To determine the characteristics of high-frequency oscillations (HFOs) of cortical somatosensory evoked potentials (SEPs), the effect of general anesthesia on HFOs and low-frequency primary cortical responses was studied. The authors recorded SEPs elicited by median nerve stimulation directly from human brains of seven patients who underwent implantation of subdural electrodes before surgical treatment of intractable epilepsy. Recordings were made before and during general anesthesia. Changes in the number of HFOs and amplitude ratios of HFOs/primary cortical responses were analyzed. Under general anesthesia, the number of HFO peaks and the amplitude ratios were significantly decreased. General anesthesia induced remarkably decreased HFO activities when compared to low-frequency SEPs, suggesting that each of those originated from different generators. Possible relations between gamma-amino-butyric acid (GABA)ergic inhibitory interneurons and HFOs are discussed.
To investigate the neural plasticity in the somatosensory cortex, changes in somatosensory evoked potentials (SSEPs) during finger ischemia were evaluated and compared with those affected by touch or movement interference. Somatosensory evoked potentials were recorded in the vicinity of the central sulcus in four patients with intractable epilepsy. During electrical stimulation to a selected finger, ischemic anesthesia was induced in another finger. Effects of tactile or movement interference were examined during electrical stimulation to the selected finger by applying tactile stimulation to or inducing voluntary movement of the other finger. Dynamic SSEPs were recorded during varying levels of sensory deprivation and different types of interference, and the dynamic nature of the SSEP changes within an individual was studied in detail. Somatosensory evoked potential changes appeared during finger ischemia and tended to persist during the postischemic stage, which is indicative of sensory plasticity and the maintenance of new conditioning. Amplitudes of the early and late cortical components increased when complete finger anesthesia was induced-a sign of the unmasking phenomenon. Amplitudes of early cortical SSEPs decreased when ischemic anesthesia was incomplete, similar to the findings when tactile or movement interference was applied. Surrounding inhibition, therefore, may become dominant before the unmasking phenomenon appears in early cortical SSEPs.
A 17-year-old male presented with paroxysmal kinesigenic choreoathetosis (PKC) associated with frontotemporal arachnoid cyst. Xenon-133 single photon emission computed tomography detected a slight but equivocal decrease in regional cerebral blood flow in the vicinity of basal ganglia associ ated with the PKC episodes. PKC continued after surgical removal of the cyst but was well controlled by oral administration of carbamazepine.Whether the pathogenesis of symptomatic PKC was associ ated with the cortical lesion could not be determined in the present case.
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