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Jordan Grafman

Publications and source records attributed to Jordan Grafman.

50 records · Page 3Linked to original sources
PubMed2003

The human amygdala: an evolved system for relevance detection.

Evidence from pioneering animal research has suggested that the amygdala is involved in the processing of aversive stimuli, particularly fear-related information. Fear is central in the evolution of the mammalian brain: it is automatically and rapidly elicited by potentially dangerous and deadly events. The view that the amygdala shares the main characteristics of modular systems, e.g. domain specificity, automaticity, and cognitive impenetrability, has become popular in neuroscience. Because of its computational properties, it has been proposed to implement a rapid-response 'fear module'. In this article, we review recent patient and neuroimaging data of the human brain and argue that the fundamental criteria for the amygdala to be a modular system are not met. We propose a different computational view and suggest the notion of a specific involvement of the human amygdala in the appraisal of relevant events that include, but are not restricted to, fear-related stimuli. Considering the amygdala as a 'relevance detector' would integrate the 'fear module' hypothesis with the concept of an evolved neural system devoted to the processing of a broader category of biologically relevant stimuli. In primates, socially relevant events appear to have become, through evolution, the dominant elements of the amygdala's domain of specificity.

Amygdala↗
PubMed2002

Medial prefrontal and subcortical mechanisms underlying the acquisition of motor and cognitive action sequences in humans.

The anterior medial prefrontal cortex (AMPC) in humans is involved in affect and in regulating goal-directed behaviors. The precise function of the AMPC, however, is poorly understood. Using magnetic resonance imaging, we found that bilateral regions in the AMPC were selectively recruited to compute the reliability of subjects' expectations that developed when subjects were learning sequences of cognitive tasks. In contrast, regions similarly recruited in learning sequences of motor acts were found in the ventral striatum. Our results show that beyond the execution of motor acts, the AMPC is selectively engaged in computing the relevance of cognitive goals that subjects intend to achieve. This indicates that the fronto-striatal circuit, including the ventral striatum and AMPC, subserves hierarchically distinct evaluative processes mediating the human ability to build behavioral plans, ranging from motor to cognitive action plans.

Adult↗
PubMed2002

Imaging cortical anatomy by high-resolution MR at 3.0T: detection of the stripe of Gennari in visual area 17.

The brain can be parcellated into numerous anatomical and functional subunits. The classic work by Brodmann (Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues. Leipzig: Barth; 1909) identified areas of the cerebral cortex based on histological differences. An alternative to his cytoarchitectonic approach is the myeloarchitectonic approach. MRI has excellent white/gray matter contrast in the brain due to the presence of myelin, and thus seems uniquely suited for in vivo studies of cortical myeloarchitecture. Here it is demonstrated that the stripe or stria of Gennari can be consistently detected in human occipital cortex. T(1)-weighted images obtained at 3T from six of 10 normal volunteers, with resolutions of 350 x 350 x 600 mu clearly demonstrate this myelin-rich intracortical layer. It is concluded that the striate cortex (area 17 of Brodmann) of the human brain can be delineated in vivo on T(1)-weighted images, potentially enabling detection of specific cortical boundaries within individual brains.

Brain Mapping↗
PubMed2002

Functional networks in emotional moral and nonmoral social judgments.

Reading daily newspaper articles often evokes opinions and social judgments about the characters and stories. Social and moral judgments rely on the proper functioning of neural circuits concerned with complex cognitive and emotional processes. To examine whether dissociable neural systems mediate emotionally charged moral and nonmoral social judgments, we used a visual sentence verification task in conjunction with functional magnetic resonance imaging (fMRI). We found that a network comprising the medial orbitofrontal cortex, the temporal pole and the superior temporal sulcus of the left hemisphere was specifically activated by moral judgments. In contrast, judgment of emotionally evocative, but non-moral statements activated the left amygdala, lingual gyri, and the lateral orbital gyrus. These findings provide new evidence that the orbitofrontal cortex has dedicated subregions specialized in processing specific forms of social behavior.

Adult↗
PubMed2002

The roles of timing and task order during task switching.

