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M C Hepp-Reymond

Publications and source records attributed to M C Hepp-Reymond.

At least 19 recordsLinked to original sources
PubMed2001

Identification of multiple nonprimary motor cortical areas with simple movements.

The human cortex reportedly contains at least five nonprimary motor areas: in the frontolateral convexity, the dorsal and ventral premotor cortex (PMd and PMv), and in the frontomesial wall, the presupplementary and supplementary motor areas (pre-SMA and SMA), and the rostral, dorsal and ventral cingulate areas (CMAr, CMAd, and CMAv). Activation of these regions in neuroimaging studies has been generally associated either with the performance of complex motor tasks or with reorganization occurring with motor recovery in the presence of pathology. Recent evidence from neuroimaging studies suggests that the same areas are activated with well controlled simple movements in healthy subjects providing support to the observation that their contribution may be more quantitative rather than exclusively specific to a certain aspect of motor behaviour. An important consequence of this observation is that activation of multiple nonprimary motor areas during simple motor tasks should not be considered unique to patients with upper or lower motoneuron lesions but rather as a normal physiological process.

Adult↗
PubMed2000

Beyond re-membering: phantom sensations of congenitally absent limbs.

Phantom limbs are traditionally conceptualized as the phenomenal persistence of a body part after deafferentation. Previous clinical observations of subjects with phantoms of congenitally absent limbs are not compatible with this view, but, in the absence of experimental work, the neural basis of such "aplasic phantoms" has remained enigmatic. In this paper, we report a series of behavioral, imaging, and neurophysiological experiments with a university-educated woman born without forearms and legs, who experiences vivid phantom sensations of all four limbs. Visuokinesthetic integration of tachistoscopically presented drawings of hands and feet indicated an intact somatic representation of these body parts. Functional magnetic resonance imaging of phantom hand movements showed no activation of primary sensorimotor areas, but of premotor and parietal cortex bilaterally. Movements of the existing upper arms produced activation expanding into the hand territories deprived of afferences and efferences. Transcranial magnetic stimulation of the sensorimotor cortex consistently elicited phantom sensations in the contralateral fingers and hand. In addition, premotor and parietal stimulation evoked similar phantom sensations, albeit in the absence of motor evoked potentials in the stump. These data indicate that body parts that have never been physically developed can be represented in sensory and motor cortical areas. Both genetic and epigenetic factors, such as the habitual observation of other people moving their limbs, may contribute to the conscious experience of aplasic phantoms.

Adult↗
PubMed2000

EMG activation patterns during force production in precision grip. III. Synchronisation of single motor units.

Motor unit (MU) synchronisation during isometric force production in the precision grip was analysed in five subjects performing a visually guided steptracking motor task with three different force levels. With this aim multi-unit electromyographic (EMG) activity of 14 intrinsic and extrinsic finger muscles from 15 experimental sessions was decomposed into the potentials of single MUs. The behaviour of 62 intrinsic and 30 extrinsic MUs in the motor task was quantified. Most MUs displayed a positive correlation between firing rate and grip force. Compared to MUs in extrinsic muscles, intrinsic MUs had steeper regression lines with negative intercepts indicating higher force sensitivity and higher recruitment thresholds. A cross-correlation analysis was performed for 69 intra- and 166 intermuscular MU pairs while steady grip force was exerted at the three force levels. Synchronisation, for at least one force level, was found in 78% of the intra- and 45% of the intermuscular pairs. The occurrence of synchronisation was not stable over the force range tested. Factors influencing the fluctuations in occurrence and strength of synchronisation were investigated. Force increase was not paralleled by increased synchronisation; in contrast, in most MU pairs, especially intermuscular pairs, synchronisation occurred preferentially at the lower force levels. The recruitment threshold appeared to play a determining role in synchronisation: the more similar the thresholds of two MUs, the greater the probability of them being synchronised at this force level. Synchronised MUs fired on average at a lower frequency than non-synchronised ones. Finally, synchronisation at the multi-unit EMG level does not indicate that all underlying MUs are synchronised, nor does the absence of temporal coupling at the multi-unit level indicate that none of the MUs is synchronised.

Electromyography↗
PubMed2000

Plasticity of the human motor cortex in patients with arteriovenous malformations: a functional MR imaging study.

