Functional activation of the left amygdala and hippocampus during associative encoding

Personality traits related to cognitive functioning in patients with functional neurological disorder

Cognitive symptoms are prevalent in patients with functional neurological disorder (FND). Several studies have suggested that personality traits such as neuroticism may play a pivotal role in the development of FND. FND has also been associated with alexithymia: patients with FND report difficulties in identifying, analyzing, and verbalizing emotions. Whether or not alexithymia and other personality traits are associated with cognitive symptomatology in patients with FND is unknown. In the current study, we explored whether the Big Five personality model factors (neuroticism, extraversion, openness, agreeableness, and conscientiousness) and alexithymia were associated with cognitive functioning in FND. Twenty-three patients with FND were assessed using a neuropsychological assessment and questionnaire assessment to explore personality traits (Neuroticism-Extraversion-Openness Five-Factor Inventory) and alexithymia (Bermond-Vorst Alexithymia Questionnaire). The results indicated that high conscientiousness was associated with lower planning scores (ρ = -0.52, p = .012) and high scores on alexithymia were associated with lower scores on verbal memory scores (ρ = -0.46, p = .032) and lower sustained attention scores (ρ = -0.45, p = .046). The results did not remain significant after controlling for multiple testing. The preliminary results of our study suggest that personality and cognitive symptomatology in patients with FND are topics that should be further explored in future studies, as cognitive symptomology can affect treatment results.

Neural correlates of cognitive bias modification for interpretation

The effectiveness of cognitive bias modification for interpretation (CBM-I), a treatment method employed to reduce social anxiety (SA), has been examined. However, the neural correlates of CBM-I remain unclear, and we aimed to elucidate brain activities during intervention and activity changes associated with CBM-I effectiveness in a pre–post intervention comparison. Healthy participants divided into two groups (CBM, control) were scanned before, during and after intervention using functional magnetic resonance imaging. Ambiguous social situations followed by positive outcomes were repeatedly imagined by the CBM group during intervention, while half of the outcomes in the control group were negative. Whole-brain analysis revealed that activation of the somatomotor and somatosensory areas, occipital lobe, fusiform gyrus and thalamus during intervention was significantly greater in the CBM than in the control group. Furthermore, altered activities in the somatomotor and somatosensory areas, occipital lobe and posterior cingulate gyrus during interpreting ambiguous social situations showed a significant group × change in SA interaction. Our result suggests that when facing ambiguous social situations, positive imagery instilled by CBM-I is recalled, and interpretations are modified to contain social reward. These findings may help to suggest an alternative manner of enhancing CBM-I effectiveness from a cognitive-neuroscience perspective.

Left, right, or bilateral amygdala activation? How effects of smoothing and motion correction on ultra-high field, high-resolution functional magnetic resonance imaging (fMRI) data alter inferences

Given the amygdala's role in survival mechanisms, and its pivotal contributions to psychological processes, it is no surprise that it is one of the most well-studied brain regions. One of the common methods for understanding the functional role of the amygdala is the use of functional magnetic resonance imaging (fMRI). However, fMRI tends to be acquired using resolutions that are not optimal for smaller brain structures. Furthermore, standard processing includes spatial smoothing and motion correction which further degrade the resolution of the data. Inferentially, this may be detrimental when determining if the amygdalae are active during a task. Indeed, studies using the same task may show differential amygdala(e) activation. Here, we examine the effects of well-accepted preprocessing steps on whole-brain submillimeter fMRI data to determine the impact on activation patterns associated with a robust task known to activate the amygdala(e). We analyzed 7T fMRI data from 30 healthy individuals collected at sub-millimeter in-plane resolution and used a field standard preprocessing pipeline with different combinations of smoothing kernels and motion correction options. Resultant amygdalae activation patterns were altered depending on which combination of smoothing and motion correction were performed, indicating that whole-brain preprocessing steps have a significant impact on the inferences that can be drawn about smaller, subcortical structures like the amygdala.

