Motor reorganization in asymptomatic carriers of a single mutant Parkin allele: a human model for presymptomatic parkinsonism

Mutations in the Parkin gene are the most common known single cause of early-onset parkinsonism. It has been shown that asymptomatic carriers with a single mutant allele have latent presynaptic dopaminergic dysfunction in the striatum. Here we used functional MRI to map movement-related neuronal activity during internally selected or externally determined finger movements in 12 asymptomatic carriers of a Parkin mutation and 12 healthy non-carriers. Mean response times were 63 ms shorter during internally selected movements than during externally guided movements (P = 0.003). There were no differences in mean response times between groups (P > 0.2). Compared with externally determined movements, the internal selection of movements led to a stronger activation of rostral motor areas, including the rostral cingulate motor area (rCMA), rostral supplementary motor area, medial and dorsolateral prefrontal cortices. The genotype had a significant impact on movement-related activation patterns. Asymptomatic carriers showed a stronger increase in movement-related activity in the right rCMA and left dorsal premotor cortex, but only if movements relied on internal cues. In addition, synaptic activity in the rCMA had a stronger influence on activity in the basal ganglia in the context of internally selected movements in asymptomatic carriers relative to non-carriers. We infer that this reorganization of striatocortical motor loops reflects a compensatory effort to overcome latent nigrostriatal dysfunction.

The anterior cingulate cortex contains distinct areas dissociating external from self-administered painful stimulation: a parametric fMRI study

The anterior cingulate cortex (ACC) has a pivotal role in human pain processing by integrating sensory, executive, attentional, emotional, and motivational components of pain. Cognitive modulation of pain-related ACC activation has been shown by hypnosis, illusion and anticipation. The expectation of a potentially noxious stimulus may not only differ as to when but also how the stimulus is applied. These combined properties led to our hypothesis that ACC is capable of distinguishing external from self-administered noxious tactile stimulation. Thermal contact stimuli with noxious and non-noxious temperatures were self-administered or externally applied at the resting right hand in a randomized order. Two additional conditions without any stimulus-eliciting movements served as control conditions to account for the certainty and uncertainty of the impending stimulus. Calculating the differences in the activation pattern between self-administered and externally generated stimuli revealed three distinct areas of activation that graded with perceived stimulus intensity: (i) in the posterior ACC with a linear increase during external but hardly any modulation for the self-administered stimulation, (ii) in the midcingulate cortex with activation patterns independent of the mode of application and (iii) in the perigenual ACC with increasing activation during self-administered but decreasing activation during externally applied stimulation. These data support the functional segregation of the human ACC: the posterior ACC may be involved in the prediction of the sensory consequences of pain-related action, the midcingulate cortex in pain intensity coding and the perigenual ACC is related to the onset uncertainty of the impending stimuli.

Listening to action-related sentences modulates the activity of the motor system: a combined TMS and behavioral study

Transcranial magnetic stimulation (TMS) and a behavioral paradigm were used to assess whether listening to action-related sentences modulates the activity of the motor system. By means of single-pulse TMS, either the hand or the foot/leg motor area in the left hemisphere was stimulated in distinct experimental sessions, while participants were listening to sentences expressing hand and foot actions. Listening to abstract content sentences served as a control. Motor evoked potentials (MEPs) were recorded from hand and foot muscles. Results showed that MEPs recorded from hand muscles were specifically modulated by listening to hand-action-related sentences, as were MEPs recorded from foot muscles by listening to foot-action-related sentences. This modulation consisted of an amplitude decrease of the recorded MEPs. In the behavioral task, participants had to respond with the hand or the foot while listening to actions expressing hand and foot actions, as compared to abstract sentences. Coherently with the results obtained with TMS, when the response was given with the hand, reaction times were slower during listening to hand-action-related sentences, while when the response was given with the foot, reaction times were slower during listening to foot-action-related sentences. The present data show that processing verbally presented actions activates different sectors of the motor system, depending on the effector used in the listened-to action.

