Amygdalar connections with middle and inferior temporal gyri of the monkey

Fish oil supplementation alters emotion-generated corticolimbic functional connectivity in depressed adolescents at high-risk for bipolar I disorder: A 12-week placebo-controlled fMRI trial

OBJECTIVE

To evaluate the effects of fish oil (FO), a source of the omega-3 polyunsaturated fatty acids (n-3 PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on emotion-generated corticolimbic functional connectivity in depressed youth at high risk for developing bipolar I disorder.

METHODS

Thirty-nine antidepressant-free youth with a current depressive disorder diagnosis and a biological parent with bipolar I disorder were randomized to 12-week double-blind treatment with FO or placebo. At baseline and endpoint, fMRI (4 Tesla) scans were obtained while performing a continuous performance task with emotional and neutral distractors (CPT-END). Seed-to-voxel functional connectivity analyses were performed using bilateral orbitofrontal cortex (OFC) and amygdala (AMY) seeds. Measures of depression, mania, global symptom severity, and erythrocyte fatty acids were obtained.

RESULTS

Erythrocyte EPA+DHA composition increased significantly in the FO group (+47%, p ≤ 0.0001) but not in the placebo group (-10%, p = 0.11). Significant group by time interactions were found for functional connectivity between the left OFC and the left superior temporal gyrus (STG) and between the right AMY and right inferior temporal gyrus (ITG). OFC-STG connectivity increased in the FO group (p = 0.0001) and decreased in the placebo group (p = 0.0019), and AMY-ITG connectivity decreased in the FO group (p = 0.0014) and increased in the placebo group (p < 0.0001). In the FO group, but not placebo group, the decrease in AMY-ITG functional connectivity correlated with decreases in Childhood Depression Rating Scale-Revised and Clinical Global Impression-Severity Scale scores.

CONCLUSIONS

In depressed high-risk youth FO supplementation alters emotion-generated corticolimbic functional connectivity which correlates with changes in symptom severity ratings.

Human hippocampal responses to network intracranial stimulation vary with theta phase

Hippocampal-dependent memory is thought to be supported by distinct connectivity states, with strong input to the hippocampus benefitting encoding and weak input benefitting retrieval. Previous research in rodents suggests that the hippocampal theta oscillation orchestrates the transition between these states, with opposite phase angles predicting minimal versus maximal input. We investigated whether this phase dependence exists in humans using network-targeted intracranial stimulation. Intracranial local field potentials were recorded from individuals with epilepsy undergoing medically necessary stereotactic electroencephalographic recording. In each subject, biphasic bipolar direct electrical stimulation was delivered to lateral temporal sites with demonstrated connectivity to hippocampus. Lateral temporal stimulation evoked ipsilateral hippocampal potentials with distinct early and late components. Using evoked component amplitude to measure functional connectivity, we assessed whether the phase of hippocampal theta predicted relatively high versus low connectivity. We observed an increase in the continuous phase-amplitude relationship selective to the early and late components of the response evoked by lateral temporal stimulation. The maximal difference in these evoked component amplitudes occurred across 180 degrees of separation in the hippocampal theta rhythm; that is, the greatest difference in component amplitude was observed when stimulation was delivered at theta peak versus trough. The pattern of theta-phase dependence observed for hippocampus was not identified for control locations. These findings demonstrate that hippocampal receptivity to input varies with theta phase, suggesting that theta phase reflects connectivity states of human hippocampal networks. These findings confirm a putative mechanism by which neural oscillations modulate human hippocampal function.

Adults vs. neonates: Differentiation of functional connectivity between the basolateral amygdala and occipitotemporal cortex

The amygdala, a subcortical structure known for social and emotional processing, consists of multiple subnuclei with unique functions and connectivity patterns. Tracer studies in adult macaques have shown that the basolateral subnuclei differentially connect to parts of visual cortex, with stronger connections to anterior regions and weaker connections to posterior regions; infant macaques show robust connectivity even with posterior visual regions. Do these developmental differences also exist in the human amygdala, and are there specific functional regions that undergo the most pronounced developmental changes in their connections with the amygdala? To address these questions, we explored the functional connectivity (from resting-state fMRI data) of the basolateral amygdala to occipitotemporal cortex in human neonates scanned within one week of life and compared the connectivity patterns to those observed in young adults. Specifically, we calculated amygdala connectivity to anterior-posterior gradients of the anatomically-defined occipitotemporal cortex, and also to putative occipitotemporal functional parcels, including primary and high-level visual and auditory cortices (V1, A1, face, scene, object, body, high-level auditory regions). Results showed a decreasing gradient of functional connectivity to the occipitotemporal cortex in adults-similar to the gradient seen in macaque tracer studies-but no such gradient was observed in neonates. Further, adults had stronger connections to high-level functional regions associated with face, body, and object processing, and weaker connections to primary sensory regions (i.e., A1, V1), whereas neonates showed the same amount of connectivity to primary and high-level sensory regions. Overall, these results show that functional connectivity between the amygdala and occipitotemporal cortex is not yet differentiated in neonates, suggesting a role of maturation and experience in shaping these connections later in life.