Modulation of effective connectivity in the default mode network at rest and during a memory task

It is known that the default mode network (DMN) may be modulated by a cognitive task and by performance level. Changes in the DMN have been examined by investigating resting-state activation levels, but there have been very few studies examining the modulation of effective connectivity of the DMN during a task in healthy older subjects. In this study, the authors examined how effective connectivity changed in the DMN between rest and during a memory task. The authors also investigated whether there was any relationship between effective connectivity modulation in the DMN and memory performance, to establish whether variations in cognitive performance are related to neural network effective connectivity, either at rest or during task performance. Twenty-eight healthy older participants underwent a resting-state functional magnetic resonance imaging scan and an emotional face-name encoding task. Effective connectivity analyses were performed on the DMN to examine the effective connectivity modulation in these two different conditions. During the resting state, there was strong self-influence in the regions of the DMN, while the main regions with statistically significant cross-regional effective connectivity were the posterior cingulate cortex (PCC) and the hippocampus (HP). During the memory task, the self-influence effective connectivities remained statistically significant across the DMN, and there were statistically significant effective connectivities from the PCC, HP, amygdala (AM), and parahippocampal region to other DMN regions. The authors found that effective connectivities from PCC, HP, and AM (in both resting state and during task) were linearly correlated to memory performance. The results suggest that superior memory ability in this older cohort was associated with effective connectivity both at rest and during the memory task of three DMN regions, which are also known to be important for memory function.

Male carriers of the FMR1 premutation show altered hippocampal-prefrontal function during memory encoding

Previous functional MRI (fMRI) studies have shown that fragile X mental retardation 1 (FMR1) fragile X premutation allele carriers (FXPCs) exhibit decreased hippocampal activation during a recall task and lower inferior frontal activation during a working memory task compared to matched controls. The molecular characteristics of FXPCs includes 55–200 CGG trinucleotide expansions, increased FMR1 mRNA levels, and decreased FMRP levels especially at higher repeat sizes. In the current study, we utilized MRI to examine differences in hippocampal volume and function during an encoding task in young male FXPCs. While no decreases in either hippocampal volume or hippocampal activity were observed during the encoding task in FXPCs, FMRP level (measured in blood) correlated with decreases in parahippocampal activation. In addition, activity in the right dorsolateral prefrontal cortex during correctly encoded trials correlated negatively with mRNA levels. These results, as well as the established biological effects associated with elevated mRNA levels and decreased FMRP levels on dendritic maturation and axonal growth, prompted us to explore functional connectivity between the hippocampus, prefrontal cortex, and parahippocampal gyrus using a psychophysiological interaction analysis. In FXPCs, the right hippocampus evinced significantly lower connectivity with right ventrolateral prefrontal cortex (VLPFC) and right parahippocampal gyrus. Furthermore, the weaker connectivity between the right hippocampus and VLPFC was associated with reduced FMRP in the FXPC group. These results suggest that while FXPCs show relatively typical brain response during encoding, faulty connectivity between frontal and hippocampal regions may have subsequent effects on recall and working memory.

Sex differences in amygdala subregions: evidence from subregional shape analysis

Each subregion of the amygdala is characterized by a distinct cytoarchitecture and function. However, most previous studies on sexual dimorphism and aging have assessed differences in the structure of the amygdala at the level of the amygdala in its entirety rather than at the subregional level. Using an amygdala subregional shape analysis, we investigated the effects of sex, age, and the sex × age interaction on the subregion after controlling for intracranial volume. We found the main effect of age in the subregions and the effect of sex in the superficial nucleus, which showed that men had a larger mean radius than women. We also found a sex × age interaction in the centromedial nucleus, in that the radius of the centromedial nucleus showed a steeper decline with age in women compared with men. Regarding the amygdala volume as a whole, we found only an age effect and did not find any other significant difference between genders. The sex difference in the amygdala subregion and its relevance to the circulating gonadal hormone were discussed.

Social anxiety modulates amygdala activation during social conditioning

Aversive social learning experiences might play a significant role in the aetiology of social anxiety disorder. Therefore, we investigated emotional learning and unlearning processes in healthy humans using a social conditioning paradigm. Forty-nine healthy subjects participated in a 2-day fMRI differential conditioning protocol. Acquisition and extinction were conducted on Day 1 and extinction recall on Day 2. BOLD responses, ratings and skin conductance responses were collected. Our data indicate successful conditioning and extinction on the neural and subjective level. As a main result, we observed a positive correlation of social anxiety and conditioning responses on the subjective level (valence and fear) as well as on the neural level with significant CS(+)/CS(-) differentiation in the left amygdala and the left hippocampus. Further, significant CS(+)/CS(-) differentiation in the left amygdala was found during extinction and was associated with lower scores in social anxiety. During extinction recall, we found a tendentially negative correlation of social anxiety and CS(+)/CS(-) differentiation in the vmPFC. In sum, we were able to show that social anxiety is related to conditionability with socially threatening stimuli. This could point to an important aspect in the aetiology of social anxiety disorder.

