A comparison of GABA-ergic (propofol) and non-GABA-ergic (dexmedetomidine) sedation on visual and motor cortical oscillations, using magnetoencephalography.

BackgroundUnderstanding the effects of anaesthetic drugs on cortical oscillations can help to elucidate the mechanistic link between receptor physiology and their clinical effects. Propofol produces divergent effects on visual cortical activity: increasing induced gamma-band responses (GBR) while decreasing stimulus-onset-evoked responses) 1. Dexmedetomidine, an 2-adrenergic agonist, differs from GABA-ergic sedatives both mechanistically and clinically as it allows easy arousability from deeper sedation with less cognitive side-effects. Here we use magnetoencephalography (MEG) to characterize and compare the effects of GABAergic (propofol) and non-GABA-ergic (dexmedetomidine) sedation, on visual and motor cortical oscillations. MethodsSixteen male participants received target-controlled infusions of propofol and dexmedetomidine, producing mild-sedation, in a placebo-controlled, cross-over study. MEG data was collected during a combined visual and motor task. ResultsThe key findings were that propofol significantly enhanced visual stimulus induced GBR (44% increase in amplitude) while dexmedetomidine decreased it (40%). Propofol also decreased the amplitudes of the M100 (27%) and M150 (52%) evoked responses, whilst dexmedetomidine had no effect on these. During the motor task, neither drug had any significant effect on motor GBR or movement related beta de-synchronisation (MRBD). However, dexmedetomidine increased (92%) post-movement beta synchronisation/rebound (PMBR) power while propofol reduced it (70%). ConclusionsDexmedetomidine and propofol, at equi-sedative doses, have contrasting effects on visual stimulus induced GBR, visual evoked responses and PMBR. These findings provide a mechanistic link between the known receptor physiology of these sedative drugs and their known clinical effects and may be used to explore mechanisms of other anaesthetic drugs on human consciousness.