In vivo-assessment of the human temporal network: Evidence for asymmetrical effective connectivity

The human temporal lobe is a multimodal association area which plays a key role in various aspects of cognition, particularly in memory formation and spatial navigation. Functional and anatomical connectivity of temporal structures is thus a subject of intense research, yet by far underexplored in humans due to ethical and technical limitations. We assessed intratemporal cortico-cortical interactions in the living human brain by means of single pulse electrical stimulation, an invasive method allowing mapping effective intracortical connectivity with a high spatiotemporal resolution. Eighteen subjects with normal anterior-mesial temporal MR imaging undergoing intracranial presurgical epilepsy diagnostics with multiple depth electrodes were included. The investigated structures were temporal pole, hippocampus, amygdala and parahippocampal gyrus. Intratemporal cortical connectivity was assessed as a function of amplitude of the early component of the cortico-cortical evoked potentials (CCEP). While the analysis revealed robust interconnectivity between all explored structures, a clear asymmetry in bidirectional connectivity was detected for the hippocampal network and for the connections between the temporal pole and parahippocampal gyrus. The amygdala showed bidirectional asymmetry only to the hippocampus. The provided evidence of asymmetrically weighed intratemporal effective connectivity in humans in vivo is important for understanding of functional interactions within the temporal lobe since asymmetries in the brain connectivity define hierarchies in information processing. The findings are in exact accord with the anatomical tracing studies in non-human primates and open a translational route for interventions employing modulation of temporal lobe function.

Guanfacine modulates the emotional biasing of amygdala-prefrontal connectivity for cognitive control

Functional interactions between amygdala and prefrontal cortex provide a cortical entry point for emotional cues to bias cognitive control. Stimulation of α2 adrenoceptors enhances the prefrontal control functions and blocks the amygdala-dependent encoding of emotional cues. However, the impact of this stimulation on amygdala-prefrontal interactions and the emotional biasing of cognitive control have not been established. We tested the effect of the α2 adrenoceptor agonist guanfacine on psychophysiological interactions of amygdala with prefrontal cortex for the emotional biasing of response execution and inhibition. Fifteen healthy adults were scanned twice with event-related functional magnetic resonance imaging while performing an emotional go/no-go task following administration of oral guanfacine (1mg) and placebo in a double-blind, counterbalanced design. Happy, sad, and neutral faces served as trial cues. Guanfacine moderated the effect of face emotion on the task-related functional connectivity of left and right amygdala with left inferior frontal gyrus compared to placebo, by selectively reversing the functional co-activation of the two regions for response execution cued by sad faces. This shift from positively to negatively correlated activation for guanfacine was associated with selective improvements in the relatively low accuracy of responses to sad faces seen for placebo. These results demonstrate the importance of functional interactions between amygdala and inferior frontal gyrus to both bottom-up biasing of cognitive control and top-down control of emotional processing, as well as for the α2 adrenoceptor-mediated modulation of these processes. These mechanisms offer a possibile method to address the emotional reactivity that is common to several psychiatric disorders.

Amygdalar function reflects common individual differences in emotion and pain regulation success

Although the co-occurrence of negative affect and pain is well recognized, the mechanism underlying their association is unclear. To examine whether a common self-regulatory ability impacts the experience of both emotion and pain, we integrated neuroimaging, behavioral, and physiological measures obtained from three assessments separated by substantial temporal intervals. Our results demonstrated that individual differences in emotion regulation ability, as indexed by an objective measure of emotional state, corrugator electromyography, predicted self-reported success while regulating pain. In both emotion and pain paradigms, the amygdala reflected regulatory success. Notably, we found that greater emotion regulation success was associated with greater change of amygdalar activity following pain regulation. Furthermore, individual differences in degree of amygdalar change following emotion regulation were a strong predictor of pain regulation success, as well as of the degree of amygdalar engagement following pain regulation. These findings suggest that common individual differences in emotion and pain regulatory success are reflected in a neural structure known to contribute to appraisal processes.

Spinogenesis and Pruning in the Anterior Ventral Inferotemporal Cortex of the Macaque Monkey: An Intracellular Injection Study of Layer III Pyramidal Cells

Pyramidal cells grow and mature at different rates among different cortical areas in the macaque monkey. In particular, differences across the areas have been reported in both the timing and magnitude of growth, branching, spinogenesis, and pruning in the basal dendritic trees of cells in layer III. Presently available data suggest that these different growth profiles reflect the type of functions performed by these cells in the adult brain. However, to date, studies have focused on only a relatively few cortical areas. In the present investigation we quantified the growth of the dendritic trees of layer III pyramidal cells in the anterior ventral portion of cytoarchitectonic area TE (TEav) to better comprehend developmental trends in the cerebral cortex. We quantified the growth and branching of the dendrities, and spinogenesis and pruning of spines, from post-natal day 2 (PND2) to four and a half years of age. We found that the dendritic trees increase in size from PND2 to 7 months of age and thereafter became smaller. The dendritic trees became increasingly more branched from PND2 into adulthood. There was a two-fold increase in the number of spines in the basal dendritic trees of pyramidal cells from PND2 to 3.5 months of age and then a 10% net decrease in spine number into adulthood. Thus, the growth profile of layer III pyramidal cells in the anterior ventral portion of the inferotemporal cortex differs to that in other cortical areas associated with visual processing.

The left amygdala knows fear: laterality in the amygdala response to fearful eyes

The detection of threat is a role that the amygdala plays well, evidenced by its increased response to fearful faces in human neuroimaging studies. A critical element of the fearful face is an increase in eye white area (EWA), hypothesized to be a significant cue in activating the amygdala. However, another important social signal that can increase EWA is a lateral shift in gaze direction, which also serves to orient attention to potential threats. It is unknown how the amygdala differentiates between these increases in EWA and those that are specifically associated with fear. Using functional magnetic resonance imaging, we show that the left amygdala distinguished between fearful eyes and gaze shifts despite similar EWA increases whereas the right amygdala was less discriminatory. Additional analyses also revealed selective hemispheric response patterns in the left fusiform gyrus. Our data show clear hemispheric differences in EWA-based fear activation, suggesting the existence of parallel mechanisms that code for emotional face information.

