Investigating differences in reaction time and preparatory activation as a result of varying accuracy requirements


The neural accumulation model of movement preparation involves an increase of neural activation in M1 from baseline to a subthreshold level following a warning signal, which is maintained until presentation of an imperative stimulus (IS). Activity then increases until reaching movement initiation threshold. This model predicts that variability in activation during preparation may influence reaction time (RT) and its variability. To test this prediction, transcranial magnetic stimulation (TMS) was used to determine neural excitability for movements with different accuracy demands. It was hypothesized that higher accuracy demands would result in lowered amplitude and/or greater variability of neural activation, and consequently slower / more variable RT. Fifteen healthy participants completed a simple RT task involving a targeted wrist extension movement under three different accuracy conditions (easy, moderate, difficult). TMS was delivered concurrently with the IS on 50% of trials during each condition. While pilot testing showed RT differences between accuracy conditions, the current data failed to detect significant differences in RT latency (F(2, 28) = .352, p = .706) or variability (F(2, 28) = .633, p = .538) between conditions . Similarly, no differences in TMS measures were observed between conditions (F(2, 28) = 2.088, p = .143). However, a subset of participants (n = 7) that did show significant RT increases between easy and hard conditions still failed to show differences in MEP amplitude (p = .29) or variability (p = .17), suggesting that preparatory levels are similar for movements involving higher accuracy demands.

Acknowledgments: Acknowledgments: Supported by NSERC and the Ontario Ministry of Research and Innovation and Science