Variability in Response to Quadripulse Stimulation of the Motor Cortex

Area of Science:

• Neuroscience
• Neurophysiology
• Brain Stimulation

Background:

• Brain stimulation protocols for inducing plasticity show high individual variability.
• Limited data exists on the variability of responses to quadripulse stimulation (QPS).

Purpose of the Study:

• Systematically assess QPS parameters for motor cortical plasticity induction.
• Investigate the variability of QPS responses using optimized parameters.

Main Methods:

• Compared two different interburst intervals (IBI) with identical pulse counts.
• Investigated three IBIs with varying pulse counts but consistent intervention duration.
• Compared after-effects of monophasic and biphasic QPS.
• Tested QPS variability in 35 healthy subjects, measuring motor evoked potentials (MEPs) for up to one hour.

Main Results:

• QPS with a 5s IBI induced plasticity dependent on interstimulus interval.
• QPS with a 2.5s IBI failed to induce plasticity, despite the same pulse count.
• QPS with a 7.5s IBI yielded variable but comparable results to conventional QPS.
• Monophasic QPS showed longer-lasting after-effects than biphasic QPS.
• Over 80% of subjects responded consistently to excitatory QPS with a 5s IBI.

Conclusions:

• IBI, procedure duration, and pulse waveform significantly influence QPS-induced plasticity.
• A majority of subjects (80%) responded predictably to excitatory QPS with a 5s IBI.