Where does consciousness come from?
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Animals↗
Biomedical subjects
Jordan Grafman
Publications and source records attributed to Jordan Grafman.
Neural correlates of script event knowledge: a neuropsychological study following prefrontal injury.
Scripts sequentially link information about daily activities and event knowledge. Patients have difficulty sequencing script events following lesions of the prefrontal cortex while showing intact access to selective aspects of script knowledge. It has been suggested that the sequencing impairment is due to a deficit in an inhibitory gating mechanisms that usually enables selection of an item from competing alternatives. If this is the case, then an inhibitory task should reveal script processing impairments on a script categorization task that is not normally associated with poor performance following prefrontal damage. To test this hypothesis, we administered a simple untimed classification task and a modified Go/NoGo task in which subjects classified events from social and non-social activities (e.g., read the menu, order the food) and related semantic items (e.g., menu, order) in terms of whether they belonged to a target activity. Participants were patients with lesions of the prefrontal cortex and matched controls. The results showed that damage to the right orbitofrontal cortex was associated with social item classification errors in the simple untimed classification task. In addition, the damage to the right prefrontal cortex was associated with increased response times to respond correctly to Go trials in the modified Go/NoGo task. The data demonstrate that damage to the right orbitofrontal cortex results in impairment in the accessibility of script and semantic representations of social activities. This impairment is exacerbated by an inefficient inhibitory gating mechanism.
Adult↗
Opinion: the neural basis of human moral cognition.
Moral cognitive neuroscience is an emerging field of research that focuses on the neural basis of uniquely human forms of social cognition and behaviour. Recent functional imaging and clinical evidence indicates that a remarkably consistent network of brain regions is involved in moral cognition. These findings are fostering new interpretations of social behavioural impairments in patients with brain dysfunction, and require new approaches to enable us to understand the complex links between individuals and society. Here, we propose a cognitive neuroscience view of how cultural and context-dependent knowledge, semantic social knowledge and motivational states can be integrated to explain complex aspects of human moral cognition.
Brain↗
Long-term memory is the representational basis for semantic verbal short-term memory.
The present study supports activation models of verbal short-term memory that include a semantic contribution to the retention process. Event-related brain potentials were used to probe the level of activation of semantic representations of a series of words in a delay interval following their presentation. The levels of activation were compared in two tasks: (1) a short-term memory task that involved a semantic judgment in the recall phase following the delay interval, and (2) a nonmemory control task. The level of semantic activation during the delay interval was higher in the short-term memory task, indicating that enhanced activation of semantic representations is involved in the short-term storage of verbal information. This result implies that activated long-term memory provides a representational basis for semantic verbal short-term memory, and hence supports theories that postulate that short- and long-term stores are not separate.
Adult↗
Eye movements in chorea-acanthocytosis.
PURPOSE: To describe the eye movement abnormalities in patients with chorea-acanthocytosis (ChAc), a form of neuroacanthocytosis. This autosomal recessive, neurodegenerative disorder with aberrant erythrocyte morphology (acanthocytosis) is caused by mutations in the VPS13A gene. In contrast to Huntington's disease (for which ChAc has occasionally been mistaken), ocular involvement in ChAc has not been systematically studied. METHODS: Three patients aged 26, 30, and 44 years with ChAc and six normal volunteers aged 31 to 48 years were included. Patients had dystonia, chorea, parkinsonism, dysarthria, dysphagia, seizures, cognitive abnormalities, and acanthocytosis. All had heterozygous VPS13A mutations and degeneration of the basal ganglia on magnetic resonance imaging (MRI) typical of ChAc. Patients had an extensive clinical and laboratory work-up. Neuro-ophthalmic examinations and eye movement recordings made with the magnetic search coil technique assessed patients' fixation characteristics, horizontal and vertical saccades, pursuit, and antisaccades. These were compared to the data of control subjects. RESULTS: Patients exhibited more than 30 square-wave jerks (small saccadic intrusions) per minute, versus 0 to 8 in the control subjects, as well as fractionated (multistep) and hypometric horizontal and vertical saccades. Decreased saccadic peak-velocity and reduced saccadic range were more pronounced for vertical saccades. Pursuit testing performed in two patients showed low gain. Results of antisaccade testing done in one patient were abnormal. CONCLUSIONS: The findings suggest brain stem involvement as an additional site of neurodegeneration outside the basal ganglia in ChAc. Patients with this progressive, intractable disease have pronounced ocular motor abnormalities. Eye movement recordings could assist in diagnosing ChAc, monitoring its progression and possible treatment evaluation.
