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  • 1
    Electronic Resource
    Electronic Resource
    Motor cortex plasticity induced by extensive training revealed by transcranial magnetic stimulation in human (2005)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 21 (2005), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: This study examines the effect of high-level skilled behaviour on motor cortex representations of upper extremity muscles of ten sportswomen. We used transcranial magnetic stimulation to map proximal medial deltoid and distal extensor carpi radialis muscle representations on both hemispheres during low-level voluntary contraction. We compared cortical representation areas between two groups of subjects and between hemispheres within subjects. The first group comprised five elite volleyball attackers and the second group five runners. Four stimuli were delivered on multiple scalp sites (1.5 cm apart) to induce motor-evoked potentials recorded by surface EMG. Maps were described in terms of excitable scalp positions and of motor-evoked potentials. We observed differences in map areas between the two groups. Volleyball players had larger cortical representations of the proximal medial deltoid muscle than runners. Furthermore, the volleyball players had larger map areas for dominant muscles compared with non-dominant muscles. There was no difference, however, in map area for either muscle between the dominant and non-dominant arm in the runner group. Our results show that heavy training in a specific skill induces an expansion of proximal muscle representation in the contralateral primary motor cortex. This enlarged map area for proximal muscle is accompanied by an increase in the overlapping of proximal and distal muscle representations. This could reflect the fact that motor learning of co-ordinated movement involves a common control of both muscles. This reorganization supports the hypothesis of a cortical plasticity driven by activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.2004.03835.x
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  • 2
    Electronic Resource
    Electronic Resource
    Intracortical connections between motor cortical zones controlling antagonistic muscles in the cat: a combined anatomical and physiological study (1998)
    Springer
    Experimental brain research 120 (1998), S. 223-232 
    Details
    ISSN: 1432-1106
    Keywords: Key words Motor cortex ; Microstimulation ; Intracortical horizontal connections ; Reciprocal inhibition ; Biocytin ; HRP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Experiments were done on nine cats anaesthetized with pentobarbitone to determine whether motor cortical zones controlling antagonistic muscles are synaptically interconnected. Motor cortical zones controlling wrist flexors, or extensors, were identified by microstimulation and intramuscular electromyographic recordings (microstimulation: 11 pulses at 333 pulses/s, current 10–40 μA). The position of each zone of interest was marked by a small ink spot on the surface of the cortex and on a scaled drawing of the cortical surface (cruciate region). Following the identification of wrist flexor and extensor zones the anterograde tracer biocytin was injected into one, or two, wrist extensor zones at three depths (400, 800 and 1500 μm) from the cortical surface. A small injection of horseradish peroxidase (HRP) – producing a dark brown spot of approximately 300–500 μm – was made in layer II–III of one or more wrist flexor zones. Similar HRP injections were made in the deep layers of wrist extensor zones that were not labelled by biocytin. The HRP injections served to mark the position of potential targets of biocytin-labelled fibres. In some experiments the biocytin was injected into a wrist flexor zone and HRP was deposited in one or more wrist extensor zones. Biocytin-labelled fibres (blue) were found throughout the expanse of the forelimb representation zone, as has been previously reported. More specifically, in all animals biocytin-labelled fibres were found in identified cortical zones controlling the same muscle(s) as well as in zones controlling an antagonist(s). Club-like swellings, indicative of synaptic boutons, were observed on these fibres. The density of labelled fibres was greater in the upper cortical layers (II–III), but a large number of terminals were also present in the lower cortical layers (V–VI). We conclude that there exist intracortical circuits linking motor cortical zones controlling antagonistic muscles. Elucidating the nature and function of these circuits is likely to be important for understanding the mode of operation of the motor cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050396
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  • 3
    Electronic Resource
    Electronic Resource
    Input-output properties and gain changes in the human corticospinal pathway (1997)
    Springer
    Experimental brain research 114 (1997), S. 329-338 
    Details
    ISSN: 1432-1106
    Keywords: Key words Motor cortex ; Magnetic stimulation ; Corticospinal pathway ; Single motor units
