Time to Move Again: Does the Bereitschaftspotential Covary with Demands on Internal Timing?

Abstract

When Bereitschaftspotentials (BPs) are measured, participants are required to voluntarily perform a predefined number of identical movements, with varying intervals between movements, exceeding some obligatory minimum interval. Participants might cope with these demands on timing by installing a slow, broadly tuned rhythm of activation, serving as an internal trigger for executing movements in time. The BP might reflect the rising phase of this activation, culminating at the movement. If so (i) not only should BP amplitudes become larger, but BPs should also have their onsets earlier before movements when longer minimum intervals are required between movements (Experiment 1). Further, (ii) BP amplitudes should covary with demands on internal timing: decrease when internal timing is less necessary and increase in the other case. Variation of timing demands was realized by requiring participants to count vs. not to count the seconds between movements (Experiment 1) and by regular vs. irregular vs. no ticking of a clock (Experiment 2). Prediction (i) was confirmed while prediction (ii) was not. Thus, BP onsets did vary in accordance with the temporal constraints about when the movements should be performed, suggesting some relation to timing mechanisms, but we could not provide evidence for the notion that the process reflected by BPs is this timing mechanism.

The independency of the Bereitschaftspotential from previous stimulus‐locked P3 in visuomotor response tasks

“…According to the proposed model, the iFg modulates excitatory influence of the pre‐SMA on the STN, and enhances the inhibitory output from the STN to M1. In addition, the BP amplitude observed in our study in the short‐ISI condition is comparable with the one observed in Verleger, Haake, et al (), wherein the minimum movement time was 1 s. In a speculative interpretation of these comparable amplitudes, the existence of a critical BP threshold during externally triggered response tasks might be proposed. This interpretation would also fit with the earlier onset of prestimulus components.…”

“…Under the assumption that in the long-ISI condition no overlap should occur between the P3 relative to the preceding stimulus (s-1 P3) and the preparatory ERPs for successive trials (s), we hypothesize that the long-ISI condition should result in a substantially unaltered BP in the last 500 ms preceding stimulus onset. In addition, in agreement with the notion that BP onset is modulated by intermovement interval in self-paced movements (e.g., Verleger, Haake, Baur, & Śmigasiewicz, 2016), we expect an earlier BP onset in the long-ISI with respect to short-ISI condition.…”

“…The comparable BP amplitude between short-and long-ISI is apparently not corroborated by previous findings that reported enhanced BP amplitude for longer time intervals of repetition in the context of self-paced movements (Verleger, Haake, et al, 2016). However, a proper comparison between self-paced and externally triggered tasks is not trivial: first, in externally triggered tasks, the interval between stimulus onset and response emission presents many positive components (P1, pP1, P2, pP2, P3) that mask the NS' (or late BP) and the MP.…”

“…This interpretation would also fit with the earlier onset of prestimulus components. Indeed, as observed in self‐paced movements (Verleger, Haake, et al, ), the increase of the ISI produces an earlier onset of the BP. According to the brake/accelerator interpretation, response preparation and response inhibition must occur concomitantly in order to obtain appropriate behaviors.…”

“…Indeed, both the pN and the BP show spatiotemporal features and topography as in the previous literature (Berchicci et al, ; Bianco, Berchicci, Perri, Quinzi, et al, ; Bianco, Russo, Perri, et al, ; Di Russo et al, ; Perri et al, ; Quinzi et al, ; Shibasaki & Hallett, ). In addition, the selection of two different baselines is supported by a previous study comparing different intertrial intervals during self‐paced movements (Verleger, Haake, et al, ). Last, to rule out any possible bias due to baseline selection, for both short‐ and long‐ISI, the baseline has been also calculated on the same interval over the entire epoch of a large EEG segmentation (−3,500/4,000).…”