Biomedical subjects

Richard E Passingham

Publications and source records attributed to Richard E Passingham.

At least 19 recordsLinked to original sources

PubMed2007

Manipulating the experienced onset of intention after action execution.

Using transcranial magnetic stimulation (TMS), we have tested the time needed for the perceived onset of spontaneous motor intention to be fully determined. We found that TMS applied over the presupplementary motor area after the execution of a simple spontaneous action shifted the perceived onset of the motor intention backward in time, and shifted the perceived time of action execution forward in time. The size of the effect was similar regardless of whether TMS was applied immediately after the action or 200 msec after. The results of three control studies suggest that this effect is time-limited, specific to modality, and also specific to the anatomical site of stimulation. We conclude that the perceived onset of intention depends, at least in part, on neural activity that takes place after the execution of action. A model, which is based on the mechanism of cue integration under the presence of noise, is offered to explain the results. The implications for the conscious control of spontaneous actions are discussed.

Evoked Potentials, Motor↗

PubMed2006

Relative blindsight in normal observers and the neural correlate of visual consciousness.

By using a paradigm based on metacontrast masking, we created experimental conditions in which the subjective report of consciousness differs but the objectively measured ability to discriminate visual targets does not. This approach allowed us to study the neural correlate of consciousness while having performance levels carefully matched in healthy human subjects. A comparison of the neural activity associated with these conditions as measured by functional MRI showed that conscious perception is associated with spatially specific activity in the mid-dorsolateral prefrontal cortex (area 46). Further analysis confirms that this activation is not only free from any performance confound, but is also not driven by differences in the timing of the physical stimuli. Our results suggest that the prefrontal cortex is important for the essentially subjective aspects of conscious perception.

Consciousness↗

PubMed2006

Seeing or doing? Influence of visual and motor familiarity in action observation.

The human brain contains specialized circuits for observing and understanding actions. Previous studies have not distinguished whether this "mirror system" uses specialized motor representations or general processes of visual inference and knowledge to understand observed actions. We report the first neuroimaging study to distinguish between these alternatives. Purely motoric influences on perception have been shown behaviorally, but their neural bases are unknown. We used fMRI to reveal the neural bases of motor influences on action observation. We controlled for visual and knowledge effects by studying expert dancers. Some ballet moves are performed by only one gender. However, male and female dancers train together and have equal visual familiarity with all moves. Male and female dancers viewed videos of gender-specific male and female ballet moves. We found greater premotor, parietal, and cerebellar activity when dancers viewed moves from their own motor repertoire, compared to opposite-gender moves that they frequently saw but did not perform. Our results show that mirror circuits have a purely motor response over and above visual representations of action. We understand actions not only by visual recognition, but also motorically. In addition, we confirm that the cerebellum is part of the action observation network.

Adolescent↗

PubMed2006

On measuring the perceived onsets of spontaneous actions.

We investigated the neural mechanisms underlying the timing procedure that was devised by Libet et al. (1983) to measure the onset of conscious motor intentions in spontaneous actions. We previously showed that, when participants were required to estimate the onset of their intentions using this procedure, the activity in the presupplementary motor area (pre-SMA) was enhanced. Here, we show that when participants were required to estimate the onset of their motor executions (instead of their intentions), the activity in the cingulate motor area was enhanced. Across participants, the degree of this neural enhancement was correlated with the degree of perceptual bias: the higher the degree of enhancement, the earlier the perception. Analysis of data from a previous experiment suggests that the same principle holds true for the relationship between the perceived onset of intentions and the activity in the pre-SMA. We therefore argue that the timing method of Libet et al. (1983) is problematic, because the measuring process affects the neural representations of action and thus also the perceived onsets that the method is designed to measure.

Attention↗

PubMed2006

Prefrontal set activity predicts rule-specific neural processing during subsequent cognitive performance.

Prefrontal neurons have been shown to represent task rules. Here we show the mechanisms by which the rule-selective activity in the prefrontal cortex influences subsequent cognitive performance based on that rule. Using functional magnetic resonance imaging, we found that the frontopolar cortex interacted with posterior areas differently depending on whether subjects were going to perform a phonological or semantic task. Moreover, we found that the sustained "set" activity in this region predicted the activity that could be recorded in the posterior areas during the performance, as well as the speed of that performance. We argue that the prefrontal set activity does not reflect simple maintenance of the task rules but the process of implementing the rule for subsequent cognitive performance and that this is done through rule-selective interactions with areas involved in execution of the tasks.

