Differential effects of insular and ventromedial prefrontal cortex lesions on risky decision-making

The ventromedial prefrontal cortex (vmPFC) and insular cortex are implicated in distributed neural circuitry that supports emotional decision-making. Previous studies of patients with vmPFC lesions have focused primarily on decision-making under uncertainty, when outcome probabilities are ambiguous (e.g. the Iowa Gambling Task). It remains unclear whether vmPFC is also necessary for decision-making under risk, when outcome probabilities are explicit. It is not known whether the effect of insular damage is analogous to the effect of vmPFC damage, or whether these regions contribute differentially to choice behaviour. Four groups of participants were compared on the Cambridge Gamble Task, a well-characterized measure of risky decision-making where outcome probabilities are presented explicitly, thus minimizing additional learning and working memory demands. Patients with focal, stable lesions to the vmPFC (n = 20) and the insular cortex (n = 13) were compared against healthy subjects (n = 41) and a group of lesion controls (n = 12) with damage predominantly affecting the dorsal and lateral frontal cortex. The vmPFC and insular cortex patients showed selective and distinctive disruptions of betting behaviour. VmPFC damage was associated with increased betting regardless of the odds of winning, consistent with a role of vmPFC in biasing healthy individuals towards conservative options under risk. In contrast, patients with insular cortex lesions failed to adjust their bets by the odds of winning, consistent with a role of the insular cortex in signalling the probability of aversive outcomes. The insular group attained a lower point score on the task and experienced more 'bankruptcies'. There were no group differences in probability judgement. These data confirm the necessary role of the vmPFC and insular regions in decision-making under risk. Poor decision-making in clinical populations can arise via multiple routes, with functionally dissociable effects of vmPFC and insular cortex damage.

Amnesia and driving

Two experienced drivers who developed severe amnesia due to bilateral hippocampal lesions participated in a series of standardized challenges of driving performance and knowledge of driving rules. During drives in a high fidelity simulator and on the road in an instrumented vehicle, they demonstrated vehicle control similar to that of normal drivers on measures of steering, speed control, safety errors, and driving with distraction. Their knowledge of driving rules, safety procedures, and road sign meaning also was normal. However, both participants were impaired at following route directions, and both had unsafe responses in a difficult crash avoidance scenario on the simulator. These findings suggest that memory impairment acquired by experienced drivers does not impair most aspects of driving performance, but may increase safety risk under some challenging circumstances.

The Iowa Gambling Task and the somatic marker hypothesis: some questions and answers

A recent study by Maia and McClelland on participants' knowledge in the Iowa Gambling Task suggests a different interpretation for an experiment we reported in 1997. The authors use their results to question the evidence for the somatic marker hypothesis. Here we consider whether the authors' conclusions are justified.

Neural systems behind word and concept retrieval

Using both the lesion method and functional imaging (positron emission tomography) in large cohorts of subjects investigated with the same experimental tasks, we tested the following hypotheses: (A) that the retrieval of words which denote concrete entities belonging to distinct conceptual categories depends upon partially segregated regions in higher-order cortices of the left temporal lobe; and (B) that the retrieval of conceptual knowledge pertaining to the same concrete entities also depends on partially segregated regions; however, those regions will be different from those postulated in hypothesis A, and located predominantly in the right hemisphere (the second hypothesis tested only with the lesion method). The analyses provide support for hypothesis A in that several regions outside the classical Broca and Wernicke language areas are involved in name retrieval of concrete entities, and that there is a partial segregation in the temporal lobe with respect to the conceptual category to which the entities belong, and partial support for hypothesis B in that retrieval of conceptual knowledge is partially segregated from name retrieval in the lesion study. Those regions identified here are seen as parts of flexible, multi-component systems serving concept and word retrieval for concrete entities belonging to different conceptual categories. By comparing different approaches the article also addresses a number of method issues that have surfaced in recent studies in this field.

Humans and great apes share a large frontal cortex

Some of the outstanding cognitive capabilities of humans are commonly attributed to a disproportionate enlargement of the human frontal lobe during evolution. This claim is based primarily on comparisons between the brains of humans and of other primates, to the exclusion of most great apes. We compared the relative size of the frontal cortices in living specimens of several primate species, including all extant hominoids, using magnetic resonance imaging. Human frontal cortices were not disproportionately large in comparison to those of the great apes. We suggest that the special cognitive abilities attributed to a frontal advantage may be due to differences in individual cortical areas and to a richer interconnectivity, none of which required an increase in the overall relative size of the frontal lobe during hominid evolution.

Emotion recognition from faces and prosody following temporal lobectomy

The anteromedial temporal lobe has been found to participate in processing emotion, but there are unresolved discrepancies in the literature. To address this issue, the authors investigated recognition of emotion from faces and from prosody in 26 participants with unilateral temporal lobectomy (15 left, 11 right) and in 50 brain-damaged controls. Participants with right, but not left, temporal lobectomy did significantly worse in recognizing fear from facial expressions. There were no group differences in recognizing emotional prosody. Neither IQ nor basic perceptual function accounted for task performance; however, there was a moderate negative correlation between extent of amygdala damage and overall performance. Consistent with some prior studies, these findings support a role for the right anteromedial temporal lobe (including amygdala) in recognizing emotion from faces but caution in drawing conclusions from small group samples.

