Amygdala Lesions Research Articles

Motor System-Dependent Effects of Amygdala and Ventral Striatum Lesions on Explore-Exploit Behaviors.

Deciding whether to forego immediate rewards or explore new opportunities is a key component of flexible behavior and is critical for the survival of the species. Although previous studies have shown that different cortical and subcortical areas, including the amygdala and ventral striatum (VS), are implicated in representing the immediate (exploitative) and future (explorative) value of choices, the effect of the motor system used to make choices has not been examined. Here, we tested male rhesus macaques with amygdala or VS lesions on two versions of a three-arm bandit task where choices were registered with either a saccade or an arm movement. In both tasks we presented the monkeys with explore-exploit tradeoffs by periodically replacing familiar options with novel options that had unknown reward probabilities. We found that monkeys explored more with saccades but showed better learning with arm movements. VS lesions caused the monkeys to be more explorative with arm movements and less explorative with saccades, although this may have been due to an overall decrease in performance. VS lesions affected the monkeys' ability to learn novel stimulus-reward associations in both tasks, while after amygdala lesions this effect was stronger when choices were made with saccades. Further, on average, VS and amygdala lesions reduced the monkeys' ability to choose better options only when choices were made with a saccade. These results show that learning reward value associations to manage explore-exploit behaviors is motor system dependent and they further define the contributions of amygdala and VS to reinforcement learning.

A uniform human multimodal dataset for emotion perception and judgment

Face perception is a fundamental aspect of human social interaction, yet most research on this topic has focused on single modalities and specific aspects of face perception. Here, we present a comprehensive multimodal dataset for examining facial emotion perception and judgment. This dataset includes EEG data from 97 unique neurotypical participants across 8 experiments, fMRI data from 19 neurotypical participants, single-neuron data from 16 neurosurgical patients (22 sessions), eye tracking data from 24 neurotypical participants, behavioral and eye tracking data from 18 participants with ASD and 15 matched controls, and behavioral data from 3 rare patients with focal bilateral amygdala lesions. Notably, participants from all modalities performed the same task. Overall, this multimodal dataset provides a comprehensive exploration of facial emotion perception, emphasizing the importance of integrating multiple modalities to gain a holistic understanding of this complex cognitive process. This dataset serves as a key missing link between human neuroimaging and neurophysiology literature, and facilitates the study of neuropsychiatric populations.

Acceleration of inferred neural responses to oddball targets in an individual with bilateral amygdala lesion compared to healthy controls

Detecting unusual auditory stimuli is crucial for discovering potential threat. Locus coeruleus (LC), which coordinates attention, and amygdala, which is implicated in resource prioritization, both respond to deviant sounds. Evidence concerning their interaction, however, is sparse. Seeking to elucidate if human amygdala affects estimated LC activity during this process, we recorded pupillary responses during an auditory oddball and an illuminance change task, in a female with bilateral amygdala lesions (BG) and in n = 23 matched controls. Neural input in response to oddballs was estimated via pupil dilation, a reported proxy of LC activity, harnessing a linear-time invariant system and individual pupillary dilation response function (IRF) inferred from illuminance responses. While oddball recognition remained intact, estimated LC input for BG was compacted to an impulse rather than the prolonged waveform seen in healthy controls. This impulse had the earliest response mean and highest kurtosis in the sample. As a secondary finding, BG showed enhanced early pupillary constriction to darkness. These findings suggest that LC-amygdala communication is required to sustain LC activity in response to anomalous sounds. Our results provide further evidence for amygdala involvement in processing deviant sound targets, although it is not required for their behavioral recognition.

Neuroanatomy of post-stroke depression: the association between symptom clusters and lesion location.

