Highlights
- •Both clonic and tonic responses can be elicited from the primary motor cortex.
- •Type I clonic responses (<20 Hz stimulation) consist of simple EMG bursts.
- •Type II clonic responses (≥20 Hz stimulation) consist of complex EMG bursts.
- •Increasing the intensity and/or frequency of stimulation generates tonic responses.
- •These motor responses, including GTC seizures, induced by cortical stimulation rely on corticospinal tract.
Abstract
Objective
To study the neurophysiology of motor responses elicited by electrical stimulation
of the primary motor cortex.
Methods
We studied motor responses in four patients undergoing invasive epilepsy monitoring
and functional cortical mapping via electrical cortical stimulation using surface
EMG electrodes. In addition, polygraphic analysis of intracranial EEG and EMG during
bilateral tonic-clonic seizures, induced by cortical stimulation, was performed in
two patients.
Results
(a) Electrical cortical stimulation: The motor responses were classified as clonic, jittery, and tonic. The clonic responses
were characterized by synchronous EMG bursts of agonist and antagonistic muscles,
alternating with silent periods. At stimulation frequencies of <20 Hz, EMG bursts
were of ≤50 ms duration (Type I clonic). At stimulation frequencies of 20–50 Hz, EMG
bursts were of >50 ms duration and had a complex morphology (Type II clonic). Increasing
the current intensity at a constant frequency converted clonic responses into jittery
and tonic contractions.
(b) Bilateral tonic-clonic seizures: The intracranial EEG showed continuous fast spiking activity during the tonic phase
along with interference pattern on surface EMG. The clonic phase was characterized
by a polyspike-and-slow wave pattern. The polyspikes were time-locked with the synchronous
EMG bursts of agonists and antagonists and the slow waves were time-locked with silent
periods.
Interpretation
These results suggest that epileptic activity involving the primary motor cortex can
produce a continuum of motor responses ranging from type I clonic, type II clonic,
and tonic responses to bilateral tonic-clonic seizures. This continuum is related
to the frequency and intensity of the epileptiform discharges with tonic seizures
representing the highest end of the spectrum.
Keywords
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Article info
Publication history
Published online: March 24, 2023
Accepted:
March 14,
2023
Received in revised form:
March 13,
2023
Received:
January 30,
2023
Identification
Copyright
© 2023 Elsevier Inc. All rights reserved.
