory DREADD viral vector with a PV promoter to rescue the cognitive deficits induced by adolescent MK801 administration in female rats. We found that targeted pharmacogenetic upregulation of prefrontal PV interneuron activity can restore E/I balance and improve cognition in the MK801 model. Our findings support the hypothesis that the reduced PV cell activity levels disrupt GABA transmission, resulting in the disinhibition of excitatory pyramidal cells. This disinhibition leads to an elevated prefrontal excitation/inhibition (E/I) balance that could be causal for cognitive impairments. Our study provides novel insights into the causal role of PV cells in cognitive function and has clinical implications for understanding the pathophysiology and management of SZ.

Zero the hero: Evidence for involvement of the ventromedial prefrontal cortex in affective bias for free items

Recent evidence from psycho-economics shows that when the price of an item decreases to the extent that it becomes available for free, one can observe a remarkable increase of subjective utility toward this item. This phenomenon, which is not observed for any other price but zero, has been termed the zero-price effect (ZPE). The ZPE is attributed to an affective heuristic where the positive affect elicited by the free status of an item provides a mental shortcut biasing choice towards that item. Given that the ZPE relies on affective processing, a key role of the ventromedial prefrontal cortex (vmPFC) has been proposed, yet neuroscientific studies of the ZPE remain scarce. This study aimed to explore the role of the vmPFC in the ZPE using a novel, within-subject assessment in participants with either an acquired (lesion patients) or degenerative (behavioural-variant frontotemporal dementia patients) lesion of the vmPFC, and age-matched healthy controls. All participants were asked to make a series of choices between pairs of items that varied in price. One choice trial involved an equal decrease of both item prices, such that one of the items was priced zero. In contrast to controls, patients with both vmPFC-lesion and behavioural-variant frontotemporal dementia showed marked reductions in zero-related changes of preference in pairs of gift-cards, but not for pairs of food items. Our findings suggest that affective evaluations driving the ZPE are altered in patients with focal or degenerative damage to the vmPFC. This supports the notion of a key role of the vmPFC in the ZPE and, more generally, the importance of this region in value-based affective decision-making. Our findings also highlight the potential utility of affective heuristic tasks in future clinical assessments.

Neural Circuits Underlying Behavioral Flexibility: Insights From Drosophila

Behavioral flexibility is critical to survival. Animals must adapt their behavioral responses based on changes in the environmental context, internal state, or experience. Studies in Drosophila melanogaster have provided insight into the neural circuit mechanisms underlying behavioral flexibility. Here we discuss how Drosophila behavior is modulated by internal and behavioral state, environmental context, and learning. We describe general principles of neural circuit organization and modulation that underlie behavioral flexibility, principles that are likely to extend to other species.

Volumetric alterations in subregions of the amygdala in adults with major depressive disorder

BACKGROUND

Although major depressive disorder (MDD) has been associated with volumetric abnormalities in the amygdala, studies investigating the association between structural alterations of the amygdala and depression have yielded varying results. Since the amygdala comprises several subregions, it is difficult to detect subtle regional changes by measuring the total amygdala volume. This study aimed to examine the volume in each amygdala subregion in adults with and without a diagnosis of MDD.

METHODS

A total of 147 participants with a current history of major depression and 144 healthy participants ranging in age from 19 to 64 years underwent 3T magnetic resonance imaging scanning. Automatic segmentation of the nine nuclei of the amygdala was performed using FreeSurfer. One-way analysis of covariance, with individual volumes as dependent variables, and age, sex, and total intracranial volume as covariates, was performed to analyze volume differences.

RESULTS

Patients with MDD had significantly lower volumes of the entire amygdala and subregions, including the lateral nucleus and anterior amygdaloid area, than healthy volunteers (HCs). There were no significant associations between subregion volumes and antidepressant use, illness duration, or depression severity.

LIMITATIONS

Our cross-sectional design cannot provide a causal relationship between the volume change in the amygdala subregion and the risk of MDD.

CONCLUSION

Our findings suggest that specific amygdala subregions are more susceptible to volumetric alterations in patients with MDD than in HCs. These findings may advance our understanding of the neuroanatomic basis on MDD.

Prefrontal cortex and cognitive aging in macaque monkeys

Cognitive impairments that accompany aging, even in the absence of neurodegenerative diseases, include deficits in executive function and memory mediated by the prefrontal cortex. Because of the unique differentiation and expansion of the prefrontal cortex in primates, investigations of the neurobiological basis of cognitive aging in nonhuman primates have been particularly informative about the potential basis for age-related cognitive decline in humans. We review the cognitive functions mediated by specific subregions of prefrontal cortex, and their corresponding connections, as well as the evidence for age-related alterations in specific regions of prefrontal cortex. We also discuss evidence for similarities and differences in the effects of aging on prefrontal cortex across species.

Inferences on a multidimensional social hierarchy use a grid-like code

Generalizing experiences to guide decision-making in novel situations is a hallmark of flexible behavior. Cognitive maps of an environment or task can theoretically afford such flexibility, but direct evidence has proven elusive. In this study, we found that discretely sampled abstract relationships between entities in an unseen two-dimensional social hierarchy are reconstructed into a unitary two-dimensional cognitive map in the hippocampus and entorhinal cortex. We further show that humans use a grid-like code in entorhinal cortex and medial prefrontal cortex for inferred direct trajectories between entities in the reconstructed abstract space during discrete decisions. These grid-like representations in the entorhinal cortex are associated with decision value computations in the medial prefrontal cortex and temporoparietal junction. Collectively, these findings show that grid-like representations are used by the human brain to infer novel solutions, even in abstract and discrete problems, and suggest a general mechanism underpinning flexible decision-making and generalization.