Long-term sequelae of prefrontal cortex damage acquired in early childhood

Frontal lobe dysfunction is often invoked as a contributing factor in developmental disorders characterized by chronic maladaptive behavior, but interpretation of relevant neuropsychological findings has been hampered by the limited information available regarding the consequences of focal prefrontal damage early in life. We describe here the long-term behavioral and cognitive sequelae of damage to prefrontal cortex in two young adult patients who had sustained their brain damage prior to 16 months of age. In the context of normal neurological examinations, both cases had remarkable histories of impaired decision making, behavioral dyscontrol, social defects, and abnormal emotion. Performances were primarily normal on a broad range of neuropsychological measures (intellect, memory, language, academic achievement, visual perception, and visuoconstruction), but selective impairments of executive function were evident. Early dysfunction in the prefrontal region may result in severe and chronic social maladjustment despite largely normal cognitive abilities. These findings can help inform neuropsychological evaluation of patients with possible prefrontal dysfunction in the setting of developmental disabilities or early brain trauma.

A role for left temporal pole in the retrieval of words for unique entities

Both lesion and functional imaging studies have implicated sectors of high-order association cortices of the left temporal lobe in the retrieval of words for objects belonging to varied conceptual categories. In particular, the cortices located in the left temporal pole have been associated with naming unique persons from faces. Because this neuroanatomical-behavioral association might be related to either the specificity of the task (retrieving a name at unique level) or to the possible preferential processing of faces by anterior temporal cortices, we performed a PET imaging experiment to test the hypothesis that the effect is related to the specificity of the word retrieval task. Normal subjects were asked to name at unique level entities from two conceptual categories: famous landmarks and famous faces. In support of the hypothesis, naming entities in both categories was associated with increases in activity in the left temporal pole. No main effect of category (faces vs. landmarks/buildings) or interaction of task and category was found in the left temporal pole. Retrieving names for unique persons and for names for unique landmarks activate the same brain region. These findings are consistent with the notion that activity in the left temporal pole is linked to the level of specificity of word retrieval rather than the conceptual class to which the stimulus belongs.

Pathological laughter and crying: a link to the cerebellum

Patients with pathological laughter and crying (PLC) are subject to relatively uncontrollable episodes of laughter, crying or both. The episodes occur either without an apparent triggering stimulus or following a stimulus that would not have led the subject to laugh or cry prior to the onset of the condition. PLC is a disorder of emotional expression rather than a primary disturbance of feelings, and is thus distinct from mood disorders in which laughter and crying are associated with feelings of happiness or sadness. The traditional and currently accepted view is that PLC is due to the damage of pathways that arise in the motor areas of the cerebral cortex and descend to the brainstem to inhibit a putative centre for laughter and crying. In that view, the lesions 'disinhibit' or 'release' the laughter and crying centre. The neuroanatomical findings in a recently studied patient with PLC, along with new knowledge on the neurobiology of emotion and feeling, gave us an opportunity to revisit the traditional view and propose an alternative. Here we suggest that the critical PLC lesions occur in the cerebro-ponto-cerebellar pathways and that, as a consequence, the cerebellar structures that automatically adjust the execution of laughter or crying to the cognitive and situational context of a potential stimulus, operate on the basis of incomplete information about that context, resulting in inadequate and even chaotic behaviour.

A role for left temporal pole in the retrieval of words for unique entities

Both lesion and functional imaging studies have implicated sectors of high-order association cortices of the left temporal lobe in the retrieval of words for objects belonging to varied conceptual categories. In particular, the cortices located in the left temporal pole have been associated with naming unique persons from faces. Because this neuroanatomical-behavioral association might be related to either the specificity of the task (retrieving a name at unique level) or to the possible preferential processing of faces by anterior temporal cortices, we performed a PET imaging experiment to test the hypothesis that the effect is related to the specificity of the word retrieval task. Normal subjects were asked to name at unique level entities from two conceptual categories: famous landmarks and famous faces. In support of the hypothesis, naming entities in both categories was associated with increases in activity in the left temporal pole. No main effect of category (faces vs. landmarks/buildings) or interaction of task and category was found in the left temporal pole. Retrieving names for unique persons and for names for unique landmarks activate the same brain region. These findings are consistent with the notion that activity in the left temporal pole is linked to the level of specificity of word retrieval rather than the conceptual class to which the stimulus belongs.

Emotion recognition from faces and prosody following temporal lobectomy

The anteromedial temporal lobe has been found to participate in processing emotion, but there are unresolved discrepancies in the literature. To address this issue, the authors investigated recognition of emotion from faces and from prosody in 26 participants with unilateral temporal lobectomy (15 left, 11 right) and in 50 brain-damaged controls. Participants with right, but not left, temporal lobectomy did significantly worse in recognizing fear from facial expressions. There were no group differences in recognizing emotional prosody. Neither IQ nor basic perceptual function accounted for task performance; however, there was a moderate negative correlation between extent of amygdala damage and overall performance. Consistent with some prior studies, these findings support a role for the right anteromedial temporal lobe (including amygdala) in recognizing emotion from faces but caution in drawing conclusions from small group samples.

