Human functional anatomy of visually guided finger movements

Bimanual versus unimanual coordination: what makes the difference?

Using fMRI, we investigated the neuronal structures controlling bimanual coordination applying a visuomotor coordination task. Recent studies suggest the existence of a widespread network for the neuronal control of bimanual coordination including primary sensorimotor cortices (M1/S1), lateral and medial premotor cortices (PMC, SMA), cingulate motor area (CMA), and cerebellum (CB). In the present study, subjects performed bimanual and unimanual tasks requiring the coordination of two fingers at a time to navigate a cursor on a computer screen. Thus, in contrast to previous studies, we are using appropriate unimanual control (UNI) tasks. By using this new motor task, we identified a similar activation network for uni- and bimanual movements. Subjects exhibited bilateral activations in PMC, SMA, posterior-parietal cortex (PPC), occipital, and inferiotemporal cortex, as well as in the contralateral M1/S1 and ipsilateral CB. We did not find any additional activation when comparing bimanual with unimanual conditions. The lack of significant activation in the comparison "bimanual > unimanual" gives reason to suggest that this network is not limited to the control of bimanual motor actions, but responsible for unimanually coordinated movements as well. Interestingly, we found stronger activations for unimanual as compared to bimanual coordination. We hypothesize that task difficulty (degrees of freedom to control, e.g., number of limbs) is more important in determining which network components are activated and to what extent, compared to the factor of bimanuality. It even seemed to be less demanding for the motor system to control the cursor bimanually compared to the unimanual performance with two adjacent fingers.

The role of V5 (hMT+) in visually guided hand movements: an fMRI study

Electrophysiological studies in animals suggest that visuomotor control of forelimb and eye movements involves reciprocal connections between several areas (striate, extrastriate, parietal, motor and premotor) related to movement performance and visuospatial coding of movement direction. The extrastriate area MT [V5 (hMT+) in humans] located in the "dorsal pathway" of the primate brain is specialized in the processing of visual motion information. The aim of our study was to investigate the functional role of V5 (hMT+) in the control of visually guided hand movements and to identify the corresponding cortex activation implicated in the visuomotor tasks using functional magnetic resonance imaging. Eight human subjects performed visually guided hand movements, either continuously tracking a horizontally moving target or performing ballistic tracking movements of a cursor to an eccentric stationary target while fixating a central fixation cross. The tracking movements were back-projected onto the screen using a cursor which was moved by an MRI-compatible joystick. Both conditions activated area V5 (hMT+), right more than left, particularly during continuous tracking. In addition, a large-scale sensorimotor circuit which included sensorimotor cortex, premotor cortex, striatum, thalamus and cerebellum as well as a number of cortical areas along the intraparietal sulcus in both hemispheres were activated. Because activity was increased in V5 (hMT+) during continuous tracking but not during ballistic tracking as compared to motion perception, it has a pivotal role during the visual control of forelimb movements as well.

The functional neuroanatomy of temporal discrimination

Two identical stimuli, such as a pair of electrical shocks to the skin, are readily perceived as two separate events in time provided the interval between them is sufficiently long. However, as they are presented progressively closer together, there comes a point when the two separate stimuli are perceived as a single stimulus. Damage to posterior parietal cortex, peri-supplementary motor area (peri-SMA), and basal ganglia can disturb this form of temporal discrimination. Our aim was to establish, in healthy subjects, the brain areas that are involved in this process. During functional magnetic resonance imaging scanning, paired electrical pulses, separated by variable inter-stimulus intervals (5-110 msec), were delivered to different sites on one forearm (8-64 mm from the midline). Subjects were required to simply detect the stimulus (control task) or to identify a stimulus property. For temporal discrimination (TD), subjects reported whether they felt one or two stimuli. For spatial discrimination, they reported whether the stimuli were located on the right or left side of the forearm. Subjects reported their choice by pressing a button with the opposite hand. Our results showed that discrimination, as opposed to simply detection, activated several brain areas. Most were common to both discrimination tasks. These included regions of prefrontal cortex, right postcentral gyrus and inferior parietal lobule, basal ganglia, and cerebellum. However, activation of pre-SMA and anterior cingulate was found to be specific to the TD task. This suggests that these two frontal regions may play a role in the temporal processing of somatosensory events.

Left hemisphere specialization for the control of voluntary movement rate

Although persuasive behavioral evidence demonstrates the superior dexterity of the right hand in most people under a variety of conditions, little is known about the neural mechanisms responsible for this phenomenon. As this lateralized superiority is most evident during the performance of repetitive, speeded movement, we used parametric rate variations to compare visually paced movement of the right and left hands. Twelve strongly right-handed subjects participated in a functional magnetic resonance imaging (fMRI) experiment involving variable rate thumb movements. For movements of the right hand, contralateral rate-related activity changes were identified in the precentral gyrus, thalamus, and posterior putamen. For left-hand movements, activity was seen only in the contralateral precentral gyrus, consistent with the existence of a rate-sensitive motor control subsystem involving the left, but not the right, medial premotor corticostriatal loop in right-handed individuals. We hypothesize that the right hemisphere system is less skilled at controlling variable-rate movements and becomes maximally engaged at a lower movement rate without further modulation. These findings demonstrate that right- and left-hand movements engage different neural systems to control movement, even during a relatively simple thumb flexion task. Specialization of the left hemisphere corticostriatal system for dexterity is reflected in asymmetric mechanisms for movement rate control.

Neural mechanisms underlying reaching for remembered targets cued kinesthetically or visually in left or right hemispace

Reaching for a target involves integrative coordinate transformation processes between the representation of the target location, the sensorimotor information of limb of reach, and body space. Although right hemisphere dominance for visuospatial information processing is well established, corresponding right hemisphere dominance for kinesthetic spatial information processing remains to be demonstrated. We explored neural mechanisms of encoding target locations using 15O-butanol positron emission tomography (PET) in normal volunteers in a factorial experiment, where modality (visual/kinesthetic) and hemispace of target presentation (left/right of midsagittal plane) were varied systematically. After target presentation, subjects reached to the encoded target location. PET data analysis using SPM99 showed increased neural activity (P < 0.05, corrected) associated with left hemispace target presentation in right hemisphere areas (sensorimotor, anterior cingulate, insular, and temporo-occipital cortex) only. By contrast, right hemispace target presentation activated bilateral temporo-occipital cortex, which extended into the right temporo-parietal cortex and left sensorimotor cortex. A significant interaction of hemispace and modality of target presentation observed in right temporo-parietal cortex resulted from an increase in neural activity with kinesthetic target presentation in right hemispace. The data support an important role for the right temporo-parietal area in visuospatial processing and suggest a specific role of the right hemisphere in kinesthetic spatial processing.