Sequence of information processing for emotions through pathways linking temporal and insular cortices with the amygdala

The amygdala has a pivotal role in deciphering the emotional significance of sensory stimuli enabling emotional memory formation. We have previously shown that prefrontal cortices in rhesus monkeys project to the amygdala mainly from their deep layers, suggesting feedback communication. If sensory areas convey signals pertinent to the state of the environment, they should issue feedforward projections to the amygdala, arising mainly from the upper layers, consistent with the flow of information from earlier- to later-processing sensory cortices. Here we addressed this hypothesis in cases with injection of tracers in sites of the amygdala known to have robust connections with prefrontal cortices and mapped connections in insular and temporal cortices associated with sensory processing and memory. The medial temporal pole, the entorhinal and perirhinal areas, and the agranular and dysgranular insula had the densest connections with the amygdala, and the lateral temporal pole, the parahippocampal region, and the granular insula had sparser connections. Most areas projected to the amygdala predominantly from the upper layers, suggesting feedforward communication, and received reciprocal amygdalar innervation primarily in their superficial layers, suggesting feedback communication. In contrast, the entorhinal cortex issued projections to the amygdala from its deep layers, suggesting feedback communication, and received reciprocal amygdalar projections most densely in layers II-III, which project to the hippocampus. These findings may help explain how the amygdala can attach emotional value to environmental stimuli, participate in the sequence of information processing of emotions, and modulate the formation of emotional memories.

Processing the socially relevant parts of faces

Faces are processed by a distributed neural system in the visual as well as in the non-visual cortex [the "core" and the "extended" systems, J.V. Haxby, E.A. Hoffman, M.I. Gobbini, The distributed human neural system for face perception, Trends Cogn. Sci. 4 (2000) 223-233]. Yet, the functions of the different brain regions included in the face processing system are far from clear. On the basis of the case study of a patient unable to recognize fearful faces, Adolphs et al. [R. Adolphs, F. Gosselin, T.W. Buchanan, D. Tranel, P. Schyns, A.R. Damasio, A mechanism for impaired fear recognition after amygdala damage, Nature 433 (2005) 68-72] suggested that the amygdala might play a role in orienting attention towards the eyes, i.e. towards the region of face conveying most information about fear. In a functional magnetic resonance (fMRI) study comparing patterns of activation during observation of whole faces and parts of faces displaying neutral expressions, we evaluated the neural systems for face processing when only partial information is provided, as well as those involved in processing two socially relevant facial areas (the eyes and the mouth). Twenty-four subjects were asked to perform a gender decision task on pictures showing whole faces, upper faces (eyes and eyebrows), and lower faces (mouth). Our results showed that the amygdala was activated more in response to the whole faces than to parts of faces, indicating that the amygdala is involved in orienting attention toward eye and mouth. Processing of parts of faces in isolation was found to activate other regions within both the "core" and the "extended" systems, as well as structures outside this network, thus suggesting that these structures are involved in building up the representation of the whole face from its parts.

A role for the 'magnocellular advantage' in visual impairments in neurodevelopmental and psychiatric disorders

Evidence exists implicating abnormal visual information processing and visually driven attention in a number of neurodevelopmental and psychiatric disorders, suggesting that research into such disorders may benefit from a better understanding of more recent advances in visual system processing. A new integrated model of visual processing based on primate single cell and human electrophysiology may provide a framework, to understand how the visual system is involved, by implicating the magnocellular pathway's role in driving attentional mechanisms in higher-order cortical regions, what we term the 'magnocellular advantage'. Evidence is also presented demonstrating visual processing occurs considerably faster than previously assumed, and emphasising the importance of top-down feedback signals into primary visual cortex, as well as considering the possibility of lateral connections from dorsal to ventral visual areas. Such organisation is argued to be important for future research highlighting visual aspects of impairment in disorders as diverse as schizophrenia and autism.

Subdivisions of inferior temporal cortex in squirrel monkeys make dissociable contributions to visual learning and memory

Inferior temporal cortex of squirrel monkeys consists of caudal (ITC), intermediate (ITI), and rostral (ITR) subdivisions, possibly homologous to TEO, posterior TE, and anterior TE of macaque monkeys. The present study compared visual learning in squirrel monkeys with ablations of ITC; ITI and ITR (group ITRd); or ITI, ITR, and more ventral cortex, including perirhinal cortex (group ITR+), with visual learning in unoperated controls. The ITC monkeys had significant impairments on pattern discriminations and milder deficits on delayed non-matching to sample (DNMS) of objects. The ITRd monkeys had deficits on some pattern discriminations but not on DNMS. The ITRd monkeys were significantly impaired on DNMS and some pattern discriminations. These results are similar to those found in macaques and support the proposed homologies.

A [17F]-fluoromethane PET/TMS study of effective connectivity

We used transcranial magnetic stimulation (TMS) in combination with positron emission tomography (PET) to investigate the effective connectivity of four cortical regions within the same study. By employing [17F]-[CH3F] ([17F]-fluoromethane) as a radiotracer of blood-flow, we were able to obtain increased sensitivity compared to [15O]-H2O for both cortical and subcortical structures. The brain areas investigated were left primary motor cortex, right primary visual cortex, and left and right prefrontal areas. We found that each site of stimulation yielded a different pattern of activation/deactivation consistent with its anatomical connectivity. Moreover, we found that TMS of prefrontal and motor cortical areas gave rise to trans-synaptic activation of subcortical circuits.