Apraxien

Apraxias are deficits in higher motor behaviour that are not primarily caused by elementary deficits of the sensorimotor system, communication problems, or dementia. These patients present with deficits such as imitating meaningful or meaningless gestures and in dexterity or purposeful use of objects. The different forms of apraxia originate from lesions of different levels/structures of the motor system, reflecting its complexity. Apraxias are caused by deficits in motor programmes generated in the frontal motor areas, in modality-specific higher sensorimotor control, or at the highest level of motor planning and motor conception. The types of apraxia differentially affect activities of daily living and hence show marked differences in the prognosis of recovery and the physiotherapeutic treatment required. Therefore, appropriate diagnosis and treatment of the different forms are of foremost clinical importance.

Cerebellar neural responses related to actively and passively applied noxious thermal stimulation in human subjects: a parametric fMRI study

Cerebellar activation is consistently found during noxious stimulation but little is known about its pain-related specificity. Under natural circumstances noxious stimuli are actively or passively delivered with concomitant tactile sensory stimulation. Using fMRI we therefore studied pain-related cerebellar activation with innocuous and noxious thermal stimuli in a parametric design taking motor execution as confounding factor into account. With respect to psychophysical pain ratings anterior vermal and ipsilateral hemispheric lobule VI activation was parametrically modulated for stimulus intensity in actively but not in passively elicited thermal stimulation. The cerebellum seems to be capable of distinguishing active from passive painful stimuli.

Left and right superior parietal lobule in tactile object discrimination

Tactile object discrimination is one of the major manual skills of humans. While the exploring finger movements are not perceived explicitly, attention to the movement-evoked kinaesthetic information gates the tactile perception of object form. Using event-related functional magnetic resonance imaging in seven healthy subjects we found one area in the right superior parietal cortex, which was specifically activated by kinaesthetic attention during tactile object discrimination. Another area with similar location in the left hemisphere was related to the maintenance of tactile information for subsequent object discrimination. We conclude that kinaesthetic information is processed in the anterior portion of the superior parietal cortex (aSPL) with a right hemispheric predominance for discrimination and a left hemispheric predominance for information maintenance.

Cerebellar activation in opsoclonus: an fMRI study

It is controversial whether opsoclonus is a cerebellar or brainstem disorder. Two patients whose opsoclonus largely disappeared on eye closure underwent fMRI. A comparison of these two states revealed neither vermal nor brainstem activation but rather a bilateral activation in the deep cerebellar nuclei in excess of what the authors found in healthy subjects. The results support a crucial role of the fastigial nucleus in opsoclonus.

Neural activity in human primary motor cortex areas 4a and 4p is modulated differentially by attention to action

The mechanisms underlying attention to action are poorly understood. Although distracted by something else, we often maintain the accuracy of a movement, which suggests that differential neural mechanisms for the control of attended and nonattended action exist. Using functional magnetic resonance imaging (fMRI) in normal volunteers and probabilistic cytoarchitectonic maps, we observed that neural activity in subarea 4p (posterior) within the primary motor cortex was modulated by attention to action, while neural activity in subarea 4a (anterior) was not. The data provide the direct evidence for differential neural mechanisms during attended and unattended action in human primary motor cortex.

[Acute low back pain with progressive sensorimotor paralysis. Differential diagnosis and therapy of acute decompression disease]

HISTORY AND CLINICAL FINDINGS

A 38-year-old man presented with acute low back pain and paraesthesia in dermatome S1. 4 hours before onset of symptoms he had finished the last of three scuba dives with a maximum depth of 30 m and a total diving time of 3 hours. No alcoholic beverages were taken during or before diving. The patient was complaining of local pain in the thoracic and lumbar spine and showed a 3/5 weakness of the big toe and impaired sensitivity in the S1 dermatome. 90 minutes later the patient developed a hemiparesis of the right side including hypaesthesia and additional meningism (stiff neck).

INVESTIGATIONS

The X-rays of the thoracic and lumbar spine in two standard planes, cerebrospinal fluid examination, a cranial spiral-computer tomographie (CCT) and laboratory investigations showed no pathologic values.

DIAGNOSIS

Acute decompression sickness (DCS) type II.