Adult↗
Deficits in social knowledge following damage to ventromedial prefrontal cortex.
Patients with damage to the frontal lobes frequently exhibit impaired social behavior, but it is not clear which specific processes are disrupted. The authors investigated the ability to interpret nonverbal emotional expression in patients with lesions involving ventromedial (N=20) or dorsolateral prefrontal cortex (N=9) and in healthy volunteers (N=23). As hypothesized, only patients with ventromedial prefrontal lesions showed impaired task performance relative to normal comparison subjects. These results suggest that deficits in social knowledge, namely difficulty interpreting nonverbal emotional expression, contribute to the aberrant social behavior observed following ventromedial prefrontal cortex lesions.
Adult↗
Psychological structure and neural correlates of event knowledge.
Humans are capable of storing and retrieving sequences of complex structured events. Here we report a study in which we establish the psychological structure of event knowledge and then use parametric event-related functional magnetic resonance imaging to identify its neural correlates. We demonstrate that event knowledge is organized along dissociable dimensions that are reflected in distinctive patterns of neural activation: social valence (amygdala and right orbitofrontal cortex), experience (medial prefrontal cortex) and engagement (left orbitofrontal cortex). Our study affirms the importance and uniqueness of the human prefrontal cortex in representing event knowledge.
Adaptation, Psychological↗
Asymmetrical involvement of frontal lobes in social reasoning.
The frontal lobes are widely implicated in logical reasoning. Recent neuroimaging studies suggest that frontal lobe involvement in reasoning is asymmetric (L>R) and increases with the presence of familiar, meaningful content in the reasoning situation. However, neuroimaging data can only provide sufficiency criteria. To determine the necessity of prefrontal involvement in logical reasoning, we tested 19 patients with focal frontal lobe lesions and 19 age- and education-matched normal controls on the Wason Card Selection Task, while manipulating social knowledge. Patients and controls performed equivalently on the arbitrary rule condition. Normal controls showed the expected improvement in the social knowledge conditions, but frontal lobe patients failed to show this facilitation in performance. Furthermore, left hemisphere patients were more affected than right hemisphere patients, suggesting that frontal lobe involvement in reasoning is asymmetric (L>R) and necessary for reasoning about social situations.
Adult↗
Brain activation in processing temporal sequence: an fMRI study.
Structured event complexes (SECs) are stored representations of sequential event knowledge, and represent sequences of activities that have been described elsewhere as scripts or schemas. Previous studies have shown that the prefrontal cortex is involved in temporal sequencing. The present study investigates the involvement of the prefrontal cortex in temporal order and membership judgments of script and category items by using functional magnetic resonance imaging. In this experiment, stimuli were either script events or category items. In experimental trials, subjects classified stimuli according to temporal order or membership category. Results show that the script order task and the chronological order task (relative to their respective memberships tasks) were associated with different patterns of PFC activation. Both order tasks activated the middle frontal gyrus bilaterally; however, script order tasks showed additional activation in right inferior frontal gyrus, and the chronological order tasks in left inferior frontal gyrus. These results suggest that while the middle frontal gyri are activated bilaterally in both script and chronological temporal ordering tasks, there are different, though largely overlapping, neural substrates for script and chronological representations during temporal ordering.
Adult↗
The neurobiology of aggression.