Toward a holistic view of value and social processing in the amygdala: Insights from primate behavioral neurophysiology

Located medially within the temporal lobes, the amygdala is a formation of heterogenous nuclei that has emerged as a target for investigations into the neural bases of both primitive and complex behaviors. Although modern neuroscience has eschewed the practice of assigning broad functions to distinct brain regions, the amygdala has classically been associated with regulating negative emotional processes (such as fear or aggression), primarily through research performed in rodent models. Contemporary studies, particularly those in non-human primate models, have provided evidence for a role of the amygdala in other aspects of cognition such as valuation of stimuli or shaping social behaviors. Consequently, many modern perspectives now also emphasize the amygdala's role in processing positive affect and social behaviors. Importantly, several recent experiments have examined the intersection of two seemingly autonomous domains; how both valence/value and social stimuli are simultaneously represented in the amygdala. Results from these studies suggest that there is an overlap between valence/value processing and the processing of social behaviors at the level of single neurons. These findings have prompted researchers investigating the neurophysiological mechanisms underlying social interactions to question what contributions reward-related processes in the amygdala make in shaping social behaviors. In this review, we will examine evidence, primarily from primate neurophysiology, suggesting that value-related processes in the amygdala interact with the processing of social stimuli, and explore holistic hypotheses about how these amygdalar interactions might be instantiated.

Cortical connectivity in the face of congenital structural changes-A case of homozygous LAMC3 mutation

The homozygous LAMC3 gene mutation is associated with severe bilateral smoothening and thickening of the lateral occipital cortex . Despite this and further significant changes in gray matter structure, a patient harboring this mutation exhibited a range of remarkably intact perceptual abilities . One possible explanation of this perceptual sparing could be that the white matter structural integrity and functional connectivity in relevant pathways remained intact. To test this idea, we used diffusion tensor and functional magnetic resonance imaging to investigate functional connectivity in resting-state networks in major structural pathways involved in object perception and visual attention and corresponding microstructural integrity in a patient with homozygous LAMC3 mutation and sex, age, education, and socioeconomically matched healthy control group. White matter microstructural integrity results indicated widespread disruptions in both intra- and interhemispheric structural connections except inferior longitudinal fasciculus. With a few exceptions, the functional connectivity between the patient's adjacent gray matter regions of major white matter tracts of interest was conserved. In addition, functional localizers for face, object, and place areas showed similar results with a representative control, providing an explanation for the patient's intact face, place, and object recognition abilities. To generalize this finding, we also compared functional connectivity between early visual areas and face, place, and object category-selective areas, and we found that the functional connectivity of the patient was not different from the control group. Overall, our results provided complementary information about the effects of LAMC3 gene mutation on the human brain including intact temporo-occipital structural and functional connectivity that are compatible with preserved perceptual abilities.

Effects of Withdrawal from Cocaine Self-Administration on Rat Orbitofrontal Cortex Parvalbumin Neurons Expressing Cre recombinase: Sex-Dependent Changes in Neuronal Function and Unaltered Serotonin Signaling

The orbitofrontal cortex (OFC) is a brain region involved in higher-order decision-making. Rodent studies show that cocaine self-administration (CSA) reduces OFC contribution to goal-directed behavior and behavioral strategies to avoid drug intake. This change in OFC function persists for many weeks after cocaine withdrawal, suggesting involvement in the process of addiction. The mechanisms underlying impaired OFC function by cocaine are not well-understood. However, studies implicate altered OFC serotonin (5-HT) function in disrupted cognitive processes during addiction and other psychiatric disorders. Thus, it is hypothesized that cocaine impairment of OFC function involves changes in 5-HT signaling, and previous work shows that 5-HT_1A and 5-HT_2A receptor-mediated effects on OFC pyramidal neurons (PyNs) are impaired weeks after cocaine withdrawal. However, 5-HT effects on other contributors to OFC circuit function have not been fully investigated, including the parvalbumin-containing, fast-spiking interneurons (OFC^PV), whose function is essential to normal OFC-mediated behavior. Here, 5-HT function in naive rats and those withdrawn from CSA were evaluated using a novel rat transgenic line in which the rat parvalbumin promoter drives Cre-recombinase expression to permit identification of OFC^PV cells by fluorescent reporter protein expression. We find that whereas CSA altered basal synaptic and membrane properties of the OFC^PV neurons in a sex-dependent manner, the effects of 5-HT on these cells were unchanged by CSA. These data suggest that the behavioral effects of dysregulated OFC 5-HT function caused by cocaine experience are primarily mediated by changes in 5-HT signaling at PyNs, and not at OFC^PV neurons.