Development of ACC-amygdala activations in processing unattended fear

The ability to assess facial expressions of others involves specialised brain systems important for emotional and social learning, a skill that emerges over childhood. We investigated the development of neural responses associated with implicit processing of facial emotions using magnetoencephalography in children (7-10 yrs), adolescents (12-15 yrs) and adults. The results demonstrated spatial-temporal activations in the ACC and amygdala emotion-processing systems that changed with age. The processing of emotions first engaged the earlier-developing amygdala responses and then involved the later-maturing ACC system. With increasing age there was a shift in lateralization of amygdala responses sensitive to the fearful faces. The findings contribute to a critical understanding of the development related to functional specialization of fear perception in the frontal-limbic emotion systems. The present study offers critical insights into the developmentally time-sensitive impact on the normal functioning of these brain regions.

Preoperative prediction of verbal episodic memory outcome using FMRI

This article focuses on an important neurosurgical problem for which functional imaging may have a role. Temporal lobe epilepsy surgery typically involves removal of much of the anterior medial temporal lobe, which is critical for encoding and retrieval of long-term episodic memories. Verbal episodic memory decline after left anterior temporal lobe resection occurs in 30% to 60% of such patients. Recent studies show that preoperative fMRI can predict the degree of verbal memory change that will occur, and that fMRI improves prediction accuracy when combined with other routine tests. The predictive power of fMRI appears to be at least as good as the Wada memory test, making fMRI a viable noninvasive alternative to the Wada for preoperative assessment.

Dynamic changes in the medial temporal lobe during incidental learning of object-location associations

The role of the medial temporal lobe (MTL) in associative memory encoding has been the focus of many memory experiments. However, there has been surprisingly little investigation of whether the contributions of different MTL subregions (amygdala, hippocampus [HPC], parahippocampal [PHc], perirhinal cortex [PRc], and temporal polar cortex [TPc]) shift across multiple presentations during associative encoding. We examined this issue using event-related functional magnetic resonance imaging and a multivoxel pattern classification analysis. Subjects performed a visual search task, becoming faster with practice to locate objects whose locations were held constant across trials. The classification analysis implicated right HPC and amygdala early in the task when the speed-up from trial to trial was greatest. The same analysis implicated right PRc and TPc late in learning when speed-up was minimal. These results suggest that associative encoding relies on complex patterns of neural activity in MTL that cannot be expressed by simple increases or decreases of blood oxygenation level-dependent signal during learning. Involvement of MTL subregions during encoding of object-location associations depends on the nature of the learning phase. Right HPC and amygdala support active integration of object and location information, while right PRc and TPc are involved when object and spatial representations become unitized into a single representation.

Reduced Hippocampal Activation During Recall is Associated with Elevated FMR1 mRNA and Psychiatric Symptoms in Men with the Fragile X Premutation

Recent studies reveal that young carriers of the fragile X premutation are at increased risk for psychiatric conditions, memory problems and executive deficits. Post mortem and structural MRI studies suggest the hippocampus is preferentially affected by the premutation. The current study utilized magnetic resonance imaging (MRI) to explore the relationship between hippocampal structure and function as well as molecular/genetic and psychiatric measures in men with the fragile X premutation. Although the groups did not differ in hippocampal volume, the premutation group showed reduced left hippocampal activation and increased right parietal activation during a recall task relative to controls. These results suggest that brain function underlying memory recall is affected by premutation status. Left hippocampal activation was negatively correlated with both FMR1 mRNA level and psychiatric symptomology in the premutation group. These associations support the theory that increased levels of FMR1 mRNA affect brain function and contribute to psychiatric symptoms.

