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Electromagnetic function of polymicrogyric cortex in congenital bilateral perisylvian syndrome

¹ Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland
² Hospital for Children and Adolescents, Department of Child Neurology, University of Helsinki, Finland
³ Department of Radiology, Helsinki University Central Hospital, University of Helsinki, Finland
⁴ Department of Clinical Genetics, Oulu University Hospital, Oulu, Finland

Correspondence to:
Correspondence to:
Dr R Paetau
Epilepsia-pkl, PO Box 280, FIN-00029 HUS, Finland; ritva.paetau{at}hus.fi

Background: Congenital bilateral perisylvian syndrome (CBPS) is characterised by bilateral perisylvian polymicrogyria and suprabulbar paresis. Mild tetraparesis, cognitive impairment, and epilepsy are frequently associated. Sensory deficits are surprisingly rare, even though polymicrogyria often extends to auditory and sensorimotor cortex.

Objectives: To study the sensorimotor and auditory cortex function and location in CBPS patients.

Methods: We mapped the sensory and motor cortex function onto brain magnetic resonance images in six CBPS patients and seven control subjects using sources of somatosensory and auditory evoked magnetic fields, and of rhythmic magnetoencephalographic (MEG) activity phase-locked to surface electromyogram (EMG) during voluntary hand muscle contraction.

Results: MEG-EMG coherence in CBPS patients varied from normal (if normal central sulcus anatomy) to absent, and could occur at abnormally low frequency. Coherent MEG activity was generated at the central sulcus or in the polymicrogyric frontoparietal cortex. Somatosensory and auditory evoked responses were preserved and also originated within the polymicrogyric cortex, but the locations of some source components could be grossly shifted.

Conclusion: Plastic changes of sensory and motor cortex location suggest disturbed cortex organisation in CBPS patients. Because the polymicrogyric cortex of CBPS patients may embed normal functions in unexpected locations, functional mapping should be considered before brain surgery.

Abbreviations: CBPS, congenital bilateral perisylvian syndrome; ECD, equivalent current dipoles; EMG, electromyogram; HPI, head position indicator; MEG, magnetoencephalography; MRI, magnetic resonance imaging; PMG, polymicrogyria; PPC, posterior parietal cortex; SEF, somatosensory evoked fields; S/N, signal-to-noise; SI cortex, primary somatosensory cortex; SII cortex, second somatosensory cortex