Neural Correlates of Naming Actions and of Naming Spatial Relations

Ina [(15)O] water PET experiment, 10 normal subjects retrieved words denoting actions (performed with or without an implement), and another 10 normal subjects retrieved words denoting the spatial relations between objects. Our objective was to test the following hypothesis: that the salient neural activity associated with naming actions and spatial relations occurs in left frontal operculum and left parietal association cortices, but not in the left inferotemporal cortices (IT) or in the right parietal association cortices. There were two control tasks, one requiring a decision on the orientation of unknown faces (a standard control task in our laboratory) and another requiring the retrieval of words denoting the concrete entities used in the action and spatial relations tasks. In accordance with the hypothesis, both naming actions and spatial relations (using the face orientation task as control activated the left frontal operculum; naming actions also activated the left parietal lobe. However, sectors of the left posterior IT were also engaged in both naming actions and spatial relations. When the naming of concrete entities was subtracted from the naming of actions performed with such entities, area MT in the posterior temporo-occipital region was activated bilaterally. On the other hand, when naming of the concrete entities was subtracted from the naming of spatial relations, left parietal activation was found, and when two tasks of naming spatial relations were contrasted to each other bilateral parietal activation was seen, right when abstract stimuli were used and left when concrete objects were used. The activity in posterior IT is thought to be related to object processing and possibly name retrieval at a subconscious level.

Single-neuron responses to emotional visual stimuli recorded in human ventral prefrontal cortex

Both lesion and functional imaging studies in humans, as well as neurophysiological studies in nonhuman primates, demonstrate the importance of the prefrontal cortex in representing the emotional value of sensory stimuli. Here we investigated single-neuron responses to emotional stimuli in an awake person with normal intellect. Recording from neurons within healthy tissue in ventral sites of the right prefrontal cortex, we found short-latency (120-160 ms) responses selective for aversive visual stimuli.

Validation of partial tissue segmentation of single-channel magnetic resonance images of the brain

We describe and evaluate a practical, automated algorithm based on local statistical mixture modeling for segmenting single-channel, T1-weighted volumetric magnetic resonance images of the brain into gray matter, white matter, and cerebrospinal fluid. We employed a stereological sampling method to assess, prospectively, the performance of the method with respect to human experts on 10 normal T1-weighted brain scans acquired with a three-dimensional gradient echo pulse sequence. The overall kappa statistic for the concordance of the algorithm with the human experts was 0.806, while that among raters, excluding the algorithm, was 0.802. The algorithm had better agreement with the modal expert decision (kappa = 0.878). The algorithm could not be distinguished from the experts by this measure. We also validated the algorithm on a simulated MR scan of a digital brain phantom with known tissue composition. Global gray matter and white matter errors were 1% and <1%, respectively, and correlation coefficients with the underlying tissue model were 0.95 for gray matter, 0.98 for white matter, and 0.95 for cerebrospinal fluid. In both approaches to validation, we evaluated both local and global performance of the algorithm. Human experts generated slightly higher global gray matter proportion estimates on the test brain scans relative to the algorithm (3.7%) and on the simulated MR scan relative to the true tissue model (4.4%). The algorithm underestimated gray in some subcortical nuclei which contain admixed gray and white matter. We demonstrate the reliability of the method on individual 1 NEX data sets of the test subjects, and its insensitivity to the precise values of initial model parameters. The output of this algorithm is suitable for quantifying cerebral cortical tissue, using a commonly performed commercial pulse sequence.

Characterization of the decision-making deficit of patients with ventromedial prefrontal cortex lesions

On a gambling task that models real-life decisions, patients with bilateral lesions of the ventromedial prefrontal cortex (VM) opt for choices that yield high immediate gains in spite of higher future losses. In this study, we addressed three possibilities that may account for this behaviour: (i) hypersensitivity to reward; (ii) insensitivity to punishment; and (iii) insensitivity to future consequences, such that behaviour is always guided by immediate prospects. For this purpose, we designed a variant of the original gambling task in which the advantageous decks yielded high immediate punishment but even higher future reward. The disadvantageous decks yielded low immediate punishment but even lower future reward. We measured the skin conductance responses (SCRs) of subjects after they had received a reward or punishment. Patients with VM lesions opted for the disadvantageous decks in both the original and variant versions of the gambling task. The SCRs of VM lesion patients after they had received a reward or punishment were not significantly different from those of controls. In a second experiment, we investigated whether increasing the delayed punishment in the disadvantageous decks of the original task or decreasing the delayed reward in the disadvantageous decks of the variant task would shift the behaviour of VM lesion patients towards an advantageous strategy. Both manipulations failed to shift the behaviour of VM lesion patients away from the disadvantageous decks. These results suggest that patients with VM lesions are insensitive to future consequences, positive or negative, and are primarily guided by immediate prospects. This 'myopia for the future' in VM lesion patients persists in the face of severe adverse consequences, i.e. rising future punishment or declining future reward.

Subcortical and cortical brain activity during the feeling of self-generated emotions

In a series of [15O]PET experiments aimed at investigating the neural basis of emotion and feeling, 41 normal subjects recalled and re-experienced personal life episodes marked by sadness, happiness, anger or fear. We tested the hypothesis that the process of feeling emotions requires the participation of brain regions, such as the somatosensory cortices and the upper brainstem nuclei, that are involved in the mapping and/or regulation of internal organism states. Such areas were indeed engaged, underscoring the close relationship between emotion and homeostasis. The findings also lend support to the idea that the subjective process of feeling emotions is partly grounded in dynamic neural maps, which represent several aspects of the organism's continuously changing internal state.