Cannabinoid Modulation of Dopamine Release During Motivation, Periodic Reinforcement, Exploratory Behavior, Habit Formation, and Attention

Motivational and attentional processes energize action sequences to facilitate evolutionary competition and promote behavioral fitness. Decades of neuropharmacology, electrophysiology and electrochemistry research indicate that the mesocorticolimbic DA pathway modulates both motivation and attention. More recently, it was realized that mesocorticolimbic DA function is tightly regulated by the brain's endocannabinoid system and greatly influenced by exogenous cannabinoids-which have been harnessed by humanity for medicinal, ritualistic, and recreational uses for 12,000 years. Exogenous cannabinoids, like the primary psychoactive component of cannabis, delta-9-tetrahydrocannabinol, produce their effects by acting at binding sites for naturally occurring endocannabinoids. The brain's endocannabinoid system consists of two G-protein coupled receptors, endogenous lipid ligands for these receptor targets, and several synthetic and metabolic enzymes involved in their production and degradation. Emerging evidence indicates that the endocannabinoid 2-arachidonoylglycerol is necessary to observe concurrent increases in DA release and motivated behavior. And the historical pharmacology literature indicates a role for cannabinoid signaling in both motivational and attentional processes. While both types of behaviors have been scrutinized under manipulation by either DA or cannabinoid agents, there is considerably less insight into prospective interactions between these two important signaling systems. This review attempts to summate the relevance of cannabinoid modulation of DA release during operant tasks designed to investigate either motivational or attentional control of behavior. We first describe how cannabinoids influence DA release and goal-directed action under a variety of reinforcement contingencies. Then we consider the role that endocannabinoids might play in switching an animal's motivation from a goal-directed action to the search for an alternative outcome, in addition to the formation of long-term habits. Finally, dissociable features of attentional behavior using both the 5-choice serial reaction time task and the attentional set-shifting task are discussed along with their distinct influences by DA and cannabinoids. We end with discussing potential targets for further research regarding DA-cannabinoid interactions within key substrates involved in motivation and attention.

Dissociable and Paradoxical Roles of Rat Medial and Lateral Orbitofrontal Cortex in Visual Serial Reversal Learning

Much evidence suggests that reversal learning is mediated by cortico-striatal circuitries with the orbitofrontal cortex (OFC) playing a prominent role. The OFC is a functionally heterogeneous region, but potential differential roles of lateral (lOFC) and medial (mOFC) portions in visual reversal learning have yet to be determined. We investigated the effects of pharmacological inactivation of mOFC and lOFC on a deterministic serial visual reversal learning task for rats. For reference, we also targeted other areas previously implicated in reversal learning: prelimbic (PrL) and infralimbic (IL) prefrontal cortex, and basolateral amygdala (BLA). Inactivating mOFC and lOFC produced opposite effects; lOFC impairing, and mOFC improving, performance in the early, perseverative phase specifically. Additionally, mOFC inactivation enhanced negative feedback sensitivity, while lOFC inactivation diminished feedback sensitivity in general. mOFC and lOFC inactivation also affected novel visual discrimination learning differently; lOFC inactivation paradoxically improved learning, and mOFC inactivation had no effect. We also observed dissociable roles of the OFC and the IL/PrL. Whereas the OFC inactivation affected only perseveration, IL/PrL inactivation improved learning overall. BLA inactivation did not affect perseveration, but improved the late phase of reversal learning. These results support opponent roles of the rodent mOFC and lOFC in deterministic visual reversal learning.

Processing of Task-Irrelevant Race Information is Associated with Diminished Cognitive Control in Black and White Individuals

The race of an individual is a salient physical feature that is rapidly processed by the brain and can bias our perceptions of others. How the race of others explicitly impacts our actions toward them during intergroup contexts is not well understood. In the current study, we examined how task-irrelevant race information influences cognitive control in a go/no-go task in a community sample of Black (n = 54) and White (n = 51) participants. We examined the neural correlates of behavioral effects using functional magnetic resonance imaging and explored the influence of implicit racial attitudes on brain-behavior associations. Both Black and White participants showed more cognitive control failures, as indexed by dprime, to Black versus White faces, despite the irrelevance of race to the task demands. This behavioral pattern was paralleled by greater activity to Black faces in the fusiform face area, implicated in processing face and in-group information, and lateral orbitofrontal cortex, associated with resolving stimulus-response conflict. Exploratory brain-behavior associations suggest different patterns in Black and White individuals. Black participants exhibited a negative association between fusiform activity and response time during impulsive errors to Black faces, whereas White participants showed a positive association between lateral OFC activity and cognitive control performance to Black faces when accounting for implicit racial associations. Together our findings propose that attention to race information is associated with diminished cognitive control that may be driven by different mechanisms for Black and White individuals.

Reactive and Proactive Adaptation of Cognitive and Motor Neural Signals during Performance of a Stop-Change Task

The ability to inhibit or suppress unwanted or inappropriate actions, is an essential component of executive function and cognitive health. The immense selective pressure placed on maintaining inhibitory control processes is exemplified by the relatively small number of instances in which these systems completely fail in the average person's daily life. Although mistakes and errors do inevitably occur, inhibitory control systems not only ensure that this number is low, but have also adapted behavioral strategies to minimize future failures. The ability of our brains to adapt our behavior and appropriately engage proper motor responses is traditionally depicted as the primary domain of frontal brain areas, despite evidence to the fact that numerous other brain areas contribute. Using the stop-signal task as a common ground for comparison, we review a large body of literature investigating inhibitory control processes across frontal, temporal, and midbrain structures, focusing on our recent work in rodents, in an effort to understand how the brain biases action selection and adapts to the experience of conflict.