Optic ataxia as a deficit specific to the on-line control of actions

Optic ataxia is characterized by inaccuracies in body movements under visual control, and is a common consequence of damage to the posterior parietal lobes in humans. It is argued here that optic ataxia can be characterized as a deficit in the visual on-line guidance of actions, with action planning remaining relatively intact. This contrasts with the common view of optic ataxia as representing a deficit in the transformations that take place between visual inputs and motor outputs. Evidence in support of the planning-control view comes from the pattern of spared and disrupted behaviors in patients with optic ataxia. It is shown that spared behaviors are those that emphasize planning, whereas disrupted behaviors are those that emphasize control. In particular, recent studies have highlighted the inability of a patient with optic ataxia to make on-line adjustments to targets that change position during the movement. Taken in sum, the data from patients with optic ataxia is more consistent with the planning-control interpretation of optic ataxia than with the visuomotor transformation interpretation.

A pain neuromatrix approach to patients with chronic pain

This paper presents an approach to rehabilitation of pain patients. The fundamental principles of the approach are (i) pain is an output of the brain that is produced whenever the brain concludes that body tissue is in danger and action is required, and (ii) pain is a multisystem output that is produced when an individual-specific cortical pain neuromatrix is activated. When pain becomes chronic, the efficacy of the pain neuromatrix is strengthened via nociceptive and non-nociceptive mechanisms, which means that less input, both nociceptive and non-nociceptive, is required to produce pain. The clinical approach focuses on decreasing all inputs that imply that body tissue is in danger and then on activating components of the pain neuromatrix without activating its output. Rehabilitation progresses to increase exposure to threatening input across sensory and non-sensory domains.

Internal vs external generation of movements: differential neural pathways involved in bimanual coordination performed in the presence or absence of augmented visual feedback

It is commonly agreed that a functional dissociation with respect to the internal vs external control of movements exists for several brain regions. This has, however, only been tested in relation to the timing and preparation of motor responses, but not to ongoing movement control. Using functional magnetic resonance imaging (fMRI), the present study addressed the neuroanatomical substrate of the internal-external control hypothesis by comparing regional brain activation for cyclical bimanual movements performed in the presence or absence of augmented visual feedback. Subjects performed a bimanual movement pattern, either with the help of on-line visual feedback of the movements (externally guided coordination) or with the eyes closed on the basis of an internal representation of the movement pattern (internally generated coordination). Visual control and baseline rest conditions were also added. Results showed a clear functional dissociation within the network involved in movement coordination. The hMT/V5+, the superior parietal cortex, the premotor cortex, the thalamus, and cerebellar lobule VI showed higher activation levels when movements were guided by visual feedback. Conversely, the basal ganglia, the supplementary motor area, cingulate motor cortex, the inferior parietal, frontal operculum, and cerebellar lobule IV-V/dentate nucleus showed higher involvement when movements were internally generated. Consequently, the present findings suggest the existence of distinct cortico-cortical and subcortico-cortical neural pathways for externally (augmented feedback) and internally guided cyclical bimanual movements. This provides a neurophysiological account for the beneficial effect of providing augmented visual feedback to optimize movements in normal and motor disordered patients.

From 'acting on' to 'acting with': the functional anatomy of object-oriented action schemata

In this chapter it is proposed that object-based actions can be broadly classified into types. In the first, objects are 'acted on' without a specific purpose. In the second, objects are 'acted with'. In the latter case the grasp reflects the subsequent goal of the subject. Recent evidence from human functional imaging suggests different neural substrates for acting on an object (dorsal parietal cortex) and for acting with an object. Specifically, it is argued that conceptual knowledge of tool use and the pragmatics of action rely on an inferior parieto-medial frontal network in the left hemisphere.

Both parietal lobes are involved in drawing: a functional MRI study and implications for constructional apraxia

In clinical studies, many researchers have reported that drawing can be disturbed by left or right unilateral parietal lobe damage (constructional apraxia). There seem to be two possible predictions about the cerebral laterality for drawing. The first is that drawing requires both parietal lobes, therefore, a lesion to either side can disrupt drawing. The second is that individuals can differ in laterality: some have only right or left activations, and some have bilateral. To test these predictions, we investigated with functional magnetic resonance imaging (fMRI) the cerebral activation whilst 17 right-handed healthy subjects performed a drawing task. The experiment consisted of two conditions: (1). naming an object in a presented picture and drawing it by using right index finger (DRAWING & NAMING); (2). naming an object in a presented picture (NAMING). We considered the brain regions that had greater activity in the DRAWING&NAMING condition than in the NAMING condition were the neural substrates of drawing. Individual analysis revealed that all subjects showed parietal activation bilaterally. We interpret that the results support the first prediction that both parietal lobes are required for drawing. By calculating the laterality indices of the individual parietal activations, it was found that there were more left dominant subjects than right dominant subjects (left, 12; right, 5). The results are inconsistent with previous studies on the incidence of constructional apraxia. In addition, we found activation in regions that were not previously reported in the literature of constructional apraxia: they are the ventral premotor area and posterior part of inferior temporal sulcus.

A functional magnetic resonance imaging study of internal modulation of an external visual cue for motor execution

The strategy to perform a task differs according to how a cue is interpreted. In order to investigate the basic mechanisms of temporal regulation in the higher motor areas, the interaction between two different types of internal modulations of an external visual cue was evaluated using functional magnetic resonance imaging (fMRI). An opposing finger movement task guided by dot prompting was employed. In the intermittent tapping experiment, two taps per second and a rest for one second were alternatively repeated in the task blocks. In the constant tapping experiments, the volunteers performed finger movements at 0.5, 1 or 2 Hz. The activation in the primary sensory motor area correlated with the amount of movement. Activities in the supplementary motor area, left dorsal pre-motor area, left superior parietal lobule and right cerebellum depended on the demand for internal modulation. Activation in these areas was maximum for the intermittent task which was a combination of two different internal modulations, and minimum for the 1 Hz movement that did not require internal modulation. It was suggested that these four areas are directly involved in the generation of a complex movement sequence driven by a visual cue, and they are organized for performance. The translation of external pacing and initiation for self-pacing may share the same neuronal basis. Activation in the left supramarginal gyrus, bilateral frontal operticula and basal ganglia did not depend on the combination of the two internal modulations.

Age-related changes in the neural correlates of motor performance

Age-related neurodegenerative and neurochemical changes are thought to underlie decline in motor and cognitive functions, but compensatory processes in cortical and subcortical function may allow maintenance of performance level in some people. Our objective was to investigate age-related changes in the motor system of the human brain using functional MRI. Twenty six right handed volunteers were scanned whilst performing an isometric, dynamic, visually paced hand grip task, using dominant (right) and non-dominant (left) hands in separate sessions. Hand grip with visual feedback activated a network of cortical and subcortical regions known to be involved in the generation of simple motor acts. In addition, activation was seen in a putative human 'grasping circuit', involving rostral ventral premotor cortex (Brodmann area 44) and intraparietal sulcus. Within this network, a number of regions were more likely to be activated the older the subject. In particular, age-related changes in task- specific activations were demonstrated in left deep anterior central sulcus when using the dominant or non-dominant hand. Additional age-related increases were seen in caudal dorsal premotor cortex, caudal cingulate sulcus, intraparietal sulcus, insula, frontal operculum and cerebellar vermis. We have demonstrated a clear age-related effect in the neural correlates of motor performance, and furthermore suggest that these changes are non-linear. These results support the notion that an adaptable and plastic motor network is able to respond to age-related degenerative changes in order to maintain performance levels.

