Contribution of different somatosensory afferent input to subcortical somatosensory evoked potentials in humans

objectives: to investigate the subcortical somatosensory evoked potentials (SEPs) to electrical stimula-tion of either muscle or cutaneous afferents. methods: SEPs were recorded in 6 patients suffering from parkinson's disease (PD) who underwent elec-trode implantation in the pedunculopontine (PPTg) nucleus area. we compared SEPs recorded from the scalp and from the intracranial electrode contacts to electrical stimuli applied to: 1) median nerve at the wrist, 2) abductor pollicis brevis motor point, and 3) distal phalanx of the thumb. also the high-frequency oscillations (HFOs) were analysed. results: after median nerve and pure cutaneous (distant phalanx of the thumb) stimulation, a P1-N1 complex was recorded by the intracranial lead, while the scalp electrodes recorded the short-latency far-field responses (P14 and N18). on the contrary, motor point stimulation did not evoke any low-frequency component in the PPTg traces, nor the N18 potential on the scalp. HFOs were recorded to stim-ulation of all modalities by the PPTg electrode contacts. conclusions: stimulus processing within the cuneate nucleus depends on modality, since only the cuta-neous input activates the complex intranuclear network possibly generating the scalp N18 potential. significance: our results shed light on the subcortical processing of the somatosensory input of different modalities. (c) 2021 International federation of clinical neurophysiology