Genetic influences on the neural basis of social cognition

The neural basis of social cognition has been the subject of intensive research in both human and non-human primates. Exciting, provocative and yet consistent findings are emerging. A major focus of interest is the role of efferent and afferent connectivity between the amygdala and the neocortical brain regions, now believed to be critical for the processing of social and emotional perceptions. One possible component is a subcortical neural pathway, which permits rapid and preconscious processing of potentially threatening stimuli, and it leads from the retina to the superior colliculus, to the pulvinar nucleus of the thalamus and then to the amygdala. This pathway is activated by direct eye contact, one of many classes of potential threat, and may be particularly responsive to the 'whites of the eyes'. In humans, autonomic arousal evoked by this stimulus is associated with the activity in specific cortical regions concerned with processing visual information from faces. The integrated functioning of these pathways is modulated by one or more X-linked genes, yet to be identified. The emotional responsiveness of the amygdala, and its associated circuits, to social threat is also influenced by functional polymorphisms in the promoter of the serotonin transporter gene. We still do not have a clear account of how specific allelic variation, in candidate genes, increases susceptibility to developmental disorders, such as autism, or psychiatric conditions, such as anxiety or depressive illness. However, the regulation of emotional responsiveness to social cues lies at the heart of the problem, and recent research indicates that we may be nearing a deeper and more comprehensive understanding.

Neural correlates of relational memory: successful encoding and retrieval of semantic and perceptual associations

Using event-related functional magnetic resonance imaging, we identified brain regions involved in successful relational memory (RM) during encoding and retrieval for semantic and perceptual associations or in general, independent of phase and content. Participants were scanned while encoding and later retrieving associations between pairs of words (semantic RM) or associations between words and fonts (perceptual RM). Encoding success activity (ESA) was identified by comparing study-phase activity for items subsequently remembered (hits) versus forgotten (misses) and retrieval success activity (RSA) by comparing test-phase activity for hits versus misses. The study yielded three main sets of findings. First, ESA-RSA differences were found within the medial temporal lobes (MTLs) and within the prefrontal cortex (PFC). Within the left MTL, ESA was greater in the anterior hippocampus, and RSA was greater in the posterior parahippocampal cortex/hippocampus. This finding is consistent with the notion of an encoding-retrieval gradient along the longitudinal MTL axis. Within the left PFC, ESA was greater in ventrolateral PFC, and RSA was greater in dorsolateral and anterior PFC. This is the first evidence of a dissociation in successful encoding and retrieval activity within left PFC. Second, consistent with the transfer-appropriate processing principle, some ESA regions were reactivated during RSA in a content-specific manner. For semantic RM, these regions included the left ventrolateral PFC, whereas for perceptual RM, they included occipitoparietal and right parahippocampal regions. Finally, only one region in the entire brain was associated with RM in general (i.e., for both semantic and perceptual ESA and RSA): the left hippocampus. This finding highlights the fundamental role of the hippocampus in RM.

A comparison of two FMRI protocols for eliciting hippocampal activation

PURPOSE

Previous research suggests that the hippocampus is modulated both by stimulus novelty and by the extent to which relational processing (formation of associations) occurs during episodic encoding. The aim of this study was to compare hippocampal activation patterns measured by functional magnetic resonance imaging (fMRI) during encoding protocols emphasizing either novelty or relational processing.

METHODS

fMRI was performed on 32 healthy volunteers while they encoded complex visual scenes or unrecognizable scrambled versions of the same scenes. In the Novelty contrast, encoding of novel scenes was compared with encoding of a repeated pair of scenes. In the Relational Processing contrast, semantic encoding of novel scenes was compared with structural encoding of scrambled scenes.

RESULTS

Both protocols elicited bilateral hippocampal activation. Overall mean activation values were similar for the two protocols, but the Relational Processing protocol resulted in a larger volume of hippocampal activation. The pattern of activation along the longitudinal hippocampal axis differed for the two protocols. The Novelty contrast produced stronger activation in the posterior hippocampus, whereas the Relational Processing contrast produced stronger activation in the anterior hippocampus.

CONCLUSIONS

Hippocampal activation is determined by both stimulus novelty and degree of relational processing during encoding. Given the importance of anterior hippocampal pathology in temporal lobe epilepsy, an approach emphasizing modulation of relational processing may be preferable for clinical fMRI of the medial temporal lobes.