Neuronal activity related to the visual representation of arm movements in the lateral cerebellar cortex

Testing the hypothesis that the lateral cerebellum forms a sensory representation of arm movements, we investigated cortical neuronal activity in two monkeys performing visually guided step-tracking movements with a manipulandum. A virtual target and cursor image were viewed co-planar with the manipulandum. In the normal task, manipulandum and cursor moved in the same direction; in the mirror task, the cursor was left-right reversed. In one monkey, 70- and 200-ms time delays were introduced on cursor movement. Significant task-related activity was recorded in 31 cells in one animal and 142 cells in the second: 10.2% increased activity before arm movements onset, 77.1% during arm movement, and 12.7% after the new position was reached. To test for neural representation of the visual outcome of movement, firing rate modulation was compared in normal and mirror step-tracking. Most task-related neurons (68%) showed no significant directional modulation. Of 70 directionally sensitive cells, almost one-half (n = 34, 48%) modulated firing with a consistent cursor movement direction, many fewer responding to the manipulandum direction (n = 9, 13%). For those "cursor-related" cells tested with delayed cursor movement, increased activity onset was time-locked to arm movement and not cursor movement, but activation duration was extended by an amount similar to the applied delay. Hence, activity returned to baseline about when the delayed cursor reached the target. We conclude that many cells in the lateral cerebellar cortex signaled the direction of cursor movement during active step-tracking. Such a predictive representation of the arm movement could be used in the guidance of visuo-motor actions.

Rapid visuomotor preparation in the human brain: a functional MRI study

An important feature of human motor behaviour is anticipation and preparation. We report a functional magnetic resonance imaging study of the neuronal activation patterns in the human brain that are associated with the rapid visuomotor preparation of discrete finger responses. Our imaging results reveal a large-scale distributed network of neural areas involved in fast visuomotor preparation, including specific areas in the frontal cortex (middle frontal gyrus, premotor and supplementary motor cortex), the parietal cortex (intra-parietal sulcus, inferior and superior parietal lobe) and the basal ganglia. Our reaction time results demonstrate that it is easier to prepare two fingers on one hand than on two hands. This hand-advantage phenomenon was associated with relatively enhanced levels of activity in the basal ganglia and relatively reduced levels of activity in the parietal cortex. These findings provide direct evidence for differential activity in a distributed brain system associated with specific neuro-computational operations subserving fast visuomotor preparation.

Investigating the generators of the scalp recorded visuo-verbal P300 using cortically constrained source localization

Considerable ambiguity exists about the generators of the scalp recorded P300, despite a vast body of research employing a diverse range of methodologies. Previous investigations employing source localization techniques have been limited largely to equivalent current dipole models, with most studies identifying medial temporal and/or hippocampal sources, but providing little information about the contribution of other cortical regions to the generation of the scalp recorded P3. Event-related potentials (ERPs) were recorded from 5 subjects using a 124-channel sensor array during the performance of a visuo-verbal Oddball task. Cortically constrained, MRI-guided boundary element modeling was used to identify the cortical generators of this target P3 in individual subjects. Cortical generators of the P3 were localized principally to the intraparietal sulcus (IPS) and surrounding superior parietal lobes (SPL) bilaterally in all subjects, though with some variability across subjects. Two subjects also showed activity in the lingual/inferior occipital gyrus and mid-fusiform gyrus. A group cortical surface was calculated by non-linear warping of each subject's segmented cortex followed by averaging and creation of a group mesh. Source activity identified across the group reflected the individual subject activations in the IPS and SPL bilaterally and in the lingual/inferior occipital gyrus primarily on the left. Activation of IPS and SPL is interpreted to reflect the role of this region in working memory and related attention processes and visuo-motor integration. The activity in left lingual/inferior occipital gyrus is taken to reflect activation of regions associated with modality-specific analysis of visual word forms.

Preoperative mapping of the supplementary motor area in patients harboring tumors in the medial frontal lobe

OBJECT

Injury to the supplementary motor area (SMA) is thought to be responsible for transient motor and speech deficits following resection of tumors involving the medial frontal lobe. Because direct intraoperative localization of SMA is difficult, the authors hypothesized that functional magnetic resonance (fMR) imaging might be useful in predicting the risk of postoperative deficits in patients who undergo resection of tumors in this region.

METHODS

Twelve patients who had undergone fMR imaging mapping while performing speech and motor tasks prior to excision of their tumor, that is, based on anatomical landmarks involving the SMA, were included in this study. The distance between the edge of the tumor and the center of SMA activation was measured and was correlated with the risk of incurring postoperative neurological deficits. In every patient, SMA activation was noted in the superior frontal gyrus on preoperative fMR imaging. Two speech and two motor deficits typical of SMA injury were observed in three of the 12 patients. The two speech deficits occurred in patients with tumors involving the dominant hemisphere, whereas one of the motor deficits occurred in a patient with a tumor in the nondominant hemisphere. The risk of developing a postoperative speech or motor deficit was 100% when the distance between the SMA and the tumor was 5 mm or less. When the distance between SMA activation and the lesion was greater than 5 mm, the risk of developing a motor or a speech deficit was 0% (p = 0.0007).

CONCLUSIONS

Early data from this study indicated that fMR imaging might be useful in localizing the SMA and in determining the risk of postoperative deficits in patients who undergo resection of tumors located in the medial frontal lobe.

The roles of the cerebellum and basal ganglia in timing and error prediction

Recent evidence that the cerebellum and the basal ganglia are activated during the performance of cognitive and attention tasks challenges the prevailing view of their primary function in motor control. The specific roles of the basal ganglia and the cerebellum in cognition, however, have been difficult to identify. At least three functional hypotheses regarding their roles have been proposed. The first hypothesis suggests that their main function is to switch attentional set. The second hypothesis states that they provide error signals regarding stimuli or rewards. The third hypothesis is that they operate as an internal timing system, providing a precise representation of temporal information. Using functional magnetic resonance imaging, we tested these three hypotheses using a task-switching experiment with a 2 x 2 factorial design varying timing (random relative to fixed) and task order (unpredictable relative to predictable). This design allowed us to test whether switching between tasks, timing irregularity and/or task order unpredictability activate the basal ganglia and/or the cerebellum. We show that the cerebellum is primarily activated with timing irregularity while the anterior striatum is activated with task order unpredictability, supporting their distinctive roles in two forms of readjustment. Task order unpredictability alone, independent of reward delivery, is sufficient to induce striatal activation. In addition, activation of the cerebellum and basal ganglia were not specific to switching attention because these regions were both activated during switching between tasks and during the simultaneous maintenance of two tasks without switching between them.

