Concurrent Deep Brain Stimulation Reduces the Direct Cortical Stimulation Necessary for Motor Output

Area of Science:

• Neuroscience
• Neuromodulation
• Movement Disorders

Background:

• Deep brain stimulation (DBS) for Parkinson's disease (PD) is thought to modulate neural circuits.
• A proposed mechanism involves normalizing primary motor cortex (M1) pathophysiology via the hyperdirect pathway.

Purpose of the Study:

• To investigate if DBS reduces the current intensity required for direct cortical stimulation (DCS) to modulate motor-evoked potentials (MEPs).
• To explore the relationship between DBS configurations, M1 modulation, and the hyperdirect pathway.

Main Methods:

• Acquired intraoperative subthalamic DBS, DCS, and diffusion tensor imaging (DTI) data in 8 PD patients.
• Applied focal DCS to M1 and measured MEPs.
• Modeled the volume of activated tissue for specific DBS configurations.

Main Results:

• DBS significantly reduced the DCS current intensity needed to elicit MEPs in 7 out of 8 patients.
• This effect was specific to certain DBS bipolar configurations.
• The volume of activated tissue for effective DBS configurations correlated with hyperdirect pathway overlap.

Conclusions:

• DBS effectively lowers the threshold for M1 modulation via DCS.
• This supports a circuit-based mechanism for DBS efficacy in PD.
• The hyperdirect pathway may play a role in the observed neuromodulation and therapeutic benefits.