TREATMENT AND COURSE

The patient received an intravenous infusion, antiinflammatory prophylaxis with dexamethasone and an immediate submission to hyperbaric oxygenation therapy. Complete recovery of neurological symptoms appeared after 4 decompression sessions in a hyperbaric chamber.

CONCLUSIONS

In patients presenting low back pain as common symptoms the differential diagnosis needs to be worked out and DCS should be included especially if progressive neurologic deficits are present. Only emergency hyperbaric oxygen therapy can compromise a sufficient therapy of these patients.

Recovery of motor functions following hemiparetic stroke: a clinical and magnetic resonance-morphometric study

Predictors for the degree of clinical recovery after stroke are still poorly defined. In this study we tried to assess the predictive value of clinical data and of lesion size for motor recovery after ischemic stroke. In 52 hemiparetic patients we monitored the course of clinical recovery by a dedicated score of sensorimotor hand function after their first stroke. The course of the lesion size was measured in proton density magnetic resonance images. Three groups of patients were identified. Patients with moderate initial motor deficit recovered almost completely within 9 days (17/17, group 1). From the patients with severe initial motor deficit, about equal numbers recovered (16/35, group 2) or remained severely impaired during the entire observation period of more than 6 months (19/35, group 3). There was no correlation between changes of lesion size and motor deficit. Logistic regression of probability of good clinical outcome on initial lesion size, initial motor score and subcortical versus cortical location of lesion showed that only the initial motor score was predictive (p = 0.006). A relative improvement of the initial motor score of about 20% in the first 4 weeks after stroke appeared to be a relevant cut point for good outcome. The data indicate that patients with mild initial motor deficits recover well, whereas severely affected patients may differ in outcome. Since lesion size was not correlated with outcome the amount of spared residual function appeared as major determinant for the capacity for motor recovery.

Recognition and imitation of pantomimed motor acts after unilateral parietal and premotor lesions: a perspective on apraxia

We compared gesture comprehension and imitation in patients with lesions in the left parietal lobe (LPAR, n=5) and premotor cortex/supplementary motor area (LPMA, n=8) in patients with damage to the right parietal lobe (RPAR, n=6) and right premotor/supplementary motor area (RPMA, n=6) and in 16 non-brain damaged control subjects. Three patients with left parietal lobe damage had aphasia. Subjects were shown 136 meaningful pantomimed motor acts on a videoscreen and were asked to identify the movements and to imitate the motor acts from memory with their ipsilesional and contralesional hand or with both hands simultaneously. Motor tasks included gestures without object use (e.g. to salute, to wave) pantomimed imitation of gestures on one's own body (e.g. to comb one's hair) and pantomimed imitation of motor acts which imply tool use to an object in extrapersonal space (e.g. to hammer a nail). Videotaped test performance was analysed by two independent raters; errors were classified as spatial errors, body part as object, parapraxic performance and non-identifiable movements. In addition, action discrimination was tested by evaluating whether a complex motor sequence was correctly performed. Results indicate that LPAR patients were most severely disturbed when imitation performance was assessed. Interestingly, LPAR patients were worse when imitating gestures on their own bodies than imitating movements with reference to an external object use with most pronounced deficits in the spatial domain. In contrast to imitation, comprehension was not or only slightly disturbed and no clear correlation was found between the severity of imitation deficits and gesture comprehension. Moreover, although the three patients with aphasia imitated the movements more poorly than non-aphasic LPAR patients, the severity of comprehension errors did not differ. Whereas unimanual imitating performance and gesture comprehension of PMA patients did not differ significantly from control subjects, bimanual tasks were severely disturbed, in particular when executing different movements simultaneously with the right and left hands.