A Neural Mechanism of Cue-Outcome Expectancy Generated by the Interaction Between Orbitofrontal Cortex and Amygdala

Taste perception is important for animals to take adequate nutrients and avoid toxins for their survival. Appetitive and aversive behaviors are produced by value evaluation of taste and taste expectation caused by other sensations. The value evaluation, coupled with a cue presentation, produces outcome expectation and guides flexible behaviors when the environment is changed. Experimental studies demonstrated distinct functional roles of basolateral amygdala (ABL) and orbitofrontal cortex (OFC) in value evaluation and adaptive behavior. ABL is involved in generating a cue-outcome association, whereas OFC makes a contribution of generating a cue-triggered expectation to guide adaptive behavior. However, it remains unclear how ABL and OFC form their functional roles, with the learning of adaptive behavior. To address this issue, we focus on an odor discrimination task of rats and develop a computational model that consists of OFC and ABL, interacting with reward and decision systems. We present the neural mechanisms underlying the rapid formation of cue-outcome association in ABL and late behavioral adaptation mediated by OFC. Moreover, we offer 2 functions of cue-selective neurons in OFC: one is that the activation of cue-selective neurons transmits value information to decision area to guide behavior and another is that persistent activity of cue-selective neurons evokes a weak activity of taste-sensitive OFC neurons, leading to cue-outcome expectation. Our model further accounts for ABL and OFC responses caused by lesions of these areas. The results provide a computational framework of how ABL and OFC are functionally linked through their interactions with the reward and decision systems.

The orbitofrontal cartographer

Theories of orbitofrontal cortex (OFC) function have evolved substantially over the last few decades. There is now a general consensus that the OFC is important for predicting aspects of future events and for using these predictions to guide behavior. Yet the precise content of these predictions and the degree to which OFC contributes to agency contingent upon them has become contentious, with several plausible theories advocating different answers to these questions. In this review we will focus on three of these ideas-the economic value, credit assignment, and cognitive map hypotheses-describing both their successes and failures. We will propose that these failures hint at a more nuanced and perhaps unique role for the OFC, particularly the lateral subdivision, in supporting the proposed functions when an underlying model or map of the causal structures in the environment must be constructed or updated. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The orbitofrontal cortex in temporal cognition

One of the most important factors in decision-making is estimating the value of available options. Subregions of the prefrontal cortex, including the orbitofrontal cortex (OFC), have been deemed essential for this process. Value computations require a complex integration across numerous dimensions, including, reward magnitude, effort, internal state, and time. The importance of the temporal dimension is well illustrated by temporal discounting tasks, in which subjects select between smaller-sooner versus larger-later rewards. The specific role of OFC in telling time and integrating temporal information into decision-making remains unclear. Based on the current literature, in this review we reevaluate current theories of OFC function, accounting for the influence of time. Incorporating temporal information into value estimation and decision-making requires distinct, yet interrelated, forms of temporal information including the ability to tell time, represent time, create temporal expectations, and the ability to use this information for optimal decision-making in a wide range of tasks, including temporal discounting and wagering. We use the term "temporal cognition" to refer to the integrated use of these different aspects of temporal information. We suggest that the OFC may be a critical site for the integration of reward magnitude and delay, and thus important for temporal cognition. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Evolving schema representations in orbitofrontal ensembles during learning

How do we learn about what to learn about? Specifically, how do the neural elements in our brain generalize what has been learned in one situation to recognize the common structure of-and speed learning in-other, similar situations? We know this happens because we become better at solving new problems-learning and deploying schemas1-5-through experience. However, we have little insight into this process. Here we show that using prior knowledge to facilitate learning is accompanied by the evolution of a neural schema in the orbitofrontal cortex. Single units were recorded from rats deploying a schema to learn a succession of odour-sequence problems. With learning, orbitofrontal cortex ensembles converged onto a low-dimensional neural code across both problems and subjects; this neural code represented the common structure of the problems and its evolution accelerated across their learning. These results demonstrate the formation and use of a schema in a prefrontal brain region to support a complex cognitive operation. Our results not only reveal a role for the orbitofrontal cortex in learning but also have implications for using ensemble analyses to tap into complex cognitive functions.

A cross-species assessment of behavioral flexibility in compulsive disorders

Lack of behavioral flexibility has been proposed as one underlying cause of compulsions, defined as repetitive behaviors performed through rigid rituals. However, experimental evidence has proven inconsistent across human and animal models of compulsive-like behavior. In the present study, applying a similarly-designed reversal learning task in two different species, which share a common symptom of compulsivity (human OCD patients and Sapap3 KO mice), we found no consistent link between compulsive behaviors and lack of behavioral flexibility. However, we showed that a distinct subgroup of compulsive individuals of both species exhibit a behavioral flexibility deficit in reversal learning. This deficit was not due to perseverative, rigid behaviors as commonly hypothesized, but rather due to an increase in response lability. These cross-species results highlight the necessity to consider the heterogeneity of cognitive deficits in compulsive disorders and call for reconsidering the role of behavioral flexibility in the aetiology of compulsive behaviors.

Animal Models for OCD Research

OCD has lagged behind other psychiatric illnesses in the identification of molecular treatment targets, due in part to a lack of significant findings in genome-wide association studies. However, while progress in this area is being made, OCD's symptoms of obsessions, compulsions, and anxiety can be deconstructed into distinct neural functions that can be dissected in animal models. Studies in rodents and non-human primates have highlighted the importance of cortico-basal ganglia-thalamic circuits in OCD pathophysiology, and emerging studies in human post-mortem brain tissue point to glutamatergic synapse abnormalities as a potential cellular substrate for observed dysfunctional behaviors. In addition, accumulated evidence points to a potential role for neuromodulators including serotonin and dopamine in both OCD pathology and treatment. Here, we review current efforts to use animal models for the identification of molecules, cell types, and circuits relevant to OCD pathophysiology. We start by describing features of OCD that can be modeled in animals, including circuit abnormalities and genetic findings. We then review different strategies that have been used to study OCD using animal model systems, including transgenic models, circuit manipulations, and dissection of OCD-relevant neural constructs. Finally, we discuss how these findings may ultimately help to develop new treatment strategies for OCD and other related disorders.

