Changes in Regional Cerebral Oxidative Metabolism Induced by Tactile Learning and Recognition in Man

We measured the regional cerebral oxidative metabolism (rCMRO2) with positron emission tomography in normal healthy volunteers in three different stages: rest, tactile learning, and tactile recognition of complicated geometrical objects. The frequency of manipulatory movements during tactile recognition was twice that of tactile learning. Tactile recognition with the right hand increased rCMRO2 in six prefrontal cortical areas, bilaterally in the supplementary motor areas, the premotor areas and supplementary sensory areas, in the left primary motor and primary sensory area, in the left anterior superior parietal lobule, bilaterally in the secondary somatosensory area, the anterior insula, lingual gyri, hippocampus, basal ganglia, anterior parasagittal cerebellum, and lobus posterior cerebelli. These structures have in other studies been found to participate in manipulatory movements and analysis of somatosensory information. Tactile learning increased rCMRO2 in the same structures as did tactile recognition. Thus we found no differences in the anatomical structures participating in storage and retrieval. However the rCMRO2 increases in the left premotor cortex, supplementary motor area, and left somatosensory hand area were larger during tactile recognition in accordance with the higher frequency of manipulatory movements and higher flux of somatosensory information from the periphery during recognition. Despite this the rCMRO2 was significantly higher in the neocerebellar cortex during tactile learning. Since there were no learning effects on the manipulatory movements, this extra metabolic activity in the lateral cerebellum was attributed to energy demanding processes associated with climbing fibre activity during storage of somatosensory information.     

Impaired mesial frontal and putamen activation in Parkinson's disease: a positron emission tomography study.

Selection of movement in normal subjects has been shown to involve the premotor, supplementary motor, anterior cingulate, posterior parietal, and dorsolateral prefrontal areas. In Parkinson's disease (PD), the primary pathological change is degeneration of the nigrostriatal dopaminergic projections, and this is associated with difficulty in initiating actions. We wished to investigate the effect of the nigral abnormality in PD on cortical activation during movement. Using C15O2 and positron emission tomography (PET), we studied regional cerebral blood flow in 6 patients with PD and 6 control subjects while they performed motor tasks. Subjects were scanned while at rest, while repeatedly moving a joystick forward, and while freely choosing which of four possible directions to move the joystick. Significant increases in regional cerebral blood flow were determined with covariance analysis. In normal subjects, compared to the rest condition, the free-choice task activated the left primary sensorimotor cortex, left premotor cortex, left putamen, right dorsolateral prefrontal cortex and supplementary motor area, anterior cingulate area, and parietal association areas bilaterally. In the patients with PD, for the free-choice task, compared with the rest condition, there was significant activation in the left sensorimotor and premotor cortices but there was impaired activation of the contralateral putamen, the anterior cingulate, supplementary motor area, and dorsolateral prefrontal cortex. Impaired activation of the medial frontal areas may account for the difficulties PD patients have in initiating movements.     

Modification of cortical somatosensory evoked potentials during tactile exploration and simple active and passive movements.

The present study compares the effects of different types of movement on median nerve somatosensory evoked potentials (SEPs) recorded from frontal, central and parietal electrodes. Test conditions included tactile exploratory movements, repetitive active and passive thumb movements and isometric contraction. All these conditions modified the SEPs in a similar manner. Parietal N20, P25, and N60, central P22 and N32, and frontal N25, N30 and P40 deflections were diminished, while later centro-parietal P40 and fronto-central N60 were unchanged. A small frontal P35 emerged during movement. The subcortical P14 was not changed in any of the conditions. The similar modulatory effects of simple active movements and of tactile exploration indicate that the modification of SEPs does not depend on the importance of proprioceptive feedback information for movement execution. As all modulatory effects were present also during passive movement, these observed effects are most likely to be caused by afferent occlusion in the ascending thalamo-cortical pathways or sensorimotor cortical cell populations.     

Neural substrates of tactile imagery: a functional MRI study

fMRI investigation on the neural substrates involved in tactile imagery is reported. Healthy subjects performed mental imagery of tactile stimulation on the dorsal aspect of the right hand. The results were compared with the regions of activation during the actual tactile stimulation. During imagery, contralateral primary and secondary somatosensory areas were activated along with activation in the left parietal lobe. Activations in left inferior frontal gyri (Brodmann's area 44), left dorsolateral prefrontal area, left precentral gyrus, left insula, and medial frontal gyrus were also observed. In the basal ganglia, activation in the left thalamus (ventral posteromedial nucleus) and putamen was found. Our results suggest that the primary and secondary somatosensory areas are recruited during tactile imagery, and have partially overlapping neural substrates for the perception of tactile stimulation.     