BACKGROUND AND PURPOSE: The capacity of the human brain to recover from damage has been explained on the basis of plasticity, according to which remaining areas assume functions that would normally have been performed by the damaged brain. Patients with cerebral arteriovenous malformations (AVMs) involving primary motor areas may present without significant neurologic deficits. We used functional MR imaging to investigate the organization of cortical motor areas in patients with AVMs. METHODS: Cortical motor hand and foot representations were mapped in nine right-handed patients harboring AVMs occupying the hand (n = 6) or foot (n = 3) region of the primary motor cortex (M1). None of the patients exhibited motor deficits. Simple movements of the hand and foot were performed. In eight patients, both right and left extremities were tested; in one patient, only the hand contralateral to the AVM was examined. Localization of activation in the affected hemisphere was compared with that in the unaffected hemisphere and evaluated with respect to the normal M1 somatotopic organization shown in earlier functional MR imaging investigations. RESULTS: Cortical activation showed three patterns: 1) functional displacement within the affected M1 independent of the structural distortion induced by the AVM (n = 4), 2) presence of activation within the unaffected M1 ipsilateral to the moving extremity without activation in the affected M1 (n = 3), and 3) prominent activation in nonprimary motor areas without activation in either the affected or unaffected M1 (n = 2). CONCLUSION: Preliminary evidence suggests that brain AVMs lead to reorganization within the somatotopic representation in M1 and to occasional abnormal expansion into nonprimary motor areas.

Adult↗
PubMed1999

Parcellation of the lateral premotor cortex of the macaque monkey based on staining with the neurofilament antibody SMI-32.

In macaque monkey, frontal and parasagittal brain sections were stained with SMI-32, an antibody directed against a nonphosphorylated neurofilament protein that labels pyramidal cells. The goal of this investigation was to find reliable criteria with which to draw the border between the motor (M1) and premotor (PM) cortex and delineate subdivisions within the lateral PM. Two-dimensional reconstruction of the staining patterns was also performed by flattening the series of frontal sections. The distribution of SMI-32 immunoreactivity in layers III and V of the cortex revealed the existence of three subregions in the ventral rostral PM and a clear mediolateral boundary within the dorsal PM defined by clusters of SMI-32-positive pyramidal cells in layer V. The border between M1 and PM was easily distinguished at the level of the dorsal PM by a strong loss of immunoreactive pyramidal cells in layers III and V. At the level of the ventral PM there was no clear disruption of layer V pattern, and the border was set using the pattern of layer III immunoreactivity.

Animals↗
PubMed1998

Task dependence of muscle synchronization in human hand muscles.

We put forward the hypothesis that synchronous muscle activation would be less frequent with increasingly more complex grip tasks. Six subjects performed a visuo-motor step-tracking task using the precision and the power grip. During the experiment transcranial magnetic stimuli were applied. Electromyographic activity was recorded from the hand muscles active in both tasks. Muscle synchronization was found to be enhanced during the power grip as compared to the precision grip. Magnetic stimulation had a stronger effect during the precision grip than during the power grip. Our findings are in favour of a variable organization of muscle activation in hand muscles during various tasks and support the stronger contribution of the corticomotoneuronal system in the precision than the power grip.

Brain↗
PubMed1995

EMG activation patterns during force production in precision grip. I. Contribution of 15 finger muscles to isometric force.

Electromyographic (EMG) activity was examined in six normal subjects, producing low isometric forces between thumb and index finger in a visually guided step-tracking task. Target forces ranged between 0.5 and 3.0 N. EMG activity of all 15 muscles acting on thumb or index finger was screened with simultaneous recordings of up to 8 muscles. Linear regression was applied to quantify the EMG activity as a function of force. The intrinsic muscles and the long flexors of the index finger had a tight relation to force, as indicated by the high correlation coefficient, as did the adductor and short flexor of the thumb. In contrast, the long extensors of the index finger did not show force-related activity. The other muscles, including the long flexor and extensor of the thumb, had varying, on average moderate, correlations to force. The slope of the regression lines, a measure for the amount of EMG modulation with increasing force, revealed the same trends. Thus the majority of the intrinsic muscles were as closely related to force as the long flexors, suggesting a more important role in production of low isometric forces in the grip than previously believed, perhaps even a primary role. Systematic interindividual differences were rarely observed. Analysis of the trial-by-trial variability of EMG activity revealed that for most muscles the observed scatter was produced by varying background activity and was not a random fluctuation of relative increases in activity from one force level to the next.

