title: The aging motor system as a model for plastic changes of GABA-mediated intracortical inhibition and their behavioral relevance.
abstract: Since GABAA-mediated intracortical inhibition has been shown to underlie plastic changes throughout the lifespan from development to aging, here, the aging motor system was used as a model to analyze the interdependence of plastic alterations within the inhibitory motorcortical network and level of behavioral performance. Double-pulse transcranial magnetic stimulation (dpTMS) was used to examine inhibition by means of short-interval intracortical inhibition (SICI) of the contralateral primary motor cortex in a sample of 64 healthy right-handed human subjects covering a wide range of the adult lifespan (age range 20-88 years, mean 47.6 ± 20.7, 34 female). SICI was evaluated during resting state and in an event-related condition during movement preparation in a visually triggered simple reaction time task. In a subgroup (N = 23), manual motor performance was tested with tasks of graded dexterous demand. Weak resting-state inhibition was associated with an overall lower manual motor performance. Better event-related modulation of inhibition correlated with better performance in more demanding tasks, in which fast alternating activation of cortical representations are necessary. Declining resting-state inhibition was associated with weakened event-related modulation of inhibition. Therefore, reduced resting-state inhibition might lead to a subsequent loss of modulatory capacity, possibly reflecting malfunctioning precision in GABAAergic neurotransmission; the consequence is an inevitable decline in motor function.
authors.affiliation: Brain Imaging and NeuroStimulation Laboratory, Department of Neurology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Kirstin-F
authors.initials: KF
authors.lastname: Heise
authors.forename: Maximo
authors.initials: M
authors.lastname: Zimerman
authors.forename: Julia
authors.initials: J
authors.lastname: Hoppe
authors.forename: Christian
authors.initials: C
authors.lastname: Gerloff
authors.forename: Karl
authors.initials: K
authors.lastname: Wegscheider
authors.forename: Friedhelm C
authors.initials: FC
authors.lastname: Hummel
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006225:Hand / Q000294:innervation; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012146:Rest; D012737:Sex Factors; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult