Objective response detection in an electroencephalogram during somatosensory stimulation.

Techniques for objective response detection aim to identify the presence of evoked potentials based purely on statistical principles. They have been shown to be potentially more sensitive than the conventional approach of subjective evaluation by experienced clinicians and could be of great clinical use. Three such techniques to detect changes in an electroencephalogram (EEG) synchronous with the stimuli, namely, magnitude-squared coherence (MSC), the phase-synchrony measure (PSM) and the spectral F test (SFT) were applied to EEG signals of 12 normal subjects under conventional somatosensory pulse stimulation to the tibial nerve. The SFT, which uses only the power spectrum, showed the poorest performance, while the PSM, based only on the phase spectrum, gave results almost as good as those of the MSC, which uses both phase and power spectra. With the latter two techniques, stimulus responses were evident in the frequency range of 20-80 Hz in all subjects after 200 stimuli (5 Hz stimulus frequency), whereas for visual recognition at least 500 stimuli are usually applied. Based on these results and on simulations, the phase-based techniques appear promising for the automated detection and monitoring of somatosensory evoked potentials.

Segmental myoclonus and basilar artery. Giant aneurysm. Case report.

A 70 years-old man was admitted at our hospital because of unstable angina pectoris. He had essential hypertension and right hemiplegia from a ischemic stroke two years before admission. On neurologic examination, it was found mental disorientation, unstable emotionality, right spastic hemiparesis with right Babinski sign, and segmental myoclonus affecting the superior lip and the palate (palatal nystagmus) on the right side. On the CT scan, a giant aneurysm of the basilar artery was detected. We conclude that the segmental myoclonus could be explained by ischemic lesions in the Guillain-Mollaret triangle.