Irregular spontaneous, action and reflex myoclonus/myoclonic tremor (cases 4, 6 and 8). (A) ‘Giant’ somatosensory evoked potentials and C-reflex at a latency of 46 ms after stimulating median nerve at the wrist (case 4). The P1 precedes the C-reflex by 20 ms. (B) JLBA (245 sweeps) revealed a biphasic spike. There is co-contraction of agonist/antagonist and a proximodistal recruitment order. The EEG spike precedes the onset of the averaged EMG from the left APB by 20 ms – this is identical to the latency observed between the P1 waveform on the SEPs and the C-reflex from the APB (C) ‘Giant’ cortical waveforms and C-reflexes in the forearm muscles (latency of 42 ms) after stimulation of the median nerve at the wrist (case 6). The P1 component of the cortical waveform precedes the onset of the C-reflexes by 17 ms. (D) JLBA revealed a biphasic cortical correlate preceding the onset of the averaged and rectified EMG discharges (EDC). The latency from the positive EEG spike to the onset of the averaged EMG is very similar to the one recorded in the SEPs between the P1 component of the cortical waveform and the long loop responses in the forearm. (E) ‘Giant’ waveforms in the somatosensory evoked potentials (median nerve at the wrist) with prominent C-reflexes following by 16 ms (EDC) the P1 component of the cortical waveform (case 8). (F) JLBA from the left EDC while left arm at rest. The averaged data (531 sweeps) show a biphasic cortical correlate in the central region – the positive spike precedes the onset of the averaged EMG from the EDC by about 17 ms. ADM = abductor digiti minimi, APB = abductor pollicis brevis, EDC = extensor digitorum communis, FCU = flexor carpi ulnaris, FDS = Flexor digitorum superficialis, SEPs = somatosensory evoked potentials.