Effects of pointing direction and direction predictability on event-related lateralizations of the EEG

In two experiments, we investigated hemispheric electroencephalography (EEG) differences in 9(12) healthy volunteers during pointing to lateral and central targets. The questions addressed were whether horizontal pointing direction and the predictability of pointing direction modulated hemispheric differences (event-related lateralizations of the EEG = ERLs). To vary pointing direction predictability, targets were displayed either randomly at one of nine different positions on a screen (random) or at the same horizontal position in five subsequent trials (sequenced) while vertical positions varied randomly. Event-related lateralizations (ERLs) varied with pointing direction. This was true across changes in target eccentricity and pointing distance. Foci of the ERLs were in premotor and posterior parietal cortex, which might reflect the critical involvement of these areas in the control of visually guided reaching. Direction predictability reduced the parietal and premotor ERL before pointing onset, probably reflecting a lesser effort in visuomotor transformation. Predictability also added an overlying N2pc component to the early ERL after target onset and increased direction effects during movement.

The role of lateral premotor-cerebellar-parietal circuits in motor sequence control: a parametric fMRI study

Functional characterisation of higher order motor systems can be obtained by modulating the processing demands imposed onto relevant motor circuitries. Here we performed whole-brain functional magnetic resonance imaging (fMRI) and parametric statistical analyses in eight healthy volunteers to study task-related recruitment of motor circuits associated with unilateral finger movement sequences of increasing length and complexity, but with equal basic motor parameters. Statistical parametric mapping software was applied for analysis. Categorical analysis of the main effect of motor action showed cerebral activation in the established cortical and subcortical motor network. Parametric analyses of the blood-oxygen-level-dependent (BOLD) contrast revealed significant signal increases correlating to sequence length and complexity in a subset of activated areas, notably contralateral ventral and dorsal premotor cortex, bilateral superior parietal cortex, left inferior frontal gyrus/Broca's area, right dentate nucleus, and left visual association cortex. These data underscore the importance of ventral premotor-cerebellar-parietal circuits in processing length and complexity of sequential finger movements.

Adaptive functional changes in the cerebral cortex of patients with nondisabling multiple sclerosis correlate with the extent of brain structural damage

In multiple sclerosis, the mechanisms underlying the accumulation of disability are poorly understood. Recently, it has been suggested that adaptive cortical changes may limit the clinical impact of multiple sclerosis injury. In this study, functional magnetic resonance imaging and a general search method were used to assess patterns of brain activation associated with a simple motor task in 14 right-handed, nondisabled relapsing-remitting multiple sclerosis patients that were compared to those from 15 right-handed, sex- and age-matched healthy volunteers. Also investigated were the extent to which the functional magnetic resonance imaging changes correlated with T2 lesion volume and severity of multiple sclerosis pathology in lesions and normal-appearing brain tissue, measured using magnetisation transfer and diffusion tensor magnetic resonance imaging. Compared to controls, multiple sclerosis patients showed increased activation in the contralateral primary sensorimotor cortex, bilaterally in the supplementary motor area, bilaterally in the cingulate motor area, in the contralateral ascending bank of the sylvian fissure, and in the contralateral intraparietal sulcus. T2 lesion volume was correlated with relative activation in the ipsilateral supplementary motor area, and in the ipsilateral and contralateral cingulate motor area. Average lesion magnetisaiton transfer ratio and average lesion water diffusivity were correlated with relative activation in the contralateral sensorimotor cortex. Average lesion magnetisation transfer ratio was also correlated with relative activation in the ipsilateral cingulate motor area. Average water diffusivity and peak height of the normal-appearing brain tissue diffusivity histogram were both correlated with relative activation in the contralateral intraparietal sulcus. This study shows that cortical activation occurs over a rather distributed sensorimotor network in nondisabled relapsing-remitting multiple sclerosis patients. It also suggests that increased recruitment of this cortical network contributes to the limitation of the functional impact of white matter multiple sclerosis injury.

Functional magnetic resonance imaging correlates of fatigue in multiple sclerosis

Although fatigue is a common and troublesome symptom of multiple sclerosis (MS), its pathogenesis is poorly understood. In this study, we used functional magnetic resonance imaging (fMRI) to test whether a different pattern of movement-associated cortical and subcortical activations might contribute to the development of fatigue in patients with MS. We obtained fMRI during the execution of a simple motor task with completely normally functioning hands from 15 MS patients with fatigue (F), 14 MS patients without fatigue (NF), and 15 sex- and age-matched healthy volunteers. F and NF MS patients were also matched for major clinical and MRI variables. FMRI data were analyzed using statistical parametric mapping. In all patients, severity of fatigue was rated using the Fatigue Severity Scale (FSS). Compared to healthy subjects, MS patients showed more significant activations of the contralateral primary somatomotor cortex, the contralateral ascending limb of the Sylvian fissure, the contralateral intraparietal sulcus (IPS), the contralateral supplementary motor area, and the ipsilateral and contralateral cingulate motor area (CMA). Compared to F MS patients, NF patients showed more significant activations of the ipsilateral cerebellar hemisphere, the ipsilateral rolandic operculum, the ipsilateral precuneus, the contralateral thalamus, and the contralateral middle frontal gyrus. In contrast, F MS patients had a more significant activation of the contralateral CMA. Significant inverse correlations were found between FSS scores and relative activations of the contralateral IPS (r = -0.63), ipsilateral rolandic operculum (r = -0.61), and thalamus (r = -0.62). This study provides additional evidence that fatigue in MS is related to impaired interactions between functionally related cortical and subcortical areas. It also suggests that fMRI might be a valuable tool to monitor the efficacy of treatment aimed at reducing MS-related fatigue.

Activation in the ipsilateral posterior parietal cortex during tool use: a PET study

The basis of perceptual assimilation of tool and hand has been considered to be in modification of body schemata, for which integration of multimodal sensory information about our body parts is required. Using positron emission tomography and H(2)(15)O, we aimed to identify brain regions that change their neural activity in association with changes in neural processing of visual and/or somatosensory information when humans use a simple tool. Normal subjects were instructed to manipulate a small graspable object with a pair of tongs or with the fingers of their right or left hand. The only site activated during manipulation with the tool, compared with the fingers, with the right hand was the lateral edge of the right intraparietal sulcus (IPS). During manipulation using the left hand with the tool, compared with using the fingers, an area in the middle part of the left IPS was activated. Areas in the contralateral hemisphere were activated during both the tool-use and the finger-use tasks compared to the control task, but there was no statistically significant difference between the tool-use and the finger-use tasks. Therefore, the results suggest that the ipsilateral posterior parietal cortex was recruited during the tool-use tasks to integrate visuosomatosensory information.

Brain activation related to the representations of external space and body scheme in visuomotor control

Regional cerebral blood flow was assessed during reaching movements with either target or finger selection. Measurements were performed with positron emission tomography in normal subjects. We thus identified two patterns of cerebral activation representing parietal command functions based on either external space or body scheme information. Directing the right-hand index finger toward one target dot in an array of five was related to activations distributed over dorsal extrastriate visual cortex (putative area V3A), along the parieto-occipital sulcus (putative V6/V6A) and the posterior intraparietal sulcus (IPS). Right-hemisphere dominance was present at the occipital extension of posterior IPS. Positioning one right-hand finger of five on the middle target dot was related with anterior IPS activation, extending over the marginal gyrus of the left inferior parietal lobe. The latter indicated a parietal role in prehension, independent of the shape of the target reached for. In both conditions of the reaching task, instructions for movement were auditorily given by random numbers 1 to 5, thus excluding visual cueing. The observed lateralization of movement-related parietal functions helps to explain neurological symptoms such as ideomotor apraxia and spatial hemineglect.

Brain areas involved in interlimb coordination: a distributed network

Whereas behavioral studies have made significant contributions toward the identification of the principles governing the coordination of limb movements, little is known about the role of higher brain areas that are involved in interlimb coordination. Functional magnetic resonance imaging (fMRI) was used to reveal the brain areas activated during the cyclical coordination of ipsilateral wrist and foot movements. Six normal subjects performed five different tasks that were presented in a random order, i.e., isolated flexion-extension movements of the right wrist (WRIST) and right foot (FOOT), cyclical coordination of wrist and foot according to the isodirectional (ISODIR) and nonisodirectional (NON-ISODIR) mode, and rest (REST). All movements were auditory paced at 66 beats/min. During the coordination of both limb segments, a distributed network was identified showing activation levels in the supplementary motor area (SMA), cingulate motor cortex (CMC), premotor cortex (PMC), primary sensorimotor cortex (M1/S1), and cerebellum that exceeded the sum of the activations observed during the isolated limb movements. In addition, coordination of the limb movements in different directions was associated with extra activation of the SMA as compared to movements in the same direction. It is therefore concluded that the SMA is substantially involved in the coordination of the nonhomologous limbs as part of a distributed motor network. Accordingly, the long-standing exclusive association that has been made between this medial frontal area and bimanual (homologous) coordination needs to be abandoned and extended towards other forms of interlimb coordination (nonhomologous).

Spatial coding of visual and somatic sensory information in body-centred coordinates

Because sensory systems use different spatial coordinate frames, cross-modal sensory integration and sensory-motor coordinate transformations must occur to build integrated spatial representations. Multimodal neurons using non-retinal body-centred reference frames are found in the posterior parietal and frontal cortices of monkeys. We used functional magnetic resonance imaging to reveal regions of the human brain using body-centred coordinates to code the spatial position of both visual and somatic sensory stimuli. Participants determined whether a visible vertical bar (visual modality) or a location touched by the right index finger (somatic sensory modality) lay to the left or to the right of their body mid-sagittal plane. This task was compared to a spatial control task having the same stimuli and motor responses and comparable difficulty, but not requiring body-centred coding of stimulus position. In both sensory modalities, the body-centred coding task activated a bilateral fronto-parietal network, though more extensively in the right hemisphere, to include posterior parietal regions around the intraparietal sulcus and frontal regions around the precentral and superior frontal sulci, the inferior frontal gyrus and the superior frontal gyrus on the medial wall. The occipito-temporal junction and other extrastriate regions exhibited bilateral activation enhancement related to body-centred coding when driven by visual stimuli. We conclude that posterior parietal and frontal regions of humans, as in monkeys, appear to provide multimodal integrated spatial representations in body-centred coordinates, and these data furnish the first indication of such processing networks in the human brain.

Feedback-dependent modulation of isometric force control: an EEG study in visuomotor integration

The primary purpose of this investigation was to examine the cortical mechanisms underlying visuomotor integration in an experiment directly manipulating visual feedback (control-signal gain) as participants executed a grasping task. This was accomplished by assessing human electroencephalograms in both time and frequency domains and relating these measures to the performance accuracy of isometric force control. The basic experimental manipulation consisted of subjects controlling a grip dynamometer and the subsequent force trace displayed on a computer monitor at various magnitudes of force output and control-signal gain. Several findings from this study were of interest. First, the effects of control-signal gain and its interplay with the magnitude of force were most evident across the parietal and frontocentral electrode locations--areas specifically related to multi-modal sensory evaluation (parietal lobe) and higher-order movement control (supplementary and mesial premotor areas). Second, electroencephalography (EEG) measures in the time domain, i.e., slow-wave potentials, were sensitive to control-signal gain only during the ramp phase of force production (period of reaching the target force), not the static phase (period of maintaining the target force level). Third, EEG measures within the frequency domain (event-related desynchronization), unlike the slow-wave potential measures, were sensitive to control-signal gain during the static phase of force production--a sensitivity that was directly related to improvements in the accuracy of isometric force control. The findings of this investigation are described in relation to the existent literature on human visuomotor integration with special attention paid to the distinct spatial and temporal electrocortical patterns exhibited under varying degrees of visual feedback and magnitudes of force output during grasping.

Attention systems and the organization of the human parietal cortex

Event-related functional magnetic resonance imaging was used to compare activity in the human parietal cortex in two attention-switching paradigms. On each trial of the visual switching (VS) paradigm, subjects attended to one of two visual stimuli on the basis of either their color or shape. Trials were presented in blocks interleaved with cues instructing subjects to either continue attending to the currently relevant dimension or to switch to the other stimulus dimension. In the response switching (RS) paradigm, subjects made one of two manual responses to the single stimulus presented on each trial. The rules for stimulus-response mapping were reversed on different trials. Trials were presented in blocks interleaved with cues that instructed subjects to either switch stimulus-response mapping rules or to continue with the current rule. Brain activity at "switch" and "stay" events was compared. The results revealed distinct parietal areas concerned with visual attentional set shifts (VS) and visuomotor intentional set shifts (RS). In VS, activity was recorded in the lateral part of the intraparietal region. In RS, activity was recorded in the posterior medial intraparietal region and adjacent posterior superior and dorsomedial parietal cortex. The results also suggest that the basic functional organization of the intraparietal sulcus and surrounding regions is similar in both macaque and human species.

The cerebellum coordinates eye and hand tracking movements

The cerebellum is thought to help coordinate movement. We tested this using functional magnetic resonance imaging (fMRI) of the human brain during visually guided tracking tasks requiring varying degrees of eye-hand coordination. The cerebellum was more active during independent rather than coordinated eye and hand tracking. However, in three further tasks, we also found parametric increases in cerebellar blood oxygenation signal (BOLD) as eye-hand coordination increased. Thus, the cerebellar BOLD signal has a non-monotonic relationship to tracking performance, with high activity during both coordinated and independent conditions. These data provide the most direct evidence from functional imaging that the cerebellum supports motor coordination. Its activity is consistent with roles in coordinating and learning to coordinate eye and hand movement.

Cortical correlates of gesture processing: clues to the cerebral mechanisms underlying apraxia during the imitation of meaningless gestures

The clinical test of imitation of meaningless gestures is highly sensitive in revealing limb apraxia after dominant left brain damage. To relate lesion locations in apraxic patients to functional brain activation and to reveal the neuronal network subserving gesture representation, repeated H2(15O)-PET measurements were made in seven healthy subjects during a gesture discrimination task. Observing paired images of either meaningless hand or meaningless finger gestures, subjects had to indicate whether they were identical or different. As a control condition subjects simply had to indicate whether two portrayed persons were identical or not. Brain activity during the discrimination of hand gestures was strongly lateralized to the left hemisphere, a prominent peak activation being localized within the inferior parietal cortex (BA40). The discrimination of finger gestures induced a more symmetrical activation and rCBF peaks in the right intraparietal sulcus and in medial visual association areas (BA18/19). Two additional foci of prominent rCBF increase were found. One focus was located at the left lateral occipitotemporal junction (BA 19/37) and was related to both tasks; the other in the pre-SMA was particularly related to hand gestures. The pattern of task-dependent activation corresponds closely to the predictions made from the clinical findings, and underlines the left brain dominance for meaningless hand gestures and the critical involvement of the parietal cortex. The lateral visual association areas appear to support first stages of gesture representation, and the parietal cortex is part of the dorsal action stream. Finger gestures may require in addition precise visual analysis and spatial attention enabled by occipital and right intraparietal activity. Pre-SMA activity during the perception of hand gestures may reflect engagement of a network that is intimately related to gesture execution.

Functional anatomy of nonvisual feedback loops during reaching: a positron emission tomography study

Reaching movements performed without vision of the moving limb are continuously monitored, during their execution, by feedback loops (designated nonvisual). In this study, we investigated the functional anatomy of these nonvisual loops using positron emission tomography (PET). Seven subjects had to "look at" (eye) or "look and point to" (eye-arm) visual targets whose location either remained stationary or changed undetectably during the ocular saccade (when vision is suppressed). Slightly changing the target location during gaze shift causes an increase in the amount of correction to be generated. Functional anatomy of nonvisual feedback loops was identified by comparing the reaching condition involving large corrections (jump) with the reaching condition involving small corrections (stationary), after subtracting the activations associated with saccadic movements and hand movement planning [(eye-arm-jumping minus eye-jumping) minus (eye-arm-stationary minus eye-stationary)]. Behavioral data confirmed that the subjects were both accurate at reaching to the stationary targets and able to update their movement smoothly and early in response to the target jump. PET difference images showed that these corrections were mediated by a restricted network involving the left posterior parietal cortex, the right anterior intermediate cerebellum, and the left primary motor cortex. These results are consistent with our knowledge of the functional properties of these areas and more generally with models emphasizing parietal-cerebellar circuits for processing a dynamic motor error signal.

Defining the cortical visual systems: "what", "where", and "how"

The visual system historically has been defined as consisting of at least two broad subsystems subserving object and spatial vision. These visual processing streams have been organized both structurally as two distinct pathways in the brain, and functionally for the types of tasks that they mediate. The classic definition by Ungerleider and Mishkin labeled a ventral "what" stream to process object information and a dorsal "where" stream to process spatial information. More recently, Goodale and Milner redefined the two visual systems with a focus on the different ways in which visual information is transformed for different goals. They relabeled the dorsal stream as a "how" system for transforming visual information using an egocentric frame of reference in preparation for direct action. This paper reviews recent research from psychophysics, neurophysiology, neuropsychology and neuroimaging to define the roles of the ventral and dorsal visual processing streams. We discuss a possible solution that allows for both "where" and "how" systems that are functionally and structurally organized within the posterior parietal lobe.

Task-related EEG-EEG coherence depends on dopaminergic activity in Parkinson's disease

We investigated whether functional coupling between different cortical areas is impaired in Parkinson's disease, using corticocortical coherence as a surrogate measure of coupling. We recorded scalp EEG from different sites in seven parkinsonian patients while they tracked a visual target using their wrist, or copied the same movement from memory. Differences in EEG-EEG coherence between the tracking and copying tasks and their respective controls, visual tracking alone and fixation of a stationary target, were determined on and off levodopa. After levodopa we found extensive task-specific and broad band cortico-cortical coherence. Off levodopa cortico-cortical coherence was much reduced. Ascending dopaminergic projections from the ventral mesencephalon may therefore be important in determining the pattern and extent of corticocortical coupling during executive tasks.

Functional anatomy of execution, mental simulation, observation, and verb generation of actions: a meta-analysis

There is a large body of psychological and neuroimaging experiments that have interpreted their findings in favor of a functional equivalence between action generation, action simulation, action verbalization, and perception of action. On the basis of these data, the concept of shared motor representations has been proposed. Indeed several authors have argued that our capacity to understand other people's behavior and to attribute intention or beliefs to others is rooted in a neural, most likely distributed, execution/observation mechanism. Recent neuroimaging studies have explored the neural network engaged during motor execution, simulation, verbalization, and observation. The focus of this metaanalysis is to evaluate in specific detail to what extent the activated foci elicited by these studies overlap.

Broca's region subserves imagery of motion: a combined cytoarchitectonic and fMRI study

Broca's region in the dominant cerebral hemisphere is known to mediate the production of language but also contributes to comprehension. Here, we report the differential participation of Broca's region in imagery of motion in humans. Healthy volunteers were studied with functional magnetic resonance imaging (fMRI) while they imagined movement trajectories following different instructions. Imagery of right-hand finger movements induced a cortical activation pattern including dorsal and ventral portions of the premotor cortex, frontal medial wall areas, and cortical areas lining the intraparietal sulcus in both cerebral hemispheres. Imagery of movement observation and of a moving target specifically activated the opercular portion of the inferior frontal cortex. A left-hemispheric dominance was found for egocentric movements and a right-hemispheric dominance for movement characteristics in space. To precisely localize these inferior frontal activations, the fMRI data were coregistered with cytoarchitectonic maps of Broca's areas 44 and 45 in a common reference space. It was found that the activation areas in the opercular portion of the inferior frontal cortex were localized to area 44 of Broca's region. These activations of area 44 can be interpreted to possibly demonstrate the location of the human analogue to the so-called mirror neurones found in inferior frontal cortex of nonhuman primates. We suggest that area 44 mediates higher-order forelimb movement control resembling the neuronal mechanisms subserving speech.

The effect of switching between sequential and repetitive movements on cortical activation

We used whole-head functional magnetic resonance imaging (fMRI) to investigate the effect of switching between different sequential and repetitive movements in the context of conditional and fixed tasks. Four different movement tasks were applied: (1) unpredictable switching between two movement sequences comprising six submovements each according to visual cues (SEQ-VC); (2) unpredictable switching between repetitive movement of one finger according to visual cues (REP-VC); (3) performance of the same sequential movements used for SEQ-VC but in a fixed mode triggered by a visual stimulus (SEQ-FIX); (4) performance of the repetitive movements used for REP-FIX but in a fixed mode by a visual stimulus (REP-FIX). The statistical group analysis of the hemodynamic responses revealed the following results: (1) the SEQ-VC compared to the SEQ-FIX condition (switching between movement sequences) engendered stronger activations in the left rostral supplementary motor area (pre-SMA), bilaterally in the posterior parietal lobule, the left ventral premotor area, and the visual cortices; (2) the REP-VC compared to the REP-FIX condition (switching between repetitive movements) only revealed stronger activation in extra-striate areas. We hypothesize that during switching of movement sequences higher motor control aspects are involved including movement selection, updating of motor plans, as well as recalling and restoring motor plans. The repetitive movements are too simple in order to evoke additional activations in the medial and lateral premotor areas, as well as in parietal areas.

Correlations between reaction time and cerebral blood flow during motor preparation

We show using positron emission tomography in normal volunteers that for four tasks involving motor preparation, regional cerebral blood flow in the ipsilateral cerebellum is negatively correlated with reaction time. Each of the tasks presented subjects with different amounts of advanced information (from none to partial to full information) prior to a signal to move one of two possible fingers in one of two possible directions. The cerebellum was the only brain area that was correlated with reaction time in all the conditions. These results are compatible with the idea that the cerebellum plays an important role in the preparation and initiation of motion.

Patterns of regional brain activation associated with different forms of motor learning

To examine the variations in regional cerebral blood flow during execution and learning of reaching movements, we employed a family of kinematically and dynamically controlled motor tasks in which cognitive, mnemonic and executive features of performance were differentiated and characterized quantitatively. During 15O-labeled water positron emission tomography (PET) scans, twelve right-handed subjects moved their dominant hand on a digitizing tablet from a central location to equidistant targets displayed with a cursor on a computer screen in synchrony with a tone. In the preceding week, all subjects practiced three motor tasks: 1) movements to a predictable sequence of targets; 2) learning of new visuomotor transformations in which screen cursor motion was rotated by 30 degrees -60 degrees; 3) learning new target sequences by trial and error, by using previously acquired routines in a task placing heavy load on spatial working memory. The control condition was observing screen and audio displays. Subtraction images were analyzed with Statistical Parametric Mapping to identify significant brain activation foci. Execution of predictable sequences was characterized by a modest decrease in movement time and spatial error. The underlying pattern of activation involved primary motor and sensory areas, cerebellum, basal ganglia. Adaptation to a rotated reference frame, a form of procedural learning, was associated with decrease in the imposed directional bias. This task was associated with activation in the right posterior parietal cortex. New sequences were learned explicitly. Significant activation was found in dorsolateral prefrontal and anterior cingulate cortices. In this study, we have introduced a series of flexible motor tasks with similar kinematic characteristics and different spatial attributes. These tasks can be used to assess specific aspects of motor learning with imaging in health and disease.

An 'automatic pilot' for the hand in human posterior parietal cortex: toward reinterpreting optic ataxia

We designed a protocol distinguishing between automatic and intentional motor reactions to changes in target location triggered at movement onset. In response to target jumps, but not to a similar change cued by a color switch, normal subjects often could not avoid automatically correcting fast aiming movements. This suggests that an 'automatic pilot' relying on spatial vision drives fast corrective arm movements that can escape intentional control. In a patient with a bilateral posterior parietal cortex (PPC) lesion, motor corrections could only be slow and deliberate. We propose that 'on-line' control is the most specific function of the PPC and that optic ataxia could result from a disruption of automatic hand guidance.

A PET study of visuomotor learning under optical rotation

We measured the regional cerebral blood flow (rCBF) in six healthy volunteers with PET (positron emission tomography) and H(15)(2)O to identify the areas of the human brain involved in sensorimotor learning. The learning task was visually guided reaching with sensorimotor discrepancy caused by optical rotation. PET measurements were performed in the early and late stages of the adaptation to the sensorimotor perturbation. Control measurements were obtained during an eye movement task and a reaching task without optical rotation. The rCBF data of each learning stage were compared to those of both control conditions. During the early stage, rCBF increases were detected in the rostral premotor cortex bilaterally, the posterior part of the left superior parietal lobule (SPL), and the right SPL including the intraparietal sulcus (IPS). During the late stage, rCBF increases were detected in the left caudal premotor area, the left supplementary motor area proper, the left SPL, the right SPL including the IPS, and the right postcentral sulcus extending to the inferior parietal lobule. These results reveal that sensorimotor learning accompanies changes in the recruited cortical areas during different stages of the adaptation, reflecting the different functional roles of each area for different components of adaptation, from learning of new sensorimotor coordination to retention or retrieval of acquired coordination.

The functional neuroanatomy and long-term reproducibility of brain activation associated with a simple finger tapping task in older healthy volunteers: a serial PET study

We examined long-term reproducibility of the functional organization of the brain associated with a simple finger tapping movement using positron emission tomography (PET). Repeat measurements of regional cerebral blood flow were obtained in 10 individuals, ages 35 to 82 years (mean 52 years), at scanning sessions separated by 6 months. Although the functional neuroanatomy of hand movements has previously been investigated with PET by a number of groups, none has reported systematic investigation of the consistency of brain activation over an extended time. As expected, we found significant activation in the left precentral gyrus [Talairach coordinate (-32, -34, 52)], postcentral gyrus (-22, -48, 56), and supplementary motor area (SMA) (-2, -18, 52) at the initial study, consistent with previous studies in younger subjects. For the follow-up study we also found significant activation in the left precentral (-36, -28, 52) and postcentral (-28, -36, 52) gyri and in the SMA (2, -16, 56). Our group results demonstrate consistent anatomical location and extent of motor activation over time. More importantly, analysis of individuals confirmed the presence of consistent sites of activation in primary sensorimotor cortex and SMA over the 6-month interval in most subjects. A high degree of consistency in location of activation in the group, and within individuals, over time suggests that changes in loci of activation may be confidently monitored using the PET method. Evidence of individual differences in extent of activation over time highlights the need for caution when interpreting similar changes in patient studies.