Neural correlates of memory for items and for associations: an event-related functional magnetic resonance imaging study

Although results from cognitive psychology, neuropsychology, and behavioral neuroscience clearly suggest that item and associative information in memory rely on partly different brain regions, little is known concerning the differences and similarities that exist between these two types of information as a function of memory stage (i.e., encoding and retrieval). We used event-related functional magnetic resonance imaging to assess neural correlates of item and associative encoding and retrieval of simple images in 18 healthy subjects. During encoding, subjects memorized items and pairs. During retrieval, subjects made item recognition judgments (old vs. new) and associative recognition judgments (intact vs. rearranged). Relative to baseline, item and associative trials activated bilateral medial temporal and prefrontal regions during both encoding and retrieval. Direct contrasts were then performed between item and associative trials for each memory stage. During en- coding, greater prefrontal, hippocampal, and parietal activation was observed for associations, but no significant activation was observed for items at the selected threshold. During recognition, greater activation was observed for associative trials in the left dorsolateral prefrontal cortex and superior parietal lobules bilaterally, whereas item recognition trials showed greater activation of bilateral frontal regions, bilateral anterior medial temporal areas, and the right temporo-parietal junction. Post hoc analyses suggested that the anterior medial temporal activation observed during item recognition was driven mainly by new items, confirming a role for this structure in novelty detection. These results suggest that although some structures such as the medial temporal and prefrontal cortex play a general role in memory, the pattern of activation in these regions can be modulated by the type of information (items or associations) interacting with memory stages.

Amygdala and hippocampal activity during acquisition and extinction of human fear conditioning

Previous functional magnetic resonance imaging (fMRI) studies have characterized brain systems involved in conditional response acquisition during Pavlovian fear conditioning. However, the functional neuroanatomy underlying the extinction of human conditional fear remains largely undetermined. The present study used fMRI to examine brain activity during acquisition and extinction of fear conditioning. During the acquisition phase, participants were either exposed to light (CS) presentations that signaled a brief electrical stimulation (paired group) or received light presentations that did not serve as a warning signal (control group). During the extinction phase, half of the paired group subjects continued to receive the same treatment, whereas the remainder received light alone. Control subjects also received light alone during the extinction phase. Changes in metabolic activity within the amygdala and hippocampus support the involvement of these regions in each of the procedural phases of fear conditioning. Hippocampal activity developed during acquisition of the fear response. Amygdala activity increased whenever experimental contingencies were altered, suggesting that this region is involved in processing changes in environmental relationships. The present data show learning-related amygdala and hippocampal activity during human Pavlovian fear conditioning and suggest that the amygdala is particularly important for forming new associations as relationships between stimuli change.

Medial temporal lobe activation during encoding and retrieval of novel face-name pairs

The human medial temporal lobe (MTL) is known to be involved in declarative memory, yet the exact contributions of the various MTL structures are not well understood. In particular, the data as to whether the hippocampal region is preferentially involved in the encoding and/or retrieval of associative memory have not allowed for a consensus concerning its specific role. To investigate the role of the hippocampal region and the nearby MTL cortical areas in encoding and retrieval of associative versus non-associative memories, we used functional magnetic resonance imaging (fMRI) to measure brain activity during learning and later recognition testing of novel face-name pairs. We show that there is greater activity for successful encoding of associative information than for non-associative information in the right hippocampal region, as well as in the left amygdala and right parahippocampal cortex. Activity for retrieval of associative information was greater than for non-associative information in the right hippocampal region also, as well as in the left perirhinal cortex, right entorhinal cortex, and right parahippocampal cortex. The implications of these data for a clear functional distinction between the hippocampal region and the MTL cortical structures are discussed.