Post-stroke depression affects about 30% of stroke patients and often hampers functional recovery. The diagnosis of depression encompasses heterogeneous symptoms at emotional, motivational, cognitive, behavioural or somatic levels. Evidence indicates that depression is caused by disruption of bio-aminergic fibre tracts between prefrontal and limbic or striatal brain regions comprising different functional networks. Voxel-based lesion-symptom mapping studies reported discrepant findings regarding the association between infarct locations and depression. Inconsistencies may be due to the usage of sum scores, thereby mixing different symptoms of depression. In this cross-sectional study, we used multivariate support vector regression for lesion-symptom mapping to identify regions significantly involved in distinct depressive symptom domains and global depression. MRI lesion data were included from 200 patients with acute first-ever ischaemic stroke (mean 0.9 ± 1.5 days of post-stroke). The Montgomery-Åsberg Depression Rating interview assessed depression severity in five symptom domains encompassing motivational, emotional and cognitive symptoms deficits, anxiety and somatic symptoms and was examined 8.4 days of post-stroke (±4.3). We found that global depression severity, irrespective of individual symptom domains, was primarily linked to right hemispheric lesions in the dorsolateral prefrontal cortex and inferior frontal gyrus. In contrast, when considering distinct symptom domains individually, the analyses yielded much more sensitive results in regions where the correlations with the global depression score yielded no effects. Accordingly, motivational deficits were associated with lesions in orbitofrontal cortex, dorsolateral prefrontal cortex, pre- and post-central gyri and basal ganglia, including putamen and pallidum. Lesions affecting the dorsal thalamus, anterior insula and somatosensory cortex were significantly associated with emotional symptoms such as sadness. Damage to the dorsolateral prefrontal cortex was associated with concentration deficits, cognitive symptoms of guilt and self-reproach. Furthermore, somatic symptoms, including loss of appetite and sleep disturbances, were linked to the insula, parietal operculum and amygdala lesions. Likewise, anxiety was associated with lesions impacting the central operculum, insula and inferior frontal gyrus. Interestingly, symptoms of anxiety were exclusively left hemispheric, whereas the lesion-symptom associations of the other domains were lateralized to the right hemisphere. In conclusion, this large-scale study shows that in acute stroke patients, differential post-stroke depression symptom domains are associated with specific structural correlates. Our findings extend existing concepts on the neural underpinnings of depressive symptoms, indicating that differential lesion patterns lead to distinct depressive symptoms in the first weeks of post-stroke. These findings may facilitate the development of personalized treatments to improve post-stroke rehabilitation.

The motivational role of the ventral striatum and amygdala in learning from gains and losses.

The ventral striatum (VS) and amygdala are two structures often implicated as essential structures for learning. The literature addressing the contribution of these areas to learning, however, is not entirely consistent. We propose that these inconsistencies are due to learning environments and the effect they have on motivation. To differentiate aspects of learning from environmental factors that affect motivation, we ran a series of experiments with varying task factors. We compared monkeys (Macaca mulatta) with VS lesions, amygdala lesions, and unoperated controls on reinforcement learning (RL) tasks that involve learning from both gains and losses as well as from deterministic and stochastic schedules of reinforcement. We found that for all three groups, performance varied by experiment. All three groups modulated their behavior in the same directions, to varying degrees, across the three experiments. This behavioral modulation is why we find deficits in some experiments, but not others. The amount of effort animals exhibited differed depending on the learning environment. Our results suggest that the VS is important for the amount of effort animals will give in rich deterministic and relatively leaner stochastic learning enivornments. We also showed that monkeys with amygdala lesions can learn stimulus-based RL in stochastic environments and environments with loss and conditioned reinforcers. These results show that learning environments shape motivation and that the VS is essential for distinct aspects of motivated behavior. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Amygdala lesions are associated with improved mood after epilepsy surgery.

