THE EFFECTS OF AGING ON COGNITIVE MOTOR CONTROL

Abstract

Introduction: Processing speed, working memory capacity, inhibitory function, and long-term memory are all aspects of information processing that become less efficient with age. Unsurprisingly, brain size, density, and proficiency regarding complex motor behavior deteriorate with the introduction of neurological disorders illness, injury, and even healthy aging. What remains unexplained is why declines in the understanding and execution of tool-related actions similar to clinical populations have been seen in the healthy aging population. However, some older individuals maintain the ability to plan and execute complex, goal-oriented movements, referred to as praxis. Whether praxis deficits are a product of neuroanatomical alterations or arise from changes in the functional properties of regions and networks normally recruited for processing tasks is currently unknown. We do know that older adults engage in scaffolding, overactivation of expected brain regions or the additional activation of regions not typically recruited by younger adults in the same task. More specifically, hemispheric asymmetry reduction is a type of scaffolding seen in the older brain (HAROLD). HAROLD activation is described as a reduced activity in the initial region and increased activation in the same area of the opposite hemisphere - reminiscent of a mirror-image. Shifts from using posterior brain regions to anterior regions (PASA) are also patterns seen in healthy older adults. Whether or not these activation patterns are helpful or harmful in compensating for the inevitable changes with healthy aging is unclear. Hypotheses: We hypothesized that the older group (OG) would show increased bilateral activity compared to the younger group (YG) in response to the ideal tool (C1) and plausible tool (C2) conditions. This was expected to be true for each region of interest (ROI): frontal, premotor, and parietal. This bilateral activation is expected to apply to the expected shift from recruiting posterior brain regions to an anterior focus expected for C1 and C2 in OG compared to YG. We also expected to see differences between the groups' ERP amplitudes and latencies indicative of greater task difficulty for OG compared to YG. Purpose: This study aimed to better understand the cortical dynamics that support the ability of some healthy older individuals to evaluate common tools in different situations by comparing the neural responses to younger adults. A better understanding of the neurophysiological differences between these two healthy populations in successful tool-use and evaluation could be helpful in creating more personalized and effective rehabilitation programs for clinical populations as well as otherwise healthy older adults presenting with performance deficits. Methods: This study included twenty-one younger and twelve older right-handed participants between the ages of 18-35 and 60-84 years-old, respectively. Participants were presented with high resolution black and white images of ideal and plausible tool use and asked to identify them based on a preceding action description. Participants indicated their choice by pressing a corresponding button on a response pad. Using a 64-channel electroencephalography cap, the neural responses of these individuals to the stimuli were recorded. The results reported here include two latency windows (0-250ms and 350-550ms post stimulus onset) over bilateral frontal, premotor, and parietal regions of interest (ROIs) for the C1 and C2. Variance was reduced using the Bootstrap resampling method and age-based comparisons of brain activation were made with non-parametric permutation-based statistics, p < 0.05. To account for false positives due to multiple comparisons, the false discovery rate was calculated and a corrected p-value (q = .0143) was used to determine statistical significance. Results: Overall, YG and OG had different approaches for evaluating ideal and plausible tools while error rate was essentially the same for both groups. C1 produced differences in the earlier processing stages in the left frontal, left premotor, and right parietal ROIs. In the same latency window, C2 produced differences in the same ROIs. During the later processing stages, C1 produced significant differences in all ROIs. C2 produced fewer differences in the same time window: the right frontal, both premotor, and right parietal ROIs. Discussion: The differences between these two populations in C1 and C2 confirmed that healthy older adults employ bilateral and anterior activation patterns seen in the literature. Because OG had similar performance to YG, these activation patterns seem to be compensating for the increased difficulty and inefficiency of praxis related areas that accompany old age. The differences in frontal, premotor, and parietal regions found here could be useful in creating more personalized and effective rehabilitation programs for clinical populations as well as the growing population of otherwise healthy older adults.