Cerebral dominance for action in the human brain: the selection of actions

PET was used to study cerebral dominance for the selection of action. In one condition the subjects moved one of two fingers depending on the cue presented (choice reaction time), and in another they moved the same finger whatever the cue (simple reaction time). There was also a baseline condition in which cues were shown but no movements were made. A conjunction analysis was performed to reveal those areas which were more activated for the choice versus simple reaction time, irrespective of whether the right or left hand was used. The activations were in prefrontal, premotor and intraparietal areas, and they were all in the left hemisphere. Thus, while there were activations in the right hemisphere for the choice versus simple reaction time task when the subjects used their left (contralateral) hand, there were activations in left prefrontal, premotor and parietal areas whether the right (contralateral) or left (ipsilateral) hands were used. It is argued that the results suggest that the left hemisphere is dominant not only for speech but also for action in general.     

Is Broca's area involved in the processing of passive sentences? An event-related fMRI study

We used functional magnetic resonance imaging (fMRI) to investigate whether activation in Broca's area is greater during the processing of passive versus active sentences in the brains of healthy subjects. Twenty Japanese native speakers performed a visual sentence comprehension task in which they were asked to read a visually presented sentence and to identify the agent or the patient in the sentence by pressing a button. We found that the processing of passive sentences elicited no greater activation than that of active sentences in Broca's area. However, passive sentences elicited greater activation than active sentences in the left frontal operculum and the inferior parietal lobule. Thus, our neuroimaging results suggest that deficits in the comprehension of passive sentences in Japanese aphasics are induced not by lesions to Broca's area, but to the left frontal operculum and/or the inferior parietal lobule.     

Involvement of area MT in bimanual finger movements in left-handers: an fMRI study

The ease with which humans are able to perform symmetric movements of both hands has traditionally been attributed to the preference of the motor system to activate homologous muscles. Recently, we have shown in right-handers, however, that bimanual index finger adduction and abduction movements in incongruous hand orientations (one palm down/other up) preferentially engaged parietal perception-associated brain areas. Here, we used functional magnetic resonance imaging to investigate the influence of hand orientation in left-handers on cerebral activation during bimanual index finger movements. Performance in incongruous orientation of either hand yielded activations involving right and left motor cortex, supplementary motor area in right superior frontal gyrus (SMA and pre-SMA), bilateral premotor cortex, prefrontal cortex, bilateral somatosensory cortex and anterior parietal cortex along the intraparietal sulcus. In addition, the occipito-temporal cortex corresponding to human area MT (hMT) in either hemisphere was activated in relation to bimanual index finger movements in the incongruous hand orientation as compared with the same movements in the congruous hand orientation or with simply viewing the pacing stimuli. Comparison with the same movement condition in right-handed subjects from a former study support these hMT activations exclusively for left-handed subjects. These results suggest that left-handers use visual motion imagery in guiding incongruous bimanual finger movements.     

Somatosensory Discrimination of Shape: Tactile Exploration and Cerebral Activation

This study of somatosensory discrimination of rectangular parallelepipeda with the right hand had three purposes: (i) to describe the exploratory finger movements; (ii) to reveal the anatomical brain structures specifically engaged in the production of exploratory finger movements; and (iii) to reveal the anatomical structures specifically engaged in the discrimination of tactually sensed shape. The thumb was the most active finger, moving with a mean exploration frequency of 2.4 Hz, as evident from videotape records of the exploratory finger movements. The cerebral structures activated during somatosensory discrimination were mapped by measurements of regional cerebral blood flow (rCBF) in six healthy male volunteers with positron emission tomography (PET) and the use of the computerized brain atlas of Greitz et al. (1991, J. Comp. Ass. Tomogr., 15, 26 - 38). The rCBF changes caused by somatosensory discrimination were compared point-to-point to a PET-study on right-hand finger movements and a PET-study on vibration stimulation of the right hand. From these results the following conclusions were drawn. The rCBF increase in the left superior parietal lobule indicated the site engaged in the analysis of shape. The rCBF increases in the left supplementary sensory area, bilaterally in premotor areas, in the left putamen, the right dentate nucleus and bilaterally in the posterior cerebellum were related to the control of the tactile exploratory finger movements. The rCBF increases in the right homologue of Broca's area, bilaterally in the superior prefrontal cortex and in the right midfrontal cortex probably resulted from working memory, the direction of attention, and the discrimination process.     

