Effect of coil orientation on strength-duration time constant and I-wave activation with controllable pulse parameter transcranial magnetic stimulation

Objective: To compare the strength-duration (S-D) time constants of motor cortex structures activated by current pulses oriented posterior-anterior (PA) or anterior-posterior (AP) across the central sulcus. Methods: Motor threshold and input–output curve, along with motor evoked potential (MEP) latencies, of first dorsal interosseus were determined at pulse widths of 30, 60, and 120 μs using a controllable pulse parameter (cTMS) device, with the coil oriented PA or AP. These were used to estimate the S-D time constant and we compared with data for responses evoked by cTMS of the ulnar nerve at the elbow. Results: The S-D time constant with PA was shorter than for AP stimulation (230.9 ± 97.2 vs. 294.2 ± 90.9 us; p<0.001). These values were similar to those calculated after stimulation of ulnar nerve (197 ± 47us). MEP latencies to AP, but not PA stimulation were affected by pulse width, showing longer latencies following short duration stimuli. Conclusion: PA and AP stimuli appear to activate the axons of neurons with different time constants. Short duration AP pulses are more selective than longer pulses in recruiting longer latency corticospinal output

Probing the Control Processes of the Motor System

International audienceRobot-assisted rehabilitation is often found to help in recovery, but its use is often experimental or limited to clinical trials. This paradox is partly explained by the difficulty in bridging the gap between the score on a robot-assisted exercise and the control processes that mediate the measured performance. Building upon recent computational model of motor control, this paper highlights the potential benefits of a multitask approach for evaluating sensorimotor control processes. The approach is illustrated with the results from normal and pathological sensorimotor behavior in humans

Cerebrospinal Fluid Analysis in Immunoglobulin G4-related Hypertrophic Pachymeningitis

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Motor Cortical Plasticity to Training Started in Childhood: The Example of Piano Players.

Converging evidence suggest that motor training is associated with early and late changes of the cortical motor system. Transcranial magnetic stimulation (TMS) offers the possibility to study plastic rearrangements of the motor system in physiological and pathological conditions. We used TMS to characterize long-term changes in upper limb motor cortical representation and interhemispheric inhibition associated with bimanual skill training in pianists who started playing in an early age. Ipsilateral silent period (iSP) and cortical TMS mapping of hand muscles were obtained from 30 strictly right-handed subjects (16 pianists, 14 naïve controls), together with electromyographic recording of mirror movements (MMs) to voluntary hand movements. In controls, motor cortical representation of hand muscles was larger on the dominant (DH) than on the non-dominant hemisphere (NDH). On the contrary, pianists showed symmetric cortical output maps, being their DH less represented than in controls. In naïve subjects, the iSP was smaller on the right vs left abductor pollicis brevis (APB) indicating a weaker inhibition from the NDH to the DH. In pianists, interhemispheric inhibition was more symmetric as their DH was better inhibited than in controls. Electromyographic MMs were observed only in naïve subjects (7/14) and only to voluntary movement of the non-dominant hand. Subjects with MM had a lower iSP area on the right APB compared with all the others. Our findings suggest a more symmetrical motor cortex organization in pianists, both in terms of muscle cortical representation and interhemispheric inhibition. Although we cannot disentangle training-related from preexisting conditions, it is possible that long-term bimanual practice may reshape motor cortical representation and rebalance interhemispheric interactions, which in naïve right-handed subjects would both tend to favour the dominant hemisphere

Asymmetry index (AI) according to Mirror movements (MMs) occurrence.

<p>The AI range from 1.0 to -1.0 and the value of 0 corresponds to perfect symmetry between the two sides (Dominant = Non Dominant).</p

Cortical motor representation of the hand muscles (mean of APB, ADM and ECR) over the dominant (LH) and non-dominant (RH) hemisphere in pianists and controls (mean and standard error).

<p><b>A.</b> Map_area in the dominant hemisphere of the control group was significantly larger compared with their non-dominant hemisphere (** p = 0.001) and with the dominant hemisphere of pianists (*p = 0.029). <b>B</b>. Example of cortical motor mapping of ADM in a pianist and a control naïve subject. MEPs amplitudes higher than 50 mV were interpolated and projected on an average brain cortical surface reconstruction using Curry software V4.6. The interhemispheric asymmetry in map_area, with larger representation of the dominant hemisphere, is of note only in the naïve subject.</p

correlation analysis among the asymmetry indices of neurophysiological parameters (map_area, iSP_duration and n-iSP_area) and hand dexterity (NHPT and FT).

<p>correlation analysis among the asymmetry indices of neurophysiological parameters (map_area, iSP_duration and n-iSP_area) and hand dexterity (NHPT and FT).</p

example of mirror movement in the right ADM during voluntary movement of the contralateral homologous muscle in a control subject.

<p>example of mirror movement in the right ADM during voluntary movement of the contralateral homologous muscle in a control subject.</p

Behavioral results.

<p>A. Nine hole peg test (NHPT) score: left hand in pianists was significantly faster than in controls (p = 0.001). In the control group the time required to perform NHPT was shorter for the right than the left hand (p = 0.003). B Finger tapping (FT) scores: a significant effect of “side” factor was observed (F_1,22 = 100.6, p<0.0001) being the right hand faster than the left hand. A trend was observed for the “group” comparison (F_1,22 = 3.8, p = 0.06) and the “side” x “group” interaction was not significant (F_1,22 = 0.18, p = 0.6). C. NHPT asymmetry index (AI) score was significantly lower in pianist than in controls indicating more symmetric motor performance in pianists (p = 0.005) D. FT AI was significantly lower in pianists than in controls (p = 0.01).</p