Adult↗

PubMed2006

Cerebral changes during performance of overlearned arbitrary visuomotor associations.

The posterior parietal cortex (PPC) is known to be involved in the control of automatic movements that are spatially guided, such as grasping an apple. We considered whether the PPC might also contribute to the performance of visuomotor associations in which stimuli and responses are linked arbitrarily, such as producing a certain sound for a typographical character when reading aloud or pressing pedals according to the color of a traffic light when driving a motor vehicle. The PPC does not appear to be necessary for learning new arbitrary visuomotor associations, but with extensive training, the PPC can encode nonspatial sensory features of task-relevant cues. Accordingly, we have tested whether the contributions of the PPC might become apparent once arbitrary sensorimotor mappings are overlearned. We have used functional magnetic resonance imaging to measure cerebral activity while subjects were learning novel arbitrary visuomotor associations, overlearning known mappings, or attempting to learn frequently changing novel mappings. To capture the dynamic features of cerebral activity related to the learning process, we have compared time-varying modulations of activity between conditions rather than average (steady-state) responses. Frontal, striatal, and intraparietal regions showed decreasing or stable activity when subjects learned or attempted to learn novel associations, respectively. Importantly, the same frontal, striatal, and intraparietal regions showed time-dependent increases in activity over time as the mappings become overlearned, i.e., despite time-invariant behavioral responses. The automaticity of these mappings predicted the degree of intraparietal changes, indicating that the contribution of the PPC might be related to a particular stage of the overlearning process. We suggest that, as the visuomotor mappings become robust to interference, the PPC may convey relevant sensory information toward the motor cortex. More generally, our findings illustrate how rich cerebral dynamics can underlie stable behavior.

Adult↗

PubMed2005

Attentional selection and action selection in the ventral and orbital prefrontal cortex.

Different accounts of the ventral and orbital prefrontal cortex (PFv+o) have emphasized either its role in learning conditional rules for action selection or the attentional selection of behaviorally relevant stimuli. Although the accounts are not mutually exclusive, it is possible that the involvement of PFv+o in conditional action selection is a consequence of its role in selecting relevant stimuli or that its involvement in attentional selection is a consequence of the conditional rules present in many attentional paradigms. Five macaques learned a conditional action-selection task in which the difficulty of identifying the stimulus relevant for guiding action selection was varied in a simple manner by either altering its distance from the action or presenting additional distracting stimuli. Simply increasing the spatial separation between the instructing stimulus led to slower responses. Experiment 1 showed that bilateral PFv+o lesions impaired conditional action selection even when attentional demands were kept to a minimum, but there was evidence that the impairment was exacerbated by manipulating stimulus selection difficulty. Experiment 2 confirmed the importance of PFv+o for conditional action selection even when stimulus selection difficulty was minimal. Experiments 3 and 4 demonstrated that the action-selection impairment was significantly increased by making identification of the behaviorally relevant stimulus difficult. PFv+o is central to the use of conditional rules when selecting courses of action, but conditional rules are also represented in premotor and striatal regions. A special contribution of PFv+o may be initial selection of behaviorally relevant stimuli.

Animals↗

PubMed2005

Neural substrate of body size: illusory feeling of shrinking of the waist.

The perception of the size and shape of one's body (body image) is a fundamental aspect of how we experience ourselves. We studied the neural correlates underlying perceived changes in the relative size of body parts by using a perceptual illusion in which participants felt that their waist was shrinking. We scanned the brains of the participants using functional magnetic resonance imaging. We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking. These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex. Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.

Body Image↗

PubMed2005

Touching a rubber hand: feeling of body ownership is associated with activity in multisensory brain areas.

In the "rubber-hand illusion," the sight of brushing of a rubber hand at the same time as brushing of the person's own hidden hand is sufficient to produce a feeling of ownership of the fake hand. We shown previously that this illusion is associated with activity in the multisensory areas, most notably the ventral premotor cortex (Ehrsson et al., 2004). However, it remains to be demonstrated that this illusion does not simply reflect the dominant role of vision and that the premotor activity does not reflect a visual representation of an object near the hand. To address these issues, we introduce a somatic rubber-hand illusion. The experimenter moved the blindfolded participant's left index finger so that it touched the fake hand, and simultaneously, he touched the participant's real right hand, synchronizing the touches as perfectly as possible. After approximately 9.7 s, this stimulation elicited an illusion that one was touching one's own hand. We scanned brain activity during this illusion and two control conditions, using functional magnetic resonance imaging. Activity in the ventral premotor cortices, intraparietal cortices, and the cerebellum was associated with the illusion of touching one's own hand. Furthermore, the rated strength of the illusion correlated with the degree of premotor and cerebellar activity. This finding suggests that the activity in these areas reflects the detection of congruent multisensory signals from one's own body, rather than of visual representations. We propose that this could be the mechanism for the feeling of body ownership.