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Adolescent↗
The hippocampal system mediates logical reasoning about familiar spatial environments.
It has recently been shown that syllogistic reasoning engages two dissociable neural systems. Reasoning about familiar situations engages a frontal-temporal lobe system, whereas formally identical reasoning tasks involving unfamiliar situations recruit a frontal-parietal visuospatial network. These two systems may correspond to the "heuristic" and "formal" methods, respectively, postulated by cognitive theory. To determine if this dissociation generalizes to reasoning about transitive spatial relations, we studied 14 volunteers using event-related fMRI, as they reasoned about landmarks in familiar and unfamiliar environments. Our main finding is a task (reasoning and baseline) by spatial content (familiar and unfamiliar) interaction. Modulation of reasoning toward unfamiliar landmarks resulted in bilateral activation of superior and inferior parietal lobules (BA 7, 40), dorsal superior frontal cortex (BA 6), and right superior and middle frontal gyri (BA 8), regions widely implicated in visuospatial processing. By contrast, modulation of the reasoning task toward familiar landmarks, engaged the right inferior/orbital frontal gyrus (BA 11/47), bilateral occipital (BA 18, 19), and temporal lobes. The temporal lobe activation included the right inferior temporal gyrus (BA 37), posterior hippocampus, and parahippocampal gyrus, regions implicated in spatial memory and navigation tasks. These results provide support for the generalization of dual mechanism theory to transitive reasoning and highlight the importance of the hippocampal system in reasoning about familiar spatial environments.
Adult↗
Impairment of social perception associated with lesions of the prefrontal cortex.
OBJECTIVE: Behavioral and social impairments have been frequently reported after damage to the prefrontal cortex in humans. This study evaluated social perception in patients with prefrontal cortex lesions and compared their performance on a social perception task with that of healthy volunteers. METHOD: Thirty-three patients with prefrontal cortex lesions and 31 healthy volunteers were tested with the Interpersonal Perception Task. In this task, subjects viewed videotaped social interactions and relied primarily on nonverbal cues to make interpersonal judgments, such as determining the degree of intimacy between two persons depicted in the videotaped scene. Patients with prefrontal cortex lesions were classified according to lesion involvement of specific regions, including the orbitofrontal cortex, dorsolateral prefrontal cortex, and anterior cingulate cortex. RESULTS: Relative to the comparison subjects, patients whose lesions involved the orbitofrontal cortex demonstrated impaired social perception. Contrary to predictions, patients with lesions in the dorsolateral prefrontal cortex also showed deficits in using social cues to make interpersonal judgments. All patients, particularly those with lesions in the dorsolateral prefrontal cortex, showed poorer insight into their deficits, relative to healthy volunteers. CONCLUSIONS: These findings of deficits in social perception after damage to the orbitofrontal cortex extend previous clinical and experimental evidence of damage-related impairment in other aspects of social cognition, such as the ability to accurately evaluate emotional facial expressions. In addition, the results suggest that the dorsolateral prefrontal cortex is recruited when inferences about social interactions are made on the basis of nonverbal information.
Brain Injuries↗
Distributed neural systems for temporal production: a functional MRI study.
Using functional magnetic resonance imaging (fMRI), we investigated the neural substrates for computing time intervals. Five right-handed males were asked to judge if a digit probe belonged to a string of digits presented immediately before but to provide their response only after 1.5s had elapsed. This time estimation condition, compared with control working memory and motor tasks, was associated with increased activity in the middle occipital gyri, in the right inferior parietal lobe, and bilaterally in the prefrontal cortex. We argue that activity elicited in the occipital lobe provides duration information about visual stimuli that can be quantified at the level of the inferior parietal lobe. Comparison with time reference information depends on the bilateral prefrontal cortex.
Adult↗
Phineas gauged: decision-making and the human prefrontal cortex.