Prefrontal contributions to action control in rodents

The rodent medial prefrontal cortex (mPFC) is typically considered to be involved in cognitive aspects of action control, e.g., decision making, rule learning and application, working memory and generally guiding adaptive behavior (Euston, Gruber, & McNaughton, 2012). These cognitive aspects often occur on relatively slow time scales, i.e., in the order of several trials within a block structure (Murakami, Shteingart, Loewenstein, & Mainen, 2017). In this way, the mPFC is able to set up a representational memory (Goldman-Rakic, 1987). On the other hand, the mPFC can also impact action control more directly (i.e., more on the motoric and less cognitive side). This impact on motor control manifests on faster time scales, i.e., on a single trial level (Hardung et al., 2017). While the more cognitive aspects have been reviewed previously as well as in other subchapters of this book, we explicitly focus on the latter aspect in this chapter, particularly on movement inhibition. We discuss models of prefrontal motor interactions, the impact of the behavioral paradigm, evidences for mPFC involvement in action control, and the anatomical connections between mPFC and motor cortex.

Quantitative assessment of amygdala in Macaca fascicularis monkeys

The amygdaloid complex (AC) is involved in very relevant cognitive and emotional pathways and exhibits changes in aging and in some neurological and psychiatric disorders. The quantitative estimators of AC could be useful to understand the impact of amygdaloid pathology in these processes, both globally and for each nucleus in particular, and their neurons. The present study analyzes morphometric and stereological estimators in the whole AC and its three main nuclei (lateral [La], basal [Ba], and accessory basal [AB]) in six Macaca fascicularis monkeys. All the brains were fixed and sectioned in the coronal plane; Nissl-stained sections were used for estimation of size and form parameters in both, the AC, and the La, Ba, and AB nuclei separately. The study includes stereological estimates of the volume and surface area of the AC; also, volume of the neurons in the amygdaloid nuclei was estimated using the point-sampled intercepts method. Our results show that the AB nucleus is smaller than both the La and Ba nuclei in both morphometric and stereological estimators. Brain hemispheric side had not significant influence on any of quantitative estimates. The neuron volume was higher in the AB nucleus relative to LA and Ba of the nuclei. These data describe some quantitative parameters of the amygdaloid complex and their main nuclei that could help us to detect small changes in neurodegenerative and other pathological processes.

Touchscreen-based location discrimination and paired associate learning tasks detect cognitive impairment at an early stage in an App knock-in mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline with accumulation of amyloid beta (Aβ) and neurofibrillary tangles that usually begins 15–30 years before clinical diagnosis. Rodent models that recapitulate aggressive Aβ and/or the pathology of neurofibrillary tangles are essential for AD research. Accordingly, non-invasive early detection systems in these animal models are required to evaluate the phenotypic changes, elucidate the mechanism of disease progression, and facilitate development of novel therapeutic approaches. Although many behavioral tests efficiently reveal cognitive impairments at the later stage of the disease in AD models, it has been challenging to detect such impairments at the early stage. To address this issue, we subjected 4–6-month-old male App^{NL−G−F/NL−G−F} knock-in (App-KI) mice to touchscreen-based location discrimination (LD), different object–location paired-associate learning (dPAL), and reversal learning tests, and compared the results with those of the classical Morris water maze test. These tests are mainly dependent on the brain regions prone to Aβ accumulation at the earliest stages of the disease. At 4–6 months, considered to represent the early stage of disease when mice exhibit initial deposition of Aβ and slight gliosis, the classical Morris water maze test revealed no difference between groups, whereas touchscreen-based LD and dPAL tasks revealed significant impairments in task performance. Our report is the first to confirm that a systematic touchscreen-based behavioral test battery can sensitively detect the early stage of cognitive decline in an AD-linked App-KI mouse model. This system could be applied in future translational research.

Damage to Orbitofrontal Areas 12 and 13, but Not Area 14, Results in Blunted Attention and Arousal to Socioemotional Stimuli in Rhesus Macaques

An earlier study in monkeys indicated that lesions to the mid-portion of the ventral orbitofrontal cortex (OFC), including Walker’s areas 11 and 13 (OFC11/13), altered the spontaneous scanning of still pictures of primate faces (neutral and emotional) and the modulation of arousal. Yet, these conclusions were limited by several shortcomings, including the lesion approach, use of static rather than dynamic stimuli, and manual data analyses. To confirm and extend these earlier findings, we compared attention and arousal to social and nonsocial scenes in three groups of rhesus macaques with restricted lesions to one of three OFC areas (OFC12, OFC13, or OFC14) and a sham-operated control group using eye-tracking to capture scanning patterns, focal attention and pupil size. Animals with damage to the lateral OFC areas (OFC12 and OFC13) showed decreased attention specifically to the eyes of negative (threatening) social stimuli and increased arousal (increased pupil diameter) to positive social scenes. In contrast, animals with damage to the ventromedial OFC area (OFC14) displayed no differences in attention or arousal in the presence of social stimuli compared to controls. These findings support the notion that areas of the lateral OFC are critical for directing attention and modulating arousal to emotional social cues. Together with the existence of face-selective neurons in these lateral OFC areas, the data suggest that the lateral OFC may set the stage for multidimensional information processing related to faces and emotion and may be involved in social judgments.