Adult↗
PubMed1995

EMG activation patterns during force production in precision grip. II. Muscular synergies in the spatial and temporal domain.

Electromyographic (EMG) activity was analyzed for the occurrence of synergistic patterns during the steady hold periods of force in the precision grip. To establish the presence of muscle synergies in the amplitude (spatial) domain, the EMG activation levels of pairs of simultaneously active muscles were linearly correlated. Cross-correlations of EMG activity were computed to quantify muscle synergies in the spatiotemporal domain (synchronization). A muscle pair was defined to be synergistically coupled or synchronously activated when the correlation (amplitude domain) or cross-correlation (time domain) was significant for at least two of the three steady state force levels. Muscle synergies in the amplitude domain were found in one-third of the 213 muscle pairs tested, distributed among 47 of the 82 tested muscle combinations. Coactivation was the predominant synergistic pattern, whereas trade-off comprised not more than 23% of the synergies. Cross-correlation peak size varied between 5 and 39% of the autocorrelation size, with delays in the range of +/- 8 ms and base width between 12 and 20 ms. Synchronization was found in one-fourth of the 213 muscle pairs tested and among 35 of the 82 muscle combinations, i.e., less frequently than covariation of EMG activity levels. However, the interindividual prevalence was higher for synchronization than for synergies in the amplitude domain, since, for the synergistic muscle combinations, almost twice as many muscle pairs were found to be synchronized than coupled in the amplitude domain. Synergies in the two domains occurred independently in some pairs and concurrently in other cases, and were observed between muscles moving the thumb, the index finger, or both digits. Synchronization was more frequent in pairs of muscles supplied by branches of the same peripheral nerve (46%) than in those innervated by different nerves (18%). Synergies in the amplitude domain were distributed in similar proportions across intrinsic, extrinsic, and combinations of both types of muscles, whereas synchronization mainly occurred in pairs of intrinsic muscles. When the task was repeated with slightly lower target forces, there were fewer synergies in the amplitude domain (in 52 of the 213 pairs, distributed among 35 of 82 muscle combinations) and their distribution changed, indicating a flexible, force-dependent mechanism. In conclusion, no strictly coherent interindividual pattern of synergies in the spatial domain could be established.

Adult↗
PubMed1994

Force-related neuronal activity in two regions of the primate ventral premotor cortex.

Neuronal activity was recorded in the ventral premotor cortex of one monkey (Macaca fascicularis) trained to exert finely graded forces with thumb and index finger on a force sensor in a visuomotor step-tracking paradigm. Trials with two or three consecutive ramp-and-hold force steps were presented randomly. Most neurons displayed similar discharge patterns in the two- and three-step trials and were assigned to one of the following classes: phasic, phasic-tonic, tonic, decreasing, and mixed. For more than 50% of the neurons with tonic activity, positive or negative correlations between firing rate and force were statistically significant. The indices of force sensitivity were on average higher for the two-step than for the three-step trials, indicating that the correlations yielded linearity over only a limited force range. The force-related cells were located in two regions of the ventral premotor cortex. One group was ying rostrally within the inferior limb of the arcuate sulcus, from which microstimulation elicited movements of fingers and hand. In the other more caudal region, adjacent to the finger region of primary motor cortex, microstimulation was rarely effective, but all neurons had clear peripheral receptive fields on finger and hand. The data indicate that two populations of neurons, located in the ventral premotor cortex, are related to movement execution. Effective microstimulation also suggests that one of the populations has fairly direct access to the spinal motor apparatus.

Animals↗
PubMed1993

Contribution of the monkey corticomotoneuronal system to the control of force in precision grip.

