Coherent cortical and muscle discharge in cortical myoclonus

Abstract

There is increasing evidence in man that the cortical drive to motor neurons is rhythmic. This oscillatory drive may be exaggerated in patients with cortical myoclonus. Spectral analysis of surface bipolar EEG and EMG activity was performed in eight such patients. Only three cases had evidence of giant cortical evoked potentials or a cortical correlate on back-averaging at the time of study. In six subjects, significant coherence between contralateral and vertex EEG and EMG was observed in ranges similar to that previously reported for normal subjects (15-30 and 30-60 Hz). Three out of these six subjects also had significant coherence at higher frequencies (up to 175 Hz). All eight patients had a correlate in the cumulant density estimate between EEG and contralateral EMG. EMG lagged EEG by about 14, 25 and 35 ms for the muscles of the forearm, hand and foot, respectively. These delays were estimated from the slope of the phase curves and the timing of the peaks in the cumulant density estimates, and are appropriate for conduction in fast pyramidal pathways. The results provide clear evidence of a cortical drive synchronizing muscle discharge over a broad range of frequencies in patients with cortical myoclonus. Fourier analysis is a promising technique in the diagnosis and investigation of such patients.

The interrelation between clinical presentation and neurophysiology of posthypoxic myoclonus

“…Moreover, the sensitivity and specificity of the neurophysiological methods used are unknown (except for SSEP as prognosticator in PAE). On the other hand, JLBA and coherence analysis have proven their role in clinical practice in evaluating anatomical origin of myoclonus and can therefore be seen as a reliable marker 11, 18, 20, 21, 22, 31. Indeed, the agreement between JLBA and coherence analysis turned out to be substantial: 17/19 patients had identical findings.…”

“…To classify the anatomical origin of PHM, five different neurophysiological methods were used, namely: (1) visual inspection of EEG, (2) EMG burst‐duration, (3) muscle recruitment order, (4) JLBA, and (5) coherence analysis 6, 9, 10, 11, 18, 19, 20, 21, 22. Cortical PHM was presumed if (1) an EEG spike prior PHM was visible on EEG, (2) a mean burst duration <75 msec was present (10 randomly assessed jerks), (3) a cranio‐caudal muscle recruitment order or only single myoclonic jerk(s) were present, (4) JLBA was positive, or (5) reliable corticomuscular coherence was present.…”

“…A strictly downstream (i.e., cranio‐caudal) muscle recruitment pattern is more likely to originate from the cortex 11. Finally, a combined EEG‐EMG approach permits identifying the origin of myoclonus by Jerk‐Locked Back Averaging (JLBA) and coherence analysis 11, 18, 20, 21, 22, 23…”

Identification of connectivity in human motor control: exciting the afferent pathways

“…Intramuscular coherence is a measure of the common input to different parts of the same muscle and is applied as a measure of the corticospinal drive (Grosse et al, 2003(Grosse et al, , 2002Brown et al, 1999). We found that the reliability and agreement of intramuscular coherence variables depends on signal processing settings (EMG high-pass filtering and rectification) and experimental condition (walking speed).…”

“…Coherence derived from a pair of EMG signals, EMG-EMG coherence, quantifies the common oscillatory drive to a pair of muscles (intermuscular coherence) or to two parts of the same muscle (intramuscular coherence). EMG-EMG coherence in the beta (15−35Hz) bands is considered to reflect the common corticospinal drive from the primary motor cortex to the muscles (Hansen et al, 2001;Grosse et al, 2003;Halliday et al, 2003;Grosse et al, 2002;Petersen et al, 2010;Brown et al, 1999) whereas also spinal circuitries could potentially contribute (Norton et al, 2004(Norton et al, , 2003. EMG-EMG coherence is an attractive approach to assess this common drive since it is easy to measure, requiring only the recording of EMG signals without the need to perturb or stimulate the system (Bo Nielsen, 2002;Barthélemy et al, 2010;Hansen et al, 2005;Norton, 2008).…”