Topographic organization of projections from the amygdala to the visual cortex in the macaque monkey

The topography of amygdaloid projections to the visual cortices in the macaque monkey was examined by injecting the fluorescent tracers Fast Blue and Diamidino Yellow at different locations in the occipital and temporal lobes and mapping the distribution of retrogradely labeled cells in the amygdala. Injections involving regions from rostral area TE to caudal area V1 all resulted in labeled cells within the basal nucleus of the amygdala. Relatively few double-labeled cells were observed even when the two injections were separated by less than 3 mm. The projections were rostrocaudally organized such that projections to caudal visual areas originated from dorsal and caudal portions of the magnocellular division of the basal nucleus while projections to more rostrally situated visual areas originated in more rostral and ventral portions of the basal nucleus. When injections involved rostral and medial portions of area TE, retrogradely labeled cells were observed in the accessory basal and lateral nuclei in addition to the basal nucleus. These data confirm that the amygdala gives rise to feedback projections to all levels of the "ventral stream" visual pathway. The projections do not appear to be diffusely distributed since few double-labeled cells were observed. The largest cells of the basal nucleus, those located in the magnocellular division, project the farthest in the visual system and innervate all occipital and temporal levels. The smaller cells, in the intermediate and parvicellular regions, project to more rostral and medial portions of the visual cortex. These results suggest that the amygdala may have substantial modulatory control over sensory processing at all stages of the ventral-stream visual cortical hierarchy.

Pulvinar and other subcortical connections of dorsolateral visual cortex in monkeys

The present study used injections of neuroanatomical tracers to determine the subcortical connections of the caudal and rostral subdivisions of the dorsolateral area (DL) and the middle temporal crescent area (MT(C)) in owl monkeys (Aotus trivirgatus), squirrel monkeys (Saimiri sciureus), and macaque monkeys (Macaca fascicularis and M. radiata). Emphasis was on connections with the pulvinar. Patterns of corticopulvinar connections were related to subdivisions of the inferior pulvinar (PI) defined by histochemical or immunocytochemical architecture. Connections of DL/MT(C) were with the PI subdivisions, PICM, PICL, and PIp; the lateral pulvinar (PL); and, more sparsely, the lateral portion of the medial pulvinar (PM). In squirrel monkeys, there was a tendency for caudal DL to have stronger connections with PICL than PICM and for rostral DL/MT(C) to have stronger connections with PICM than PICL. In all three primates, DL/MT(C) had reciprocal connections with the pulvinar and claustrum; received afferents from the locus coeruleus, dorsal raphe, nucleus annularis, central superior nucleus, pontine reticular formation, lateral geniculate nucleus, paracentral nucleus, central medial nucleus, lateral hypothalamus, basal nucleus of the amygdala, and basal nucleus of Meynert/substantia innominata; and sent efferents to the pons, superior colliculus, reticular nucleus, caudate, and putamen. Projections from DL/MT(C) to the nucleus of the optic tract were also observed in squirrel and owl monkeys. Similarities in the subcortical connections of the dorsolateral region, especially those with the pulvinar, provide further support for the conclusion that the DL regions are homologous in the three primate groups.

Functional neuroanatomy of emotion: a meta-analysis of emotion activation studies in PET and fMRI

Neuroimagingstudies with positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have begun to describe the functional neuroanatomy of emotion. Taken separately, specific studies vary in task dimensions and in type(s) of emotion studied and are limited by statistical power and sensitivity. By examining findings across studies, we sought to determine if common or segregated patterns of activations exist across various emotional tasks. We reviewed 55 PET and fMRI activation studies (yielding 761 individual peaks) which investigated emotion in healthy subjects. Peak activation coordinates were transformed into a standard space and plotted onto canonical 3-D brain renderings. We divided the brain into 20 nonoverlapping regions, and characterized each region by its responsiveness across individual emotions (positive, negative, happiness, fear, anger, sadness, disgust), to different induction methods (visual, auditory, recall/imagery), and in emotional tasks with and without cognitive demand. Our review yielded the following summary observations: (1) The medial prefrontal cortex had a general role in emotional processing; (2) fear specifically engaged the amygdala; (3) sadness was associated with activity in the subcallosal cingulate; (4) emotional induction by visual stimuli activated the occipital cortex and the amygdala; (5) induction by emotional recall/imagery recruited the anterior cingulate and insula; (6) emotional tasks with cognitive demand also involved the anterior cingulate and insula. This review provides a critical comparison of findings across individual studies and suggests that separate brain regions are involved in different aspects of emotion.

Connections between the amygdala and auditory cortical areas in the macaque monkey

Connections between the amygdala and auditory cortical areas TC, and the rostral, intermediate and caudal regions of area TA (TAr, TAi and TAc, respectively) in the macaque monkey (Macaca fuscata and Macaca nemestrina) were investigated following placements of cortical deposits of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Areas TC and TAc received weak projections and these derived only from the lateral basal nucleus. Areas TAi and TAr received projections from the lateral, lateral basal and accessory basal nuclei. In contrast, corticopetal projections to the amygdala originated in areas TAi and TAr, but never in TAc or TC. The projections from areas TAi and TAr terminated only in the lateral nucleus, and in particular at the lateral part of the middle and caudal portions of the amygdala. Thus, the amygdalofugal projections to the auditory cortices are more widespread and more complex than the amygdalopetal projections of the auditory cortices. As judged from experiments in which deposits were made at different sites along the rostrocaudal axis of the auditory cortex, there was a progressive increase seen in density of the amygdala connections with more anteriorly-placed injection sites.