1. The contribution of 33 corticomotoneuronal (CM) cells, recorded in the primary motor cortex, to the production of precision grip force has been investigated in four monkeys (Macaca nemestrina). These CM cells were shown, by spike-triggered averaging, to facilitate electromyographic (EMG) activity of hand and forearm muscles. 2. Single-cell recordings were obtained as the monkey performed a low force precision grip task under either isometric or auxotonic conditions. The monkey had to produce independent control of the forces exerted by the thumb and index finger and maintain them for 1-1.5 s. Steady force segments of data were selected trial-by-trial from these hold periods. For each segment the following mean values were determined: 1) CM cell firing rate, 2) EMG activity of facilitated muscles, and 3) index finger, thumb, and total force. 3. Of the 33 CM cells, 18 had a phasic-tonic pattern of discharge during the task, 7 were tonic, 5 had a ramplike increase, and 3 were deactivated during the hold period. 4. Of the 33 cells analyzed, 11 showed a significant positive (P < 0.05) correlation of their mean firing rate with static force; 4 of them had high correlation coefficients (P < 0.001). There was a considerable trial-by-trial variability in the cells' activity-force relationship. Six CM cells had significant negative correlations between their activity and isometric force (5 at the P < 0.001 level), showing lower firing rates with higher forces. 5. The force sensitivity of the CM cells, calculated from the rate-force slopes, was higher for either the thumb or the index finger force. Under isometric conditions the mean rate-force slopes, calculated from the best correlated digit force, was 32.4 Hz/N for eight positively correlated cells and -21.3 Hz/N for the cells with a negative correlation. 6. Correlation between CM cell spike activity and force was more common among neurons with slowly conducting axons (4/6 correlated) than for those with fast axons (13/27). 7. Significant correlations between target muscle EMG and force were always positive. The correlations between CM cell firing rate and target muscle EMG were comparable with those found between firing rate and force. Three of the CM cells with a negative correlation to force also had a negative correlation with EMG in one of their target muscles. 8. Each CM cell facilitated the EMG activity of one to five target muscles; postspike facilitation (PSF) was most common among intrinsic hand muscles (68/82 CM cell/muscle combinations).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Listing's law for eye, head and arm movements and their synergistic control.

We have recorded eye, head, and upper arm rotations in five healthy human subjects using the three-dimensional search coil technique. Our measurements show that the coordination of eye and head movements during gaze shifts within +/- 25 deg relative to the forward direction is organized by restricting the rotatory trajectories of the two systems to almost parallel planes. These so-called "Listing planes" for eye-in-space and head-in-space rotations are workspace-oriented, not body-fixed. Eye and head trajectories in their respective planes are closely related in direction and amplitude. For pointing or grasping, the rotatory trajectories of the arm are also restricted to a workspace-oriented Listing plane. During visually guided movements, arm follows gaze, and the nine-dimensional rotatory configuration space for eye-head-arm-synergies (three degrees of freedom for each system) is reduced to a two-dimensional plane in the space of quaternion vectors.

Arm↗
PubMed1991

Contrasting properties of monkey somatosensory and motor cortex neurons activated during the control of force in precision grip.

1. Single cell activity was investigated in the precentral motor (MI) and postcentral somatosensory (SI) cortex of the monkey to compare the neuronal activity related to the control of isometric force in the precision grip and to assess the participation of SI in motor control. 2. Three monkeys (Macaca fascicularis) were trained in a visual step-tracking paradigm to generate and precisely maintain force on a transducer held between thumb and index finger. Great care was taken to have the monkeys use only their fingers without moving the wrist or proximal joints. In two monkeys electromyographic (EMG) activity was checked in 23 muscles over several sessions. 3. Five similar classes of task-related firing patterns were found in both SI and MI cortical hand and finger representations, but their relative proportions differed. The majority of the SI neurons were phasically or phasic-tonically active (61%), whereas in MI the neurons that decreased their firing rate with force were most frequent (42%). 4. The timing of activity changes related to the onset of force increase from low to higher levels strongly differed in the two neuronal populations. In SI, only 14% of the task-related neurons increased or decreased their firing rate before the onset of force increase, in contrast to 56% in MI. Only 3% of the SI neurons showed changes before the earliest EMG activation. 5. In both SI and MI neurons with tonic and phasic-tonic, increasing or decreasing discharge patterns disclosed a relationship between neuronal activity and static force. Distinction was made between neurons modulating their activity in a monotonic way and those that were active only at one force level and had a kind of recruitment or deactivation threshold. The latter ones were more frequent in MI than in SI, and in the neuron population with decreasing firing patterns. For the neurons with increases in activity, statistically significant linear correlations between firing rate and force were found more frequently in MI than in SI, where the proportion of nonsignificant correlations was relatively high (35% vs. 15% in MI). In SI the indexes of force sensitivity, calculated from the slopes of the regression lines, covered a wider range than in MI; and their distribution was bimodal, with one mean of 30 Hz/N and the other of 155 Hz/N. In contrast, the mean rate-force slope in MI was 69 Hz/N.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Responses of motor cortex neurons to visual stimulation in the alert monkey.