Tactile discrimination of grating orientation: fMRI activation patterns

Grating orientation discrimination is employed widely to test tactile spatial acuity. We used functional magnetic resonance imaging (fMRI) to investigate the neural circuitry underlying performance of this task. Two studies were carried out. In the first study, an extensive set of parietal and frontal cortical areas was activated during covert task performance, relative to a rest baseline. The active regions included the postcentral sulcus bilaterally and foci in the left parietal operculum, left anterior intraparietal sulcus, and bilateral premotor and prefrontal cortex. The second study examined selective recruitment of cortical areas during discrimination of grating orientation (a task with a macrospatial component) compared to discrimination of grating spacing (a purely microspatial task). The foci activated on this contrast were in the left anterior intraparietal sulcus, right postcentral sulcus and gyrus, left parieto-occipital cortex, bilateral frontal eye fields, and bilateral ventral premotor cortex. These findings not only confirm and extend previous studies of the neural processing underlying grating orientation discrimination, but also demonstrate that a distributed network of putatively multisensory areas is involved.     

Motor execution and imagination networks in post-stroke dystonia

Reorganization of motor execution and imagination networks was studied in six patients with unilateral dystonia secondary to a subcortical stroke and compared with seven control subjects using fMRI. Patients performed imagined and real auditory-cued hand movements. Movements of the dystonic hand resulted in overactivity in bilateral motor, premotor, and prefrontal cortex, insula, precuneus, and cerebellum, in parietal areas and the striatum contralateral to the lesion. Movements of the unaffected hand resulted in overactivity in bilateral preSMA, prefrontal, and parietal areas, insula and cerebellum, the ipsilateral premotor cortex and the contralateral striatum to the lesion. Mental representation of movements with each hand resulted in overactivity in bilateral parietal, premotor and prefrontal areas. These results suggest that execution and mental representation of movement are altered in these patients.     

The attentional role of the left parietal cortex: the distinct lateralization and localization of motor attention in the human brain

It is widely agreed that visuospatial orienting attention depends on a network of frontal and parietal areas in the right hemisphere. It is thought that the visuospatial orienting role of the right parietal lobe is related to its role in the production of overt eye movements. The experiments reported here test the possibility that other parietal regions may be important for directing attention in relation to response modalities other than eye movement. Specifically, we used positron emission tomography (PET) to test the hypothesis that a 'left' parietal area, the supramarginal gyrus, is important for attention in relation to limb movements (Rushworth et al., 1997; Rushworth, Ellison, & Walsh, in press). We have referred to this process as 'motor attention' to distinguish it from orienting attention. In one condition subjects spent most of the scanning period covertly attending to 'left' hand movements that they were about to make. Activity in this first condition was compared with a second condition with identical stimuli and movement responses but lacking motor attention periods. Comparison of the conditions revealed that motor attention-related activity was almost exclusively restricted to the 'left' hemisphere despite the fact that subjects only ever made ipsilateral, left-hand responses. Left parietal activity was prominent in this comparison, within the parietal lobe the critical region for motor attention was the supramarginal gyrus and the adjacent anterior intraparietal sulcus (AIP), a region anterior to the posterior parietal cortex identified with orienting attention. In a second part of the experiment we compared a condition in which subjects covertly rehearsed verbal responses with a condition in which they made verbal responses immediately without rehearsal. A comparison of the two conditions revealed verbal rehearsal-related activity in several anterior left hemisphere areas including Broca's area. The lack of verbal rehearsal-related activity in the left supra-marginal gyrus confirms that this area plays a direct role in motor attention that cannot be attributed to any strategy of verbal mediation. The results also provide evidence concerning the importance of ventral premotor (PMv) and Broca's area in motor attention and language processes.     

Differential cerebral activation during observation of expressive gestures and motor acts

We compared brain activation involved in the observation of isolated right hand movements (e.g. twisting a lid), body-referred movements (e.g. brushing teeth) and expressive gestures (e.g. threatening) in 20 healthy subjects by using functional magnetic resonance imaging (fMRI). Perception-related areas in the occipital and inferior temporal lobe but also the mirror neuron system in the lateral frontal (ventral premotor cortex and BA 44) and superior parietal lobe were active during all three conditions. Observation of body-referred compared to common hand actions induced increased activity in the bilateral posterior superior temporal sulcus (STS), the left temporo-parietal lobe and left BA 45. Expressive gestures involved additional areas related to social perception (bilateral STS, temporal poles, medial prefrontal lobe), emotional processing (bilateral amygdala, bilateral ventrolateral prefrontal cortex (VLPFC), speech and language processing (Broca's and Wernicke's areas) and the pre-supplementary motor area (pre-SMA). In comparison to body-referred actions, expressive gestures evoked additional activity only in the left VLPFC (BA 47). The valence-ratings for expressive gestures correlated significantly with activation intensity in the VLPFC during expressive gesture observation. Valence-ratings for negative expressive gestures correlated with right STS-activity. Our data suggest that both, the VLPFC and the STS are coding for differential emotional valence during the observation of expressive gestures.     