The neuroanatomical correlates of route learning impairment

Recent functional imaging studies of topographical learning point to the participation of a large network of cortical and subcortical regions. Nevertheless, areas which are crucial remain poorly specified due to the absence of group studies of subjects with focal lesions distributed throughout the brain. We assessed the ability of 127 subjects with stable, focal lesions to learn a complex real-life route, a critical aspect of topographical functioning. Results indicated that impairment in route learning was highly associated with damage to medial occipital and posterior parahippocampal cortices in either hemisphere, the right hippocampus, and the right inferotemporal region. Impairment was seen among 86% of the subjects with damage to any these regions, in contrast to impairment among 31% of subjects with lesions in other regions. The importance of medial occipitotemporal cortices bilaterally and right inferotemporal cortex likely reflects the critical role of the ability to quickly and accurately perceive and learn multiple topographical scenes. The importance of the right (and probably left) posterior parahippocampal gyrus and of the right hippocampus likely reflects their critical, distinctive roles forming an integrated representation of the extended topographical environment (i.e., the appearance of places and spatial relationships between specific places), and consolidating that representation into multifaceted contextual knowledge of the environment.

Lesion segmentation and manual warping to a reference brain: intra- and interobserver reliability

The study of subjects with acquired brain damage has been an invaluable tool for exploring human brain function, and the description of lesion locations within and across subjects is an important component of this method. Such descriptions usually involve the separation of lesioned from nonlesioned tissue (lesion segmentation) and the description of the lesion location in terms of a standard anatomical reference space (lesion warping). The objectives of this study were to determine the sources and magnitude of variability involved in lesion segmentation and warping using the MAP-3 approach. Each of two observers segmented the lesion volume in ten brain-damaged subjects twice, so as to permit pairwise comparisons of both intra- and interobserver agreement. The segmented volumes were then warped to a reference brain using both a manual (MAP-3) and an automated (AIR-3) technique. Observer agreement between segmented and warped volumes was analyzed using four measures: volume size, distance between the volume surfaces, percentage of nonoverlapping voxels, and percentage of highly discrepant voxels. The techniques for segmentation and warping produced high agreement within and between observers. For example, in most instances, the warped volume surfaces created by different observers were separated by less than 3 mm. The performance of the automated warping technique compared favorably to the manual technique in most subjects, although important exceptions were found. Overall, these results establish benchmark parameters for expert and automated lesion transfer, and indicate that a high degree of confidence can be placed in the detailed anatomical interpretation of focal brain damage based upon the MAP-3 technique.

A role for somatosensory cortices in the visual recognition of emotion as revealed by three-dimensional lesion mapping

Although lesion and functional imaging studies have broadly implicated the right hemisphere in the recognition of emotion, neither the underlying processes nor the precise anatomical correlates are well understood. We addressed these two issues in a quantitative study of 108 subjects with focal brain lesions, using three different tasks that assessed the recognition and naming of six basic emotions from facial expressions. Lesions were analyzed as a function of task performance by coregistration in a common brain space, and statistical analyses of their joint volumetric density revealed specific regions in which damage was significantly associated with impairment. We show that recognizing emotions from visually presented facial expressions requires right somatosensory-related cortices. The findings are consistent with the idea that we recognize another individual's emotional state by internally generating somatosensory representations that simulate how the other individual would feel when displaying a certain facial expression. Follow-up experiments revealed that conceptual knowledge and knowledge of the name of the emotion draw on neuroanatomically separable systems. Right somatosensory-related cortices thus constitute an additional critical component that functions together with structures such as the amygdala and right visual cortices in retrieving socially relevant information from faces.

Emotion, decision making and the orbitofrontal cortex

The somatic marker hypothesis provides a systems-level neuroanatomical and cognitive framework for decision making and the influence on it by emotion. The key idea of this hypothesis is that decision making is a process that is influenced by marker signals that arise in bioregulatory processes, including those that express themselves in emotions and feelings. This influence can occur at multiple levels of operation, some of which occur consciously and some of which occur non-consciously. Here we review studies that confirm various predictions from the hypothesis. The orbitofrontal cortex represents one critical structure in a neural system subserving decision making. Decision making is not mediated by the orbitofrontal cortex alone, but arises from large-scale systems that include other cortical and subcortical components. Such structures include the amygdala, the somatosensory/insular cortices and the peripheral nervous system. Here we focus only on the role of the orbitofrontal cortex in decision making and emotional processing, and the relationship between emotion, decision making and other cognitive functions of the frontal lobe, namely working memory.