Motor impairment in patients with parietal lesions: disturbances of meaningless arm movement sequences

The execution of meaningless movement sequences was studied in 12 patients with lesions of the parietal cortex in comparison to the performance of age- and sex-matched controls. Five sequences of increasing complexity had to be performed by imitation and after verbal instruction. The performance errors were qualitatively scored by means of four error categories (temporal or spatial error, addition or omission of movement components). This study examined whether the error scores depended on instruction modality, movement complexity or lesion side. Patients with left parietal lesions produced more errors than those with right parietal lesions and control subjects. While additions or omissions of movement components occurred almost equally in all groups, temporal and spatial errors were more frequent in patients with left parietal lesions only. In addition, only the latter group showed a significant increase of error rates with increasing movement complexity. There were no significant differences between the contra- and ipsilesional hand in any group. These results demonstrate that lesions in the left parietal lobe lead to a disturbed spatio-temporal organisation of movement that becomes increasingly prominent for more complex movements.

Activation of frontoparietal cortices during memorized triple-step sequences of saccadic eye movements: an fMRI study

To determine the cortical areas controlling memory-guided sequences of saccadic eye movements, we performed functional magnetic resonance imaging (fMRI) in six healthy adults. Subjects had to perform a memorized sequence of three saccades in darkness, after a triple-step stimulus of successively flashed laser targets. To assess the differential contribution of saccadic subfunctions, we applied several control conditions, such as central fixation with or without triple-step visual stimulation, self-paced saccades in darkness, visually guided saccades and single memory-guided saccades. Triple-step saccades strongly activated the regions of the frontal eye fields, the adjacent ventral premotor cortex, the supplementary eye fields, the anterior cingulate cortex and several posterior parietal foci in the superior parietal lobule, the precuneus, and the middle and posterior portion of the intraparietal sulcus, the probable location of the human parietal eye field. Comparison with the control conditions showed that the right intraparietal sulcus and parts of the frontal and supplementary eye fields are more involved in the execution of triple-step saccades than in the other saccade tasks. In accordance with evidence from clinical lesion studies, we propose that the supplementary eye field essentially controls the triggering of memorized saccadic sequences, whereas activation near the middle portion of the right intraparietal sulcus appears to reflect the necessary spatial computations, including the use of extraretinal information (efference copy) about a saccadic eye displacement for updating the spatial representation of the second or third target of the triple-step sequence.

A new approach to measure single-event related brain activity using real-time fMRI: feasibility of sensory, motor, and higher cognitive tasks

Real-time fMRI is a rapidly emerging methodology that enables monitoring changes in brain activity during an ongoing experiment. In this article we demonstrate the feasibility of performing single-event sensory, motor, and higher cognitive tasks in real-time on a clinical whole-body scanner. This approach requires sensitivity optimized fMRI methods: Using statistical parametric mapping we quantified the spatial extent of BOLD contrast signal changes as a function of voxel size and demonstrate that sacrificing spatial resolution and readout bandwidth improves the detection of signal changes in real time. Further increases in BOLD contrast sensitivity were obtained by using real-time multi-echo EPI. Real-time image analysis was performed using our previously described Functional Imaging in REal time (FIRE) software package, which features real-time motion compensation, sliding window correlation analysis, and automatic reference vector optimization. This new fMRI methodology was validated using single-block design paradigms of standard visual, motor, and auditory tasks. Further, we demonstrate the sensitivity of this method for online detection of higher cognitive functions during a language task using single-block design paradigms. Finally, we used single-event fMRI to characterize the variability of the hemodynamic impulse response in primary and supplementary motor cortex in consecutive trials using single movements. Real-time fMRI can improve reliability of clinical and research studies and offers new opportunities for studying higher cognitive functions.

Action observation activates premotor and parietal areas in a somatotopic manner: an fMRI study

Functional magnetic resonance imaging (fMRI) was used to localize brain areas that were active during the observation of actions made by another individual. Object- and non-object-related actions made with different effectors (mouth, hand and foot) were presented. Observation of both object- and non-object-related actions determined a somatotopically organized activation of premotor cortex. The somatotopic pattern was similar to that of the classical motor cortex homunculus. During the observation of object-related actions, an activation, also somatotopically organized, was additionally found in the posterior parietal lobe. Thus, when individuals observe an action, an internal replica of that action is automatically generated in their premotor cortex. In the case of object-related actions, a further object-related analysis is performed in the parietal lobe, as if the subjects were indeed using those objects. These results bring the previous concept of an action observation/execution matching system (mirror system) into a broader perspective: this system is not restricted to the ventral premotor cortex, but involves several somatotopically organized motor circuits.