Serotonergic Innervations of the Orbitofrontal and Medial-prefrontal Cortices are Differentially Involved in Visual Discrimination and Reversal Learning in Rats

Cross-species studies have identified an evolutionarily conserved role for serotonin in flexible behavior including reversal learning. The aim of the current study was to investigate the contribution of serotonin within the orbitofrontal cortex (OFC) and medial prefrontal cortex (mPFC) to visual discrimination and reversal learning. Male Lister Hooded rats were trained to discriminate between a rewarded (A+) and a nonrewarded (B−) visual stimulus to receive sucrose rewards in touchscreen operant chambers. Serotonin was depleted using surgical infusions of 5,7-dihydroxytryptamine (5,7-DHT), either globally by intracebroventricular (i.c.v.) infusions or locally by microinfusions into the OFC or mPFC. Rats that received i.c.v. infusions of 5,7-DHT before initial training were significantly impaired during both visual discrimination and subsequent reversal learning during which the stimulus–reward contingencies were changed (A− vs. B+). Local serotonin depletion from the OFC impaired reversal learning without affecting initial discrimination. After mPFC depletion, rats were unimpaired during reversal learning but slower to respond at the stimuli during all the stages; the mPFC group was also slower to learn during discrimination than the OFC group. These findings extend our understanding of serotonin in cognitive flexibility by revealing differential effects within two subregions of the prefrontal cortex in visual discrimination and reversal learning.

Review of Orbitofrontal Cortex in Alcohol Dependence: A Disrupted Cognitive Map?

Alcoholism is a persistent worldwide problem associated with long-lasting impairments to decision making processes. Some aspects of dysfunction are thought to reflect alcohol-induced changes to relevant brain areas such as the orbitofrontal cortex (OFC). In this review, we will examine how chronic alcohol exposure alters OFC function to potentially contribute to maladaptive decision making, and explore experimental behavioral approaches that may be better suited to test whether alcohol dependence disrupts OFC's function. We argue that although past works suggest impairments in aspects of OFC function, more information may be gained by specifically targeting tasks to the broader function of OFC as put forth by the recent hypothesis of OFC as a "cognitive map" of task space. Overall, we suggest that such a focus could provide a better understanding of how OFC function changes in alcohol dependence, and could inform better assessment tools and treatment options for clinicians working with this population.

The ever-changing OFC landscape: What neural signals in OFC can tell us about inhibitory control

Despite decades of research on OFC function, the exact function(s) of OFC remain elusive. In recent years, 1 of the earliest hypotheses about OFC function, namely its involvement in inhibitory control, has drifted to the periphery of the functional OFC landscape in favor of theories suggesting a role for OFC in the representation of task or state space. The reasons for this drift are valid, owing in part to the development of more sensitive behavioral approaches, a clear emphasis on cross-species and cross-method comparisons, as well as the elegant integration of reinforcement learning theories. However, recent evidence recording from OFC during the performance of traditional inhibitory control tasks has found new evidence supporting a role for OFC in inhibitory control. While the extent to which these findings can be integrated into existing frameworks is in its infancy, this review seeks to highlight these findings with the goal of providing new insights into function of OFC. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Glutamatergic and Serotonergic Modulation of Rat Medial and Lateral Orbitofrontal Cortex in Visual Serial Reversal Learning

Adapting behavior to a dynamic environment requires both steadiness when the environment is stable and behavioral flexibility in response to changes. Much evidence suggests that cognitive flexibility, which can be operationalized in reversal learning tasks, is mediated by cortico-striatal circuitries, with the orbitofrontal cortex (OFC) playing a prominent role. The OFC is a functionally heterogeneous region, and we have previously reported differential roles of lateral (lOFC) and medial (mOFC) regions in a touchscreen serial visual reversal learning task for rats using pharmacological inactivation. Here, we investigated the effects of pharmacological overactivation of these regions using a glutamate transporter 1 (GLT-1) inhibitor, dihydrokainate (DHK), which increases extracellular glutamate by blocking its reuptake. We also tested the impact of antagonism of the serotonin 2A receptor (5-HT_2AR), which modulates glutamate action, in the mOFC and lOFC on the same task. Overactivation induced by DHK produced dissociable effects in the mOFC and lOFC, with more prominent effects in the mOFC, specifically improving performance in the early, perseveration phase. Intra-lOFC DHK increased the number of omitted responses without affecting errors. In contrast, blocking the 5-HT_2AR in the lOFC impaired reversal learning overall, while mOFC 5-HT_2AR blockade had no effect. These results further support dissociable roles of the rodent mOFC and lOFC in deterministic visual reversal learning and indicate that modulating glutamate transmission through blocking the GLT-1 and the 5-HT_2AR have different roles in these two structures.

This study further supports dissociable roles of specific orbitofrontal subregions, as well as glutamatergic and serotonergic transmission in these subregions, in cognitive flexibility. This knowledge will add to the understanding of specific neural mechanisms underlying inflexible behaviour across psychiatric disorders.

Prefrontal Cortex Predicts State Switches during Reversal Learning

Reinforcement learning allows organisms to predict future outcomes and to update their beliefs about value in the world. The dorsal-lateral prefrontal cortex (dlPFC) integrates information carried by reward circuits, which can be used to infer the current state of the world under uncertainty. Here, we explored the dlPFC computations related to updating current beliefs during stochastic reversal learning. We recorded the activity of populations up to 1,000 neurons, simultaneously, in two male macaques while they executed a two-armed bandit reversal learning task. Behavioral analyses using a Bayesian framework showed that animals inferred reversals and switched their choice preference rapidly, rather than slowly updating choice values, consistent with state inference. Furthermore, dlPFC neural populations accurately encoded choice preference switches. These results suggest that prefrontal neurons dynamically encode decisions associated with Bayesian subjective values, highlighting the role of the PFC in representing a belief about the current state of the world.

