Motor mapping by transcranial magnetic stimulation reveals persistent ipsilateral corticospinal connections in the epileptic hemisphere in patients with intractable focal epilepsy.
Abstract number :
1.063
Submission category :
3. Neurophysiology
Year :
2015
Submission ID :
2327722
Source :
www.aesnet.org
Presentation date :
12/5/2015 12:00:00 AM
Published date :
Nov 13, 2015, 12:43 PM
Authors :
Harper L. Kaye, Roman Gersner, Alexander Rotenberg
Rationale: While corticospinal connections are overwhelmingly contralateral in children after the toddler years, ipsilateral corticospinal connections, particularly for the foot, are still identified in older children and adults. To test whether such preserved ipsilateral corticospinal connectivity occurs with bias toward either the affected or unaffected hemisphere in focal epilepsy we reviewed the anatomical findings for the tibialis anterior (TA) representation in patients with intractable focal epilepsy without gross motor cortex abnormality, who underwent motor mapping by navigated transcranial magnetic stimulation (nTMS) as part of epilepsy surgery evaluation.Methods: All patients (n=22) underwent nTMS with a figure-of-eight coil. Stimuli were applied at scalp sites overlying the superior motor cortex bilaterally, while motor evoked potentials (MEPs) were recorded by surface electromyography of the left and right TA muscle. Inclusion criteria for analysis of laterality of preserved ipsilateral TA representation were: (1) focal, unilateral seizures, (2) preserved ipsilateral TA representation in only one hemisphere, (3) absence of MRI lesion in the region of the motor cortex or corticospinal tract.Results: 11 of 22 patients with focal, unilateral, seizures had ipsilateral TA motor representation in at least one hemisphere, and 7 patients had ipsilateral TA representation in only one hemisphere. 1 of 7 patients with unihemispheric ipsilateral TA representation had bilateral periventricular white matter and cortical injury – the remainder (N=6) had no apparent motor cortex injury on MRI. 6 of 6, 100% of patients with unilateral ipsilateral TA representation and MRI-intact motor anatomy had the preserved ipsilateral corticospinal signal in the epileptic hemisphere.Conclusions: In the patients with a unilateral seizure focus, our nTMS findings suggest a pathologically-preserved immature motor lateralization, perhaps due to sustained abnormal electrical activity that maintains ipsilateral motor representation.
Neurophysiology