Loss of memory for auditory–spatial associations following unilateral medial temporal-lobe damage

The goal of the present experiment was to determine the role of medial temporal-lobe structures in episodic memory of auditory-spatial associations. By using a two-alternative forced choice paradigm in which an association between eight different sounds and their spatial location must be recognized, learning abilities over 10 learning sessions were tested in 19 patients who had undergone a right or a left medial temporal-lobe resection for the relief of intractable seizures as well as in nine normal control participants. The data demonstrated that significant learning took place over the successive sessions for all the participants. In addition, the results showed that patients with left but not right medial temporal-lobe lesion were impaired in this learning task as compared to normal participants, suggesting the predominant implication of left medial temporal-lobe structures in auditory-spatial associative learning. The predominant role of left hemisphere structures in this memory task could be explained by a spatial categorical coding, which was enhanced by the use of eight loud-speakers. This result also suggests that the ability to store an episodic event associated with a rich spatial (or temporal) context depends on the left medial temporal-lobe structures. Thus, this finding provides an interesting parallel with data obtained in the visual modality by documenting for the first time the role of the left medial temporal-lobe in episodic learning of auditory-spatial associations.

Acute amygdalar activation induces an upregulation of multiple monoamine G protein coupled pathways in rat hippocampus

A "partial" rodent model for schizophrenia has been used to characterize the regulation of hippocampal genes in response to amygdalar activation. At 96 h after the administration of picrotoxin into the basolateral nucleus, we have observed an increase in the expression of genes associated with 18 different monoamine (ie adrenergic alpha 1, alpha 2 and beta 2, serotonergic 5HT5b and 5HT6, dopamine D4 and muscarinic m1, m2 and m3) and peptide (CCK A and B, angiotensin 1A, mu and kappa opiate, FSH, TSH, LH, GNRH, and neuropeptide Y) G-protein coupled receptors (GPCRs). These latter receptors are associated with three different G protein signaling pathways (Gq, Gs, and Gi) in which significant changes in gene expression were also noted for adenylate cyclase (AC4), phosphodiesterase (PDE4D), protein kinase A (PKA), and protein kinase C (PKC). Quantitative RT-PCR was used to validate the results and demonstrated that there were predictable increases of three GPCRs selected for this analysis, including the dopamine D4, alpha 1b, and CCK-B receptors. Eight out of the nine monoamine receptors showing these changes have moderate to high affinity for the atypical antipsychotic, clozapine. Taken together, these results suggest that amygdalar activation may play a role in the pathophysiology and treatment of psychosis by regulating the activity of multiple GPCR and metabolic pathways in hippocampal cells.

Pain processing in dementia and its relation to neuropathology

Most clinical studies of pain in dementia have focused on assessment procedures that are sensitive to pain in "demented" or "cognitively impaired" elderly patients. The neuropathology of dementia has not played a major part in pain assessment. In this review, the neuropathological effects of dementia on the medial and the lateral pain systems are discussed. We focus on Alzheimer's disease (AD), vascular dementia, and frontotemporal dementia. Lewy-body disease and Creutzfeldt-Jakob disease are briefly reviewed. The results of the studies reviewed show that, although the subtypes of dementia show common neuropathological features (such as atrophy and white-matter lesions), the degree by which they occur and affect pain-related areas determine the pattern of changes in pain experience. More specifically, in AD and even more so in frontotemporal dementia, a decrease in the motivational and affective components of pain is generally present whereas vascular dementia might be characterised by an increase in affective pain experience. Future studies should combine data from experimental pain studies and neuropathological information for pain assessment in dementia.

Real-time fMRI of temporolimbic regions detects amygdala activation during single-trial self-induced sadness

Temporolimbic circuits play a crucial role in the regulation of human emotion. A highly sensitive single-shot multiecho functional magnetic resonance imaging (fMRI) technique with gradient compensation of local magnetic field inhomogeneities and real-time data analysis were used to measure increases in amygdala activation during single 60-s trials of self-induced sadness. Six healthy male and female subjects performed a validated mood induction paradigm with randomized presentation of sad or neutral faces in 10 trials per scan. Subjects reported the intensity of experienced sadness after each trial. Immediate feedback of amygdala activation was given to the subjects during the ongoing scan to reinforce mood induction. Correspondence between increased intensity of predominantly left sided amygdala activation and self-rating of sadness was found in 78% of 120 sad trials, in contrast to only 14% of neutral trials. Amygdala activation was reproducible during repeated scanning sessions and displayed the strongest correlation with self-rating among all regions. These results suggest that amygdala activation may be closely associated with self-induced sadness. This novel real-time fMRI technology is applicable to a wide range of neuroscience studies, particularly those of the limbic system, and to neuropsychiatric conditions, such as depression, in which pathology of the amygdala has been implicated.

