Mechanisms of excitatory-inhibitory functions and neural oscillations in human sensor-motor cortex

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1) To examine high frequency oscillations (HFOs) of somatosensory evoked potentials (SEPs) recorded directly from subdural electrodes to investigate the relationship between the primary somatosensory cortex and HFOs. SEPs were recorded directly from subdural electrodes previously implanted in 3 patients for clinical evaluation prior to surgical treatment of intractable epilepsy. The primary sensory cortex (area 36) was proposed as the source of somatosensory HFOs, because the distribution of HFOs recorded from the subdural electrodes agreed with the distribution of the N20-P20 components of the somatosensory evoked potential. The somatosensory HFOs showed a strictly somatotopic source arrangement. There was a polarity inversion of the prophase component and also the N20-P20 component of HFOs across the central sulcus. However, the phase was synchronized in the latter part of the HFOs. We proposed that the origins of the early and latter parts of HFOs are different, and that there was a … More clear somatotopy.2) To examine event-related synchronization and desynchronization of corticogram during voluntary movement to evaluate the relationship between the negative motor area and voluntary movement. Corticograms were recorded from subdural electrodes implanted in 4 patients with intractable partial epilepsy. Negative motor area had event-related alpha desynchronization preceding the onset of movement and post-movement beta synchronization. The analysis of cortical activity suggested that the negative motor area had a important role for preparation of voluntary movement.3) To evaluated the focal nature of the early and late inhibition of corticospinal neurons demonstrated by a paired-pulse stimulation paradigm. We performed paired-electric pulse stimulation studies using subdural electrodes implanted in 4 patients with intractable partial epilepsy. Inhibition of motor evoked potentials in the first dorsal interosseous muscle was obtained by paired-pulse stimulation of the hand motor cortex (M1) with a subthreshold conditioning stimulus at conditioning-test intervals between 1 and 6 ms. This early inhibition was abolished when the conditioning stimulus was moved to the sensory cortex (S1) or the arm M1. The inhibition was also produced by paired-pulse stimulation of the hand M1 with a suprathreshold conditioning stimulus between 50 and 300 ms in all 3 patients. This late inhibition was still recognized when moving the conditioning stimulus to the hand S1 only in one of 3 patients. The early inhibition arises from very small areas in the M1 but the S1 may be related to the generation of the late inhibition in some cases. Less