Behavioural exposure and sleep do not modify corticospinal and intracortical excitability in the human motor system.
OBJECTIVE
Behavioural exposure and sleep may bidirectionally modify the excitability of cortical networks including those in the motor cortex. Here we tested whether the excitability of intracortical inhibitory and excitatory networks within the primary motor cortex exhibited changes suggestive of a time of day influence.


METHODS
Short-interval intracortical inhibition (SICI) and facilitation (ICF), and input-output curves (IO curves) were investigated using transcranial magnetic stimulation (TMS). Recordings were made from the resting right first dorsal interosseous (FDI) muscle in 10 healthy subjects on three occasions: 9A.M. and 4P.M. of the same day, and 9A.M. of the following day.


RESULTS
There was no significant change in any of the measures across the three assessments.


CONCLUSIONS
These findings provide evidence that time of day does not significantly influence corticospinal and intracortical excitability in the primary motor cortex.


CONCLUSIONS
These results provide no support for the hypothesis that synapses within the motor cortex undergo potentiation due to daytime use and behavioural experiences. Additionally, these findings provide evidence that measurement of motor cortical excitability is not systematically biased by time-of-day dependent variability and thus does not pose a confound in studies assessing corticospinal excitability longitudinally.
Doeltgen
Sebastian H
SH
The Robinson Institute, School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, Australia. sebastian.doeltgen@adelaide.edu.au
Ridding
Michael C
MC
D000328:Adult; D001519:Behavior / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D004777:Environment; D004780:Environment, Controlled; D019054:Evoked Potentials, Motor / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D053444:Inhibitory Postsynaptic Potentials / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement / Q000502:physiology; D009415:Nerve Net / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D012890:Sleep / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult