title: Relationship between excitability, plasticity and thickness of the motor cortex in older adults.
abstract: The relationship between brain structure, cortical physiology, and learning ability in older adults is of particular interest in understanding mechanisms of age-related cognitive decline. Only a few studies addressed this issue so far, yielding mixed results. Here, we used comprehensive multiple regression analyses to investigate associations between brain structure on the one hand, i.e., cortical thickness (CT), fractional anisotropy (FA) of the pyramidal tract and individual coil-to-cortex distance, and cortical physiology on the other hand, i.e. motor cortex excitability and long-term potentiation (LTP)-like cortical plasticity, in healthy older adults (mean age 64 years, 14 women). Additional exploratory analyses assessed correlations between cortical physiology and learning ability in the verbal domain. In the regression models, we found that cortical excitability could be best predicted by CT of the hand knob of the primary motor cortex (CT-M1HAND) and individual coil-to-cortex distance, while LTP-like cortical plasticity was predicted by CT-M1HAND and FA of the pyramidal tract. Exploratory analyses revealed a significant inverse correlation between cortical excitability and learning ability. In conclusion, higher cortical excitability was associated with lower CT and lower learning ability in a cohort of healthy older adults, in line with previous reports of increased cortical excitability in patients with cortical atrophy and cognitive deficits due to Alzheimer's Disease. Cortical excitability may thus be a parameter to identify individuals at risk for cognitive decline and gray matter atrophy, a hypothesis to be explored in future longitudinal studies.
authors.affiliation: Department of Neurology, Charité - University Hospital, Berlin, Germany; Center for Stroke Research Berlin, Charité - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: List
authors.forename: Jan C
authors.initials: JC
authors.lastname: Kübke
authors.forename: Robert
authors.initials: R
authors.lastname: Lindenberg
authors.forename: Nadine
authors.initials: N
authors.lastname: Külzow
authors.forename: Lucia
authors.initials: L
authors.lastname: Kerti
authors.forename: Veronica
authors.initials: V
authors.lastname: Witte
authors.forename: Agnes
authors.initials: A
authors.lastname: Flöel
mesh_terms: D000368:Aged; D056324:Diffusion Tensor Imaging; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D007858:Learning / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000033:anatomy & histology* / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation
keywords: AD; APB; AVLT; Alzheimer's Dementia; CCD; CT; Cortical thickness; DTI; Diffusion tensor imaging; FA; FLAIR; GABA; GLM; LTP; M1; MEP; MRI; N-methyl-d-aspartate; NMDA; PAS; PT; Paired associative stimulation; ROI; Resting motor threshold; TE; TMS; TMT; TR; Transcranial magnetic stimulation; VD; WMH; abductor pollicis brevis muscle; auditory verbal learning test; coil-to-cortex distance; cortical thickness; diffusion tensor imaging; echo time; fluid attenuation inversion recovery; fractional anisotropy; gamma amino butyric acid; general linear model; long term potentiation; magnetic resonance imaging; motor evoked potential; paired associative stimulation; primary motor cortex; pyramidal tract; rMT; region of interest; repetition time; resting motor threshold; trail making test; transcranial magnetic stimulation; vascular dementia; white matter hyperintensities