Alterations in oculomotor behavior in healthy aging and mild cognitive impairment

Abstract

Age-related changes in saccade behavior on short timescales (a few seconds) is often ascribed to changes in sensorimotor processing, working memory, or executive functioning. Visual exploration is additionally guided, at long timescales (minutes to hours), by memory representations supported by the hippocampal and broader medial temporal lobe system. Here, we examined whether age-related and neurodegenerative changes to the memory system impact more immediate saccade behavior by comparing the performance of younger adults (YA), healthy older adults (HOA), and older adults diagnosed with amnestic mild cognitive impairment (aMCI). 27 YA (18-35 years), 34 HOA (60-86 years) and 9 aMCI (46-84 years) performed a set of saccade tasks that systematically manipulated memory demands and the complexity of saccadic behaviour. A subset of tasks involved single saccades directed to a target 1) immediately (visually-guided task), 2) after a variable delay 500-1500 ms (gap), and 3) to a remembered location after a variable delay 300-3000 ms (memory-guided task). In another set of memory-guided tasks, participants directed saccades to two remembered targets in sequential and reverse order after a variable delay (double-step forward and backward). Using a multivariate partial least squares analysis, HOA and MCI groups were shown to have longer initial saccade latencies than YA in all but the visually-guided task. HOA and MCI initial saccade latencies did not differ significantly. Second saccade latencies in the double-step forward task were shorter for HOA than YA but longer for MCI as compared to the other two groups. Spatial errors did not differ across groups, suggesting that the differences in latencies were not due to differences in speed-accuracy tradeoffs across groups. Our results confirm previous findings of the impact of age-related changes in sensorimotor processing on saccade behavior. Our findings suggest that functional changes in the medial temporal lobe may affect oculomotor guidance on short timescales.