Non-invasive measurements of sensory nerve and cortical responses to skin stimulation : Integration of EEG,MEG and fMRI

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1. We developed 3 point air-puff stimulators which can be controlled independently for eliciting sensory nerve action potentials and somatosensory evoked potentials.2. We developed 3 point vibratory stimulators for studying somatosensory evoked fields associated with perception of frequency, duration and intensity in the somatosensory system.3. We visualized displacements of the skin following air-puff stimulation with a high speed camera which were correlated with a sensory threshold and magnitude estimations.4. We visualized a moving quadrupole along the median nerve with multi-chnnel measurements of action fields over the elbow.5. In peripheral nerve lesions, we found a peculiar oscillation pattern of electrically evoked action fields at or distal to the lesion sites. We performed a computer simulation for the oscillation using the Hodgikin-Huxley equations and found that the increase of Na conductance was related to the oscillation.6. We measured magnetic fields following trigemina … More l stimulation from the decorticated piglets and showed that the subcortically generated fields are strong enough to the detectable outside the head.7. We measured N20m primary response during wakefulness and sleep with subsequent digital high-pass (>300 Hz) and low-pass (>300 Hz) filtering. The estimated source for the high-frequency oscillations (HFOs) was the area 3b very close to that for the N20m. During sleep, the HFOs showed a dramatic diminution in amplitude while the N20m amplitude exhibited a moderate increment. This reciprocal relation between the HFOs and the N20m during a wake-sleep cycle suggests that they represent opposing generator substrates. We speculate that the HFOs represent a localized activity of the GABAergic inhibitory interneurons of layr 4, which have been shown in animal experiments to respond monosynaptically to thalamo-cortical input with a high-frequency (600-900 Hz) burst of short duration spikes. On the other hand, the underlying N20m represents activity of pyramidal neurons which receive monosynaptic excitatory input from the thalamus as well as a feed-forward inhibition from the interneurons. This hypothesis has been further supported by our recent experiments manipulating the amplitude of N20m during wakefulness ; the reciprocal relation between HFOs and N20m hold not only during a wake-sleep cycle but also during wakefulness. Less