Dorsal and ventral striatal dopamine D1 and D2 receptors differentially modulate distinct phases of serial visual reversal learning

Impaired cognitive flexibility in visual reversal-learning tasks has been observed in a wide range of neurological and neuropsychiatric disorders. Although both human and animal studies have implicated striatal D2-like and D1-like receptors (D2R; D1R) in this form of flexibility, less is known about the contribution they make within distinct sub-regions of the striatum and the different phases of visual reversal learning. The present study investigated the involvement of D2R and D1R during the early (perseverative) phase of reversal learning as well as in the intermediate and late stages (new learning) after microinfusions of D2R and D1R antagonists into the nucleus accumbens core and shell (NAcC; NAcS), the anterior and posterior dorsomedial striatum (DMS) and the dorsolateral striatum (DLS) on a touchscreen visual serial reversal-learning task. Reversal learning was improved after dopamine receptor blockade in the nucleus accumbens; the D1R antagonist, SCH23390, in the NAcS and the D2R antagonist, raclopride, in the NAcC selectively reduced early, perseverative errors. In contrast, reversal learning was impaired by D2R antagonism, but not D1R antagonism, in the dorsal striatum: raclopride increased errors in the intermediate phase after DMS infusions, and increased errors across phases after DLS infusions. These findings indicate that D1R and D2R modulate different stages of reversal learning through effects localised to different sub-regions of the striatum. Thus, deficits in behavioral flexibility observed in disorders linked to dopamine perturbations may be attributable to specific D1R and D2R dysfunction in distinct striatal sub-regions.

A little history goes a long way toward understanding why we study consciousness the way we do today

Consciousness is currently a thriving area of research in psychology and neuroscience. While this is often attributed to events that took place in the early 1990s, consciousness studies today are a continuation of research that started in the late 19th century and that continued throughout the 20th century. From the beginning, the effort built on studies of animals to reveal basic principles of brain organization and function, and of human patients to gain clues about consciousness itself. Particularly important and our focus here is research in the 1950s, 1960s, and 1970s involving three groups of patients-amnesia, split brain, and blindsight. Across all three groups, a similar pattern of results was found-the patients could respond appropriately to stimuli that they denied seeing (or in the case of amnesiacs, having seen before). These studies paved the way for the current wave of research on consciousness. The field is, in fact, still grappling with the implications of the findings showing that the ability to consciously know and report the identity of a visual stimulus can be dissociated in the brain from the mechanisms that underlie the ability to behave in a meaningful way to the same stimulus.

Performance in delayed non-matching to sample task predicts the diagnosis of obsessive-compulsive disorder

Electrical stimulation studies have recently evidenced the involvement of orbitofrontal cortex (OFC) in obsessive-compulsive disorder (OCD). In addition, lateral OFC is activated in healthy subjects during delayed non-matching-to-sample task (DNMS). In the present study, we hypothesized that OCD results from a specific defect of lateral OFC processing that can be evidenced via a DNMS task. To this end, we compared the DNMS performances of 20 OCD patients vs 20 demographically matched healthy controls. As predicted, our results showed that OCD patients performed worse than healthy controls at DNMS task. To test for the specificity of this behavioral impairment, we furthermore compared OCD patients and healthy subjects on a different task not involving directly the lateral OFC: the delayed match-to-sample task (DMS). As expected, OCD patients are more impaired for both the DNMS and the DMS task, compared with healthy subjects. Moreover, OCD patients tend statistically to perform worse for the DNMS task than for DMS task. Our results suggest the DNMS task specifically target the malfunctioning areas in OCD, such as the lateral OFC. In light of these results, lateral OFC should therefore be the focus of future therapeutic interventions.

Specializations for reward-guided decision-making in the primate ventral prefrontal cortex

The estimated values of choices, and therefore decision-making based on those values, are influenced by both the chance that the chosen items or goods can be obtained (availability) and their current worth (desirability) as well as by the ability to link the estimated values to choices (a process sometimes called credit assignment). In primates, the prefrontal cortex (PFC) has been thought to contribute to each of these processes; however, causal relationships between particular subdivisions of the PFC and specific functions have been difficult to establish. Recent lesion-based research studies have defined the roles of two different parts of the primate PFC - the orbitofrontal cortex (OFC) and the ventral lateral frontal cortex (VLFC) - and their subdivisions in evaluating each of these factors and in mediating credit assignment during reward-based decision-making.

Sex differences in color discrimination and serial reversal learning in mollies and guppies

Behavioral flexibility provides an individual with the ability to adapt its behavior in response to environmental changes. Studies on mammals, birds, and teleosts indicate greater behavioral flexibility in females. Conversely, males appear to exhibit greater behavioral persistence. We, therefore, investigated sex differences in behavioral flexibility in 2 closely related molly species (Poecilia latipinna, P. mexicana) and their more distant relative, the guppy P. reticulata by comparing male and female individuals in a serial, visual reversal learning task. Fish were first trained in color discrimination, which was quickly learned by all females (guppies and mollies) and all molly males alike. Despite continued training over more than 72 sessions, male guppies did not learn the general test procedure and were, therefore, excluded from further testing. Once the reward contingency was reversed serially, molly males of both species performed considerably better by inhibiting their previous response and reached the learning criterion significantly faster than their respective conspecific females. Moreover, Atlantic molly males clearly outperformed all other individuals (males and females) and some of them even reached the level of 1-trial learning. Thus, the apparently universal pattern of higher female behavioral flexibility seems to be inverted in the 2 examined molly species, although the evolutionary account of this pattern remains highly speculative. These findings were complemented by the observed lower neophobia of female sailfin mollies compared with their male conspecifics. This sex difference was not observed in Atlantic mollies that were observed to be significantly less distressed in a novel situation than their consexuals. Hypothetically, sex differences in behavioral flexibility can possibly be explained in terms of the different roles that males and females play in mating competition, mate choice, and reproduction or, more generally, in complex social interactions. Each of these characteristics clearly differed between the closely related mollies and the more distantly related guppies.

