Investigation of age-related changes in responsiveness of mirror neuron systems using fMRI

Abstract

Observational learning, or the ability to learn a new skill by watching that same skill being performed by others, is one of the fundamental principles of motor learning. It is believed to be driven by a neural network known as the mirror neuron system (MNS), a group of brain regions that show a specialized response to both the observation and performance of motor activities. The MNS is traditionally thought to involve the inferior parietal lobule (IPL), ventral premotor cortex (vPMC), and inferior frontal gyrus (IFG), which are located in brain regions known to atrophy with age. It is not yet known if the responsiveness of the MNS declines or otherwise changes as a result of atrophy caused by natural aging. The current study used functional magnetic resonance imaging (fMRI) to observe the MNS in three increasing age groups with the purpose of determining whether there are any observable differences in MNS activity at different stages of aging. Methods: Thirty-two participants, in three age groups (Group 1 = 18-40 years, Group 2 = 41-60 years, Group 3 = 61-80 years), were given an observational learning task while undergoing fMRI. fMRI data were analysed using general linear models (GLMs) on an individual and group level. Groups were compared using a two-way repeated measures ANOVA and a cluster threshold estimation with 1000 permutations to determine minimum cluster size to avoid false positives. A cluster threshold of 300 was set to find areas representing the greatest differences in signal change between groups. Results: Group 2 showed significantly higher activation (percent signal change) than groups 1 and 3 in the IFG, precuneus, and insula, as well as lower activity in the putamen. Group 2 showed higher signal change than Group 1 in the IPL. Group 3 was higher than group 1 in the vPMC and postcentral gyrus. Discussion: The MNS does not appear to be immune to effects of aging. The changes in IPL and IGF with age, in combination with the observation of more widespread and bilateral brain regions suggest that older participants not only work the motor circuits harder, but also recruit more cognitive brain regions in order to complete the tasks at the same level of efficiency. Capitalizing on these cognitive compensatory networks may be beneficial in improving on video therapy techniques in the future.