Cognitive correlates of medial temporal lobe development across adolescence: a magnetic resonance imaging study

Adolescent development involves progressive changes in brain structure and cognitive function, but relatively few studies have documented the cognitive correlates of differences in structural brain volumes in this age group. We examined the relations among age, cognitive processing, and mesial temporal lobe volume in 37 children and adolescents. Participants completed a brief cognitive assessment battery and underwent volumetric structural magnetic resonance imaging. For the sample as a whole, amygdala volume correlated positively with age, and larger volumes of both the left and right amygdala were significantly associated with better performance on several cognitive tasks assessing academic skills and acquired knowledge in long-term memory. In contrast, hippocampal volumes did not correlate with adolescents' age and were less frequently correlated with cognitive performance. Amygdala volumes were most predictive of cognitive abilities in boys, whereas for girls, the volume of the hippocampus contributed more frequently to the prediction of cognitive abilities. These data suggest that measurable differences in mesial temporal volumes during adolescence are reliably associated with long-term cognitive abilities, particularly academic skills and the acquisition of intellectual knowledge, and that these relationships may differ as a function of the sex of the child.

Hippocampal contributions to episodic encoding: insights from relational and item-based learning

The integrity of the hippocampus and surrounding medial-temporal cortices is critical for episodic memory, with the hippocampus being posited to support relational or configural associative learning. The present event-related functional magnetic resonance imaging (fMRI) study investigated the role of specific medial-temporal lobe structures in learning during relational and item-based processing, as well as the extent to which these structures are engaged during item-based maintenance of stimuli in working memory. fMRI indexed involvement of the hippocampus and underlying cortical regions during performance of two verbal encoding conditions, one that required item-based maintenance of word triplets in working memory and the other that entailed the formation of inter-item associations across the words in each triplet. Sixteen subjects were scanned using a rapid event-related fMRI design while they encountered the item-based and relational processing trials. To examine the correlation between fMRI signal in medial-temporal structures during learning and the subject's subsequent ability to remember the stimuli (a measure of effective memory formation), subjects were administered a yes-no recognition memory test following completion of the encoding scans. Results revealed that the hippocampus proper was engaged during both relational and item-based processing, with relational processing resulting in a greater hippocampal response. By contrast, entorhinal and parahippocampal gyri were differentially engaged during item-based processing, providing strong evidence for a functional neuroanatomic distinction between hippocampal and parahippocampal structures. Analysis of the neural correlates of subsequent memory revealed that activation in the bilateral hippocampus was reliably correlated with behavioral measures of effective memory formation only for those stimuli that were encoded in a relational manner. Taken together, these data provide evidence that the hippocampus, while engaged during item-based working memory maintenance, differentially subserves the relational binding of items into an integrated memory trace so that the experience can be later remembered.

Differential prefrontal cortex and amygdala habituation to repeatedly presented emotional stimuli

Repeated presentations of emotional facial expressions were used to assess habituation in the human brain using fMRI. Significant fMRI signal decrement was present in the left dorsolateral prefrontal and premotor cortex, and right amygdala. Within the left prefrontal cortex greater habituation to happy vs fearful stimuli was evident, suggesting devotion of sustained neural resources for processing of threat vs safety signals. In the amygdala, significantly greater habituation was observed on the right compared to the left. In contrast, the left amygdala was significantly more activated than the right to the contrast of fear vs happy. We speculate that the right amygdala is part of a dynamic emotional stimulus detection system, while the left is specialized for sustained stimulus evaluations.

Sex-specific developmental changes in amygdala responses to affective faces

It is hypothesized that adolescent development involves a redistribution of cerebral functions from lower subcortical structures to higher regions of the prefrontal cortex to provide greater self-control over emotional behavior. We further hypothesized that this redistribution is likely to be moderated by sex-specific hormonal changes. To examine developmental sex differences in affective processing, 19 children and adolescents underwent fMRI while viewing photographs of faces expressing fear. Males and females differed in the pattern of their amygdala vs prefrontal activation during adolescent maturation. With age, females showed a progressive increase in prefrontal relative to amygdala activation in the left hemisphere, whereas males failed to show a significant age related difference. There appear to be sex differences in the functional maturation of affect-related prefrontal-amygdala circuits during adolescence.