Specialized neural systems underlying representations of sequential movements

The ease by which movements are combined into skilled actions depends on many factors, including the complexity of movement sequences. Complexity can be defined by the surface structure of a sequence, including motoric properties such as the types of effectors, and by the abstract or sequence-specific structure, which is apparent in the relations amongst movements, such as repetitions. It is not known whether different neural systems support the cognitive and the sensorimotor processes underlying different structural properties of sequential actions. We investigated this question using whole-brain functional magnetic resonance imaging (fMRI) in healthy adults as they performed sequences of five key presses involving up to three fingers. The structure of sequences was defined by two factors that independently lengthen the time to plan sequences before movement: the number of different fingers (1-3; surface structure) and the number of finger transitions (0-4; sequence-specific structure). The results showed that systems involved in visual processing (extrastriate cortex) and the preparation of sensory aspects of movement (rostral inferior parietal and ventral premotor cortex (PMv)) correlated with both properties of sequence structure. The number of different fingers positively correlated with activation intensity in the cerebellum and superior parietal cortex (anterior), systems associated with sensorimotor, and kinematic representations of movement, respectively. The number of finger transitions correlated with activation in systems previously associated with sequence-specific processing, including the inferior parietal and the dorsal premotor cortex (PMd), and in interconnecting superior temporal-middle frontal gyrus networks. Different patterns of activation in the left and right inferior parietal cortex were associated with different sequences, consistent with the speculation that sequences are encoded using different mnemonics, depending on the sequence-specific structure. In contrast, PMd activation correlated positively with increases in the number of transitions, consistent with the role of this area in the retrieval or preparation of abstract action plans. These findings suggest that the surface and the sequence-specific structure of sequential movements can be distinguished by distinct distributed systems that support their underlying mental operations.

Time perception and motor timing: a common cortical and subcortical basis revealed by fMRI

Though it is well known that humans perceive the temporal features of the environment incessantly, the brain mechanisms underlying temporal processing are relatively unexplored. Functional magnetic resonance imaging was used in this study to identify brain activations during sustained perceptual analysis of auditorally and visually presented temporal patterns (rhythms). Our findings show that the neural network supporting time perception involves the same brain areas that are responsible for the temporal planning and coordination of movements. These results indicate that time perception and motor timing rely on similar cerebral structures.

Coherence of sequential movements and motor learning

The analysis of oscillatory EEG phenomena such as interregional coherence (task-related coherence [TRCoh] or event-related coherence) has advanced our knowledge of neurophysiological processes underlying the performance and learning of skilled finger movements. It has become clear that various types of higher task demands are reflected by changes in the functional coupling of different cortical areas and not only by changes in regional activation. Neuroscientists are merely starting to understand how coherent oscillations might encode information in the human motor system ("sensorimotor binding") and how well this can be measured from the surface EEG. However, interregional coherence is a potentially independent mechanism that can, up to now, only be investigated with electrophysiological techniques such as EEG and MEG. The studies reviewed below focus on coherence of finger movements and motor learning: increasing complexity of a movement sequence, internal rhythm generation, visuomotor integration, deficits in interhemispheric coupling, and bimanual coordination. Evidence is presented for a special functional significance of TRCoh in the beta frequency range (13 to 21 Hz) for information processing in large-scale sensorimotor networks during motor tasks.

Brain structures related to active and passive finger movements in man

A PET study was performed in six normal volunteers to elucidate the functional localization of the sensory afferent component during finger movement. Brain activation during the passive movement driven by a servo-motor was compared with that during an auditory-cued active movement which was controlled kinematically in the same way as the passive one. A newly developed device was used for selectively activating proprioception with a minimal contribution from tactile senses. Active movement was associated with activation of multiple areas, including the contralateral primary sensorimotor cortex, premotor cortex, supplementary motor area (SMA), bilateral secondary somatosensory areas and basal ganglia and ipsilateral cerebellum. In contrast, only the contralateral primary and secondary somatosensory areas were activated by the passive movement. It is likely that the contribution of proprioceptive input to the activation of the premotor cortex, SMA, cerebellum and basal ganglia, if any, is small. However, the present results do not rule out the possibility that the cutaneous afferent input or the combination of cutaneous and proprioceptive input participates in the activation of those areas during the active movement.

The effects of learning and intention on the neural network involved in the perception of meaningless actions

PET was used to explore the neural network involved in the perception of meaningless action. In two conditions, subjects observed learned and unknown meaningless actions without any purpose. In two other conditions, subjects observed the same type of stimuli for later imitation. The control condition, which consisted of the presention of stationary hands, served as a baseline. Unsurprisingly, a common network that forms part of the dorsal pathway was engaged in all conditions when compared with stationary hands, and this was interpreted as being devoted to the analysis of hand movements. One of the most striking results of the present study was that some brain areas were strongly modulated by the learning level, independent of the subject's intention. Two different effects were observed: a reduced activity in posterior regions within the common network, which correlated with specific increases in the frontopolar area 10 and in the angular gyrus during the perception of learned meaningless actions compared with the perception of unknown actions. Finally, the major effect of the subject's intention to imitate was a strong increase in the dorsal pathway extending to the lateral premotor cortex and to the dorsolateral prefrontal cortex, which reflects the information processing needed for prospective action. Overall, our results provide evidence for both an effect of the visuomotor learning level and of the subject's intention on the neural network involved during the perception of human meaningless actions.

A fronto-parietal circuit for object manipulation in man: evidence from an fMRI-study

Functional magnetic resonance imaging (fMRI) was used to localize brain areas active during manipulation of complex objects. In one experiment subjects were required to manipulate complex objects for exploring their macrogeometric features as compared to manipulation of a simple smooth object (a sphere). In a second experiment subjects were asked to manipulate complex objects and to silently name them upon recognition as compared to manipulation of complex not recognizable objects without covert naming. Manipulation of complex objects resulted in an activation of ventral premotor cortex [Brodmann's area (BA) 44], of a region in the intraparietal sulcus (most probably corresponding to the anterior intraparietal area in the monkey), of area SII and of a sector of the superior parietal lobule. When the objects were covertly named additional activations were found in the opercular part of BA 44 and in the pars triangularis of the inferior frontal gyrus (BA 45). We suggest that a fronto-parietal circuit for manipulation of objects exists in humans and involves basically the same areas as in the monkey. It is proposed that area SII analyses the intrinsic object characteristics whilst the superior parietal lobule is related to kinaesthesia.

Pain and functional imaging

Functional neuroimaging has fundamentally changed our knowledge about the cerebral representation of pain. For the first time it has been possible to delineate the functional anatomy of different aspects of pain in the medial and lateral pain systems in the brain. The rapid developments in imaging methods over the past years have led to a consensus in the description of the central pain responses between different studies and also to a definition of a central pain matrix with specialized subfunctions in man. In the near future we will see studies where a systems perspective allows for a better understanding of the regulatory mechanisms in the higher-order frontal and parietal cortices. Also, pending the development of experimental paradigms, the functional anatomy of the emotional aspects of pain will become better known.