Search results
Found 12143 matches for
Role of the human rostral supplementary motor area and the basal ganglia in motor sequence control: investigations with H2 15O PET.
The aim of this study was to investigate the functional anatomy of distributed cortical and subcortical motor areas in the human brain that participate in the central control of overlearned complex sequential unimanual finger movements. On the basis of previous research in nonhuman primates, a principal involvement of basal ganglia medial premotor loops [corrected] was predicted for central control of finger sequences performed automatically. In pertinent areas, a correlation of activation levels with the complexity of a motor sequence was hypothesized. H2 15O positron emission tomography (PET) was used in a group of seven healthy male volunteers [mean age 32.0 +/- 10.4 yr] to determine brain regions where levels of regional cerebral blood flow (rCBF) correlated with graded complexity levels of five different key-press sequences. All sequences were overlearned before PET and involved key-presses of fingers II-V of the right hand. Movements of individual fingers were kept constant throughout all five conditions by external pacing at 1-Hz intervals. Positive correlations of rCBF with increasing sequence complexity were identified in the contralateral rostral supplementary motor area (pre-SMA) and the associated pallido-thalamic loop, as well as in right parietal area 7 and ipsilateral primary motor cortex (M1). In contrast, while rCBF in contralateral M1 and [corrected] extensive parts of caudal SMA was increased compared with rest during task performance, significant correlated increases of rCBF with sequence complexity were not observed. Inverse correlations of rCBF with increasing sequence complexity were identified in mesial prefrontal-, medial temporal-, and anterior cingulate areas. The findings provide further evidence in humans supporting the notion of a segregation of SMA into functionally distinct subcomponents: although pre-SMA was differentially activated depending on the complexity of a sequence of learned finger movements, such modulation was not detectable in caudal SMA (except the most antero-superior part), implicating a motor executive role. Our observations of complexity-correlated rCBF increases in anterior globus pallidus suggest a specific role for the basal ganglia in the process of sequence facilitation and control. They may act to filter and focus input from motor cortical areas as patterns of action become increasingly complex.
The nucleus accumbens in monkeys (Macaca fascicularis): II. Emotion and motivation.
Changes 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.
Premotor cortex in the rat.
Donoghue and Wise (1982) identified an area AGm in the rat that they take to be a nonprimary motor area. In the present experiments, therefore, this area was removed bilaterally in rats. The animals were poor at relearning a visual conditional motor task but were able to learn spatial delayed alternation as rapidly as unoperated animals. Thus removing this area in rats has a similar effect to removing premotor cortex in monkeys. It is argued that this dorsomedial shoulder area should not be regarded as part of prefrontal cortex in the rat.
Memory of monkeys (Macaca mulatta) with lesions in prefrontal cortex.
It is controversial whether damage to prefrontal cortex causes an impairment of memory. In this experiment, the tissue in sulcus principalis was removed in rhesus monkeys, and they were given 25 spatial locations to remember. They were poor at the task from the first. The same animals were able to indicate which of two locations they had touched if there was no delay before they were allowed to make their report. One possibility is that frontal mechanisms operate on information in working memory.
An assessment of the reinforcing properties of foods after amygdaloid lesions in rhesus monkeys.
The reinforcing strengths of foods were assessed in rhesus monkeys before and after bilateral radio-frequency lesions of the lateral amygdala (n = 4), basolateral amygdala (n = 4), and total amygdala (n = 3). None of these lesions altered preoperative preferences between three highly palatable foods. Moreover, the lesions had no discernible effect on the animals' responses to different food rewards as measured by a progressive ratio schedule, although performance on this schedule proved sensitive to the size and type of food reward and to the degree of deprivation. The results suggest that amygdalectomy leaves a normal appreciation of at least this one class of rewards, foods. The dietary changes typically seen after amygdalectomy, such as meat eating, which were also observed in the same animals, probably reflect a loss of neophobia.
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.
Signal-, set- and movement-related activity in the human brain: an event-related fMRI study.