Neuroimaging studies in healthy and clinical populations strongly associate the amygdala with emotion, especially negative emotions. The consequences of surgical resection of the amygdala on mood are not well characterized. We tested the hypothesis that amygdala resection would result in mood improvement. In this study, we evaluated a cohort of 52 individuals with medial temporal lobectomy for intractable epilepsy who had resections variably involving the amygdala. All individuals achieved good post-surgical seizure control and had pre- and post-surgery mood assessment with the Beck Depression Inventory (BDI) ratings. We manually segmented the surgical resection cavities and performed multivariate lesion-symptom mapping of change in BDI. Our results showed a significant improvement in average mood ratings from pre- to post-surgery across all patients. In partial support of our hypothesis, resection of the right amygdala was significantly associated with mood improvement (r = 0.5, p = 0.008). The lesion-symptom map also showed that resection of the right hippocampus and para-hippocampal gyrus was associated with worsened post-surgical mood. Future studies could evaluate this finding prospectively in larger samples while including other neuropsychological outcome measures.

Transdiagnostic overlap in brain correlates of affective and cognitive theory of mind deficits.

Social cognitive symptoms characterize multiple neurological disorders, including brain tumours and neurodegeneration. Recently, Campanella and colleagues1 investigated deficits in cognitive and affective theory of mind (TOM) in 105 tumour patients using a non-verbal task of 18 stimuli that required patients to select one out of three possible endings of a cartoon story, i.e. the Story-based Empathy Task (SET).2 The SET includes three conditions [Causal Inference (CI), Intention Attribution (IA) and Emotion Attribution (EA)], reflecting the type of inference the items tap into: inference of physical properties, intentions, or characters’ emotional state, respectively. The behavioural results of Campanella’s study revealed specific EA deficits in patients with temporal lobe tumours. Furthermore, the authors used parcel-based lesion-symptom mapping (PLSM) and reported an association between a right anterior temporal cluster and EA performance. Right amygdalar lesions showed a stronger association with EA than with IA. The association between EA deficits and amygdalar volume has also been also reported in behavioural variant frontotemporal dementia (bvFTD),3 a neurodegenerative disorder, characterized by deficits in social cognition, including cognitive and affective TOM. Consistent with the findings of Campanella, we also observed an association between performance on the EA condition and grey matter volume of the right temporal lobe and amygdala3 (Fig. 1). As documented by Campanella and colleagues, such common neural correlates of EA performance largely overlap with a ‘reasoning about emotions’ network derived from a recent meta-analysis of functional brain imaging studies in healthy participants.4 These combined findings converge in supporting a critical role of the right amygdala and temporal lobe in emotion attribution.

Peripherally-administered amphetamine induces plasticity in medial prefrontal cortex and nucleus accumbens in rats with amygdala lesions: implications for neural models of memory modulation.

The amygdala has been implicated in a variety of functions linked to emotions. One popular view is that the amygdala modulates consolidation in other brain systems thought to be mainly involved in learning and memory processes. This series of experiments represents a further exploration into the role of the amygdala in memory modulation and consolidation. One interesting line of research has shown that drugs of abuse, like amphetamine, produce dendritic changes in select brain regions and these changes are thought to be equivalent to a usurping of normal plasticity processes. We were interested in the possibility that this modulation of plasticity processes would be dependent on interactions with the amygdala. According to the modulation view of amygdala function, amphetamine would activate modulation mechanisms in the amygdala that would alter plasticity processes in other brain regions. If the amygdala was rendered dysfunctional, these effects should not occur. Accordingly, this series of experiments evaluated the effects of extensive neurotoxic amygdala damage on amphetamine-induced dendritic changes in the nucleus accumbens and prefrontal cortex. The results showed that rats with large lesions of the amygdala showed the normal pattern of dendritic changes in these brain regions. This pattern of results suggests that the action of not all memory modulators, activated during emotional events, require the amygdala to impact memory.

Attention to Stimuli of Learned versus Innate Biological Value Relies on Separate Neural Systems.

