Objective: To identify if low intensity transcranial electric stimulation targeting the pallidum influences motor cortex excitability.

Background: Low intensity electrical stimulation has been shown to modulate cortical excitability in Controls and PD patients. Here we explore the effect of new electrode posititons and rotating electrical fields.

Method: Low intensity transcranial electric stimulation was applied in normal subjects and PD patients in altogether 7 protocols. Three different electrode montages were derived from simulations with the open source software SimNIBS in order to generate optimal current intensity in the pallidum bilaterally. They include rotating electric fields (employing 8 channels with 16 electrodes) in order to dilute cortical stimulation intensities, a bitemporal stimulation with four electrodes on each side and conventional M1 stimulation with the return electrode at the contralateral forehead as a control. Motor evoked potentials (MEPs), silent periods, and short-interval intracortical inhibition (SICI) were measured by single- and paired pulse transcranial magnetic stimulation (TMS) in 20 control subjects and 12 PD patients so far at baseline and post stimulation across three subsequent time points. The intervention involved transcranial Alternating Current Stimulation (tACS) at a frequency of 130 Hz and transcranial Random Noise Stimulation (tRNS) 0.1 – 640 Hz with intensities of 2 mA (peak-to-peak). The individual mean values of MEP amplitudes were calculated for all subjects. The post-intervention mean MEP amplitudes were normalized to the respective individual’s mean baseline MEP amplitude. Parkinsonian medication with dopaminergic agents has been maintained stable during all experiments, which were separated by at least a week.

Results: In 20 controls a first analysis before MEP artifact rejection revealed no significant influence of stimulation on motor cortex excitability, these data and those of 12 PD patients are under analysis. A preliminary analysis of the motor score of 7 PD patients showed an overall reduction across all 6 active interventions by 27 %. This score changed with sham stimulation by 19 %.

Conclusion: This study shall clarify if diluting electrical stimulation intensity at the cortical surface and focusing current flow to the pallidum is superior to conventional stimulation in controls and PD patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/non-invasive-transcranial-eectrical-stimulation-trns-and-tacs-targeting-the-pallidum-in-normal-controls-and-pd-patients-by-rotating-electrical-fields/