Distribution of cat-301 immunoreactivity in the frontal and parietal lobes of the macaque monkey

The distribution of the monoclonal antibody Cat-301 was examined in the frontal and parietal cortex of macaque monkeys. In both regions the distribution was uniform within cytoarchitecturally defined areas (or subareas) but varied between them. In all areas, Cat-301 labeled the soma and proximal dendrites of a restricted population of neurons. In the frontal lobe, Cat-301-positive neurons were intensely immunoreactive and present in large numbers in the motor cortex (area 4), premotor cortex (area 6, excluding its lower ventral part), the supplementary motor area (SMA), and the caudal prefrontal cortex (areas 8a, 8b and 45). In the parietal lobe, large numbers of intensely immunoreactive neurons were evident in the post-central gyrus (areas 1 and 2), the superior parietal lobule (PE/5), and the dorsal bank (PEa), fundus (IPd), and deep half of the ventral bank (POa(i] of the intraparietal sulcus (IPS). Two major patterns of laminar distribution were evident. In motor, supplementary motor, premotor (excluding the lower part of its ventral division), and the caudal prefrontal cortex (Walker's areas 8a, 8b and 45), and throughout the parietal cortex (with the exception of area 3), Cat-301-positive neurons were concentrated in the lower part of layer III and in layer V. The laminar positions of labeled cells in these areas were remarkably constant, as were the proportions of labeled neurons that had pyramidal and nonpyramidal morphologies (means of 30.2% and 69.8%, respectively). In contrast, in prefrontal areas 9, 10, 11, 12, 13, 14, and 46, in the cingulate cortex (areas 23, 24 and 25), and in the lower part of the ventral premotor cortex, Cat-301-positive neurons were spread diffusely across layers II to VI and a mean of 3.6% of the labeled neurons were pyramidal while 96.4% were nonpyramidal. Area 3 was unique among frontal and parietal areas, in that the labeled neurons in this area were concentrated in layers IV and VI. The areas in the frontal lobe which were heavily labeled are thought to be involved in the control of somatic (areas 4 and 6) and ocular (areas 8 and 45) movements. Those in parietal cortex may be classified as areas with somatosensory functions (1, 2, PE/5, and PEa) and areas which may participate in the analysis of visual motion (Pandya and Seltzer's IPd and POa(i), which contain Maunsell and Van Essen's VIP). The parietal somatosensory areas are connected to frontal areas with somatic motor functions, while POa(i) is interconnected with the frontal eye fields (8a and 45).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Attending to and remembering tactile stimuli: a review of brain imaging data and single-neuron responses.

Clinical and neuroimaging observations of the cortical network implicated in tactile attention have identified foci in parietal somatosensory, posterior parietal, and superior frontal locations. Tasks involving intentional hand-arm movements activate similar or nearby parietal and frontal foci. Visual spatial attention tasks and deliberate visuomotor behavior also activate overlapping posterior parietal and frontal foci. Studies in the visual and somatosensory systems thus support a proposal that attention to the spatial location of an object engages cortical regions responsible for the same coordinate referents used for guiding purposeful motor behavior. Tactile attention also biases processing in the somatosensory cortex through amplification of responses to relevant features of selected stimuli. Psychophysical studies demonstrate retention gradients for tactile stimuli like those reported for visual and auditory stimuli, and suggest analogous neural mechanisms for working memory across modalities. Neuroimaging studies in humans using memory tasks, and anatomic studies in monkeys support the idea that tactile information relayed from the somatosensory cortex is directed ventrally through the insula to the frontal cortex for short-term retention and to structures of the medial temporal lobe for long-term encoding. At the level of single neurons, tactile (such as visual and auditory) short-term memory appears as a persistent response during delay intervals between sampled stimuli.     

