Low- and high-frequency subcortical SEP amplitude reduction during pure passive movement

• Pure passive movement reduces the amplitude of both cortical and subcortical SEPs.
• Amplitude reduction is higher for cortical than subcortical SEPs.
• Amplitude reduction depends on both movement rate and excursion.

ObjectivesTo investigate the effect of pure passive movement on both cortical and subcortical somatosensory evoked potentials (SEPs).MethodsMedian nerve SEPs were recorded in 8 patients suffering from Parkinson’s disease (PD) and two patients with essential tremor. PD patients underwent electrode implantation in the subthalamic (STN) nucleus (3 patients) and pedunculopontine (PPTg) nucleus (5 patients), while 2 patients with essential tremor were implanted in the ventral intermediate nucleus (VIM) of the thalamus. In anesthetized patients, SEPs were recorded at rest and during a passive movement of the thumb of the stimulated wrist from the intracranial electrode contacts and from the scalp. Also the high-frequency oscillations (HFOs) were analyzed.ResultsAmplitudes of both deep and scalp components were decreased during passive movement, but the reduction was higher at cortical than subcortical level. Also the HFOs were reduced by movement.ConclusionThe different amount of the movement-related decrease suggests that the cortical SEP gating is not only the result of a subcortical somatosensory volley attenuation, but a further mechanism acting at cortical level should be considered.SignificanceOur results are important for understanding the physiological mechanism of the sensory–motor interaction during passive movement.