Electrophysiological studies on monkeys have been able to distinguish sensory and motor signals close in time by pseudorandomly delaying the cue that instructs the movement from the stimulus that triggers the movement. We have used a similar experimental design in functional magnetic resonance imaging (fMRI), scanning subjects while they performed a visuomotor conditional task with instructed delays. One of four shapes was presented briefly. Two shapes instructed the subjects to flex the index finger; the other two shapes coded the flexion of the middle finger. The subjects were told to perform the movement after a tone. We have exploited a novel use of event-related fMRI. By systematically varying the interval between the visual and acoustic stimuli, it has been possible to estimate the significance of the evoked haemodynamic response (EHR) to each of the stimuli, despite their temporal proximity in relation to the time constant of the EHR. Furthermore, by varying the phase between events and image acquisition, we have been able to achieve high temporal resolution while scanning the whole brain. We dissociated sensory and motor components of the sensorimotor transformations elicited by the task, and assessed sustained activity during the instructed delays. In calcarine and occipitotemporal cortex, the responses were exclusively associated with the visual instruction cues. In temporal auditory cortex and in primary motor cortex, they were exclusively associated with the auditory trigger stimulus. In ventral prefrontal cortex there were movement-related responses preceded by preparatory activity and by signal-related activity. Finally, responses associated with the instruction cue and with sustained activity during the delay period were observed in the dorsal premotor cortex and in the dorsal posterior parietal cortex. Where the association between a visual cue and the appropriate movement is arbitrary, the underlying visuomotor transformations are not achieved exclusively through frontoparietal interactions. Rather, these processes seem to rely on the ventral visual stream, the ventral prefrontal cortex and the anterior part of the dorsal premotor cortex.
Functional anatomy of the mental representation of upper extremity movements in healthy subjects.
1. Differences in the distribution of relative regional cerebral blood flow during motor imagery and execution of a joy-stick movement were investigated in six healthy volunteers with the use of positron emission tomography (PET). Both tasks were compared with a common baseline condition, motor preparation, and with each other. Data were analyzed for individual subjects and for the group, and areas of significant flow differences were related to anatomy by magnetic resonance imaging (MRI). 2. Imagining movements activated a number of frontal and parietal regions: medial and lateral premotor areas, anterior cingulate areas, ventral opercular premotor areas, and parts of superior and inferior parietal areas were all activated bilaterally when compared with preparation to move. 3. Execution of movements compared with imagining movements led to additional activations of the left primary sensorimotor cortex and adjacent areas: dorsal parts of the medial and lateral premotor cortex; adjacent cingulate areas; and rostral parts of the left superior parietal cortex. 4. Functionally distinct rostral and caudal parts of the posterior supplementary motor area (operationally defined as the SMA behind the coronal plane at the level of the anterior commissure) were identified. In the group, the rostral part of posterior SMA was activated by imagining movements, and a more caudoventral part was additionally activated during their execution. A similar dissociation was observed in the cingulate areas. Individual subjects showed that the precise site of these activations varied with the individual anatomy; however, a constant pattern of preferential activation within separate but adjacent gyri of the left hemisphere was preserved. 5. Functionally distinct regions were also observed in the parietal lobe: the caudal part of the superior parietal cortex [medial Brodmann area (BA) 7] was activated by imagining movements compared with preparing to execute them, whereas the more rostral parts of the superior parietal lobe (BA 5), mainly on the left, were additionally activated by execution of the movements. 6. Within the operculum, three functionally distinct areas were observed: rostrally, prefrontal areas (BA 44 and 45) were more active during imagined than executed movements; a ventral premotor area (BA 6) was activated during both imagined and executed movements; and more caudally in the parietal lobe, an area was found that was mainly activated by execution presumably SII. 7. These data suggest that imagined movements can be viewed as a special form of "motor behavior' that, when compared with preparing to move, activate areas associated heretofore with selection of actions and multisensory integration.(ABSTRACT TRUNCATED AT 400 WORDS)
The nucleus accumbens in monkeys (Macaca fascicularis): I. The organization of behaviour.
A behavioural comparison was made between six unoperated control monkeys and six monkeys which received bilateral ibotenic acid lesions of the nucleus accumbens. Two of the control monkeys were subsequently given bilateral lesions of the anterior cingulate and medial frontal cortex (areas 24, 25 and 32) and were retested on the behavioural tasks. The NA lesioned monkeys, but not the anterior cingulate lesioned monkeys, were significantly impaired on a hoarding task in which they were required to remove 18 peanuts from their shells and store them in their cheek pouches. These same monkeys were not impaired when the nuts were presented without shells. Evidence is provided which suggests that this deficit is not motivational or due to gross motor impairments. A second task in which the animals were required to search through four boxes to retrieve food revealed a decrease in the tendency for the NA and cingulate lesioned animals to use an organized pattern of searching. Both groups were found to return to a previously opened box more often than controls. However, neither group showed signs of perseverative behaviour. Data from a ten-box version of this task suggest that these return errors were not due to a decrease in working memory. Together these studies suggest that both the NA and the anterior cingulate cortex contribute to the ability to organize behaviour temporally and spatially.
Is the prefrontal cortex necessary for establishing cognitive sets?