Evolution of functional reorganization in hemiplegic stroke: a serial positron emission tomographic activation study

We used serial positron emission tomography (PET) to study the evolution of functional brain activity within 12 weeks after a first subcortical stroke. Six hemiplegic stroke patients and three normal subjects were scanned twice (PET 1 and PET 2) by using passive elbow movements as an activation paradigm. Increases of regional cerebral blood flow comparing passive movements and rest and differences of regional cerebral blood flow between PET 1 and PET 2 in patients and normal subjects were assessed by using statistical parametric mapping. In controls, activation was found in the contralateral sensorimotor cortex, supplementary motor area, and bilaterally in the inferior parietal cortex with no differences between PET 1 and PET 2. In stroke patients, at PET 1, activation was observed in the bilateral inferior parietal cortex, contralateral sensorimotor cortex, and ipsilateral dorsolateral prefrontal cortex, supplementary motor area, and cingulate cortex. At PET 2, significant increases of regional cerebral blood flow were found in the contralateral sensorimotor cortex and bilateral inferior parietal cortex. A region that was activated at PET 2 only was found in the ipsilateral premotor area. Recovery from hemiplegia is accompanied by changes of brain activation in sensory and motor systems. These alterations of cerebral activity may be critical for the restoration of motor function.     

Eye muscle proprioception is represented bilaterally in the sensorimotor cortex

The cortical representation of eye position is still uncertain. In the monkey a proprioceptive representation of the extraocular muscles (EOM) of an eye were recently found within the contralateral central sulcus. In humans, we have previously shown a change in the perceived position of the right eye after a virtual lesion with rTMS over the left somatosensory area. However, it is possible that the proprioceptive representation of the EOM extends to other brain sites, which were not examined in these previous studies. The aim of this fMRI study was to sample the whole brain to identify the proprioceptive representation for the left and the right eye separately. Data were acquired while passive eye movement was used to stimulate EOM proprioceptors in the absence of a motor command. We also controlled for the tactile stimulation of the eyelid by removing from the analysis voxels activated by eyelid touch alone. For either eye, the brain area commonly activated by passive and active eye movement was located bilaterally in the somatosensory area extending into the motor and premotor cytoarchitectonic areas. We suggest this is where EOM proprioception is processed. The bilateral representation for either eye contrasts with the contralateral representation of hand proprioception. We suggest that the proprioceptive representation of the two eyes next to each other in either somatosensory cortex and extending into the premotor cortex reflects the integrative nature of the eye position sense, which combines proprioceptive information across the two eyes with the efference copy of the oculomotor command.     

Transcranial magnetic stimulation to the parietal lobes reduces detection of contralateral somatosensory stimuli

OBJECTIVES: Neglect has been described in patients with lesions of the parietal cortex and has been interpreted as a disorder of the allocation of spatial attention. The persistence of neglect has been linked to poor rehabilitation outcome in patients suffering from acute stroke. Transcranial magnetic stimulation (TMS) applied to the parietal cortex has been shown to induce changes in the perception of stimuli including tactile stimulation of the fingers contra- and ipsilateral to the stimulated hemisphere. MATERIAL AND METHODS: In the current study, eleven normal young subjects performed a detection task for cutaneous electrical stimuli to the left or right forearm that had been precued by a preceding visual warning stimulus. To investigate the role of the parietal cortical areas for attentional processes TMS was applied to frontal and parietal scalp sites of each hemisphere in the cue-target interval before the somatosensory stimulus. RESULTS: Right and left parietal stimulation led to reduced detection sensitivity for near threshold stimuli to the forearm contralateral to the stimulated hemisphere without hemispheric differences. Ipsilateral tactile perception was not influenced by parietal TMS and there was no change in perception after frontal stimulation to left or right scalp sites. CONCLUSION: This pattern of results is consistent with a role of the right and left parietal lobe in the distribution of spatial attention and provides an experimental basis for possible therapeutical application of TMS to improve attentional deficits in stroke patients.     

How does brain activation differ in children with unilateral cerebral palsy compared to typically developing children, during active and passive movements, and tactile stimulation? An fMRI study

The aim of the functional magnetic resonance imaging (fMRI) study was to investigate brain activation associated with active and passive movements, and tactile stimulation in 17 children with right-sided unilateral cerebral palsy (CP), compared to 19 typically developing children (TD). The active movements consisted of repetitive opening and closing of the hand. For passive movements, an MRI-compatible robot moved the finger up and down. Tactile stimulation was provided by manually stroking the dorsal surface of the hand with a sponge cotton cloth. In both groups, contralateral primary sensorimotor cortex activation (SM1) was seen for all tasks, as well as additional contralateral primary somatosensory cortex (S1) activation for passive movements. Ipsilateral cerebellar activity was observed in TD children during all tasks, but only during active movements in CP children. Of interest was additional ipsilateral SM1 recruitment in CP during active movements as well as ipsilateral S1 activation during passive movements and tactile stimulation. Another interesting new finding was the contralateral cerebellum activation in both groups during different tasks, also in cerebellar areas not primarily linked to the sensorimotor network. Active movements elicited significantly more brain activation in CP compared to TD children. In both groups, active movements displayed significantly more brain activation compared to passive movements and tactile stimulation.