Somatosensory evoked high frequency oscillations recorded from subdural electrodes

Objectives: 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. Methods: SEPs were recorded directly from subdural electrodes previously implanted in 3 patients for clinical evaluation prior to surgical treatment of intractable epilepsy. Results: The primary sensory cortex (area 3b) 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. Conclusions: We propose that the origins of the early and latter parts of HFOs are different, and that there was a clear somatotopy.