The neural bases of attention, a set of neural processes that promote behavioral selection, is a subject of intense investigation. In humans, rewarded cues influence attention, even when those cues are irrelevant to the current task. Because the amygdala plays a role in reward processing, and the activity of amygdala neurons has been linked to spatial attention, we reasoned that the amygdala may be essential for attending to rewarded images. To test this possibility, we used an attentional capture task, which provides a quantitative measure of attentional bias. Specifically, we compared reaction times (RTs) of adult male rhesus monkeys with bilateral amygdala lesions and unoperated controls as they made a saccade away from a high- or low-value rewarded image to a peripheral target. We predicted that: (1) RTs will be longer for high- compared with low-value images, revealing attentional capture by rewarded stimuli; and (2) relative to controls, monkeys with amygdala lesions would exhibit shorter RT for high-value images. For comparison, we assessed the same groups of monkeys for attentional capture by images of predators and conspecifics, categories thought to have innate biological value. In performing the attentional capture task, all monkeys were slowed more by high-value relative to low-value rewarded images. Contrary to our prediction, amygdala lesions failed to disrupt this effect. When presented with images of predators and conspecifics, however, monkeys with amygdala lesions showed significantly diminished attentional capture relative to controls. Thus, separate neural pathways are responsible for allocating attention to stimuli with learned versus innate value.SIGNIFICANCE STATEMENT Valuable objects attract attention. The amygdala is known to contribute to reward processing and the encoding of object reward value. We therefore examined whether the amygdala is necessary for allocating attention to rewarded objects. For comparison, we assessed the amygdala's contribution to attending to objects with innate biological value: predators and conspecifics. We found that the macaque amygdala is necessary for directing attention to images with innate biological value, but not for directing attention to recently learned reward-predictive images. These findings indicate that the amygdala makes selective contributions to attending to valuable objects. The data are relevant to mental health disorders, such as social anxiety disorders and small animal phobias, that arise from biased attention to select categories of objects.

Effect of Lesion of Central Amygdala on Heart Rate Variability in Albino Wistar Rats

Background and Aim: Heart rate variability (HRV) reflects the pre-frontal cortex (PFC) and amygdalar connections. HRV is also influenced by emotions, which is controlled by limbic system. Thus, amygdala-limbic connection is suggested to be the major integrator of HRV and the alterations in the regulation lead to cardiometabolic risks. The present study was conducted to assess the central amygdala in the heart rate variability in albino Wistar rats. Methods: A total of 8 albino Wistar rats were taken for the study. Stereotaxic procedure was performed and lesion was made into the central amygdalar nuclei bilaterally. HRV was assessed before and after lesion of central amygdala. Results: Following lesion of central amygdala, there was decrease in total power (TP), high frequency (HF), and other time domain indices of HRV, while there was increase in low frequency (LF) and LF-HF ratio. Conclusion: Lesion of central amygdala decreased TP indicating the crucial role of central amygdala in the control of HRV. The control of central amygdala on sympathovagal balance is profound.

Bilateral oligodendroglial hamartomas: A rare cause of drug-resistant epilepsy in a pediatric patient.

Intractable or drug-resistant seizures in pediatric patients are often secondary to cortical malformations, hamartomas, or mass lesions. Various subtypes of intracerebral hamartomas, associated with seizure disorders, have been described. In this report, we describe a subtype of intracerebral hamartoma associated with intractable epilepsy in a 10-year-old patient. Initial MR imaging demonstrated a mildly expansile, T2/FLAIR hyperintense, T1 isointense, nonenhancing lesion with blurring of the gray-white junction in the left amygdala. Surgical resection was performed, and pathology confirmed oligodendroglial hamartoma. Patient’s seizures recurred after a two-year interval with imaging demonstrating a similar lesion in the right amygdala which in retrospect was also seen on multiple imaging studies. This case report demonstrates the importance of recognizing oligodendroglial hamartomas as a cause of intractable seizures given the imaging findings, distinguishing it from ganglioglioma, dysembryoplastic neuroepithelial tumor, and oligodendroglioma, and the importance of closely looking/searching for contralateral lesions, which has important therapeutic and prognostic implications.

Stimulation of medial amygdala GABA neurons with kinetically different channelrhodopsins yields opposite behavioral outcomes.