The neural bases of the different processes involved in task switching remain poorly identified. Whether distinct brain regions are involved according to the overall structure of the task sequence and the predictability of task timing during task switching is unknown. To address this question, we used functional magnetic resonance imaging and a 2 x 2 factorial design varying timing (fixed/random) and task order (predictable/unpredictable). We hypothesized that predictable task order should activate brain regions involved in long-term memory retrieval because retrieving which task has to be performed constitutes the essential part of what subjects can do to prepare before stimulus presentation. When examining the "pure" main effects of task order/timing predictability/ unpredictability, we found that anticipating task order activated the right hippocampus, the anterior medial prefrontal cortex, and the posterior cingulate cortex, while anticipating task onset timing activated the left middle and superior frontal gyrus. Furthermore, task order unpredictability activated the intraparietal cortex bilaterally while random relative to fixed timing activated the right cerebellum. Interactions between task order and timing were found in a network, which included the left frontopolar cortex and the lateral prefrontal cortex bilaterally. Specifically, the left frontopolar cortex was more activated when both timing and task order were predictable, while the lateral prefrontal cortices were more activated when both task order and timing were unpredictable. These results indicate a hierarchic organization of the prefrontal cortex along a posterioanterior axis as the task becomes more endogenously guided. Finally, we found no evidence for specific brain regions involved in task switching because a bilateral prefronto-parietal network, which was activated in task switching relative to performing each task separately, was no longer activated relative to a control condition, which required subjects to maintain two tasks in memory without switching between them.

Adult↗
PubMed2002

Story processing in patients with damage to the prefrontal cortex.

The prefrontal cortex is known to be involved in performing complex cognitive tasks requiring reasoning, planning and decision-making. Neuropsychological evidence also supports the idea that the prefrontal cortex is generally involved in encoding and retrieving complex events, such as action and narrative knowledge. Patients with frontal lobe damage are reported to have difficulty in processing different aspects of narrative representations, such as the figurative moral meaning, syntactic features, and inference generation. In the present study, we examined story processing in 17 patients with frontal lobe lesions and compared their performance to 7 amnesic patients and 17 normal controls. Two stories were presented by using two slightly different processing demands in order to assess the subject's ability to draw inferences on-line during the course of comprehension or later retrieval. Although all patients had impaired story memory, patients with frontal lobe lesions showed a pattern of deficit at an early stage of story comprehension that specifically involved the ability to reconstruct the sequential links among events and to extract inferential knowledge from the text during encoding. Amnesic patients were severely impaired in recalling story semantic units, including single events and larger narrative constituents, as well as in the event recognition task. Consequently, they were unable to establish inferential relations among the events and, thus, the global sequential structure of the stories during retrieval. In contrast, they had no difficulty in extracting inferential knowledge during story comprehension on the basis of readily available information. This study shows that damage to different cortical regions may induce impairments at various levels of story processing.

Adult↗
PubMed2002

The roles of the cerebellum and basal ganglia in timing and error prediction.

Recent evidence that the cerebellum and the basal ganglia are activated during the performance of cognitive and attention tasks challenges the prevailing view of their primary function in motor control. The specific roles of the basal ganglia and the cerebellum in cognition, however, have been difficult to identify. At least three functional hypotheses regarding their roles have been proposed. The first hypothesis suggests that their main function is to switch attentional set. The second hypothesis states that they provide error signals regarding stimuli or rewards. The third hypothesis is that they operate as an internal timing system, providing a precise representation of temporal information. Using functional magnetic resonance imaging, we tested these three hypotheses using a task-switching experiment with a 2 x 2 factorial design varying timing (random relative to fixed) and task order (unpredictable relative to predictable). This design allowed us to test whether switching between tasks, timing irregularity and/or task order unpredictability activate the basal ganglia and/or the cerebellum. We show that the cerebellum is primarily activated with timing irregularity while the anterior striatum is activated with task order unpredictability, supporting their distinctive roles in two forms of readjustment. Task order unpredictability alone, independent of reward delivery, is sufficient to induce striatal activation. In addition, activation of the cerebellum and basal ganglia were not specific to switching attention because these regions were both activated during switching between tasks and during the simultaneous maintenance of two tasks without switching between them.

Adaptation, Physiological↗
PubMed2002

Quantification of brain lesions using interactive automated software.

We developed an interactive program, Analysis of Brain Lesions (ABLe) so that researchers studying the effects of brain lesions on cognition could have a user-friendly tool that could quantitatively characterize such lesions. The program was prepared in Tcl/Tk and will run on any UNIX or PC LINUX platform with the MEDx medical imaging software package. The ABLe is almost completely automated and determines the brain lesion size as well as which cytoarchitectonic brain regions (Brodmann areas) are contained within the boundaries of the lesion. Lesion data from multiple subjects can be grouped together and the degree of lesion overlap displayed. All images are analyzed and displayed within standard Talairach coordinate space, and the precision of the match between the ABLe Brodmann area graphics and the subject/patient brain is easily confirmed. The program is the first easy-to-use software that contains these specific features and is available for interested researchers with a background in lesion analysis.

