皮膚電気刺激による感覚神経誘発電位の増減とそのモデリングについて

摘要

モールス符号で変調された皮膚電気刺激では2電極で文字情報を呈示できるが，連続する刺激が融合して知覚されると伝送速度の限界が生じる。この融合は末梢と脳内での処理過程で生じると考えられるが，その詳細には不明な点が多い。そこで本研究では末梢神経の読発電位を計測・解析して最適な皮膚電気刺激法を見出すことを目的とし，尺骨神経の誘発電位応答を計測した。その結果，刺激パルスの系列内位置によって誘発応答振幅が増減する場合があった。刺激に対する誘発応答振幅の増減の理由の推定を行うために生体興奮膜モデルで周期的刺激に対する分周比を数値計算し，パルス間隔とパルス刺激の強さで表した分周比の地図を作成した。分周比が0．5では，2刺激に1発火であり，誘発電位振幅が増減した可能性があった。また，分周比が1では，1刺激に1発火となる神経線維が増え，誘発電位振幅の増減が減ると推測された。皮膚電気刺激で感覚聞値を求める実験を行うと数値計算された分周比の0と0以外の境界線の形状に近い場合があった。%It is known that character information can be transmitted using Morse code through dermal electrical stimulation by two electrodes. However, consecutive transmission degrades the perception of adjacent signals and in effect limits the transmission speed. This merging of adjacent signals is believed to occur during processing inside the brain and in the peripheral nervous system. However, proof of this is unknown. This study aims to find the appropriate method for dermal electrical stimulation by measuring and analysing evoked potential of the peripheral nervous system. In particular, the response of the ulnar nerve was used. One key observation made was that there are cases where the amplitude of the response reciprocally fluctuated during application of consecutive stimuli. To investigate the relationship between the pulse stimulus and the fluctuation in the responses, numerical simulation of the response of a neuron model to periodic pulse stimuli was performed. The result of the simulation was used to create a map representing the division ratio with respect to the pulse period and the pulse amplitude. A division ratio of 0.5 was found indicating the possibility of fluctuations in the evoked potential. Inferences were also made in cases where the division ratio was 1 there was an increase in nerve fibres causing a decrease in the fluctuations of evoked potentials. Furthermore, the map shows that the boundary line between zero and non-zero division ratios and the electrical stimulation threshold line showed close similarities.