Organization of connections of the basal and accessory basal nuclei in the monkey amygdala

The present study investigated the intrinsic connections of the basal and accessory basal nuclei of the Macaca fascicularis monkey by means of the anterograde tracers Phaseolus vulgaris-leucoagglutinin (PHA-L) and biotinylated dextran amine (BDA). Analysis of the intranuclear connections of the basal nucleus indicates that there are five modules: dorsal, intermediate, ventral lateral, ventral medial and periamygdaloid sulcal cortex. The dorsal division projects to the intermediate division. Laterally, the intermediate division projects to the ventral lateral division and dorsal parts of the ventral medial division. Ventrally, the ventral lateral division projects to the ventral medial division and periamygdaloid sulcal cortex, which appears to constitute a medial extension of the basal nucleus onto the cortical surface of the amygdala. Medially, the ventral medial division projects to the intermediate and dorsal divisions. Thus, the connections between these modules form functional microcolumns within the nucleus with distinct patterns of information flow that are dorsal to ventral laterally, lateral to medial ventrally, and ventral to dorsal medially. Observations on the intranuclear connections of the accessory basal nucleus suggest that they are organized into two relatively distinct domains: the dorsal division projects to the ventral division and the ventral division projects primarily to the ventromedial division. Projections to other amygdaloid areas originate in select divisions of the basal and accessory basal nuclei, and are topographically distributed. The organization of intrinsic connections of the basal nuclei correlates with specific amygdalo-cortical connections and suggests that extensive convergence of information takes place within the amygdala, which potentially influences activity at both the temporal and parietal pathways and hippocampal fields.

Organization of the intrinsic connections of the monkey amygdaloid complex: projections originating in the lateral nucleus

We have used the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L) to study the intrinsic projections of the lateral nucleus of the Macaca fascicularis monkey amygdaloid complex. A reanalysis of the monkey lateral nucleus indicated that there are at least four distinct cytoarchitectonic divisions: dorsal, dorsal intermediate, ventral intermediate, and ventral. The major projections within the lateral nucleus originate in the dorsal, dorsal intermediate, and ventral intermediate divisions and terminate in the ventral division. The ventral division also projects to itself but does not project significantly to the other divisions of the lateral nucleus. Thus, the ventral division appears to be a site of convergence for information entering all other portions of the lateral nucleus. There are substantial regional and topographic differences in the projections from each of the lateral nucleus divisions to other amygdaloid nuclei. The dorsal division projects to all divisions of the basal and accessory basal nuclei, to the periamygdaloid cortex, the nucleus of the lateral olfactory tract, the dorsal division of the amygdalohippocampal area, and the lateral capsular nuclei. The dorsal intermediate division projects to the intermediate and parvicellular divisions of the basal nucleus, to the parvicellular division of the accessory basal nucleus, and to the periamygdaloid cortex. The ventral intermediate division projects to the magnocellular division of the accessory basal nucleus and to the parvicellular division of the basal nucleus. The major projections from the ventral division are directed to the parvicellular division of the basal nucleus, the parvicellular division of the accessory basal nucleus, the medial nucleus, and the periamygdaloid cortex. Projections from all portions of the lateral nucleus to the central nucleus are generally very light. It appears, therefore, that each division of the lateral nucleus originates topographically organized projections to the other amygdaloid areas that terminate in distinct portions of the target regions. The topographic organization of intrinsic amygdaloid projections raises the possibility that serial and parallel sensory processing may take place within the amygdaloid complex.

Organization of corticostriatal and corticoamygdalar projections arising from the anterior inferotemporal area TE of the macaque monkey: a Phaseolus vulgaris leucoagglutinin study

Corticostriatal and corticoamygdalar projections arising from area TE of the macaque monkey were studied by focal injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin into the dorsolateral and ventromedial subdivisions of the anterior TE (TEad and TEav, respectively). This approach yielded several new results. First, the global distributions of labeled terminals revealed that both TEad and TEav projected to the ventrocaudal striatum, including the tail of the caudate nucleus and the adjacent ventral putamen, and the dorsolateral aspect of the deep amygdaloid nuclei. TEav also projected to the medial basal nucleus of the amygdala and the ventral striatum. Second, the reconstructed single axons (n = 18) demonstrated that some axons originating from TEav or TEad projected simultaneously to the ventrocaudal striatum and the dorsolateral aspect of the deep amygdaloid nuclei by giving off collaterals. TEav axons projected to the medial basal nucleus of the amygdala also had collaterals projecting to the perirhinal cortex or area TG. And third, it was revealed that the axons originating from a focal TEav or TEad projected to a restricted territory (3.4-3.6 mm rostrocaudally) in the ventrocaudal striatum with four to six dispersed, rostrocaudally elongated, rod-like modules. Individual axons with multiple arbors innervated many of these modules. These findings add the evidence that the anterior part of TE is anatomically heterogeneous and suggest that the deep amygdaloid nuclei may be functionally dissociated, with the dorsolateral aspect more closely related to the ventrocaudal striatum and the medial basal nucleus more closely related to the perirhinal cortex.

Intact enhancement of declarative memory for emotional material in amnesia

Emotional arousal has been demonstrated to enhance declarative memory (conscious recollection) in humans in both naturalistic and experimental studies. Here, we examined this effect in amnesia. Amnesic patients and controls viewed a slide presentation while listening to an accompanying emotionally arousing story. In both groups, recognition memory was enhanced for the emotionally arousing story elements. The magnitude of the enhancement was proportional for both amnesic patients and controls. Emotional reactions to the story were also equivalent. The results suggest that the enhancement of declarative memory associated with emotional arousal is intact in amnesia. Together with findings from patients with bilateral amygdala lesions, the results indicate that the amygdala is responsible for the enhancement effect.