Adult↗

PubMed2005

Dissociating response selection and conflict in the medial frontal surface.

Response conflict and random response selection have both been associated with activations on the medial frontal surface. Random response selection was typically studied using a 'free selection' paradigm, in which subjects have to select between equally legitimate responses which are in competition with each other. Therefore, one interpretation is that the generation of spontaneous actions is merely a special case of the induction of response conflict. It has been reported that the generation of spontaneous actions is tightly associated with activity in the pre-supplementary motor area (pre-SMA). Most studies of response conflict, on the other hand, suggest that activations in a different and more ventral area, the anterior cingulate, reflect response conflict. Nonetheless, contradictory results have also been reported. To clarify this issue, in this experiment, we have put together a version of the Eriksen flanker task and a free selection task to allow for a direct comparison. We confirmed our hypothesis that free selection is associated with the pre-SMA, whereas response conflict is associated in the anterior cingulate. The two clusters of activation do not overlap, and the peaks of them were about 30 mm apart. We conclude that the activity in the pre-SMA is related to the endogenous generation of action rather than response conflict.

Adult↗

PubMed2004

The prefrontal cortex shows context-specific changes in effective connectivity to motor or visual cortex during the selection of action or colour.

The role of the prefrontal cortex remains controversial. Neuroimaging studies support modality-specific and process-specific functions related to working memory and attention. Its role may also be defined by changes in its influence over other brain regions including sensory and motor cortex. We used functional magnetic imaging (fMRI) to study the free selection of actions and colours. Control conditions used externally specified actions and colours. The prefrontal cortex was activated during free selection, regardless of modality, in contrast to modality-specific activations outside prefrontal cortex. Structural equation modelling (SEM) of fMRI data was used to test the hypothesis that although the same regions of prefrontal cortex may be active in tasks within different domains, there is task-dependent effective connectivity between prefrontal cortex and non-prefrontal cortex. The SEM included high-order interactions between modality, selection and regional activity. There was greater coupling between prefrontal cortex and motor cortex during free selection and action tasks, and between prefrontal cortex and visual cortex during free selection of colours. The results suggest that the functions of the prefrontal cortex may be defined not only by selection-specific rather than modality-specific processes, but also by changing patterns of effective connectivity from prefrontal cortex to motor and sensory cortices.

Adult↗

PubMed2004

That's my hand! Activity in premotor cortex reflects feeling of ownership of a limb.

When we look at our hands, we immediately know that they are part of our own body. This feeling of ownership of our limbs is a fundamental aspect of self-consciousness. We have studied the neuronal counterparts of this experience. A perceptual illusion was used to manipulate feelings of ownership of a rubber hand presented in front of healthy subjects while brain activity was measured by functional magnetic resonance imaging. The neural activity in the premotor cortex reflected the feeling of ownership of the hand. This suggests that multisensory integration in the premotor cortex provides a mechanism for bodily self-attribution.

Body Image↗

PubMed2004

Brain mechanisms for inferring deceit in the actions of others.

During social interactions, it is important to judge accurately whether a person is honest or deceitful. We often use nonverbal cues to infer whether others are trying to deceive us. Using functional magnetic resonance imaging, we studied subjects watching videos of actors lifting a box and judged whether or not the actors were trying to deceive them concerning the real weight of the box. When the subjects judged the actions as reflecting deceptive intention, there was activation of the amygdala and rostral anterior cingulate cortex. These areas were not activated when subjects made judgements about the beliefs rather than the intentions of others. We suggest that these activations reflect the observers' judgements of social intentions toward themselves and might reflect an emotional response to being deceived.

Adult↗

PubMed2004

Prefrontal selection and medial temporal lobe reactivation in retrieval of short-term verbal information.

Both the prefrontal cortex (PFC) and medial temporal lobe (MTL) are involved in memory retrieval. Here we distinguish between their roles by manipulating demand for interference resolution and reactivation of maintained information. Subjects were tested on a letter working memory task with distractors. When the memory delay was interrupted with letter distractors, there was higher activity in the middle frontal gyrus at retrieval compared to when the delay was interrupted by number distractors, suggesting the role of the PFC in interference resolution. By contrast, activity in the parahippocampal gyrus did not differ between the two conditions. The two structures were then compared using the dataset of our previous study on memory reactivation, where subjects performed a letter working memory task with arithmetic distractors or non-distractors. The activity in the parahippocampal gyrus at retrieval was higher when distractors interrupted rehearsal than when the intervening task was non-distracting and subjects continued to rehearse, suggesting the role of the MTL in reactivating the stored information. By contrast, the activity in the middle frontal gyrus did not differ between the two conditions. Taking these results together, we have shown the double dissociation between the PFC and MTL in memory retrieval.

