Atsumi Takenobu

Somatosensory evoked high-frequency oscillations recorded directly from the human cerebral cortex

OBJECTIVE To elucidate the generator sources of high-frequency oscillations of somatosensory evoked potentials (SEPs), we recorded somatosensory evoked high-frequency oscillations directly from the human cerebral cortex. SUBJECTS AND METHODS Seven patients, 6 with intractable partial epilepsy and one with a brain tumor, were studied. With chronically implanted subdural electrodes, we recorded SEPs to median nerve stimulation in all patients, and also recorded SEPs to lip and posterior tibial nerve stimulation in one. High-frequency oscillations were recorded using a restricted bandpass filter (500-2000 Hz). RESULTS For the median nerve oscillations, all oscillation potentials were maximum at the electrodes closest to the primary hand sensorimotor area. Most oscillations were distributed similar to or more diffusely than P20/N20. Some later oscillations after the peak of P20 or N20 were present in a very restricted cortical area similar to P25. We investigated the phase change of each oscillation potential around the central sulcus. One-third of the oscillations showed phase reversal around the central sulcus, while later oscillations elicited in a restricted cortical area did not. High-frequency oscillations to posterior tibial nerve and lip stimulation were also maximum in the sensorimotor areas. Most of the lip oscillations showed phase reversal around the central sulcus, but most of the posterior tibial nerve oscillations did not. CONCLUSION High-frequency oscillations are generated near the primary sensorimotor area. There are at least two different generator mechanisms for the median nerve high-frequency oscillations. We suspect that most oscillations are derived from the terminal segments of thalamocortical radiations or from the primary sensorimotor cortex close to the generator of P20/N20, and some later oscillations from the superficial cortex close to the generator of P25.

Germinoma originating in the basal ganglia : report of a case showing unusual appearance on MRI

SummaryA case of germinoma originating in the basal ganglia is presented. Preoperative MRI showed an area of a reticulated core of mixed signal intensity with a surrounding rim of low signal intensity in the right basal ganglia on T2-weighted image. This finding was reported to be characteristic of cavernous angioma, but the tumor was histopathologically identified to be a germinoma with old hemorrhage. The pitfall of MRI in diagnosing brain tumors is discussed.

Microanatomy of Medial Temporal Area and Subtemporal Amygdalohippocampectomy

For seizure control in temporal lobe epilepsy, the head of the hippocampus to the choroidal point, parahippocampal gyrus, entorhinal area, uncus, and at least the basolateral nucleus of the amygdala should be completely removed. The subtemporal approach should be selected for removal of these structures, and it does not interrupt the temporal stem and optic radiation. Pre- and postoperative neuropsychological examinations revealed that there is no significant decline of scores of various examinations including WAIS, WMS, Randt memory, and verbal associates learning tests, even if the resection were performed on the language dominant side. Seizure control for the 20 non-lesional patients operated with this approach is 60% (Class I and II), without definite permanent complications.