The activity of the brain during observation or imagination of movements might facilitate the relearning of motor functions after stroke. The present study examines whether there is an additional effect of imagination over observation-only. Eight healthy subjects observed and observed-and-imagined a movement of a hand; 64-channel EEG was used to measure brain activity. The synchronization of the theta (4-8 Hz), alpha (8-13 Hz) and beta (13-25 Hz) frequency bands was calculated and plotted in topoplots. The temporal changes of the sensorimotor area (C3, C4) and the centro-parietal cortex (Pz) were analyzed in the two experimental conditions. During observation-and-imagination, a significant larger desynchronization (p = 0.004) in the sensorimotor area was found compared to observation-only in all electrodes and frequency bands. In addition, temporal differences were found between observation and observation-and-imagination in the alpha frequency bands. During observation-and-imagination, modulations of EEG rhythms were stronger than during observation-only in the theta, alpha and beta frequency bands and during almost the whole activity fragment. These findings suggest an additive effect of imagination to observation in the rehabilitation after stroke.

Muscle motor evoked potentials (MEPs) from transcranial electrical stimulation (TES) became a standard technique for monitoring the motor functions of the brain and spinal cord at risk during spinal and brain surgery. However, a wide range of criteria based on the percentage of amplitude decrease is used in practice. A survey of the current literature on clinical outcome parameters reveals a variety of percentages in a range of 30% to 100% (50% to 100% spinal procedures) with no consensus. The interpretation of muscle MEPs is hampered by their sensitivity to many interfering factors. Trial-to-trial MEP variations may partly be reduced by controllable parameters of which TES parameters are in the hands of the neuromonitorist. We propose an operational model based on basic neurophysiologic knowledge to interpret the characteristics of MEP-TES voltage curves and predict the influences of the location on the sigmoid voltage curve on spontaneous MEP-variations and influences of factors affecting the voltage curve. The model predicts a correlation between the slope, expressed by a gain, and variations of muscle MEP amplitudes. This complies with two case examples. The limited specificity/sensitivity of warning criteria based on the percentage of amplitude reduction can possibly be improved by developing standards for set-up procedures of TES paradigms. These procedures include strategies for desensitizing MEPs for variations of controllable parameters. The TES voltage or current is a feasible controlling parameter and should be related to the motor threshold and the onset of the supramaximal level being landmarks of MEP-voltage functions. These parameters may offer a valuable addition to multicenter outcome studies.

Introduction Transcranial electrical (TES) and magnetic stimulation (TMS) are both used for assessment of the motor function of the spinal cord in horses. Muscular motor evoked potentials (mMEP) were compared intra-individually for both techniques in five healthy horses. mMEPs were measured twice at increasing stimulation intensity steps over the extensor carpi radialis (ECR), tibialis cranialis (TC), and caninus muscles. Significance was set at p < 0.05. To support the hypothesis that both techniques induce extracranially elicited mMEPs, literature was also reviewed. Results Both techniques show the presence of late mMEPs below the transcranial threshold appearing as extracranially elicited startle responses. The occurrence of these late mMEPs is especially important for interpretation of TMS tracings when coil misalignment can have an additional influence. Mean transcranial motor latency times (MLT; synaptic delays included) and conduction velocities (CV) of the ECR and TC were significantly different between both techniques: respectively, 4.2 and 5.5 ms (MLT TMS – -MLT TES ), and −7.7 and −9.9 m/s (CV TMS -CV TES ). TMS and TES show intensity-dependent latency decreases of, respectively, −2.6 (ECR) and −2.7 ms (TC)/30% magnetic intensity and −2.6 (ECR) and −3.2 (TC) ms/30V. When compared to TMS, TES shows the lowest coefficients of variation and highest reproducibility and accuracy for MLTs. This is ascribed to the fact that TES activates a lower number of cascaded interneurons, allows for multipulse stimulation, has an absence of coil repositioning errors, and has less sensitivity for varying degrees of background muscle tonus. Real axonal conduction times and conduction velocities are most closely approximated by TES. Conclusion Both intracranial and extracranial mMEPs inevitably carry characteristics of brainstem reflexes. To avoid false interpretations, transcranial mMEPs can be identified by a stepwise latency shortening of 15–20 ms when exceeding the transcranial motor threshold at increasing stimulation intensities. A ring block around the vertex is advised to reduce interference by extracranial mMEPs. mMEPs reflect the functional integrity of the route along the brainstem nuclei, extrapyramidal motor tracts, propriospinal neurons, and motoneurons. The corticospinal tract appears subordinate in horses. TMS and TES are interchangeable for assessing the functional integrity of motor functions of the spinal cord. However, TES reveals significantly shorter MLTs, higher conduction velocities, and better reproducibility.

Introduction: Adhesive surface electrodes are worthwhile to explore in detail as alternative to subcutaneous needle electrodes to assess myogenic evoked potentials (MEP) in human and horses. Extramuscular characteristics of both electrode types and different brands are compared in simultaneous recordings by also considering electrode impedances and background noise under not mechanically secured (not taped) and taped conditions. Methods: In five ataxic and one non-ataxic horses, transcranial electrical MEPs, myographic activity, and noise were simultaneously recorded from subcutaneous needle (three brands) together with pre-gelled surface electrodes (five brands) on four extremities. In three horses, the impedances of four adjacent-placed surfaceelectrode pairs of different brands were measured and compared. The similarity between needle and surface EMGs was assessed by cross-correlation functions, pairwise comparison of motor latency times (MLT), and amplitudes. The influence of electrode noise and impedance on the signal quality was assessed by a failure rate (FR) function. Geometric means and impedance ranges under not taped and taped conditions were derived for each brand. Results: High coherencies between EMGs of needle-surface pairs degraded to 0.7 at moderate and disappeared at strong noise. MLTs showed sub-millisecond simultaneous differences while sequential variations were several milliseconds. Subcutaneous MEP

Monitoring the complete nervous system during an XLIF procedure is found to be helpful since nerve roots, lumbar plexus as well as the intradural neural structures may be at risk. TESMEP has additional value to sEMG and tEMG during XLIF procedure: (1) it informed about otherwise unnoticed events, and (2) it confirmed and added information to events measured using sEMG.

Biphasic stimulation at C3C4 is advised when constant voltage stimulation is used to monitor the spinal cord during orthopedic spine surgery. MTvoltage of corkscrew and small needle electrodes are highly sensitive to electrode impedances.

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