72 research outputs found
Connectivity fingerprints: From areal descriptions to abstract spaces
No full textFifteen years ago, Passingham and colleagues proposed that brain areas can be described in terms of their unique pattern of input and output connections with the rest of the brain, and that these connections are a crucial determinant of their function. We explore how the advent of neuroimaging of connectivity has allowed us to test and extend this proposal. We show that describing the brain in terms of an abstract connectivity space, as opposed to physical locations of areas, provides a natural and powerful framework for thinking about brain function and its variation across the brains of individuals, populations, and species
The nucleus accumbens in monkeys (Macaca fascicularis): II. Emotion and motivation.
No full textChanges in incentive and emotion have been demonstrated in monkeys with amygdala lesions and monkeys with cingulate and medial frontal lesions. The nucleus accumbens (NA) receives inputs from the amygdala, hippocampus and anterior cingulate cortex. In order to better understand the role of the NA and anterior cingulate cortex in processing emotional and motivational stimuli, studies were undertaken which compared the emotional and motivational behaviour of monkeys with NA lesions or anterior cingulate lesions with previous studies on amygdala-lesioned monkeys. A food preference task, a food vs. non-food discrimination task, and a approach-avoidance task were used with monkeys which received lesions of the NA or lesion of the anterior cingulate and medial frontal cortex. These tasks had previously been used to examine the emotional response of monkeys with amygdala lesions. In addition, the lesioned monkeys were tested on a frustration tasks and a button press acquisition-extinction task. Unlike amygdala-lesioned monkeys (Aggleton, J.P. and Passingham, R.E., J. Comp. Physiol. Psychol., 96 (1981) 961-977 and 96 (1982) 71-77), the NA-lesioned monkeys maintained normal food preferences, did not show signs of hyperorality in the food vs. non-food task, and performed normally on the approach-avoidance tasks. The NA-lesioned monkeys did, however, show an increase in activity, and violent and aggressive behaviour in response to stress in both the frustration task and the button press extinction task. In addition, the NA-lesioned monkeys performed normally during a button press acquisition task, but extinguished faster on a button press extinction task than the control monkeys. The anterior cingulate-lesioned monkeys were also found to exhibit an increased responsiveness to frustration. Results of the food preference, food vs. non-food discrimination, and approach-avoidance tasks were similar to those obtained with NA lesioned. These studies suggest that lesions of the NA or the anterior cingulate cortex result in substantial changes in emotional behavior, however, these changes do not mimic those found following lesions of the amygdala
The representation of abstract task rules in the human prefrontal cortex
No full textWe have previously reported sustained activation in the ventral
prefrontal cortex while participants prepared to perform 1 of 2 tasks
as instructed. But there are studies that have reported activation
reflecting task rules elsewhere in prefrontal cortex, and this is true in
particular when it was left to the participants to decide which rule to
obey. The aim of the present experiment was to use functional
magnetic resonance imaging (fMRI) to find whether there was
activation in common, irrespective of the way that the task rules
were established. On each trial, we presented a word after a variable
delay, and participants had to decide either whether the word was
abstract or concrete or whether it had 2 syllables. The participants
either decided before the delay which task they would perform or
were instructed by written cues. Comparing the self-generated with
the instructed trials, there was early task set activation during the
delay in the middle frontal gyrus. On the other hand, a conjunction
analysis revealed sustained activation in the ventral prefrontal and
polar cortex for both conditions. We argue that the ventral prefrontal
cortex is specialized for handling conditional rules regardless of how
the task rules were established
The cerebellum and cognition: cerebellar lesions impair sequence learning but not conditional visuomotor learning in monkeys.
No full textClaims that the cerebellum contributes to cognitive processing in humans have arisen from both functional neuroimaging and patient studies. These claims challenge traditional theories of cerebellar function that ascribe motor functions to this structure. We trained monkeys to perform both a visuomotor conditional associative learning task and a visually guided sequence task, and studied the effects of bilateral excitotoxic lesions in the lateral cerebellar nuclei. In the first experiment three operated monkeys showed a small impairment in post-operative retention of a visuomotor associative task (A) but were then not impaired in learning a new task (B). However, the impairment on A could have been due to a problem in making the movements themselves. In a second experiment we therefore gave the three control animals a further pre-operative retest on both A and B and then tested after surgery on retention of both tasks. Though again the animals showed motor problems on task A, they reached criterion, and at this stage could clearly make both movements satisfactorily. The critical test was then retention of task B, and they were not impaired. In the final experiment (serial reaction time task) the monkeys response times on a repeating visuomotor sequence were compared with those for a pseudo-random control sequence. After bilateral nuclei lesions they were slow to execute the pre-operatively learned sequence but were still faster on this than on the control task. However, when they were then given a new repeating sequence to learn, they never performed the sequence as quickly as they had on retention of the first sequence. We conclude that the cerebellum is not essential for the learning or recall of stimulus-response associations but that it is crucially involved in the process by which motor sequences become automatic with extended practice
Action observation and acquired motor skills: An fMRI study with expert dancers
No full textWhen we observe someone performing an action, do our brains simulate making that action? Acquired motor skills offer a unique way to test this question, since people differ widely in the actions they have learned to perform. We used functional magnetic resonance imaging to study differences in brain activity between watching an action that one has learned to do and an action that one has not, in order to assess whether the brain processes of action observation are modulated by the expertise and motor repertoire of the observer. Experts in classical ballet, experts in capoeira and inexpert control subjects viewed videos of ballet or capoeira actions. Comparing the brain activity when dancers watched their own dance style versus the other style therefore reveals the influence of motor expertise on action observation. We found greater bilateral activations in premotor cortex and intraparietal sulcus, right superior parietal lobe and left posterior superior temporal sulcus when expert dancers viewed movements that they had been trained to perform compared to movements they had not. Our results show that this 'mirror system' integrates observed actions of others with an individual's personal motor repertoire, and suggest that the human brain understands actions by motor simulation
Amygdala activation when one is the target of deceit: did he lie to you or to someone else?
No full textThe ability to figure out whether a person is being honest or deceitful is an important part of social competence. Reactions to deceit may however differ depending on whether one is being deceived oneself or observes a deceitful exchange between others. In the present study, we investigated whether personal involvement influenced the neural responses associated with the detection of deceit. Subjects watched videos of actors lifting a box and judged whether the actors had been misled about the real weight of the box. Personal involvement was manipulated by having the participants themselves among the actors. The critical finding was that there was activity in amygdala and fusiform gyrus only for the condition in which participants observed themselves being deceived. In contrast, the superior temporal sulcus and anterior cingulate cortex were activated irrespective of whether the participants detected that the experimenter had deceived themselves or another. These four brain areas are all interconnected and are part of the discrete neural system subserving social cognition. Our results provide direct evidence, using judgments of deceit in a social context, that the crucial factor for amygdala activation is the involvement of the subjects because they are the target of the deceit. We interpret the activation of the amygdala in this situation as reflecting the greater affective reaction when one is deceived oneself. Our results suggest that when one is personally involved, deceit is taken as a potential threat
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