Journal of Okayama Medical Association
Published by Okayama Medical Association

Full-text articles are available 3 years after publication.


松本 祐蔵 岡山大学医学部脳神経外科学教室
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Visual evoked responses (VER) were recorded from the thalamus and the scalp during stereotaxic thalamotomy in our service. The study involved fourteen patients with various involuntary movement disorders and intractable pain. Routine monopolar EEGs were recorded, from the ventrolateral nuclens and the centremedian of the thalamus, with multipolar electrodes and from the vertex and the occipital region with needle electrodes simultaneously. VERs have been analysed by means of averaging techniques as well as spectral analysis of the EEGs. Experimental studies were also performed with chronically implanted electrodes in the ventrolateral nucleus, the lateral geniculate body, the visual cortex and the anterior sigmoid gyrus of the cats. The results were as follows: 1) Visual evoked responses (VERs) from the occipital regions were well demonstrated in seven out of fourteen cases. The responses had typical seven components (Ⅰ-Ⅶ) with rhythmic after-discharge, documented by Ciganek's report. 2) The evoked responses from the vertex showed practically no early components. Therefore, four components of the response, namely P(1), N(1), P(2) and N(2), were started with P(1) of the peak latency of 105.2msec. This response was corresponded to so-called vertex potential, of which pattern had no similarity to the VER from the occipital region. 3) The evoked responses from the human thalamic VL and CM nuclei showed very similar patterns to the vertex potentials with four components. Peak latencies of them were noted P(1) with 96.4±12.8msec, N(1) with 134.6±19.4msec, P(2) with 196.0±25.5msec and N(2) with 260.9±29.3msec. The thalamic responses always tended to lead off the vertical one about 8.8 to 18.3msec in all cases. 4) In the animal (cat) experiments, VER from visual cortex showed similar pattern to the one from the lateral geniculate body, and VER from the thalamic VL nucleus resembled to the one from the anterior sigmoid gyrus. 5) Rhythmic after-discharges were noted in the thalamus as well as the vertex after their wave components. The after-discharges of the vertex were not disappeared after VL thalamotomy, while spontaneous spindle discharges were disappeared after the thalamotomy. Therefore, rhythmic after-discharges were thought to be involved some other physiological mechanisms to that of spantaneous spindle activity. 6) Spectral analysis of EEGs showed high value of coherence between the thalamic and thevertical EEGs before and during photic stimulation. On the other hand, low coherence were obtained between the vertical and the occipital EEGs in all cases. 7) Photic stimulation provoked VERs in the occipital cortex as well as the vertex potentials through the VL or CM nucleus of the thalamus. It is most interesting that, while the VL nucleus is known as one of specific thalamic nuclei physiologically, the nucleus is also concerned with one of non-specific response such as vertex potentials.