Functional double dissociation between two inferior temporal cortical areas: perirhinal cortex versus middle temporal gyrus

There is both anatomic and cytoarchitectural evidence for dorsal-ventral subdivisions of the inferior temporal cortex. Despite this, there has been only limited evidence of corresponding functional subdivisions and no evidence that two adjacent cortical areas within the inferior temporal cortex, namely area TE and the perirhinal cortex, have distinctly different roles in vision and memory. We assessed the color discrimination abilities of cynomolgus monkeys with either bilateral ablation of the perirhinal cortex or bilateral ablation of the middle temporal gyrus. The stimuli were isoluminant colored squares presented on a touch screen. In each trial the subject had to learn to discriminate and select the correct choice (green) from among a maximum of eight other foils, each varying in either hue or saturation. Relative to unoperated controls, monkeys with middle temporal gyrus lesions were severely impaired in the color discrimination task, whereas monkeys with perirhinal lesions were unimpaired on this task. We also assessed the visual recognition abilities, as measured by a basic delayed nonmatching-to-sample task with trial-unique objects presented in a Wisconsin General Test Apparatus, of rhesus monkeys with bilateral middle temporal gyrus lesions. We then tested the monkeys' postoperative performance on a delayed nonmatching-to-sample task with delays and extended list lengths. The results from this experiment were compared with those from two other groups of rhesus monkeys, an unoperated control group and a group with bilateral perirhinal cortex lesions, both of which had performed the identical tasks in a previous experiment. Relative to unoperated controls, monkeys with perirhinal cortex lesions were severely impaired both in relearning the basic delayed nonmatching-to-sample task and on the postoperative performance test. In contrast, monkeys with middle temporal gyrus lesions were only mildly affected in relearning the basic nonmatching task and were unimpaired on the postoperative performance test. Thus our data demonstrate a clear functional double dissociation between the perirhinal cortex and the middle temporal gyrus. This result gives strong support to the hypothesis that the perirhinal cortex and the adjacent area TE have distinctly different roles in visual learning and memory.

Divergent projections from the anterior inferotemporal area TE to the perirhinal and entorhinal cortices in the macaque monkey

Area TE is located at the latter part of the ventral visual cortical pathway, which is essential for visual recognition of objects. TE projects heavily to the perirhinal region, which is important for visual recognition memory of objects. To study the organization of projections from TE to the perirhinal (areas 35 and 36) and entorhinal (area 28) cortices, we made focal injections of Phaseolus vulgaris leucoagglutinin (PHA-L) and large injections of biocytin or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into anterior levels of TE in macaque monkeys. Injections of PHA-L into the ventral part of anterior TE (TEav) resulted in labeling of terminals distributed widely in area 36 (approximately one-half of its total extent), although the injection sites were limited to 0.7 mm in width. The labeled terminals tended to be denser in the medial part of area 36. There was less dense but definite labeling in area 35 and the lateral part of area 28. After a single injection of PHA-L or WGA-HRP into the dorsal part of anterior TE (TEad), labeled terminals were confined to a small region at the lateral part of area 36 (less than one-tenth of its total extent). The projections to areas 35 and 28 from TEad were much sparser than those from TEav. The different patterns of projections to the perirhinal and entorhinal cortices, together with previously reported differences in their afferent and other efferent connections, suggest the functional differentiation between TEav and TEad. The divergent projection from TEav to the perirhinal cortex may facilitate the association of different visual features in the perirhinal cortex.

Qualitative and quantitative features of axons projecting from caudal to rostral inferior temporal cortex of squirrel monkeys

On the basis of cortical and subcortical connections and architectonics, inferior temporal (IT) cortex of squirrel monkeys consists of a caudal region, ITC, with dorsal (ITCd) and ventral (ITCv) subdivisions; a rostral region, ITR; and possibly a third region intermediate to ITC and ITR, ITI (Weller & Steele, 1992; Steele & Weller, 1993). The present study qualitatively and quantitatively examined the terminal arborizations of 26 axons in ITR and ITI labeled by injections of biocytin or, in one case, horseradish peroxidase, in ITCv. The majority of axons gave rise to a single terminal arbor, with a small number branching into two overlapping or nearby arbors. Presumptive terminal specializations consisted of rounded, bead-like swellings, most often located en passant. All axons terminated in layer 4 of cortex, and most had additional terminations in layers 3 and 5. The total extent of each axon's terminal arbor was 125-750 microns dorsoventrally (mean = 360.6 microns) and 150-725 microns anteroposteriorly (mean = 328.1 microns; all values uncorrected for shrinkage). In most axons, especially those with larger terminal fields, boutons were not uniformly distributed, but formed 2-4 clumps (mean = 2.2), with a mean width of 149 microns, separated by narrower regions of fewer boutons. Based on a cluster analysis of characteristics of the 26 axons, axons projecting from caudal (ITCv) to rostral (ITR or ITI) IT cortex of squirrel monkeys comprised three groups that we called Type I, Type II, and Type III. Type I axons, the smallest in area extent of terminal arbor, terminated predominantly in dorsal ITR. Type III axons, largest in areal extent, and Type II axons, intermediate in areal extent, terminated in ventral ITR and throughout ITI. The three classes of axons may correspond to different types of visual information entering rostral IT cortex. The clumping of boutons suggests that individual axons terminate in limited patches within their terminal fields.