Evidence for visually evoked activity in single neurons of area 4 is presented. These neurons modulated their activity in relation to stimuli moving across the visual field of the monkey, without showing habituation. Some of them even had direction sensitivity. Their activity was independent of eye movements and unrelated to muscle contractions. The visually activated neurons were distributed throughout the depth of motor cortex.

Animals↗
PubMed1989

Sensorimotor cortical control of isometric force in the monkey.

Recordings from single neurones in the primary somatosensory (SI) and motor (MI) cortex of monkeys trained to precisely regulate force between thumb and index finger have disclosed the following contrasting properties between neurones in these two cortical regions: (1) the existence of neurones with similar discharge patterns within MI and SI but, between these regions, significantly different distributions of the classes of discharge patterns; (2) a late onset of activity change in SI neurones in relation to force increase as compared to significantly earlier changes in MI neurones; (3) linear relations between firing rate and isometric force for SI and MI neurones, however with a larger range of rate-force slopes in SI as compared to MI; (4) infrequent motor reactions to intracortical microstimulation in SI but frequent reactions in MI; (5) a majority of SI neurones with cutaneous afferent input in contrast to predominant input from deep tissues to MI neurones; and (6) context independent visually evoked activity observed exclusively in MI neurones. These major differences suggest that SI neuronal activity most likely reflects the input from peripheral receptors rather than, as postulated for MI neurones, the participation in movement initiation and the control of muscular contractions.

Animals↗
PubMed1986

Neuronal activity in the postcentral cortex related to force regulation during a precision grip task.

Recordings from single neurons in the primary somatosensory cortex of the monkey during force regulation between the fingers showed following characteristics: the existence of classes of discharge patterns similar to those in motor cortex, but with differences in their distribution, a late onset of activity changes in relation to force increase and a linear relation to force, but with shallow mean rate-force slope.

Animals↗
PubMed1986

Neural correlates of isometric force in the "motor" thalamus.

The relationship between single cell activity in the "motor" thalamus and the generation of isometric force between the fingers has been investigated in 2 monkeys. Neurons related to the task were found in the thalamic motor regions VLo, VPLo, and VA where microstimulation occasionally elicited motor reactions in hand and fingers. 58% of these 55 neurons, designated "typical", showed modulation of their discharge patterns with force similar to neurons in precentral cortex and could be assigned to one of 5 discharge patterns described for the motor cortex. Only a small percentage of the thalamic neurons were found to have phasic activity. The other "atypical" neurons (42%) had discharge patterns with complex sequences of phasic and tonic activation with respect to force. For 18 typical and atypical neurons with tonic and phasic-tonic modulation of their firing rate with force significant regression coefficients between firing rate and static force were observed. The mean index of force sensitivity (rate-force slope) was 54.5 Hz/N for the neurons increasing their discharge rate with force, i.e. approximately that of precentral cells. Neurons tested for their sensory properties had receptive fields located on hand and/or fingers and were activated mainly by stimulation of muscle and joint receptors. The characteristics of these thalamic neurons are compared to those of precentral cells recorded under identical experimental conditions and are discussed in relation to the known input-output relationships of the motor thalamic nuclei. The data strongly support the hypothesis that parameters of movement, in particular force are represented by the activity of neurons in the "motor" thalamus.

Animals↗
PubMed1982

Cross-correlation analysis of interneuronal connectivity in the motor cortex of the monkey.

Pairs of neurones were recorded within the hand region of the precentral motor cortex of monkeys trained to squeeze a force transducer between the thumb and index finger. Neuronal discharges of a pair of cells, recorded through the same electrode, were first examined for their co-variation with force. The discharges of those pairs with a consistent co-variation were cross-correlated during periods of constant isometric force. Cross-correlograms in the majority of cases had either a sharp peak or trough at latencies suggesting monosynaptic causal relations between the cell discharges. A peak was associated with pairs of cells whose discharges co-varied similarly with force and when a trough was observed, the cell discharges of the pair generally differed in their force co-variation. It is concluded that the action of motor cortical neurones is linked by common and recurrent collateral inputs during isometric co-contraction of finger muscles.

Action Potentials↗