Adult↗
PubMed2002

Neuroimaging reveals automatic speech coding during perception of written word meaning.

The extent to which visual word perception engages speech codes (i.e., phonological recoding) remains a crucial question in understanding mechanisms of reading. In this study, we used functional magnetic resonance imaging techniques combined with behavioral response measures to examine neural responses to focused versus incidental phonological and semantic processing of written words. Three groups of subjects made simple button-pressing responses in either phonologically (rhyming-judgment) or semantically (category-judgment) focused tasks or both tasks with identical sets of visual stimuli. In the phonological tasks, subjects were given both words and pseudowords separated in different scan runs. The baseline task required feature search of scrambled letter strings created from the stimuli for the experimental conditions. The results showed that cortical regions associated with both semantic and phonological processes were strongly activated when the task required active processing of word meaning. However, when subjects were actively processing the speech sounds of the same set of written words, brain areas typically engaged in semantic processing became silent. In addition, subjects who performed both the rhyming and the semantic tasks showed diverse and significant bilateral activation in the prefrontal, temporal, and other brain regions. Taken together, the pattern of brain activity provides evidence of a neural basis supporting the theory that in normal word reading, phonological recoding is automatic and facilitates semantic processing of written words, while rapid comprehension of word meaning requires devoted attention. These results also raise questions about including multiple cognitive tasks in the same neuroimaging sessions.

Adult↗
PubMed2001

Prefrontal lesions impair the implicit and explicit learning of sequences on visuomotor tasks.

OBJECTIVE: (1) To verify whether the prefrontal cortex (PFC) is specifically involved in visuomotor sequence learning as opposed to other forms of motor learning and (2) to establish the role of executive functions in visuomotor sequence learning. BACKGROUND: Visuomotor skill learning depends on the integrity of the premotor and parietal cortex; the prefrontal cortex, however, is essential when the learning of a sequence is required. METHODS: We studied 25 patients with PFC lesions and 86 controls matched for age and educational level. Participants performed: (1) a Pursuit Tracking Task (PTT), composed of a random tracking task (perceptual learning) and a pattern tracking task (explicit motor sequence learning with learning indicated by the decrease in mean root square error across trial blocks), (2) a 12-item sequence version of a serial reaction time task (SRTT) with specific implicit motor sequence learning indicated by the rebound increase in response time when comparing the last sequence block with the next random block, and (3) a neuropsychological battery that assessed executive functions. RESULTS: PFC patients were impaired in sequence learning on the pattern tracking task of the PTT and on the SRTT as compared to controls, but performed normally on the PTT random tracking task. Learning on the PTT did not correlate with learning on the SRTT. PTT performance correlated with planning functions while SRTT performance correlated with working memory capacity. CONCLUSIONS: The PFC is specifically involved in explicit and implicit motor sequence learning. Different PFC regions may be selectively involved in such learning depending on the cognitive demands of the sequential task.

Adult↗
PubMedDate not supplied

Patients with right frontal lesions are unable to assess and use advice to make predictive judgments.

Frontal lobe damage impairs decision-making. Most studies have employed gambling and probabilistic tasks, which have an emotional (reward-punishment) component and found that patients with ventromedial sector lesions have exceptional difficulty performing normally on these tasks. We have recently presented an economic decision-making task to patients and normal volunteers that required them to not only forecast an economic outcome but also to weigh advice from four advisors about the possible outcome across 40 trials. We studied 20 patients with right frontal lobe lesions and 9 patients with parietal lobe lesions and compared their performance to 20 matched controls. Frontal lobe lesion patients were inconsistent at using advice and their forecasts were poor. Patients with dorsolateral but not orbito-frontal lesions showed some ability to assess advice. Patients with parietal lobe lesions were good at assessing advice but were slow at doing so; they were consistent but poor at using advice and their use of advice was unrelated to their forecasting. All three patient groups were overconfident in their own performance. In contrast, controls could both use and assess advice, their ability to use advice was mediated by their ability to assess it, and they were not overconfident. Group differences on an overall measure of accuracy on this task were associated with an ability to accurately plan. Differences in ability to assess and forecast were associated with planning and working memory performance. These findings indicate that patients with both right dorsolateral and orbito-frontal lesions may be impaired when required to make complex decisions related to forecasting and judgment. Our findings enlarge the scope of decision-making deficits seen in patients with frontal lobe lesions and indicate additional circumstances in which patients with frontal lobe lesions will have difficulty in deciding.

Adult↗