Transient subcortical connections of inferior temporal areas TE and TEO in infant macaque monkeys

As part of a long-term study designed to examine the ontogeny of visual memory in monkeys and its underlying neural circuitry, we have examined the subcortical connections of the inferior temporal cortex in infant monkeys and compared them to those previously described in adult monkeys (Webster et al. [1993] J. Comp. Neurol. 335:73-91). Inferior temporal areas TEO and TE were injected with wheat germ agglutinin conjugated to horseradish peroxidase and tritiated amino acids, respectively, or vice versa, in 1-week-old (N = 6) and 3-4-year-old (N = 6) Macaca mulatta, and the distributions of labeled cells and terminals were examined in subcortical structures. Although the connections of inferior temporal cortex with subcortical structures were found to be similar in infant and adult monkeys, several projections appear to undergo refinement during development. Quantitative analysis showed that 1) whereas the projection from TE to the superior colliculus is consistent (5 of 5 cases) and widespread in infants, it is less reliable (2 of 7 cases) and limited in areal extent in adults; 2) although the projections from TE to nucleus medialis dorsalis and the tail of the caudate are present in infants and adults, they are reduced in adults; and 3) TEO receives input from the dorsal lateral geniculate nucleus in both infants and adults, but the number of cells giving rise to this projection is lower in adults. There was also a suggestion that TE projects to nucleus paracentralis in infants (2 of 5 cases) but not in adults (0 of 7 cases). No differences between infants and adults were apparent in other subcortical connections, including those with the pulvinar, reticular nucleus, claustrum, and putamen.

The effects of number of stimuli and prior exposure on performance of concurrent visual discriminations during suppression of inferotemporal cortex with cold

The visual part of the temporal cortex, cytoarchitectural area TE has been split into dorsal (TEd) and ventral (TEv) subdivisions. TE has long been associated with the identification of objects. However, in order to explain retrieval deficits with suppression of prestriate cortex, but not with suppression of TE, we hypothesized that object identification might take place in a working memory in the prestriate cortex upstream from TE. Exposure to the stimuli before suppressing TEd was hypothesized to cause its contribution to be relayed to prestriate cortex in anticipation of further work with them. This predicts that during TEd suppression there is a loss of access to some long-term visual memory, and without that access, large numbers of stimuli should overwhelm the limited capacity working memory. It also predicts that prior exposure to stimuli should protect them from loss during TEd suppression. We challenged these predictions in two experiments. In the first, we tested the animals on three concurrent discriminations requiring them to retrieve 8 pairs of stimuli for each one. The animals performed well on some of the discriminations during TEd suppression, but failed on others, which is consistent with the prediction. Also, different animals failed with different stimuli. However, when we tested with only the failed discriminations, they still did badly with one or two pairs, which is not consistent with the prediction. In the second experiment, we tested them with 1, 4, 7 or 10 pairs of visual discriminations drawn from a set of 23 the animals had learned. Half of the discriminations were presented immediately before suppression and half were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Subcortical connections of subdivisions of inferior temporal cortex in squirrel monkeys

On the basis of cortical connections and architectonics, inferior temporal (IT) cortex of squirrel monkeys consists of a caudal, prestriate-recipient region, ITC; a rostral region, ITR; and possibly an intermediate region along the border of ITC and ITR, "ITI" (Weller & Steele, 1992). ITC contains dorsal (ITCd) and ventral (ITCV) areas. The subcortical connections of these subdivisions of IT cortex were determined in the present study from the results of cortical injections of wheat-germ agglutinin conjugated to horseradish peroxidase, [3H]-amino acids and fast blue. ITC and ITR receive afferents from the locus coeruleus, dorsal raphe, nucleus annularis, central superior nucleus, pontine reticular formation, lateral hypothalamus, paracentral nucleus, and central medial nucleus; send efferents to the superior colliculus, reticular nucleus, and striatum; and have both afferent and efferent connections with the pretectum, pulvinar, claustrum, amygdala, and basal nucleus of Meynert. ITC and ITR have different patterns of connections with a number of subcortical structures, including the pulvinar and amygdala. Injections in ITC strongly label multiple nuclei of the inferior pulvinar and the medial division of the lateral pulvinar (PLM), and moderately label the medial pulvinar (PM), whereas injections in ITR strongly label PM and moderately label PLM. Injections in ITC label sparse projections to the lateral nucleus of the amygdala, in contrast to injections in ITR that label strong projections to the lateral and basal nuclei of the amygdala. Injections in "ITI" produce a pattern of subcortical label that has some features of that observed from injections in ITC and that observed from injections in ITR. Although most of the connections of ITCd and ITCv appear similar, only injections involving ITCd label the middle nucleus of the inferior pulvinar (PIM). Comparison of the subcortical connections of subdivisions of IT cortex in squirrel monkeys and what is presently known of the subcortical connections of subdivisions of IT cortex in macaque monkeys supports the previous suggestion that ITC of squirrel monkeys may be comparable to area TEO of macaques, ITI may be comparable to posterior area TE, and ITR may be comparable to anterior area TE (Weller & Steele, 1992).