The brain and its main anatomical subdivisions in living hominoids using magnetic resonance imaging

Primary comparative data on the hominoid brain are scarce and major neuroanatomical differences between humans and apes have not yet been described satisfactorily, even at the gross level. Basic questions that involve the evolution of the human brain cannot be addressed adequately unless the brains of all extant hominoid species are analyzed. Contrary to the scarcity of original data, there is a rich literature on the topic of human brain evolution and several debates exist on the size of particular sectors of the brain, e.g., the frontal lobe. In this study we applied a non-invasive imaging technique (magnetic resonance) on living human, great ape and lesser ape subjects in order to investigate the overall size of the hominoid brain. The images were reconstructed in three dimensions and volumetric estimates were obtained for the brain and its main anatomical sectors, including the frontal and temporal lobes, the insula, the parieto-occipital sector and the cerebellum.A remarkable homogeneity is present in the relative size of many of the large sectors of the hominoid brain, but interspecific and intraspecific variation exists in certain parts of the brain. The human cerebellum is smaller than expected for an ape brain of human size. It is suggested that the cerebellum increased less than the cerebrum after the split of the human lineage from the African ancestral hominoid stock. In contrast, humans have a slightly larger temporal lobe and insula than expected, but differences are not statistically significant. Humans do not have a larger frontal lobe than expected for an ape brain of human size and gibbons have a relatively smaller frontal lobe than the rest of the hominoids. Given the fact that the frontal lobe in humans and great apes has similar relative size, it is parsimonious to suggest that the relative size of the whole of the frontal lobe has not changed significantly during hominid evolution in the Plio-Pleistocene.

Auditory cortex on the human posterior superior temporal gyrus

The human superior temporal cortex plays a critical role in hearing, speech, and language, yet its functional organization is poorly understood. Evoked potentials (EPs) to auditory click-train stimulation presented binaurally were recorded chronically from penetrating electrodes implanted in Heschl's gyrus (HG), from pial-surface electrodes placed on the lateral superior temporal gyrus (STG), or from both simultaneously, in awake humans undergoing surgery for medically intractable epilepsy. The distribution of averaged EPs was restricted to a relatively small area on the lateral surface of the posterior STG. In several cases, there were multiple foci of high amplitude EPs lying along this acoustically active portion of STG. EPs recorded simultaneously from HG and STG differed in their sensitivities to general anesthesia and to changes in rate of stimulus presentation. Results indicate that the acoustically active region on the STG is a separate auditory area, functionally distinct from the HG auditory field(s). We refer to this acoustically sensitive area of the STG as the posterior lateral superior temporal area (PLST). Electrical stimulation of HG resulted in short-latency EPs in an area that overlaps PLST, indicating that PLST receives a corticocortical input, either directly or indirectly, from HG. These physiological findings are in accord with anatomic evidence in humans and in nonhuman primates that the superior temporal cortex contains multiple interconnected auditory areas.

Auditory cortex on the human posterior superior temporal gyrus

The human superior temporal cortex plays a critical role in hearing, speech, and language, yet its functional organization is poorly understood. Evoked potentials (EPs) to auditory click-train stimulation presented binaurally were recorded chronically from penetrating electrodes implanted in Heschl's gyrus (HG), from pial-surface electrodes placed on the lateral superior temporal gyrus (STG), or from both simultaneously, in awake humans undergoing surgery for medically intractable epilepsy. The distribution of averaged EPs was restricted to a relatively small area on the lateral surface of the posterior STG. In several cases, there were multiple foci of high amplitude EPs lying along this acoustically active portion of STG. EPs recorded simultaneously from HG and STG differed in their sensitivities to general anesthesia and to changes in rate of stimulus presentation. Results indicate that the acoustically active region on the STG is a separate auditory area, functionally distinct from the HG auditory field(s). We refer to this acoustically sensitive area of the STG as the posterior lateral superior temporal area (PLST). Electrical stimulation of HG resulted in short-latency EPs in an area that overlaps PLST, indicating that PLST receives a corticocortical input, either directly or indirectly, from HG. These physiological findings are in accord with anatomic evidence in humans and in nonhuman primates that the superior temporal cortex contains multiple interconnected auditory areas.

Impairment of social and moral behavior related to early damage in human prefrontal cortex

The long-term consequences of early prefrontal cortex lesions occurring before 16 months were investigated in two adults. As is the case when such damage occurs in adulthood, the two early-onset patients had severely impaired social behavior despite normal basic cognitive abilities, and showed insensitivity to future consequences of decisions, defective autonomic responses to punishment contingencies and failure to respond to behavioral interventions. Unlike adult-onset patients, however, the two patients had defective social and moral reasoning, suggesting that the acquisition of complex social conventions and moral rules had been impaired. Thus early-onset prefrontal damage resulted in a syndrome resembling psychopathy.

Different contributions of the human amygdala and ventromedial prefrontal cortex to decision-making

The somatic marker hypothesis proposes that decision-making is a process that depends on emotion. Studies have shown that damage of the ventromedial prefrontal (VMF) cortex precludes the ability to use somatic (emotional) signals that are necessary for guiding decisions in the advantageous direction. However, given the role of the amygdala in emotional processing, we asked whether amygdala damage also would interfere with decision-making. Furthermore, we asked whether there might be a difference between the roles that the amygdala and VMF cortex play in decision-making. To address these two questions, we studied a group of patients with bilateral amygdala, but not VMF, damage and a group of patients with bilateral VMF, but not amygdala, damage. We used the "gambling task" to measure decision-making performance and electrodermal activity (skin conductance responses, SCR) as an index of somatic state activation. All patients, those with amygdala damage as well as those with VMF damage, were (1) impaired on the gambling task and (2) unable to develop anticipatory SCRs while they pondered risky choices. However, VMF patients were able to generate SCRs when they received a reward or a punishment (play money), whereas amygdala patients failed to do so. In a Pavlovian conditioning experiment the VMF patients acquired a conditioned SCR to visual stimuli paired with an aversive loud sound, whereas amygdala patients failed to do so. The results suggest that amygdala damage is associated with impairment in decision-making and that the roles played by the amygdala and VMF in decision-making are different.

