Considerable effects of lateralization and aging in intracortical excitation and inhibition

Zhongfei Bai; Feifei Zhu; Xiaoyu Lou; Jack Jiaqi Zhang; Minxia Jin; Wenting Qin; Chaozheng Tang; Jie Li; Jiani Lu; Jianhua Lin; Lingjing Jin; Qi Qi; Kenneth N K Fong

doi:10.3389/fnins.2023.1269474

Considerable effects of lateralization and aging in intracortical excitation and inhibition

Front Neurosci. 2023 Nov 16:17:1269474. doi: 10.3389/fnins.2023.1269474. eCollection 2023.

Authors

Affiliations

¹ Department of Rehabilitation, Shanghai YangZhi Rehabilitation Hospital (Shanghai Sunshine Rehabilitation Centre), School of Medicine, Tongji University, Shanghai, China.
² Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China.
³ Capacity Building and Continuing Education Center, National Health Commission of the People's Republic of China, Beijing, China.
⁴ School of Electronic and Information Engineering, Tongji University, Shanghai, China.

Abstract

Introduction: Findings based on the use of transcranial magnetic stimulation and electromyography (TMS-EMG) to determine the effects of motor lateralization and aging on intracortical excitation and inhibition in the primary motor cortex (M1) are inconsistent in the literature. TMS and electroencephalography (TMS-EEG) measures the excitability of excitatory and inhibitory circuits in the brain cortex without contamination from the spine and muscles. This study aimed to investigate the effects of motor lateralization (dominant and non-dominant hemispheres) and aging (young and older) and their interaction effects on intracortical excitation and inhibition within the M1 in healthy adults, measured using TMS-EMG and TMS-EEG.

Methods: This study included 21 young (mean age = 28.1 ± 3.2 years) and 21 older healthy adults (mean age = 62.8 ± 4.2 years). A battery of TMS-EMG measurements and single-pulse TMS-EEG were recorded for the bilateral M1.

Results: Two-way repeated-measures analysis of variance was used to investigate lateralization and aging and the lateralization-by-aging interaction effect on neurophysiological outcomes. The non-dominant M1 presented a longer cortical silent period and larger amplitudes of P60, N100, and P180. Corticospinal excitability in older participants was significantly reduced, as supported by a larger resting motor threshold and lower motor-evoked potential amplitudes. N100 amplitudes were significantly reduced in older participants, and the N100 and P180 latencies were significantly later than those in young participants. There was no significant lateralization-by-aging interaction effect in any outcome.

Conclusion: Lateralization and aging have independent and significant effects on intracortical excitation and inhibition in healthy adults. The functional decline of excitatory and inhibitory circuits in the M1 is associated with aging.

Keywords: TMS-EEG; aging; intracortical inhibition; lateralization; motor-evoked potentials.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by the General Research Fund (GRF) (Grant No. 15105919M) to KF, Shanghai Sailing Program, Shanghai, China (No. 20YF1445100) to ZB, Shanghai Sailing Program, Shanghai, China (No. 22YF1443200) to MJ, Clinical Research Program of Shanghai Municipal Health Commission Clinical Research Program (No. 20224Y0220) to ZB, Science and Technology Innovation Program of Shanghai Municipal Science and Technology (Nos. 22Y31900200 and 22Y31900203) to LJ, and Special Project of Clinical Research in Health Industry of Shanghai Municipal Health Commission (20214Y0287) to WQ.