The medial amygdala (MeA) receives pheromone information about conspecifics and has crucial functions in social behaviors. A previous study showed that activation of GABA neurons in the postero-dorsal MeA (MeApd) with channelrhodopsin-2H134R (ChR2) stimulates inter-male aggression. When performing these experiments using the faster channelrhodopsinH134R,E123T (ChETA), we find the opposite behavioral outcome. A systematic comparison between the two channelrhodopsin variants reveals that optogenetic activation of MeApd GABA neurons with ChETA suppresses aggression, whereas activation under ChR2 increases aggression. Although the mechanism for this paradoxical difference is not understood, we observe that activation of MeApd GABA neurons with ChR2 causes larger plateau depolarizations, smaller action potentials, and larger local inhibition than with ChETA. Thus, the channelrhodopsin variant used for invivo optogenetic experiments can radically influence the behavioral outcome. Future work should continue to study the role of specific sub-populations of MeApd GABA neurons in aggression control.

Effects of left and right medial temporal lobe resections on hemodynamic correlates of negative and neutral scene processing.

Enhanced visual cortex activation by negative compared to neutral stimuli is often attributed to modulating feedback from the amygdala, but evidence from lesion studies is scarce, particularly regarding differential effects of left and right amygdala lesions. Therefore, we compared visual cortex activation by negative and neutral complex scenes in an event‐related fMRI study between 40 patients with unilateral temporal lobe resection (TLR; 19 left [lTLR], 21 right [rTLR]), including the amygdala, and 20 healthy controls. We found preserved hemodynamic emotion modulation of visual cortex in rTLR patients and only subtle reductions in lTLR patients. In contrast, rTLR patients showed a significant decrease in visual cortex activation irrespective of picture content. In line with this, healthy controls showed small emotional modulation of the left amygdala only, while their right amygdala was activated equally by negative and neutral pictures. Correlations of activation in amygdala and visual cortex were observed for both negative and neutral pictures in the controls. In both patient groups, this relationship was attenuated ipsilateral to the TLR. Our results support the notion of reentrant mechanisms between amygdala and visual cortex and suggest laterality differences in their emotion‐specificity. While right medial temporal lobe structures including the amygdala seem to influence visual processing in general, the left medial temporal lobe appears to contribute specifically to emotion processing. Still, effects of left TLR on visual emotion processing were relatively subtle. Therefore, hemodynamic correlates of visual emotion processing are likely supported by a distributed cerebral network, challenging an amygdalocentric view of emotion processing.

The mirror neuron system compensates for amygdala dysfunction - associated social deficits in individuals with higher autistic traits

The amygdala is a core node in the social brain which exhibits structural and functional abnormalities in Autism spectrum disorder and there is evidence that the mirror neuron system (MNS) can functionally compensate for impaired emotion processing following amygdala lesions. In the current study, we employed an fMRI paradigm in 241 subjects investigating MNS and amygdala responses to observation, imagination and imitation of dynamic facial expressions and whether these differed in individuals with higher (n = 77) as opposed to lower (n = 79) autistic traits. Results indicated that individuals with higher compared to lower autistic traits showed worse recognition memory for fearful faces, smaller real-life social networks, and decreased left basolateral amygdala (BLA) responses to imitation. Additionally, functional connectivity between the left BLA and the left inferior frontal gyrus (IFG) as well as some other MNS regions was increased in individuals with higher autistic traits, especially during imitation of fearful expressions. The left BLA-IFG connectivity significantly moderated the autistic group differences on recognition memory for fearful faces, indicating that increased amygdala-MNS connectivity could diminish the social behavioral differences between higher and lower autistic trait groups. Overall, findings demonstrate decreased imitation-related amygdala activity in individuals with higher autistic traits in the context of increased amygdala-MNS connectivity which may functionally compensate for amygdala dysfunction and social deficits. Training targeting the MNS may capitalize on this compensatory mechanism for therapeutic benefits in Autism spectrum disorder.

Amygdala or hippocampus damage only minimally impacts affective responding to threat.