Premotor and prefrontal correlates of category-related lexical retrieval

It has been shown that the retrieval of words denoting visually presented concrete entities engages neural systems in the left temporal lobe and that the precise pattern of activation within the temporal lobe depends in part on the conceptual category to which the entity belongs. Here, we used [15O]water positron emission tomography to test the hypothesis that the pattern of activation associated with word retrieval in left frontal lobe would also be related to conceptual category. The design entailed the performance of three tasks requiring the retrieval of words denoting animals, tools, and unique persons. The visual stimuli were presented at different rates, to produce equal performance success across categories, a feature which also had the effect of equalizing the proportion of scan time spent in mental search. All three word retrieval tasks activated the left inferior frontal gyrus, but they differed in their recruitment of two other premotor and prefrontal areas. Activity in a portion of the middle frontal gyrus, corresponding to Brodmann area 46, bore a linear relation to response latency and may index the extent of mental search. This region was most active when subjects named persons. Activity in the anterior bank of the precentral gyrus, along the inferior and middle frontal gyri, was most marked for naming tools. This region overlaps the area activated when subjects generate words for actions. We suggest that it is engaged by the retrieval of words denoting actions or objects with characteristic actions. The data presented here provide additional support for the notion that "nonclassical" language areas in extrasylvian frontal and temporal regions mediate word retrieval and that the pattern of their engagement relates to conceptual category.

Dissociation Of working memory from decision making within the human prefrontal cortex

We tested the hypothesis that cognitive functions related to working memory (assessed with delay tasks) are distinct from those related to decision making (assessed with a gambling task), and that working memory and decision making depend in part on separate anatomical substrates. Normal controls (n = 21), subjects with lesions in the ventromedial (VM) (n = 9) or dorsolateral/high mesial (DL/M) prefrontal cortices (n = 10), performed on (1) modified delay tasks that assess working memory and (2) a gambling task designed to measure decision making. VM subjects with more anterior lesions (n = 4) performed defectively on the gambling but not the delay task. VM subjects with more posterior lesions (n = 5) were impaired on both tasks. Right DL/M subjects were impaired on the delay task but not the gambling task. Left DL/M subjects were not impaired on either task. The findings reveal a cognitive and anatomic double dissociation between deficits in decision making (anterior VM) and working memory (right DL/M). This presents the first direct evidence of such effects in humans using the lesion method and underscores the special importance of the VM prefrontal region in decision making, independent of a direct role in working memory.

A neural basis for the retrieval of conceptual knowledge

Both clinical reports and systematic neuropsychological studies have shown that patients with damage to selected brain sites develop defects in the retrieval of conceptual knowledge for various concrete entities, leading to the hypothesis that the retrieval of knowledge for entities from different conceptual categories depends on partially segregated large-scale neural systems. To test this hypothesis, 116 subjects with focal, unilateral lesions to various sectors of the telencephalon, and 55 matched controls, were studied with a procedure which required the visual recognition of entities from three categories--unique persons, non-unique animals and non-unique tools. Defective recognition of persons was associated with maximal lesion overlap in right temporal polar region; defective recognition of animals was associated with maximal lesion overlap in right mesial occipital/ventral temporal region and also in left mesial occipital region; and defective recognition of tools was associated with maximal lesion overlap in the occipital-temporal-parietal junction of the left hemisphere. The findings support the hypothesis that the normal retrieval of knowledge for concrete entities from different conceptual domains depends on partially segregated neural systems. These sites may operate as catalysts for the retrieval of the multidimensional aspects of knowledge which are necessary and sufficient for the mental representation of a concept of a given entity.

The evolution of the frontal lobes: a volumetric analysis based on three-dimensional reconstructions of magnetic resonance scans of human and ape brains

Scenarios regarding the evolution of cognitive function in hominids depend largely on our understanding of the organization of the frontal lobes in extant humans and apes. The frontal lobe is involved in functions such as creative thinking, planning of future actions, decision making, artistic expression, aspects of emotional behavior, as well as working memory, language and motor control. It is often claimed that the frontal lobe is disproportionately larger in humans than in other species, but conflicting reports exist on this issue. The brain of the apes in particular remains largely unknown. In this report we measure the volume of the frontal lobe as a whole and of its main sectors (including cortex and immediately underlying white matter) in living humans, and in post-mortem brains of the chimpanzee, gorilla, orang-utan, gibbon and the macaque using three-dimensional reconstructions of magnetic resonance (MR) scans of the brain. On the basis of these data we suggest that although the absolute volume of the brain and the frontal lobe is largest in humans, the relative size of the frontal lobe is similar across hominoids, and that humans do not have a larger frontal lobe than expected from a primate brain of the human size. We also report that the relative size of the sectors of the frontal lobe (dorsal, mesial, orbital) is similar across the primate species studied. Our conclusions are preliminary, because the size of our sample, although larger than in previous studies, still remains small. With this caveat we conclude that the overall volume of the frontal lobe in hominids enlarged in absolute size along with the rest of the brain, but did not become relatively larger after the split of the human line from the ancestral African hominoid stock. Aspects other than relative volume of the frontal lobe have to be responsible for the cognitive specializations of the hominids.