Adult↗

PubMed2004

Attention to intention.

Intention is central to the concept of voluntary action. Using functional magnetic resonance imaging, we compared conditions in which participants made self-paced actions and attended either to their intention to move or to the actual movement. When they attended to their intention rather than their movement, there was an enhancement of activity in the pre-supplementary motor area (pre-SMA). We also found activations in the right dorsal prefrontal cortex and left intraparietal cortex. Prefrontal activity, but not parietal activity, was more strongly coupled with activity in the pre-SMA. We conclude that activity in the pre-SMA reflects the representation of intention.

Attention↗

PubMed2004

Cortico-basal ganglia pathways are essential for the recall of well-established visuomotor associations.

Recent human neuroimaging studies, supported by lesion studies with nonhuman primates, have suggested that learning arbitrary associations between sensory cues and behavioural responses requires interactions between the infero-temporal, prefrontal and premotor cortices. We directly tested the hypothesis suggested from our neuroimaging experiments that functional links between the basal ganglia and premotor cortex are involved in the process via which task performance becomes automatic. We made unilateral excitotoxic lesions, centred on the internal pallidum, in four macaques previously given extensive experience on the associations between nonspatial visual cues and movements of a joystick. The basal ganglia lesion was later combined with a premotor cortical lesion in the opposite hemisphere so as to interrupt the connections between them. Three of the animals were subsequently found to be impaired in relearning pre-operatively acquired associations; they eventually succeeded but made three-times as many errors. A fourth animal was unimpaired but its premotor cortex lesion was later found to be incomplete. Response times were only marginally increased and the learning of novel associations appeared relatively unaffected by these lesions. As a control, the effects of a unilateral premotor cortex lesion were assessed with two additional animals but this lesion did not result in a relearning impairment. We therefore suggest that when visuomotor associations have become well established through over-training, performance depends on connections between the basal ganglia and premotor cortex.

Animals↗

PubMed2003

Prefrontal interactions reflect future task operations.

When task instructions are given, the human brain establishes a task set before the task is actually performed. By introducing a delay between the instruction and the task, we have identified the neural correlates of task sets using functional magnetic resonance imaging (fMRI). Subjects were instructed to remember a sequence of positions or letters, either in the order presented or in the reverse order. Spatial or verbal processing areas were active during the delay, depending on whether positions or letters were to be remembered, whereas the anterior region of the prefrontal cortex (PFC) was active regardless of the domain of the items. Furthermore, the nature of the interaction between the anterior PFC and the domain-specific posterior prefrontal areas (superior frontal sulcus and left inferior frontal gyrus) depended on whether the items were to be remembered in the forward or backward order. Thus we have identified inter-regional interactions that reflect preparation for task performance.

Adult↗

PubMed2002

Parahippocampal reactivation signal at retrieval after interruption of rehearsal.

Verbal information is maintained on-line within working memory by rehearsal. However, we still can recall the verbal information when rehearsal is interrupted. Here we show that this is achieved by reactivation of maintained information. We used event-related functional magnetic resonance imaging to identify brain activation at encoding, during memory delay, and at retrieval, within the same trial of a verbal working memory task. On half of the trials, retrieval was tested after arithmetic distraction to interrupt rehearsal of the remembered verbal items. We found that the parahippocampal cortex (PHC) was highly active at retrieval on trials with distraction compared with trials without distraction. The PHC did not show sustained activation during the memory delay. By contrast, the dorsolateral prefrontal cortex (DLPF), left superior temporal region (ST), and Broca's area showed sustained activation during the memory delay, suggesting their role in maintenance of verbal items. After arithmetic distraction, the DLPF and ST were engaged in arithmetic processing. Thus, these areas could not maintain the verbal items during the distraction. At retrieval of verbal items after the distraction, the DLPF, ST and Broca's area were also active. The activity was taken to reflect reactivated representation of the verbal items. The primary role of the PHC in retrieval may be to trigger the reactivation of these cortical areas that had maintained the remembered items, thereby reactivating the information that is no longer maintained on-line.

Adult↗