Decades of research studying the behavioral effects of damage to structures in medial temporal lobe of rhesus monkeys have documented that such damage, particularly damage to the amygdala, causes animals to become hyporesponsive to threat and hyper-social. This phenotype, a subset of the behaviors known as "Klüver-Bucy Syndrome," is one of the most well-known phenomena in behavioral neuroscience. Carrying on the tradition of evaluating hyposensitivity to threat in monkeys with temporal lobe lesions, we evaluated the responses of rhesus monkeys with bilateral ibotenic acid lesions of the amygdala or hippocampus and procedure-matched control animals to the presentation of an unfamiliar human intruder and threatening objects of varying complexity. All animals behaved as expected-calibrating their responses to the ostensible threat value of the stimuli such that they were most responsive to the most potent stimuli and least responsive to the least potent stimuli. Contrary to an earlier report (Mason et al., 2006), lesion status did not impact the pattern of responses across multiple dependent measures (overt behaviors, position in cage, etc.). The only lesion induced difference consistent with hyposensitivity to threat was that monkeys with amygdala lesions retrieved food rewards placed near reptile-like objects more rapidly than did control animals. These findings call into question the assumption that amygdala damage causes robust, stereotyped changes to affective behavior. They also highlight the importance of replication in neuroscientific studies using nonhuman primates. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Clinical outcome of selective amygdalectomy in a series of patients with resistant temporal lobe epilepsy

Background: Selective amygdalohippocampectomy is one of the main approaches for treating medial temporal lobe epilepsy (TLE). We herewith describe seven cases of amygdala lesions treated with selective amygdalectomy with the hippocampus saving procedure. Furthermore, we explain the trans-middle temporal gyrus transventricular approach for selective amygdalectomy.Methods: We studied patients with TLE who underwent selective amygdalectomy with hippocampal saving procedure between March 2012 and July 2018. We preferred the trans-middle temporal gyrus transventricular approach. We adopted pterional craniotomy with extensive exposure of the base and posterior of the temporal lobe. The posterior margin of resection in the intraventricular part of the amygdala was considered the inferior choroidal point. Medially anterior part of the uncus was resected until reaching the ambient cistern. We applied the transcortical transventricular approach for selective amygdalectomy in all patients.Results: We present 11 cases having an amygdala lesion in our series, seven of whom underwent selective amygdalectomy with hippocampal sparing. Nine patients had neoplastic lesions, and in two of them, gliosis was evident. Total resection of the lesion was achieved in all cases based on postoperative magnetic resonance imaging. No unusual complication or surgically-related new neurological deficit occurred.Conclusion: We consider the resection of the amygdala until the inferior choroidal point sufficient for the disconnection of its circuits, which results in more effective control of seizures and reduction of surgery time and complications.

Impairment of emotional expression detection after unilateral medial temporal structure resection

Detecting emotional facial expressions is an initial and indispensable component of face-to-face communication. Neuropsychological studies on the neural substrates of this process have shown that bilateral amygdala lesions impaired the detection of emotional facial expressions. However, the findings were inconsistent, possibly due to the limited number of patients examined. Furthermore, whether this processing is based on emotional or visual factors of facial expressions remains unknown. To investigate this issue, we tested a group of patients (n = 23) with unilateral resection of medial temporal lobe structures, including the amygdala, and compared their performance under resected- and intact-hemisphere stimulation conditions. The participants were asked to detect normal facial expressions of anger and happiness, and artificially created anti-expressions, among a crowd with neutral expressions. Reaction times for the detection of normal expressions versus anti-expressions were shorter when the target faces were presented to the visual field contralateral to the intact hemisphere (i.e., stimulation of the intact hemisphere; e.g., right visual field for patients with right hemispheric resection) compared with the visual field contralateral to the resected hemisphere (i.e., stimulation of the resected hemisphere). Our findings imply that the medial temporal lobe structures, including the amygdala, play an essential role in the detection of emotional facial expressions, according to the emotional significance of the expressions.