Deciding advantageously before knowing the advantageous strategy

Deciding advantageously in a complex situation is thought to require overt reasoning on declarative knowledge, namely, on facts pertaining to premises, options for action, and outcomes of actions that embody the pertinent previous experience. An alternative possibility was investigated: that overt reasoning is preceded by a nonconscious biasing step that uses neural systems other than those that support declarative knowledge. Normal participants and patients with prefrontal damage and decision-making defects performed a gambling task in which behavioral, psychophysiological, and self-account measures were obtained in parallel. Normals began to choose advantageously before they realized which strategy worked best, whereas prefrontal patients continued to choose disadvantageously even after they knew the correct strategy. Moreover, normals began to generate anticipatory skin conductance responses (SCRs) whenever they pondered a choice that turned out to be risky, before they knew explicitly that it was a risky choice, whereas patients never developed anticipatory SCRs, although some eventually realized which choices were risky. The results suggest that, in normal individuals, nonconscious biases guide behavior before conscious knowledge does. Without the help of such biases, overt knowledge may be insufficient to ensure advantageous behavior.

Brainvox: an interactive, multimodal visualization and analysis system for neuroanatomical imaging

A study of cognition emerging from a neurobiological perspective, as opposed to one emerging from a purely computational or psychological perspective, begins with observations of the human brain in normal and pathological states and is furthered by the investigation of hypotheses which are articulated using neuroanatomical nomenclature. Brainvox is an interactive three-dimensional brain imaging software package designed to permit such research through the support of the description and quantification of brain pathology in magnetic resonance images and of the experimental investigation of human cognition in lesion and functional imaging studies. Important general features of Brainvox, for these purposes, are: (1) adaptation of volume rendering for brain lesions and for corendered datasets; (2) shared memory architecture, which enables the user to identify and label anatomical structures, while inspecting the brain in multiple views simultaneously; (3) modular program design, including interlocking command-line utilities, which make Brainvox extensible and empower users without programming expertise to implement new analysis techniques through Unix shell scripting; and (4) full integration of three-dimensional tools for visualization with tools for analysis. Specific features include a new object templating technique (MAP-3) for studies of groups of brain-lesioned subjects, a complete and extensible suite of command-line processing utilities, a three-dimensional optimal graph-searching tool, and a method for planning PET slices and matching MR and PET slices (MP_FIT).

Cortical systems for the recognition of emotion in facial expressions

This study is part of an effort to map neural systems involved in the processing of emotion, and it focuses on the possible cortical components of the process of recognizing facial expressions. We hypothesized that the cortical systems most responsible for the recognition of emotional facial expressions would draw on discrete regions of right higher-order sensory cortices and that the recognition of specific emotions would depend on partially distinct system subsets of such cortical regions. We tested these hypotheses using lesion analysis in 37 subjects with focal brain damage. Subjects were asked to recognize facial expressions of six basic emotions: happiness, surprise, fear, anger, disgust, and sadness. Data were analyzed with a novel technique, based on three-dimensional reconstruction of brain images, in which anatomical description of surface lesions and task performance scores were jointly mapped onto a standard brain-space. We found that all subjects recognized happy expressions normally but that some subjects were impaired in recognizing negative emotions, especially fear and sadness. The cortical surface regions that best correlated with impaired recognition of emotion were in the right inferior parietal cortex and in the right mesial anterior infracalcarine cortex. We did not find impairments in recognizing any emotion in subjects with lesions restricted to the left hemisphere. These data provide evidence for a neural system important to processing facial expressions of some emotions, involving discrete visual and somatosensory cortical sectors in right hemisphere.

A chronic microelectrode investigation of the tonotopic organization of human auditory cortex

We investigated the functional organization of human auditory cortex using a new chronic microelectrode technique. Tonotopic mapping data was obtained at the single unit level for the first time in humans. All sound-driven units were noted to have frequency-dependent response patterns. The majority of units (73%) demonstrated sharply tuned excitatory best-frequency responses. Twenty seven percent of units showed wide receptive fields, representing excitatory responses to almost the entire range of frequencies presented. A tonotopic pattern was observed with best frequencies systematically increasing as more medial-caudal recording sites were sampled.

A neural basis for lexical retrieval

Two parallel studies using positron emission tomography, one conducted in neurological patients with brain lesions, the other in normal individuals, indicate that the normal process of retrieving words that denote concrete entities depends in part on multiple regions of the left cerebral hemisphere, located outside the classic language areas. Moreover, anatomically separable regions tends to process words for distinct kinds of items.

