Neurophysiological modulations in the (pre)motor-motor network underlying age-related increases in reaction time and the role of GABA levels – a bimodal TMS-MRS study
Stefanie Verstraelen,
Koen Cuypers,
Celine Maes,
Melina Hehl,
Shanti Van Malderen,
Oron Levin,
Mark Mikkelsen,
Raf L.J. Meesen,
Stephan P. Swinnen
Affiliations
Stefanie Verstraelen
Neuroplasticity and Movement Control Research Group, Rehabilitation Research Institute (REVAL), Hasselt University, 3590 Diepenbeek, Belgium
Koen Cuypers
Neuroplasticity and Movement Control Research Group, Rehabilitation Research Institute (REVAL), Hasselt University, 3590 Diepenbeek, Belgium; Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium; Corresponding author.
Celine Maes
Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium; KU Leuven Brain Institute (LBI), Leuven, Belgium
Melina Hehl
Neuroplasticity and Movement Control Research Group, Rehabilitation Research Institute (REVAL), Hasselt University, 3590 Diepenbeek, Belgium; Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium
Shanti Van Malderen
Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium
Oron Levin
Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium
Mark Mikkelsen
Russel H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States
Raf L.J. Meesen
Neuroplasticity and Movement Control Research Group, Rehabilitation Research Institute (REVAL), Hasselt University, 3590 Diepenbeek, Belgium; Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium
Stephan P. Swinnen
Movement Control & Neuroplasticity Research Group, Department of Movement Sciences, Group Biomedical Sciences, KU Leuven, 3001 Heverlee, Belgium; KU Leuven Brain Institute (LBI), Leuven, Belgium
It has been argued that age-related changes in the neurochemical and neurophysiological properties of the GABAergic system may underlie increases in reaction time (RT) in older adults. However, the role of GABA levels within the sensorimotor cortices (SMC) in mediating interhemispheric interactions (IHi) during the processing stage of a fast motor response, as well as how both properties explain interindividual differences in RT, are not yet fully understood.In this study, edited magnetic resonance spectroscopy (MRS) was combined with dual-site transcranial magnetic stimulation (dsTMS) for probing GABA+ levels in bilateral SMC and task-related neurophysiological modulations in corticospinal excitability (CSE), and primary motor cortex (M1)-M1 and dorsal premotor cortex (PMd)-M1 IHi, respectively. Both CSE and IHi were assessed during the preparatory and premotor period of a delayed choice RT task. Data were collected from 25 young (aged 18–33 years) and 28 older (aged 60–74 years) healthy adults.Our results demonstrated that older as compared to younger adults exhibited a reduced bilateral CSE suppression, as well as a reduced magnitude of long latency M1-M1 and PMd-M1 disinhibition during the preparatory period, irrespective of the direction of the IHi. Importantly, in older adults, the GABA+ levels in bilateral SMC partially accounted for task-related neurophysiological modulations as well as individual differences in RT. In contrast, in young adults, neither task-related neurophysiological modulations, nor individual differences in RT were associated with SMC GABA+ levels.In conclusion, this study contributes to a comprehensive initial understanding of how age-related differences in neurochemical properties and neurophysiological processes are related to increases in RT.