Rat Orbitofrontal Ensemble Activity Contains Multiplexed but Dissociable Representations of Value and Task Structure in an Odor Sequence Task

The orbitofrontal cortex (OFC) has long been implicated in signaling information about expected outcomes to facilitate adaptive or flexible behavior. Current proposals focus on signaling of expected value versus the representation of a value-agnostic cognitive map of the task. While often suggested as mutually exclusive, these alternatives may represent extreme ends of a continuum determined by task complexity and experience. As learning proceeds, an initial, detailed cognitive map might be acquired, based largely on external information. With more experience, this hypothesized map can then be tailored to include relevant abstract hidden cognitive constructs. The map would default to an expected value in situations where other attributes are largely irrelevant, but, in richer tasks, a more detailed structure might continue to be represented, at least where relevant to behavior. Here, we examined this by recording single-unit activity from the OFC in rats navigating an odor sequence task analogous to a spatial maze. The odor sequences provided a mappable state space, with 24 unique "positions" defined by sensory information, likelihood of reward, or both. Consistent with the hypothesis that the OFC represents a cognitive map tailored to the subjects' intentions or plans, we found a close correspondence between how subjects were using the sequences and the neural representations of the sequences in OFC ensembles. Multiplexed with this value-invariant representation of the task, we also found a representation of the expected value at each location. Thus, the value and task structure co-existed as dissociable components of the neural code in OFC.

NMDA receptor deletion on dopamine neurons disrupts visual discrimination and reversal learning

The dopamine (DA) system is critical for various forms of learning about salient environmental stimuli. Prior work has shown that deletion of the obligatory NR1 subunit of the N-methyl-_D-aspartate (NMDA) receptor on neurons expressing the DA transporter (DAT) in mice results in reduced phasic release from DA-containing neurons. To further investigate the contribution of phasic DA release to reward-related learning and cognitive flexibility, the current study evaluated DAT-NR1 null mutant mice in a touchscreen-based pairwise visual discrimination and reversal learning paradigm. Results showed that these mutants were slower to attain a high level of choice accuracy on the discrimination task, but showed improved late reversal performance on sessions where correct choice was above chance. A number of possible interpretations are offered for this pattern of effects, including the opposing possibilities that discrimination memory was either stronger by the completion of training (overtraining effect) or weaker (learning deficit), both of which could potentially produce faster reversal. These data add to the extensive literature ascribing a critical role for DAergic neurotransmission in cognitive functions and the regulation of reward-related behaviors of relevance to addictions.

More rapid reversal learning following overtraining in the rat is evidence that behavioural and cognitive flexibility are dissociable

Cognitive flexibility is a term used to describe the brain processes underlying the phenomenon of adaptive change in behaviour in response to changed contingencies in the internal or external environment. Cognitive flexibility is often assessed in complex tasks measuring perceptual attentional shifting or response or task switching, but, arguably, reversal learning is a simple assay of cognitive flexibility. Reversal learning requires the detection of a changed outcome, the cessation of a previously-rewarded response and the selection of an alternative, previously-unrewarded, response. This study addressed the issue of the relationship between reversal learning and cognitive flexibility. In a single testing session, rats completed a series of 2-alternative forced-choice discriminations between digging bowls. The bowls differed according to both the medium within the bowl and the odor of the bowl. Having learned which cue (one of the odors or one of the digging media) indicated the food-baited bowl, half the rats were given additional trials of "over-training". To test reversal learning, the meaning of the cues predictive of reward/non-reward was then switched. There was a robust effect of over-training, with over-trained rats performing reversal learning in fewer trials than rats trained to criterion only. The pattern of errors supported the hypothesis that more rapid reversing results from the formation of an attentional set. This is the same attentional mechanism that results in less rapid shifting or switching. We conclude that the behavioural flexibility demonstrated in reversal learning does not provide a scale on which cognitive flexibility can be measured.

Memory systems 2018 - Towards a new paradigm

The multiple memory systems theory (MMS) postulates that the brain stores information based on the independent and parallel activity of a number of modules, each with distinct properties, dynamics, and neural basis. Much of the evidence for this theory comes from dissociation studies indicating that damage to restricted brain areas cause selective types of memory deficits. MMS has been the prevalent paradigm in memory research for more than thirty years, even as it has been adjusted several times to accommodate new data. However, recent empirical results indicating that the memory systems are not always dissociable constitute a challenge to fundamental tenets of the current theory because they suggest that representations formed by individual memory systems can contribute to more than one type of memory-driven behavioral strategy. This problem can be addressed by applying a dynamic network perspective to memory architecture. According to this view, memory networks can reconfigure or transiently couple in response to environmental demands. Within this context, the neural network underlying a specific memory system can act as an independent unit or as an integrated component of a higher order meta-network. This dynamic network model proposes a way in which empirical evidence that challenges the idea of distinct memory systems can be incorporated within a modular memory architecture. The model also provides a framework to account for the complex interactions among memory systems demonstrated at the behavioral level. Advances in the study of dynamic networks can generate new ideas to experimentally manipulate and control memory in basic or clinical research.