There is evidence from neuroimaging that the prefrontal cortex may be involved in establishing task set activity in advance of presentation of the task itself. To find out whether it plays an essential role, we examined patients with unilateral lesions of the rostral prefrontal cortex. They were first instructed as to whether to perform a spatial or a verbal working memory task and then given spatial and verbal items after a delay of 4-12 s. The patients showed an increase in switch costs, making more errors by repeating what they had done on the previous trial. They were able to establish regional task set activity during the instruction delay, as evidenced by sustained changes in the blood oxygenation level-dependent signal in caudal frontal regions. However, in contrast to healthy controls, they were less able to maintain functional connectivity among the surviving task-related brain regions, as evidenced by reduced correlations between them during instruction delays. The results suggest that the left rostral prefrontal cortex is indeed required for establishing a cognitive set but that the essential function is to support the functional connectivity among the task-related regions.
Cortical and subcortical afferents to the amygdala of the rhesus monkey (Macaca mulatta).
The afferent projections to the primate amygdala were studied using horseradish peroxidase. The potential advantages of this technique are discussed compared with those previously used to determine amygdaloid afferents. The findings indicate that certain agranular or dysgranular cortical regions may project directly to the amygdala: in particular, the orbital frontal cortex, anterior cingulate gyrus, subcallosal gyrus, temporal pole and anterior insula. These projections probably terminate predominantly in either the lateral or accessory basal nuclei. Other cortical projections from the inferotemporal and superior temporal gyri are described. Evidence was found for a heavy projection from the superior temporal sulcus to the lateral nucleus. Subcortical afferents were found from the hypothalamus, substantia innominata, diagonal band, thalamus, periaqueductal central gray, peripeduncular nucleus and from a band of cells extending medially from the peripeduncular nucleus to the midline, just ventral to the thalamus. In the thalamus, labelled cells were restricted to the non-specific nuclei, and were common in the rostral midline nuclei. No projection was observed from the dorsomedial nucleus of the thalamus. We discuss the implications of these results for interpreting the functions of the amygdala.
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.
Unconscious activation of the cognitive control system in the human prefrontal cortex.
Using functional magnetic resonance imaging, we tested whether unconscious information can influence the cognitive control system in the human prefrontal cortex. Volunteers had to prepare to perform either a phonological judgment or a semantic judgment on an upcoming word, based on the instruction given at the beginning of each trial. However, in some trials they were visually primed to prepare for the alternative (i.e., "wrong") task, and this impaired their performance. This priming effect is taken to depend on unconscious processes because the effect was present even when the volunteers could only discriminate the identity of the primes at chance level. Furthermore, the effect was stronger when the visibility of the prime was near zero than when the visibility of the prime was significantly higher. When volunteers were unconsciously primed to perform the alternative task, there was also decreased neural activity in the brain areas relevant to the instructed task and increased neural activity in the brain areas relevant to the alternative task, which shows that the volunteers were actually engaged in the wrong task, instead of simply being distracted. Activity in the mid-dorsolateral prefrontal cortex was also found to be associated with this unconscious priming effect. These results suggest that the cognitive control system in the prefrontal cortex is not exclusively driven by conscious information, as has been believed previously.
The effect of movement frequency on cerebral activation: a positron emission tomography study.
Knowledge of the effect of performance frequency on activation of motor areas in positron emission tomography (PET) studies is crucial to the interpretation of experiments in which performance is a variable. We studied this effect in six normal right-handed volunteers using H2(15)O PET to measure regional cerebral blood flow (rCBF). Subjects were scanned at rest and while executing joystick movements with the right hand in freely chosen directions at different frequencies. Significant frequency dependent increases in rCBF were demonstrated in contralateral sensorimotor cortex, lateral premotor cortex bilaterally, posterior supplementary motor area (SMA), and ipsilateral cerebellar hemisphere and vermis. The striatum and the right dorsal prefrontal cortex were also activated by joystick movement compared with rest, but the magnitude of activation found in these areas was independent of the frequency of movement. The results suggest that primary motor cortex, posterior SMA, lateral premotor cortex and cerebellum are involved in determining the basic parameters of movement. Frequency dependent activation in these areas suggests phasic activity related to movement. In contrast, activation of the dorsal prefrontal cortex and the striatum is not frequency dependent. This may reflect continuous rather than phasic activity in these areas during the task and suggests their role is not simply related to movement execution but higher level during this free selection joystick task.
Motor practice and neurophysiological adaptation in the cerebellum: a positron tomography study.
We have used positron tomography (PET) to demonstrate that some parts of the motor system exhibit physiological adaptation during the repeated performance of a simple motor task, but others do not. In contrast to the primary sensori-motor cortex, the cerebellum exhibits a decrease in physiological activation (increases in regional blood flow during performance) with practice. A new application of factorial experimental design to PET activation studies was used to make these measurements in four normal males. This design allowed adaptation to be examined by testing for an interaction between regional cerebral blood flow (rCBF) increases brought about by a motor task and the number of trials (time). These findings are interpreted as the neurophysiological correlates of synaptic changes in the cerebellum associated with motor learning in man.