Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Neurosciences, Neuroimaging, Radiology, Nuclear Medicine & Medical Imaging, Neurosciences & Neurology, Aging, Interhemispheric interaction, GABA, choice reaction time, MRS, TMS, TRANSCRANIAL MAGNETIC STIMULATION, PRIMARY MOTOR CORTEX, INTERHEMISPHERIC INHIBITION, OLDER-ADULTS, CORTICOSPINAL EXCITABILITY, INTRACORTICAL INHIBITION, DORSAL PREMOTOR, FUNCTIONAL CONNECTIVITY, COGNITIVE NEUROSCIENCE, INDIVIDUAL-DIFFERENCES, Adolescent, Adult, Aged, Evoked Potentials, Motor, Female, Functional Laterality, Humans, Magnetic Resonance Spectroscopy, Male, Middle Aged, Motor Cortex, Neural Inhibition, Reaction Time, Sensorimotor Cortex, Transcranial Magnetic Stimulation, Young Adult, gamma-Aminobutyric Acid, Interhemispheric Interaction, 11F6921N|11F6923N#55783277, C16/15/070#53326576, G089818N#54517617, I005018N#54777490, 11 Medical and Health Sciences, 17 Psychology and Cognitive Sciences, Neurology & Neurosurgery, 32 Biomedical and clinical sciences, 42 Health sciences

Abstract:

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.