The cortical N1 response to balance perturbation is associated with balance and cognitive function in different ways between older adults with and without Parkinson’s disease

Abstract

Mechanisms underlying associations between balance and cognitive impairments in older adults with and without Parkinson's disease (PD) are poorly understood. Balance disturbances evoke a cortical N1 response that is associated with both balance and cognitive abilities in unimpaired populations. We hypothesized that the N1 response reflects a neural mechanism that is shared between balance and cognitive function, and would therefore be associated with both balance and cognitive impairments in PD. Although N1 responses did not differ at the group level they showed distinct associations with balance and cognitive function in the PD vs. control (noPD) groups. In noPD, higher N1 amplitudes were correlated with lower cognitive set shifting ability and lower balance confidence. However, in PD, higher N1 amplitudes were correlated with lower overall cognitive function, while earlier and narrower N1 peaks were correlated with more severe PD and balance impairments. Our results show that balance and cognitive impairments are dissociable and associated with distinct features of the N1 response, suggesting that the N1 response reflects coordination of distinct mechanisms for balance and cognitive function. Identifying coordinated but dissociable mechanisms underlying balance and cognitive processes may reveal potential targets for rehabilitation of comorbid balance and cognitive impairments.

The balance N1 and the ERN correlate in amplitude across individuals in small samples of younger and older adults

“…While the large effect size provides promising preliminary support of our hypothesis, it will be necessary to confirm these findings in a larger sample. The ERN was not the primary focus of these studies (Payne et al, 2022; Payne et al, 2021; Payne & Ting, 2020a; Payne & Ting, 2020c), and was always collected at the end of the session, after the physically active balance task. Although acute exercise does not necessarily influence the ERN (Themanson & Hillman, 2006), it is possible that the fixed task order had some effect.…”

“…Although acute exercise does not necessarily influence the ERN (Themanson & Hillman, 2006), it is possible that the fixed task order had some effect. Using the same perturbation series across populations would have enabled more comparisons, but the older adults received much easier perturbations as a control population being compared against Parkinson’s disease in another study (Payne et al, 2022). Although the excellent internal consistency reliability of the balance N1 suggests that a reliable estimate could be obtained using fewer trials, the possibility for habituation across initial trials should be carefully considered, especially where differences in habituation could present an additional source of individual differences (Payne et al, 2019a).…”

“…While the balance N1 is also smaller in older adults (Duckrow et al, 1999), a similar comparison in the present data would be confounded by the smaller perturbation magnitudes in the older group. Although the same balance perturbations could have been used between the young and older adult groups, these studies were originally designed to address different experimental questions related to the balance N1 potential (Payne et al, 2022; Payne et al, 2021; Payne & Ting, 2020a; Payne & Ting, 2020c).…”

“…Importantly, balance errors are experimentally controllable, allowing the exact same series of errors to be repeated across individuals (Adkin et al, 2006; Welch & Ting, 2014). The balance N1 can be evoked in nearly anyone able to stand without an assistive device, from toddlers (Berger, Horstmann, & Dietz, 1990; Berger, Quintern, & Dietz, 1987) through the elderly (Duckrow, Abu-Hasaballah, Whipple, & Wolfson, 1999; Payne, McKay, & Ting, 2022; Payne, Palmer, McKay, & Ting, 2021). We previously suggested the balance N1 and ERN may arise from overlapping neural processes based on their similar dependencies on motivation, perceived consequences, perceptual salience, expectation, development, and aging (Payne, Ting, & Hajcak, 2019b).…”