Biology subjects

Tresilian, J. R.

Publications and source records attributed to Tresilian, J. R..

3 recordsLinked to original sources

bioRxiv2020

Responses to Loud Acoustic Stimuli: Short and Long Timescale Effects on Cortical and Sub-Cortical Preparation Reflect Conditional Probability.

The presentation of Loud Acoustic Stimuli (LAS) during preparation can trigger motor actions at very short latencies in a phenomenon called the StartReact effect. It was initially proposed that a special, separate sub-cortical mechanism which by-passes slower cortical processes could be involved. We sought to examine the evidence for a separate mechanism against the alternative that responses to LAS can be explained by a combination of stimulus intensity effects and preparatory-states - as proposed by activation models of motor control. To investigate whether cortically mediated preparatory processes are involved in shaping reactions to LAS, we used an auditory reaction task where we manipulated preparation-level within each trial. We contrasted responses to non-intense tones and LAS and examined whether cortical activation, sub-cortical excitability (measured by pre-stimulus EEG and eye-blink startle reflexes, respectively) and the motor response were influenced by preparation-level. As predicted by the activation model, increases in preparation-level were marked by gradual reductions in RT coupled with increases in cortical activation and sub-cortical excitability - at both condition- and trial-levels. Changes in cortical activation influenced motor and auditory but not visual areas - highlighting the wide-spread yet selective nature of preparation. RTs were shorter to LAS than tones, but the overall pattern of preparation-level effects were the same for both stimuli. These results demonstrate that LAS responses are indeed shaped by cortically mediated preparatory processes. The concurrent changes observed in brain and behaviour with increasing preparation reinforces the notion that preparation is marked by evolving brain states which shape the motor response. Key PointsO_LIReactions to Loud Acoustic Stimuli can be explained by stimulus intensity and preparation state C_LIO_LIWe manipulated movement preparation by altering the temporal position of the imperative stimulus C_LIO_LIPreparation was marked by reductions in RT, and increased cortical and sub-cortical excitability C_LIO_LIPreparation had the same effect on reactions to Loud Acoustic Stimuli and non-intense tones C_LIO_LIThe results highlight the widespread, evolving, and strategic nature of movement preparation C_LI

neuroscience↗

bioRxiv2020

Preparatory Suppression and Facilitation of Voluntary and Involuntary Responses to Loud Acoustic Stimuli in an Anticipatory Timing Task.

In this study, we sought to characterise the effects of intense sensory stimulation at different stages of preparation for an anticipated action on voluntary and involuntary behaviours. In our experiment, we presented unexpected loud acoustic stimuli (LAS) at four critical times during movement preparation to probe the state of the nervous system (Baseline, -1192 ms, -392 ms, and 0 ms relative to expected movement onset), and measured their effect on voluntary and involuntary motor actions (finger-press and eye-blink startle reflex, respectively). Voluntary responses were largely facilitated by the LAS, leading to earlier and more forceful responses compared to Control and Baseline conditions. Notably, voluntary responses were significantly facilitated on trials where the LAS was presented early during preparation (-1192 ms). Eye-blink reflexes elicited by the LAS at -392 ms were significantly reduced and delayed compared to other time-points, indicating suppression of sub-cortical excitability. Despite being in a suppressive state, voluntary responses on these trials were still facilitated by the LAS. The results provide insight into the mechanisms involved in preparing anticipatory actions. Induced activation can persist in the nervous system and can modulate subsequent actions for a longer time period than previously thought, highlighting that movement preparation is a continuously evolving process that is susceptible to external influence throughout the preparation period. Suppression of sub-cortical excitability shortly before movement onset is consistent with previous work showing corticospinal suppression which may be a necessary step before the execution of any voluntary response.

neuroscience↗

bioRxiv2020

Cumulative distribution functions: An alternative approach to examine the triggering of prepared motor actions in the StartReact effect

There has been much debate concerning whether startling sensory stimuli can activate a fast-neural pathway for movement triggering (StartReact) which is different from that of voluntary movements. Activity in sternocleidomastoid (SCM) electromyogram is suggested to indicate activation of this pathway. We evaluated whether SCM activity can accurately identify trials which may differ in their neurophysiological triggering and assessed the use of cumulative distribution functions (CDFs) of reaction time (RT) data to identify trials with the shortest RTs for analysis. Using recent datasets from the StartReact literature, we examined the relationship between RT and SCM activity. We categorised data into short/longer RT bins using CDFs and used linear mixed effects models to compare potential conclusions that can be drawn when categorising data on the basis of RT versus on the basis of SCM activity. The capacity of SCM to predict RT is task-specific, making it an unreliable indicator of distinct neurophysiological mechanisms. Classification of trials using CDFs is capable of capturing potential task- or muscle-related differences in triggering whilst avoiding the pitfalls of the traditional SCM activity based classification method. We conclude that SCM activity is not always evident on trials that show the early triggering of movements seen in the StartReact phenomenon. We further propose that a more comprehensive analysis of data may be achieved through the inclusion of CDF analyses. These findings have implications for future research investigating movement triggering as well as for potential therapeutic applications of StartReact.

neuroscience↗