Tactile apraxia: unimodal apractic disorder of tactile object exploration associated with parietal lobe lesions

Tactile apraxia is characterized by an isolated disturbance of hand movements for use of and interaction with an object (transitive movements) in the presence of preserved intransitive movements (movements without use of an object, for example repetitive movements or gestures). It is, however, still unclear whether motor and sensory abnormalities represent causal or associated features of tactile apraxia. To address this question, quantitative kinematic recordings of exploratory finger movements (transitive movements) and rapid alternating finger movements (intransitive movements) were studied in 20 healthy volunteers and 22 patients with focal lesions of the parietal, anterofrontal and motor cortex. The most severe deficits of manual object exploration were found in patients with parietal lesions, using the hand contralateral to the lesion. Patients with lesions of the anterior parietal lobe who exhibited prominent sensory deficits and astereognosia showed a decrease in frequency and regularity of exploratory finger movements and a marked increase in exploration space. Patients with posterior parietal lesions exhibiting severe astereognosia, apraxia and deficits in dexterity had a greater decrease in frequency and regularity of manipulative movements, but a less pronounced increase of exploration space than the patients with anterior parietal lesions. Although the patients with parietal lobe lesions could generate rapid alternating finger movements, the regularity of these movements was also impaired. In comparison, patients with frontal lobe lesions exhibited impaired contralesional manipulatory and rapid alternating finger movements but no sensory abnormalities or astereognosia. We conclude that tactile apraxia represents a deficit in the programming of exploratory finger movements mediated by the parietal lobe. The comparison with lesions of other regions participating in the cortical network for tactile exploration reveals that apraxia of exploratory movements in parietal lobe lesions represents a disturbance distinct from elementary motor or sensory abnormalities, but closely related to stereognostic functioning.

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.

A new approach to measure single-event related brain activity using real-time fMRI: feasibility of sensory, motor, and higher cognitive tasks

Real-time fMRI is a rapidly emerging methodology that enables monitoring changes in brain activity during an ongoing experiment. In this article we demonstrate the feasibility of performing single-event sensory, motor, and higher cognitive tasks in real-time on a clinical whole-body scanner. This approach requires sensitivity optimized fMRI methods: Using statistical parametric mapping we quantified the spatial extent of BOLD contrast signal changes as a function of voxel size and demonstrate that sacrificing spatial resolution and readout bandwidth improves the detection of signal changes in real time. Further increases in BOLD contrast sensitivity were obtained by using real-time multi-echo EPI. Real-time image analysis was performed using our previously described Functional Imaging in REal time (FIRE) software package, which features real-time motion compensation, sliding window correlation analysis, and automatic reference vector optimization. This new fMRI methodology was validated using single-block design paradigms of standard visual, motor, and auditory tasks. Further, we demonstrate the sensitivity of this method for online detection of higher cognitive functions during a language task using single-block design paradigms. Finally, we used single-event fMRI to characterize the variability of the hemodynamic impulse response in primary and supplementary motor cortex in consecutive trials using single movements. Real-time fMRI can improve reliability of clinical and research studies and offers new opportunities for studying higher cognitive functions.

Control of action as mediated by the human frontal lobe

Conscious control of action involves the voluntary initiation and the continuous adjustment of motor activity. Neuroimaging data provide evidence that the plan for a movement is developed with respect to the behavioral context in prefrontal cortex, while the synergies of a motor program are coded by premotor cortex and the specific movement parameters by the motor cortex. It is suggested that the initiational aspects of conscious motor activity are implemented in a medial system of information flow and the integrative aspects in a lateral system of the human frontal lobe.

