Movement preparation and cortical processing of afferent inputs in cortical tremor: An event-related (de)synchronization (ERD/ERS) study

ObjectiveWe sought to characterize cortical activity related to motor control in patients presenting with isolated cortical tremor, in order to determine whether or not myoclonus-related impairments are a source of event-related desynchronization/synchronization (ERD/ERS) disruption.MethodsNine patients presenting with isolated cortical tremor were compared with controls. Mu and beta ERD/ERS were computed over the scalp and brain surfaces using 128-channel electroencephalographic (EEG) recording during voluntary and passive finger extensions. We recorded somatosensory-evoked potentials following median nerve stimulation and performed myoclonic jerk-locked back-averaging of EEG activity.ResultsBack-averaging revealed a cortical premyoclonic spike in all patients. Five of the nine patients had exaggerated SEPs. The amplitude of mu ERD was greater in patients. Beta ERD/ERS did not differ from that seen in controls. Localizations of mu and beta ERD/ERS did not differ from controls and were identified in pre- and post-central sensorimotor cortical areas.ConclusionsThe present results suggest a hyperexcitability of the cortico-subcortical loops responsible for movement preparation and execution. Post-movement inhibition related to cortical processing of afferent input is unaffected in isolated cortical myoclonus.SignificanceIntracortical abnormalities can differ in patients suffering from cortical myoclonus, according to whether or not the individuals have associated epileptic symptoms.

► We show that patients suffering from isolated cortical tremor present a greater mu event-related desynchronization (ERD) compared to controls, while beta event-related desynchronization/synchronization (ERD/ERS) is unchanged.
► This reveals increased neuronal recruitment during motor preparation resulting from abnormal excitability of thalamo-cortical loops.
► Intracortical abnormalities in isolated cortical tremor are different and less severe than with patients suffering from cortical myoclonus associated to epileptic symptoms.