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Experiments were done to determine the form of the input-output relation (i.e. stimulus intensity vs response amplitude) of the corticospinal pathway of the first dorsal interosseous and the tibialis anterior, respectively. Our purpose was to determine from these quantitative relations which input-output parameters would be useful measures in studies dealing with motor cortical task dependence. The motor cortex was excited by focal transcranial magnetic stimuli and the evoked motor response were recorded with surface electromyographic electrodes. In some experiments the discharge probability of single motor units in response to magnetic stimuli of increasing intensity was determined from intramuscular recordings. For both muscles the form of the input-output relation was sigmoidal. The steepness of the relation increased, up to 4–7 times the value at rest, with increasing tonic background activity. The threshold decreased, but only slightly, with increasing tonic background activity. The minimum value of the threshold was reached at activation levels of about 10–20% of the maximum tonic effort, whereas the steepness of the relation reached its maximum at higher activation levels, typically about 30–40% of the maximum tonic effort. These observations imply that these two input-output parameters of the corticospinal pathway – one reflecting the bias level (threshold) and the other the gain (slope) – are determined by different neural mechanisms. The plateau level of the sigmoidal input-output relation was not influenced by the background activation level, except that in some subjects (4/9) it could not be reached when no background motor activity was present. This was probably due, for the most part, to limitation of the maximum stimulator output. Additionally, this finding may reflect a change in the intrinsic excitability of the motor cortex in going from rest to activity, or that convergent inputs from different descending and afferent systems are required for maximal activation of motoneuron pools. Thus, the threshold, steepness and plateau level characterize the input-output parameters of the human corticospinal pathway for a given level of motor activity. In contrast to the nonlinear input-output relation of the corticospinal pathway as whole, which includes the motoneuron pool and any spinal interneuronal relays, the discharge probability of all single motor units was a linearly increasing function of the stimulus strength (r≥0.9, P〈0.01). Thus, the sigmoidal input-output relation of the corticospinal pathway, as a whole, is not due to the input-output properties of single motoneurons. The possible neural mechanisms which underlie the shape and parameters of the input-output relation as well as the methodological implications of the results are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005641
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  • 4
    Electronic Resource
    Electronic Resource
    Role of proprioceptive information in the temporal coordination between joints (1998)
    Springer
    Experimental brain research 119 (1998), S. 58-64 
    Details
    ISSN: 1432-1106
    Keywords: Key words Motor synchronization ; Muscle spindle information ; Jaw ; Ankle ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Ten subjects made rapid, simultaneous movements of jaw (elevation or lowering) and right foot (ankle flexion or extension) in two experimental situations: (1) in response to an external signal (reaction-time situation), and (2) in a self-paced situation. We calculated the mean time intervals between the onsets of electromyographic (EMG) activity of agonist muscles (tibialis anterior or gastrocnemius lateralis compared with masseter or digastricus pars anterior) and those between the onsets of movement acceleration at each joint. Despite the fact that subjects reported simultaneous jaw-foot movements, there was always a short time interval between the two movements as between the agonist EMG activities. When the subjects were asked to perform a jaw elevation movement simultaneously with an ankle movement (flexion or extension), the sign of the time interval was dependent on the situation of movement initiation. In the reaction-time situation, the jaw motor activity preceded that of the ankle, whereas the reverse temporal order was observed in the self-paced situation. This is consistent with a previous hypothesis suggesting that the simultaneity of two motor actions is centrally established through two separate central processes: reactive or predictive. When subjects tried to perform simultaneous jaw lowering and foot flexion or extension movements, the strict temporal order observed when considering jaw elevation and ankle movements disappeared. The jaw motor activity generally preceded that of ankle in the reactive situation, but, depending on the subjects, it preceded or followed the ankle motor activity during self-paced movements. It is likely that the specific spindle supply of jaw muscles accounts for these results. Indeed, the jaw depressor muscles, in contrast to the elevators, lack muscle spindles. Our results suggest that the kinesthetic inputs used by the upper central nervous system to synchronize two rapid voluntary movements are mainly those from spindles located in the muscles that accelerate the movement, suggesting a strong α-γ linkage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050319
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