Cerebral correlates of working memory for temporal information

Studies of neural correlates of working memory functions in the auditory-verbal, visuo-spatial and visuo-object domain suggest a category-specific organization of working memory processes in prefrontal cortex. Here, we used fMRI to explore brain areas that underlie different working memory operations directed to the temporal domain, which so far has been widely neglected. Significant activations related to memory updating and comparison processes were found right-accentuated in prefrontal and lateral premotor cortices. Furthermore, both subvocal rhythm encoding and maintenance enhanced left-lateralized activity in Broca's and supplementary motor area as well as in the sensorimotor cortex. Hemispheric lateralization effects of brain activity during temporal processing tasks may depend on the presence or absence of subvocal rehearsal strategies.

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.

Cerebral midline structures in bimanual coordination

In six healthy right-handed volunteers, we compared the cerebral activation pattern related to unimanual right- and left-hand movements and to bimanual in-phase and anti-phase movements using functional magnetic resonance imaging (fMRI). Internally paced unimanual finger-to-thumb opposition movements led to a strong contralateral activation of primary sensorimotor areas in all six subjects. Midline activity was lateralized to the left side during right-hand movements, but to both sides during left-hand movements. Activity patterns of bimanual in-phase movements resembled the combined activity patterns of the two unimanual conditions: right and left hemispheric activations of the primary sensorimotor cortices and predominantly left-sided medial frontal activity. In contrast, during anti-phase movements, we observed a clear increase in activity, in both right and left frontal midline areas and in right hemispheric, mainly dorsolateral premotor areas compared to in-phase movements. These results indicate that frontal midline activity is not specific for bimanual movements per se. It can already be involved during simple unimanual movements but becomes progressively more involved during more complex aspects of movement control.

A parieto-premotor network for object manipulation: evidence from neuroimaging

Functional magnetic resonance imaging (fMRI) was used to assess cerebral activation during manipulation of various complex meaningless objects as compared to manipulation of a single simple object (a sphere). Significant activation was found bilaterally in the ventral premotor cortex (Brodmann's area 44), in the cortex lining the anterior part of the intraparietal sulcus (most probably corresponding to monkey anterior intraparietal area, AIP), in the superior parietal lobule and in the opercular parietal cortex including the secondary somatosensory area (SII). We suggest that the cortex lining the anterior part of the intraparietal sulcus and area 44 are functionally connected and mediate object manipulation in humans.

The role of diaschisis in stroke recovery

BACKGROUND AND PURPOSE

Recovery from hemiparesis after stroke has been shown to involve reorganization in motor and premotor cortical areas. However, whether poststroke recovery also depends on changes in remote brain structures, ie, diaschisis, is as yet unresolved. To address this question, we studied regional cerebral blood flow in 7 patients (mean+/-SD age, 54+/-8 years) after their first hemiparetic stroke.

METHODS

We analyzed imaging data voxel by voxel using a principal component analysis by which coherent changes in functional networks could be disclosed. Performance was assessed by a motor score and by the finger movement rate during the regional cerebral blood flow measurements.

RESULTS

The patients had recovered (P<0. 001) from severe hemiparesis after on average 6 months and were able to perform sequential finger movements with the recovered hand. Regional cerebral blood flow at rest differentiated patients and controls (P<0.05) by a network that was affected by the stroke lesion. During blindfolded performance of sequential finger movements, patients were differentiated from controls (P<0.05) by a recovery-related network and a movement-control network. These networks were spatially incongruent, involving motor, sensory, and visual cortex of both cerebral hemispheres, the basal ganglia, thalamus, and cerebellum. The lesion-affected and recovery-related networks overlapped in the contralesional thalamus and extrastriate occipital cortex.

CONCLUSIONS

Motor recovery after hemiparetic brain infarction is subserved by brain structures in locations remote from the stroke lesion. The topographic overlap of the lesion-affected and recovery-related networks suggests that diaschisis may play a critical role in stroke recovery.

