Age related interhemispheric differences in time preparation

Abstract

Introduction This study investigates age related interhemispheric differences in time preparation. Imaging studies indicate differences in cortical activation subserving the generation of voluntary movement in elderly and young subjects. Particularly, elderly showed more bilateral distribution of activity and increased activation (Heuninckx et al., 2005 & 2007). However, few is known about differences in task preparation patterns between elderly and young. Therefore we hypothesize that elderly will use different cortical activation patterns in preparation for a choice reaction time (CRT) task compared to young subjects. Methods Twenty-seven right-handed healthy volunteers participated in this study i.e. 14 young adults (21 - 27yr), and 13 elderly (61 - 75yr). Subjects were instructed to perform a CRT task by moving either the left or right index finger in relation to a illuminating LED (GO-signal). TMS (110% RMT) was given at 0.5, 0.4, 0.3, 0.2, 0.1 and 0s before the GO-signal on the hotspot of the FDI (both hemispheres alternately). MEP amplitudes of the contralateral FDI were measured using EMG. Results A 2x2x5 ANOVA (GROUP x HEMI x TIME) revealed a GROUP x HEMI interaction (p < .05) indicating a different pattern in cortical activation between young adults and elderly. Whereas elderly show similar patterns in both hemispheres, young adults showed only a resembling pattern for the dominant hemisphere but not for the non-dominant hemisphere. In comparison to the dominant hemisphere which was inhibited preceding the GO-signal, the non-dominant hemisphere seems to be inhibited later. Additionally, there was a main effect of TIME (p < .05) indicating an overall increasing cortical inhibition towards the emergence of the GO-signal. Conclusion Elderly use different cortical activation patterns in preparation of a CRT-task, compared to young subjects. Different inhibition patterns showed a more general asymmetry between the two hemispheres in young subjects in terms of response planning. Inhibition may play a prominent role in preventing responses prior to the imperative signal.