Age-related changes in oscillatory power affect motor action

With increasing age cognitive performance slows down. This includes cognitive processes essential for motor performance. Additionally, performance of motor tasks becomes less accurate. The objective of the present study was to identify general neural correlates underlying age-related behavioral slowing and the reduction in motor task accuracy. To this end, we continuously recorded EEG activity from 18 younger and 24 older right-handed healthy participants while they were performing a simple finger tapping task. We analyzed the EEG records with respect to local changes in amplitude (power spectrum) as well as phase locking between the two age groups. We found differences between younger and older subjects in the amplitude of post-movement synchronization in the beta band of the sensory- motor and medial prefrontal cortex (mPFC). This post-movement beta amplitude was significantly reduced in older subjects. Moreover, it positively correlated with the accuracy with which subjects performed the motor task at the electrode FCz, which detects activity of the mPFC and the supplementary motor area. In contrast, we found no correlation between the accurate timing of local neural activity, i. e. phase locking in the delta-theta frequency band, with the reaction and movement time or the accuracy with which the motor task was performed. Our results show that only post-movement beta amplitude and not delta-theta phase locking is involved in the control of movement accuracy. The decreased post-movement beta amplitude in the mPFC of older subjects hints at an impaired deactivation of this area, which may affect the cognitive control of stimulus-induced motor tasks and thereby motor output

Age-related changes in oscillatory power affect motor action - Fig 3

<p>Phase-locking index in older subjects at all 61 electrodes in the visually-cued tapping condition with the left (A) or right index finger (B). At electrodes where the PLIs were not significantly larger than those of the corresponding baselines, the panels were left blank (dark blue) as in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187911#pone.0187911.ref009" target="_blank">9</a>]. In all panels, the horizontal axis is the time axis in the interval [-1400, 1400] ms, and the vertical axis is the frequency axis in the band 2–9 Hz. The onset of the movement, as determined by the accelerometer, is at time t = 0. The color bar at the bottom right indicates the value of the PLI in the individual panels.</p

Illustration of our hypothesis that the older subjects may show a decreased δ-θ phase locking index (H1) or β amplitude (H2) since the variability of the motor performance increases with age.

<p>In the upper panel, the dots represent the phase distribution in the δ-θ frequency band across trials in both younger (YS, blue) and older (OS, red) participants. In the lower panels, amplitude changes in the β frequency band (ERD and ERS) are displayed as they may appear in younger (YS, blue) and older (OS, red) subjects.</p

Age-related changes in oscillatory power affect motor action - Fig 5

<p>Amplitude (power spectrum) at all 61 electrodes in the visually-cued right-hand tapping condition in younger (A) and older subjects (B). In all panels, the horizontal axis is the time in the interval [-1400, 1400] ms, and the vertical axis is frequency in the range 2–48 Hz. The onset of the movement, as determined by the accelerometer, is at t = 0. The color bar at the bottom right indicates the value of the amplitude (power) at a given frequency in the individual panels.</p

Correlation between the time-averaged post-movement β amplitude and the accuracy rate (averaged over all index finger tappings) in the visually-cued tapping condition in older subjects.

<p>The horizontal axis in each panel is the β amplitude averaged in the time interval [500, 1250] ms, and the vertical axis is the accuracy rate.</p

Age-related changes in oscillatory power affect motor action - Fig 2

<p>(A) Movement time in the visually-cued and the self-initiated tapping condition for younger (YS, blue) and older (OS, red) participants. (B) Reaction time and (C) accuracy rate (averaged over all index finger tappings) in the visually-cued tapping condition of younger (YS, blue) and older (OS, red) subjects. Stars above the bars denote a statistically significant (p < 0.05) between-group difference.</p