Mirror agnosia and mirror ataxia constitute different parietal lobe disorders

We describe two new clinical syndromes, mirror agnosia and mirror ataxia, both characterized by the deficit of reaching for an object through a mirror in association with a lesion of either parietal lobe. Clinical investigation of 13 patients demonstrated that the impairments affected both sides of the body. In mirror agnosia, the patients always reached toward the virtual object in the mirror and they were not capable of changing their behavior even after presentation of the position of the object in real visual space. In mirror ataxia (resembling optic ataxia) although some patients initially tended to reach for the virtual object in the mirror, they soon learned to guide their arms toward the real object, all of them producing many directional errors. Both patient groups performed poorly on mental rotation, but only the patients with mirror agnosia were impaired in line orientation. Only 1 of the patients suffered from neglect and 3 from apraxia. Magnetic resonance imaging showed that in mirror agnosia the common zone of lesion overlap was scattered around the posterior angular gyrus/superior temporal gyrus and in mirror ataxia around the postcentral sulcus. We propose that both these clinical syndromes may represent different types of dissociation of retinotopic space and body scheme, or likewise, of allocentric and egocentric space normally adjusted in the parietal lobe.

Stimulation of peripheral nerves using a novel magnetic coil

Magnetic nerve stimulation (MNS) using a novel figure-8 magnetic coil was compared with conventional electric nerve stimulation (ENS) in normal subjects and in patients with disorders of the peripheral nervous system. In contrast to previously tested coils, the virtual cathode of the novel coil was independent of the geometrical or electric conditions of the stimulated tissue. Maximal compound muscle action potentials (CMAPs) were elicited by MNS in all motor nerves tested. The slopes of the recruitment curves of ENS were steeper than those of MNS, indicating a comparatively lower maximal stimulation intensity and a higher intensity resolution of the magnetic stimulator. In four patients with entrapment syndromes at the ulnar groove, motor conduction velocities and amplitudes were similar for MNS and ENS across the affected nerve segment. However, in two patients with chronic inflammatory demyelinating polyneuropathy (CIDP), CMAPs were slightly smaller following MNS. This new technique is a promising step toward the ultimate goal of replacing ENS with MNS.

The role of ventral medial wall motor areas in bimanual co-ordination. A combined lesion and activation study

Two patients with midline tumours and disturbances of bimanual co-ordination as the presenting symptoms were examined. Both reported difficulties whenever the two hands had to act together simultaneously, whereas they had no problems with unimanual dexterity or the use of both hands sequentially. In the first patient the lesion was confined to the cingulate gyrus; in the second it also invaded the corpus callosum and the supplementary motor area. Kinematic analysis of bimanual in-phase and anti-phase movements revealed an impairment of both the temporal adjustment between the hands and the independence of movements between the two hands. A functional imaging study in six volunteers, who performed the same bimanual in-phase and anti-phase tasks, showed strong activations of midline areas including the cingulate and ventral supplementary motor area. The prominent activation of the ventral medial wall motor areas in the volunteers in conjunction with the bimanual co-ordination disorder in the two patients with lesions compromising their function is evidence for their pivotal role in bimanual co-ordination.

Somatic and limbic cortex activation in esophageal distention: a functional magnetic resonance imaging study

Little is known about the cerebral representations of visceral sensations in humans. Using functional magnetic resonance imaging (fMRI), we mapped the cortical areas of the human brain that were activated by mechanical stimulation of the esophagus in 5 healthy volunteers. Stimulation probes were placed into the distal part of the esophagus and inflated to produce a local distention. The cerebral activation pattern was related to the strength and quality of the stimulus. The weakest stimulus accompanied by a well-localized albeit weak retrosternal sensation activated only the parietal opercular cortices, probably including the secondary somatosensory cortex (SII). Additional activation of the primary sensorimotor cortex (SI) at the level of the face and mouth representation as well as of the right premotor cortex was found during repetitive distention of the esophagus at 0.5 Hz. Repetitive stimulation at 1 Hz additionally activated the insula bilaterally. The strongest distention stimulus, which caused a painful retrosternal sensation, resulted in an activation of the anterior cingulate cortex. Our findings demonstrate that SII is the primary cortical target of visceral afferents originating in the esophagus. Limbic structures become engaged when the visceral sensation is unpleasant or painful.

Role of the premotor cortex in recovery from middle cerebral artery infarction

OBJECTIVE

To study the mechanisms underlying recovery from middle cerebral artery infarction in 7 patients with an average age of 53 years who showed marked recovery of hand function after acute severe hemiparesis caused by their first-ever stroke.

