Oscillatory cortical drive to isometrically contracting muscle in Unverricht-Lundborg type progressive myoclonus epilepsy (ULD).
OBJECTIVE
We investigated with whole-scalp magnetoencephalography (MEG) oscillatory cortical drive to isometrically contracting muscle in 8 genetically verified, and thus etiologically homogeneous, Unverricht-Lundborg type progressive myoclonus epilepsy (ULD) patients suffering from cortical myoclonus and generalized tonic-clonic seizures. The results were compared with those of 8 healthy control subjects.


METHODS
Cortical MEG signals were measured simultaneously with surface electromyography (EMG) during isometric contraction of the left and right first dorsal interosseus muscles. Cortex-muscle coherence and cross-correlograms between MEG and EMG signals were calculated as indicators of oscillatory cortical drive to muscle. The cortical areas involved in the maximum cortex-muscle coherence were also identified.


RESULTS
In patients, the strengths of the dominant coherent peaks were 2-4 fold compared with the healthy controls. Whereas the coherence was found strictly in the contralateral primary motor cortex in controls, additional coherent activity was observed ipsilaterally in 5 out of 8 patients.


CONCLUSIONS
The remarkably increased MEG-EMG coherence in ULD patients suggests altered oscillatory cortical drive to the muscle during isometric contraction. We suggest that the enhanced cortex-muscle coherence in ULD patients reflects reduced inhibition in the motor cortex, and may contribute to disturbed voluntary movements.
Silén
Teija
T
Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, P.O. Box 2200, FIN-02015 HUT, Espoo, Finland. tsilen@neuro.hut.fi
Forss
N
N
Salenius
S
S
Karjalainen
T
T
Hari
R
R
D000293:Adolescent; D000328:Adult; D001683:Biological Clocks / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D016018:Least-Squares Analysis; D015225:Magnetoencephalography / Q000379:methods; D008297:Male; D020194:Unverricht-Lundborg Syndrome / Q000503:physiopathology*