Poor social judgment and decision-making abilities have often been attributed to people who have suffered injury to the ventromedial prefrontal cortex (VMPFC). However, few laboratory tests of decision-making have been conducted on these patients. The exception to this is the Iowa Gambling Task which has often, but not always, demonstrated differential performance between patients and controls. Results from patients with prefrontal cortex lesions on a novel test of decision-making are presented. Participants explored and chose from pairs of gambles that differed in their underlying distributions, primarily in the variance of their respective outcomes. In accordance with many findings from the behavioral decision-making literature, both young normal participants and older patient controls demonstrated a marked avoidance of risk and selected largely from secure, low variance gambles. In contrast, patients with ventromedial lesions were divided into two clear sub-groups. One group behaved similarly to normals, showing a risk-averse strategy. The other group displayed a distinctive risk-seeking behavior pattern, choosing predominantly from the high-variance, high-risk decks. This research demonstrates some of the advantages of using methods and theories from traditional decision-making research to study the behavior of patients, as well as the benefits of examining individual participants, and provides new insights into the nature of the decision-making deficit in patients with ventromedial prefrontal cortex lesions.
Adult↗
Inhibitory attentional control in patients with frontal lobe damage.
The performance of a group of frontal lobe lesion and a group of frontal lobe dementia patients was compared with the performance of their respective matched normal control groups on two tests of inhibitory attentional control-the stop-signal reaction time task and a negative priming task. Both patient groups responded significantly slower than their respective normal control groups, but they showed only marginally significant selective impairments on the measures of inhibition. The data suggest that the specific inhibitory processes evaluated by these two tests are, in general, spared in patients with focal frontal lobe lesions or frontal lobe degeneration.
Adult↗
Working memory retention systems: a state of activated long-term memory.
High temporal resolution event-related brain potential and electroencephalographic coherence studies of the neural substrate of short-term storage in working memory indicate that the sustained coactivation of both prefrontal cortex and the posterior cortical systems that participate in the initial perception and comprehension of the retained information are involved in its storage. These studies further show that short-term storage mechanisms involve an increase in neural synchrony between prefrontal cortex and posterior cortex and the enhanced activation of long-term memory representations of material held in short-term memory. This activation begins during the encoding/comprehension phase and evidently is prolonged into the retention phase by attentional drive from prefrontal cortex control systems. A parsimonious interpretation of these findings is that the long-term memory systems associated with the posterior cortical processors provide the necessary representational basis for working memory, with the property of short-term memory decay being primarily due to the posterior system. In this view, there is no reason to posit specialized neural systems whose functions are limited to those of short-term storage buffers. Prefrontal cortex provides the attentional pointer system for maintaining activation in the appropriate posterior processing systems. Short-term memory capacity and phenomena such as displacement of information in short-term memory are determined by limitations on the number of pointers that can be sustained by the prefrontal control systems.
Animals↗
Human prefrontal cortex: processing and representational perspectives.
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Attention↗
Dissociating the roles of the rostral anterior cingulate and the lateral prefrontal cortices in performing two tasks simultaneously or successively.
A fundamental question about the nature of cognitive control is whether performing two tasks successively or simultaneously activates distinct brain regions. To investigate this question, we designed a functional magnetic resonance imaging (fMRI) study that compared task-switching and dual-task performance. The results showed that performing two tasks successively or simultaneously activated a common prefronto-parietal neural network relative to performing each task separately. More importantly, we found that the anterior cingulate and the lateral prefrontal cortices were differently activated in dual-task and task-switching situations. When performing two tasks simultaneously, as compared to performing them in succession, activation was found in the rostral anterior cingulate cortex. In contrast, switching between two tasks, relative to performing them simultaneously, activated the left lateral prefrontal cortex and the bilateral intra-parietal sulcus region. We interpret these results as indicating that the rostral anterior cingulate cortex serves to resolve conflicts between stimulus-response associations when performing two tasks simultaneously, while the lateral prefrontal cortex dynamically selects the neural pathways needed to perform a given task during task switching.
Adult↗