Social motives in a patient with bilateral selective amygdala lesions: Shift in prosocial motivation but not in social value orientation

Humans hold social motives that are expressed in social preferences and influence how they evaluate and share payoffs. Established models in psychology and economics quantify social preferences such as general social value orientation, which captures people's tendency to be prosocial or individualistic. Prosocials further differ by how much they maximize joint gains or minimize inequality. Functional neuroimaging studies have linked increased amygdala activity in prosocials to payoff inequality between self and other. However, it is unclear whether amygdala lesions alter social motives. We used two tasks to test a patient with selective bilateral amygdala lesions and three healthy samples (a priori matched control sample N = 20, online sample N = 603, student sample N = 40), which allowed us to assess and model social motives across a relatively large number of participants. In a social value orientation task, the patient was categorized as prosocial and her social value orientation score did not differ from healthy participants. Importantly, the patient differed in prosocial motivation by maximizing joint gains rather than minimizing payoff inequality. In a joint payoff evaluation task, Bayesian model comparisons revealed that participants' evaluations were best described by models, which link participants' evaluations to the payoff magnitude and to inequality. Overall, amygdala lesions did not seem to alter general social value orientation but shifted prosocial motivation toward maximizing joint gains.

Interaction between decision-making and interoceptive representations of bodily arousal in frontal cortex

Decision-making and representations of arousal are intimately linked. Behavioral investigations have classically shown that either too little or too much bodily arousal is detrimental to decision-making, indicating that there is an inverted "U" relationship between bodily arousal and performance. How these processes interact at the level of single neurons as well as the neural circuits involved are unclear. Here we recorded neural activity from orbitofrontal cortex (OFC) and dorsal anterior cingulate cortex (dACC) of macaque monkeys while they made reward-guided decisions. Heart rate (HR) was also recorded and used as a proxy for bodily arousal. Recordings were made both before and after subjects received excitotoxic lesions of the bilateral amygdala. In intact monkeys, higher HR facilitated reaction times (RTs). Concurrently, a set of neurons in OFC and dACC selectively encoded trial-by-trial variations in HR independent of reward value. After amygdala lesions, HR increased, and the relationship between HR and RTs was altered. Concurrent with this change, there was an increase in the proportion of dACC neurons encoding HR. Applying a population-coding analysis, we show that after bilateral amygdala lesions, the balance of encoding in dACC is skewed away from signaling either reward value or choice direction toward HR coding around the time that choices are made. Taken together, the present results provide insight into how bodily arousal and decision-making are signaled in frontal cortex.

Case of Asperger's Syndrome and Lesion of the Right Amygdala: Deficits in Implicit and Explicit Fearful Face Recognition.

Introduction: Studies of brain-damaged patients revealed that amygdala lesions cause deficits in the processing and recognition of emotional faces. Patients with autism spectrum disorders (ASD) have similar deficits also related to dysfunctions of the limbic system including the amygdala.Methods: We investigated a male patient who had been diagnosed with Asperger's syndrome. He also presented with a lesion of the right mesial temporal cortex, including the amygdala. We used functional magnetic resonance imaging (fMRI) to investigate neuronal processing during a passive viewing task of implicit and explicit emotional faces. Clinical assessment included a facial emotion recognition task.Results: There was no amygdala activation on both sides during the presentation of masked emotional faces compared to the no-face control condition. Presentation of unmasked happy and angry faces activated the left amygdala compared to the no-face control condition. There was no amygdala activation in response to unmasked fearful faces on both sides. In the facial emotion recognition task, the patient biased positive and neutral expressions as negative.Conclusions: This case report describes a male patient with right amygdala damage and an ASD. He displayed a non-response of the amygdala to fearful faces and tended to misinterpret fearful expressions. Moreover, a non-reactivity of both amygdalae to emotional facial expressions at an implicit processing level was revealed. It is discussed whether the deficient implicit processing of facial emotional information and abnormalities in fear processing could contribute and aggravate the patient's impairments in social behavior and interaction.