INTERVENTIONS

Assessment of motor functions, transcranial magnetic stimulation, somatosensory evoked potentials, magnetic resonance imaging, and positron emission tomographic measurements of regional cerebral blood flow during finger movement activity.

RESULTS

The infarctions involved the cerebral convexity along the central sulcus from the Sylvian fissure up to the hand area but spared the caudate nucleus, thalamus, middle and posterior portions of the internal capsule, and the dorsal part of the precentral gyrus in each patient. After recovery (and increase in motor function score of 57%, P<.001), the motor evoked potentials in the hand and leg muscles contralateral to the infarctions were normal, whereas the somatosensory evoked potentials from the contralateral median nerve were reduced. During fractionated finger movements of the recovered hand, regional cerebral blood flow increases occurred bilaterally in the dorsolateral and medial premotor areas but not in the sensorimotor cortex of either hemisphere.

CONCLUSIONS

Motor recovery after cortical infarction in the middle cerebral artery territory appears to rely on activation of premotor cortical areas of both cerebral hemispheres. Thereby, short-term output from motor cortex is likely to be initiated.

Human anterior intraparietal area subserves prehension: a combined lesion and functional MRI activation study

It has been shown in nonhuman primates that the posterior parietal cortex is involved in coordination of arm and eye movements in space, whereas the anterior intraparietal area in the anterior lateral bank of the intraparietal sulcus plays a crucial role in fine finger movements, such as grasping. In this study we show by optoelectronic movement recordings that patients with cortical lesions involving the anterior lateral bank of the intraparietal sulcus have selective deficits in the coordination of finger movements required for object grasping, whereas reaching is much less disturbed. Patients with parietal lesions sparing the cortex lining the anterior intraparietal sulcus showed intact grasping behavior. Complementary evidence was obtained from functional MRI in normal control subjects showing a specific activation of the anterior lateral bank of the intraparietal sulcus during grasping. In conclusion, this combined lesion and activation study suggests that the anterior lateral bank of the intraparietal sulcus, possibly including the human homologue of the anterior intraparietal area, mediates the processing of sensorimotor integration of precisely tuned finger movements in humans.

The motor syndrome associated with exaggerated inhibition within the primary motor cortex of patients with hemiparetic

Following transcranial magnetic stimulation (TMS) at stimulation strength of 1.5 times the resting motor threshold, a silent period (SP) of approximately 180 ms duration can be observed in surface EMG-registrations of tonically activated small hand muscles. This SP is believed to be generated cortically and can be prolonged in stroke patients, but it is not known whether a prolongation of the SP has any functional significance. In order to answer the question of whether enhanced cortical inhibition can contribute to pathophysiology of motor dysfunction we studied stroke patients with clearly prolonged SP durations in the first dorsal interosseus muscle (> 2 times that of the intact side), but with normal magnetically evoked motor potentials. Sixteen patients out of a cohort of 174 consecutive patients presenting with acute hemiparetic stroke fulfilled the inclusion criteria. Serial TMS investigations were performed for up to 2 years post-stroke. In all patients, the SP duration decreased in parallel with clinical improvement. In two patients, intermittent clinical deterioration was accompanied by an increase in the SP duration. In four patients, in addition to a markedly prolonged SP duration, the phenomenon of a complete inability to initiate voluntary muscle activity for several seconds, following TMS, could be observed in a number of trials ('motor arrest'). Detailed clinical analysis revealed that, in addition to hemiparesis, distinct motor disturbances in patients with SP prolongation could be observed. These motor disturbances resembled those of motor neglect and were characterized by motivationally dependent under-utilization of the affected arm, impairment of movement initiation, inability to maintain a constant force level and to scale forces, and impairment of individual finger movements. In 12 of the 16 patients at least one additional behavioural manifestation of neglect was present. We suggest that in stroke patients severe motor dysfunction may be caused by hyperactivity of cortical inhibitory interneurons rather than by direct lesions of descending motor tracts. Cortical hyperinhibition may, in turn, result from damage to any of a number of afferent pathways to the motor cortex which modulate local interneuronal activity.