Correlation of unit recordings with regional cell counts in epileptogenic human temporal lobe

The previously reported diminished incidence of neuronal activity recorded from areas ipsilateral to a seizure focus may result from either cell loss or pathophysiologic changes in hippocampus and related structures. We examined records of single-cell discharge from 471 electrode bundles in 62 patients who later had cell counts taken from samples of resected tissue. Analysis of variance showed that amygdala and parahippocampal gyrus had more activity than hippocampus and the subicular complex and that the resected side had less activity overall. Only the posterior subicular complex showed more high-amplitude (> 50 microV) activity on the epileptogenic side; all other areas showed more activity contralaterally. Activity between 25 and 50 microV did not differ across sides or structures. Percentage of maximal cell count was correlated with the number of electrodes with high-amplitude activity only in the subicular complex. Low-amplitude activity in nonresected hippocampus, however, was strongly negatively correlated with cell counts on the resected side, perhaps owing to compensatory mechanisms. Cell counts in hippocampus correlated negatively with high-amplitude unit activity in resected amygdala, suggesting reciprocity between these areas. These results suggest that the amount of cell activity recorded from mesiotemporal structures involves bilateral factors more complex than simple cell loss.

Retrograde transport of D-[3H]-aspartate injected into the monkey amygdaloid complex

The possibility that certain of the afferents of the primate amygdaloid complex use an excitatory amino acid transmitter was evaluated by injecting D-[3H]-aspartate into the amygdala of two Macaca fascicularis monkeys. The distribution of D-[3H]-aspartate labeled neurons was compared with those labeled with the nonselective retrograde tracer WGA-HRP injected at the same location as the isotope. Retrogradely labeled cells of both types were observed in a variety of cortical and subcortical structures observed in a variety of cortical and subcortical structures and in discrete regions within the amygdala. D-[3H]-aspartate labeled neurons were observed in layers III and V of the frontal, cingulate, insular and temporal cortices. In the hippocampal formation, heavily labeled cells were observed in the CA1 region and in the deep layers of the entorhinal cortex. Of the subcortical afferents, the claustrum and the midbrain peripeduncular nucleus contained the greatest number of D-[3H]-aspartate labeled cells. Subcortical afferents that are not thought to use excitatory amino acids, such as the cholinergic neurons of the basal nucleus of Meynert, did not retrogradely transport the isotope. Within the amygdala, the most conspicuous labeling was in the paralaminar nucleus which forms the rostral and ventral limits of the amygdala. When the D-[3H]-aspartate injection involved the basal nucleus, many labeled cells were also observed in the lateral nucleus. Retrograde transport of D-[3H]-aspartate injected into the amygdala, therefore, appears to demonstrate a subpopulation of inputs that may use an excitatory amino acid transmitter.

Projections from the amygdala to basoventral and mediodorsal prefrontal regions in the rhesus monkey

The sources of ipsilateral projections from the amygdala to basoventral and mediodorsal prefrontal cortices were studied with retrograde tracers (horseradish peroxidase or fluorescent dyes) in 13 rhesus monkeys. The basoventral regions injected with tracers included the orbital periallocortex and proisocortex, orbital areas 13, 11, and 12, lateral area 12, and ventral area 46. The mediodorsal regions included portions of medial areas 25, 32, 14, and dorsal area 8. The above sites represent areas within two architectonic series of cortices referred to as basoventral or mediodorsal on the basis of their anatomic location. Each series consists of areas that show a gradual increase in the number of layers and their delineation in a direction from the caudal orbital and medial limbic cortices, which have an incipient laminar organization, towards the eulaminated periarcuate cortices (Barbas and Pandya, J. Comp. Neurol. 286: 353-375, '89). Labeled neurons projecting to the prefrontal cortex were found in the basolateral, basomedial (also known as accessory basal), lateral, and ventral cortical nuclei, and in the anterior amygdaloid and amygdalopiriform areas. The distribution of labeled neurons differed both quantitatively and qualitatively depending on whether the injection sites were in basoventral or mediodorsal prefrontal cortices. Cases with caudal orbital injections had the most labeled neurons in the amygdala, followed by cases with injections in cortices situated medioventrally. The latter received a high proportion of their amygdaloid projections from the basomedial nucleus. The lateral amygdaloid nucleus sent a robust projection to the least architectonically differentiated orbital periallocortex, and a weaker projection to the adjoining orbital proisocortical regions, but did not appear to project to either medial proisocortical sites or to the more differentiated ventrolateral or dorsolateral prefrontal cortices. In addition, there were topographical differences in the origin of projections from one amygdaloid nucleus directed to various prefrontal cortices. These differences were correlated either with the destination of the axons of afferent amygdaloid neurons to basoventral or to mediodorsal prefrontal cortices and/or with their projection to areas with varying degrees of laminar organization within the basoventral or mediodorsal sector. The clearest topography was observed for projections originating in the basolateral nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Direct projections from the ventral TE area of the inferotemporal cortex to hippocampal field CA1 in the monkey

Anterogradely labeled terminals were found densely in field CA1, but not in any other field, of the hippocampal formation following injections of horseradish peroxidase into the ventral TE area of the inferotemporal cortex, whereas no label was seen in any field of the hippocampal formation following injections into the dorsal TE area. The labeled terminals were distributed mainly in a medial part of the stratum moleculare of field CA1 throughout its rostrocaudal extent. The present finding provides the first demonstration of direct projections from the inferotemporal cortex to the hippocampal formation.

A direct projection from hippocampal field CA1 to ventral area TE of inferotemporal cortex in the monkey

Retrogradely labeled cells were found in field CA1 of the hippocampal formation in monkeys following injections of horseradish peroxidase in ventral area TE of inferotemporal cortex. No hippocampal label was found following injections in dorsal area TE and area TEO. The findings provide the first demonstration of a direct projection from hippocampal field CA1 to area TE.