Direct cortical stimulation with cylindrical depth electrodes in the interhemispheric fissure for leg motor evoked potential monitoring

ObjectiveTo evaluate cylindrical depth electrodes in the interhemispheric fissure as an alternative to subdural strip electrodes for direct cortical stimulation (DCS) leg motor evoked potential (MEP) monitoring.MethodsA cylindrical depth electrode was positioned in the interhemispheric fissure of 37 patients who underwent supratentorial brain surgery. Leg sensory and motor cortices were localized by highest tibial nerve somatosensory evoked potential amplitude and lowest DCS leg MEP threshold; the lowest-threshold electrode was then used for DCS leg MEP monitoring.ResultsIntraoperative leg MEPs were obtained from all the patients in the series. The mean intensity applied for leg MEP monitoring with the cylindrical depth electrode was 15.2 ± 4.0 mA. No complications secondary to neurophysiological monitoring were detected.ConclusionsLower extremity MEPs were consistently recorded using a multi-contact cylindrical depth electrode in the interhemispheric fissure by DCS.SignificanceCylindrical depth electrodes may be a safe and effective alternative for DCS in the interhemispheric fissure, where subdural strips are difficult to place.     

Toward the establishment of neurophysiological indicators for neuropsychiatric disorders using transcranial magnetic stimulation‐evoked potentials: A systematic review

Transcranial magnetic stimulation (TMS) can depolarize the neurons directly under the coil when applied to the cerebral cortex, and modulate the neural circuit associated with the stimulation site, which makes it possible to measure the neurophysiological index to evaluate excitability and inhibitory functions. Concurrent TMS and electroencephalography (TMS‐EEG) has been developed to assess the neurophysiological characteristics of cortical regions other than the motor cortical region noninvasively. The aim of this review is to comprehensively discuss TMS‐EEG research in the healthy brain focused on excitability, inhibition, and plasticity following neuromodulatory TMS paradigms from a neurophysiological perspective. A search was conducted in PubMed to identify articles that examined humans and that were written in English and published by September 2018. The search terms were as follows: (TMS OR ‘transcranial magnetic stimulation’) AND (EEG OR electroencephalog*) NOT (rTMS OR ‘repetitive transcranial magnetic stimulation’ OR TBS OR ‘theta burst stimulation’) AND (healthy). The study presents an overview of TMS‐EEG methodology and neurophysiological indices and reviews previous findings from TMS‐EEG in healthy individuals. Furthermore, this review discusses the potential application of TMS‐EEG neurophysiology in the clinical setting to study healthy and diseased brain conditions in the future. Combined TMS‐EEG is a powerful tool to probe and map neural circuits in the human brain noninvasively and represents a promising approach for determining the underlying pathophysiology of neuropsychiatric disorders.