Ageing effects on stimulus-induced motor preparation processes : an event-related potential study

Abstract

Sensorimotor processing begins from stimulus onset to movement onset and contains separate but partially overlapping stages, including stimulus perception, response selection, and motor response generation. Different factors may modulate different stages of sensorimotor processing. The current study aimed to explore the changes in stimulus-induced motor preparation and execution associated with aging and how different factors, such as laterality and complexity of sequence finger movements, modulate these age-related changes on movement preparation. We hypothesized that aging would affect performance on finger-tapping tasks in the late response selection stage and that the motor response generation stage and factors, such as sequence length and complexity, would affect motor preparation processing. We studied a total of 41 right-handed volunteers [20 younger subjects aged (mean ± SD) 24.1 ± 3.6 years and 21 older subjects aged 63.4 ± 3.1 years]. Both block-based choice-reaction and simple-reaction tasks were used in this study. Reaction time (RT), accuracy rate (ACC), and electroencephalography (EEG) were recorded during task performance. The behavioral results of the CRT tasks showed an overall slowness in RT in the older groups compared with the younger groups (p<0.001), and the accuracy rate was higher in the younger than the older groups (p<0.001). The ACC for older group decreased with increasing task complexity, and RT was prolonged with increased sequence complexity. The prolongation of N1 latency in the older group may suggest a delay in visual stimulus processing stage (p=0.004). The amplitude of the P3 component was more positive in the younger group and the P3 peak amplitude differed due to different cueing types (p<0.001). In younger group, the P3 amplitude for left-handinitiated sequence presented a more negative waveform than that of the right-handinitiated sequence (p=0.036). The amplitude of s-LRP was influenced by sequence complexity (p=0.005) and response by hand (p=0.001). The peak amplitude was higher in the older group in the right-hand-initiated sequences and the r-LRP latency was longer for the older group. The larger P3 amplitude for older group indicated that more attention resources need increased with aging. The P3 component is related to attention and memory-related operations; thus, the delayed P3 latency in the older group may not contribute to behavioral slowness in RT because no age-related delay in onset latency of s-LRP was found (p>0.050). The s-LRP results suggested that would influence less on the association of the shape-and-arrow configurations with the specific finger tapping sequence, as well as the response selection processes. The age-related difference in the onset latency of r-LRP suggests that aging may have had an effect on the motor response generation stage. For the right-handinitiated tapping sequence, extra-neural activity from the contralateral motor cortex was required for movement execution in older subjects. The prolonged onset latency of r-LRP on the left-hand-initiated tapping sequence of older group demonstrated that the contralateral brain cortex was recruited more for non-dominant hand side movement in the older group when movement planning and execution processes were needed for a given task. The longer r-LRP raising time for right-hand-initiated movements represented a stronger facilitation for left hand movement that originated from the right hemisphere. The delayed latency and reduced amplitude of r-LRP with aging may indicate a top-down regulation and functional facilitation. The results of the r-LRP also suggested decreased inter-hemispheric differences due to increased inhibitory control from the contralateral hemisphere.