There have now been roughly 130,000 papers on fMRI. While these have clearly contributed to our understanding of the functional anatomy of the human brain, it is less clear that they have changed the ...way in which we think about the brain. The issue, in other words, is whether they have established new principles about how the brain works. In this paper we offer as an example one new principle, partly to lay down the criteria that are required for establishing a new principle, and partly to encourage others to offer other principles.
Our example concerns the flexible flow of information through the cortex that must occur according to the demands of the task or current context. We suggest that this flexibility is achieved by feedback connections from the prefrontal and parietal cortex, and that these include connections to sensory and motor areas. However, the nature of the selective effect differs. The parietal cortex can select both within and across processing streams. By across streams we mean that it can have the same influence on different streams, for example the dorsal and ventral visual systems. However, only the prefrontal cortex can also select between processing streams. The difference between the prefrontal and parietal effects is due to their different positions within the processing hierarchy.
How does the brain maintain information in working memory while challenged by incoming distractions? Using functional magnetic resonance imaging (fMRI), we measured human brain activity during the ...memory delay of a spatial working memory task with distraction. We found that, in the prefrontal cortex (PFC), the magnitude of activity sustained throughout the memory delay was significantly higher on correct trials than it was on error trials. By contrast, the magnitude of sustained activity in posterior areas did not differ between correct and error trials. The correlation of activity between posterior areas was, however, associated with correct memory performance after distraction. On the basis of these findings, we propose that memory representations gain resistance against distraction during a period of active maintenance within working memory. This may be mediated by interactions between prefrontal and posterior areas.
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.
Components of Switching Intentional Set Rushworth, Matthew F. S.; Passingham, R. E.; Nobre, A. C.
Journal of cognitive neuroscience,
11/2002, Letnik:
14, Številka:
8
Journal Article
Recenzirano
Despite the intuition that we can shift cognitive set on instruction, some behavioral studies have suggested that set shifting might only be accomplished once we engage in performance of the new ...task. It is possible that set switching consists of more than one component cognitive process and that the component processes might segregated in time. We recorded event-related potentials (ERPs) during two set-switching tasks to test whether different component processes were responsible for (i) set initiation and reconfiguration when presented with the instruction to switch, and (ii) the implementation of the new set once subjects engaged in performing the new task. The response switching (RS) task required shifts of intentional set; subjects selected between responses according to one of two conflicting intentional sets. The results demonstrated the existence of more than one constituent process. Some of the processes were linked to the initiation and reconfiguration of the set prior to actual performance of the new task. Other processes were time locked to performance of new task items. Set initiation started with modulation of medial frontal ERPs and was followed by modulation over parietal electrodes. Implementation of intentional set was associated with modulation of response-related ERPs.
Actions are said to be ‘willed’ if we consciously pay attention to their selection. It has been suggested that they are associated with activations in the dorsal prefrontal cortex (area 46). However, ...because previous experiments typically used a ‘free selection’ paradigm to examine this hypothesis, it is unclear whether the results reflected the attention to the selection of action or the freedom of choice allowed by the tasks. In this experiment, we minimized the difference of working memory demand across task conditions by using novel stimuli in each trial. We found that activation in the dorsal prefrontal cortex on a free selection task was not significantly different from that induced by another task that required attention to the selection of action, although the responses were externally specified. This suggests that the dorsal prefrontal cortex is in fact associated with attention to the selection of action, but does not play a unique role in the generation of internally initiated actions. However, the presupplementary motor area (pre-SMA) may subserve this function as activity in this region was found to be tightly associated with the free selection of responses.
PET was used to study cerebral dominance for the selection of action. In one condition the subjects moved one of two fingers depending on the cue presented (choice reaction time), and in another they ...moved the same finger whatever the cue (simple reaction time). There was also a baseline condition in which cues were shown but no movements were made. A conjunction analysis was performed to reveal those areas which were more activated for the choice versus simple reaction time, irrespective of whether the right or left hand was used. The activations were in prefrontal, premotor and intraparietal areas, and they were all in the left hemisphere. Thus, while there were activations in the right hemisphere for the choice versus simple reaction time task when the subjects used their left (contralateral) hand, there were activations in left prefrontal, premotor and parietal areas whether the right (contralateral) or left (ipsilateral) hands were used. It is argued that the results suggest that the left hemisphere is dominant not only for speech but also for action in general.
It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic ...resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.
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.
Macaques were taught a reward-conditional response selection task; they learned to associate each of two different actions to each of two different rewards and to select actions that were appropriate ...for particular rewards. They were also taught a visual discrimination learning task. Cingulate lesions significantly impaired selection of responses associated with different rewards but did not interfere with visual discrimination learning or performance. The results suggest that 1) the cingulate cortex is concerned with action reward associations and not limited to just detecting when actions lead to errors and 2) that the cingulate cortex's function is limited to action reinforcer associations and it is not concerned with stimulus reward associations.
It is widely agreed that visuospatial orienting attention depends on a network of frontal and parietal areas in the right hemisphere. It is thought that the visuospatial orienting role of the right ...parietal lobe is related to its role in the production of overt eye movements. The experiments reported here test the possibility that other parietal regions may be important for directing attention in relation to response modalities other than eye movement. Specifically, we used positron emission tomography (PET) to test the hypothesis that a ‘left’ parietal area, the supramarginal gyrus, is important for attention in relation to limb movements (Rushworth et al., 1997; Rushworth, Ellison, & Walsh, in press). We have referred to this process as ‘motor attention’ to distinguish it from orienting attention. In one condition subjects spent most of the scanning period covertly attending to ‘left’ hand movements that they were about to make. Activity in this first condition was compared with a second condition with identical stimuli and movement responses but lacking motor attention periods. Comparison of the conditions revealed that motor attention related activity was almost exclusively restricted to the ‘left’ hemisphere despite the fact that subjects only ever made ipsilateral, left-hand responses. Left parietal activity was prominent in this comparison, within the parietal lobe the critical region for motor attention was the supramarginal gyrus and the adjacent anterior intraparietal sulcus (AIP), a region anterior to the posterior parietal cortex identified with orienting attention. In a second part of the experiment we compared a condition in which subjects covertly rehearsed verbal responses with a condition in which they made verbal responses immediately without rehearsal. A comparison of the two conditions revealed verbal rehearsal-related activity in several anterior left hemisphere areas including Broca's area. The lack of verbal rehearsal-related activity in the left supra-marginal gyrus confirms that this area plays a direct role in motor attention that cannot be attributed to any strategy of verbal mediation. The results also provide evidence concerning the importance of ventral premotor (PMv) and Broca's area in motor attention and language processes.
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