Failure to respond autonomically to anticipated future outcomes following damage to prefrontal cortex

Following damage to specific sectors of the prefrontal cortex, humans develop a defect in real-life decision making, in spite of otherwise normal intellectual performance. The patients so affected may even realize the consequences of their actions but fail to act accordingly, thus appearing oblivious to the future. The neural basis of this defect has resisted explanation. Here we identify a physiological correlate for the defect and discuss its possible significance. We measured the skin conductance responses (SCRs) of 7 patients with prefrontal damage, and 12 normal controls, during the performance of a novel task, a card game that simulates real-life decision making in the way it factors uncertainty, rewards, and penalties. Both patients and controls generated SCRs after selecting cards that were followed by penalties or by reward. However, after a number of trials, controls also began to generate SCRs prior to their selection of a card, while they pondered from which deck to choose, but no patients showed such anticipatory SCRs. The absence of anticipatory SCRs in patients with prefrontal damage is a correlate of their insensitivity to future outcomes. It is compatible with the idea that these patients fail to activate biasing signals that would serve as value markers in the distinction between choices with good or bad future outcomes; that these signals also participate in the enhancement of attention and working memory relative to representations pertinent to the decision process; and that the signals hail from the bioregulatory machinery that sustains somatic homeostasis and can be expressed in emotion and feeling.

Fear and the human amygdala

We have previously reported that bilateral amygdala damage in humans compromises the recognition of fear in facial expressions while leaving intact recognition of face identity (Adolphs et al., 1994). The present study aims at examining questions motivated by this finding. We addressed the possibility that unilateral amygdala damage might be sufficient to impair recognition of emotional expressions. We also obtained further data on our subject with bilateral amygdala damage, in order to elucidate possible mechanisms that could account for the impaired recognition of expressions of fear. The results show that bilateral, but not unilateral, damage to the human amygdala impairs the processing of fearful facial expressions. This impairment appears to result from an insensitivity to the intensity of fear expressed by faces. We also confirmed a double dissociation between the recognition of facial expressions of fear, and the recognition of identity of a face: these two processes can be impaired independently, lending support to the idea that they are subserved in part by anatomically separate neural systems. Based on our data, and on what is known about the amygdala's connectivity, we propose that the amygdala is required to link visual representations of facial expressions, on the one hand, with representations that constitute the concept of fear, on the other. Preliminary data suggest the amygdala's role extends to both recognition and recall of fearful facial expressions.

Double dissociation of conditioning and declarative knowledge relative to the amygdala and hippocampus in humans

A patient with selective bilateral damage to the amygdala did not acquire conditioned autonomic responses to visual or auditory stimuli but did acquire the declarative facts about which visual or auditory stimuli were paired with the unconditioned stimulus. By contrast, a patient with selective bilateral damage to the hippocampus failed to acquire the facts but did acquire the conditioning. Finally, a patient with bilateral damage to both amygdala and hippocampal formation acquired neither the conditioning nor the facts. These findings demonstrate a double dissociation of conditioning and declarative knowledge relative to the human amygdala and hippocampus.

Impaired recognition of emotion in facial expressions following bilateral damage to the human amygdala

Studies in animals have shown that the amygdala receives highly processed visual input, contains neurons that respond selectively to faces, and that it participates in emotion and social behaviour. Although studies in epileptic patients support its role in emotion, determination of the amygdala's function in humans has been hampered by the rarity of patients with selective amygdala lesions. Here, with the help of one such rare patient, we report findings that suggest the human amygdala may be indispensable to: (1) recognize fear in facial expressions; (2) recognize multiple emotions in a single facial expression; but (3) is not required to recognize personal identity from faces. These results suggest that damage restricted to the amygdala causes very specific recognition impairments, and thus constrains the broad notion that the amygdala is involved in emotion.

How reliable are occipital asymmetry measurements?

In vivo occipital asymmetry (OA) measurements have been used to infer functional asymmetries such as language dominance. We investigated the degree of correlation between OA measurements derived by the same rater from different scans of the same subject. We used magnetic resonance (MR) and computerized axial tomography (CT) to study correlations between MR:MR, CT:CT and CT:MR. The highest intrasubject correlation was for MR:MR (r = 0.79). The CT:CT value was similar (r = 0.78) and the CT:MR correlation was slightly lower (r = 0.72). The findings indicate that the reliability of occipital asymmetry measurements is modest at best, setting a low ceiling on the valid use of this variable to infer other indexes.

Sensorimotor skill learning in amnesia: additional evidence for the neural basis of nondeclarative memory

We investigated sensorimotor skill learning, a form of nondeclarative (implicit) memory, in 28 subjects with declarative (explicit) memory defects caused by either mesial temporal (n = 15) or basal forebrain (n = 13) damage and in 66 normal control subjects. All 28 amnesics had normal learning of a rotor pursuit task. We also studied in detail the sensorimotor skill learning of patient Boswell. As a result of bilateral damage to both mesial and lateral aspects of the temporal lobes and to the basal forebrain, Boswell has one of the most severe impairments ever reported for learning of all types of declarative knowledge. Compared to matched controls, Boswell acquired and retained normally the skills associated with performing motor tasks. We conducted a long-term (2-year) followup study of Boswell's retention of the rotor pursuit task, and we found that he retained the skill as well as normal controls. Our study builds on previous work in the following respects: (1) It provides evidence, for the first time, that skill learning is normal in basal forebrain amnesics; (2) it shows that patient Boswell has normal learning and long-term retention of sensorimotor skills, in spite of his extensive damage; and (3) it offers additional evidence that mesial temporal lobe damage spares skill learning. These findings demonstrate unequivocally that sensorimotor skill learning does not require structures in mesial and lateral temporal regions nor in basal forebrain.