Cortical involvement in the StartReact effect

Abstract

The rapid release of prepared movements by a loud acoustic stimulus capable of eliciting a startle response has been termed the StartReact effect (Valls-Solé et al., 1999), and premotor reaction times (PMTs) of <70 ms are often observed. Two explanations have been given for these short latency responses. The subcortical storage and triggering hypothesis suggests movements that can be prepared in advance of a “go” signal are stored and triggered from subcortical areas by a startling acoustic stimulus (SAS) without cortical involvement. Alternatively, it has been hypothesized that the SAS can trigger movements from cortical areas through a faster pathway ascending from subcortical structures. Two experiments were designed to examine the possible role of primary motor cortex in the StartReact effect. In Experiment 1, we used suprathreshold transcranial magnetic stimulation (TMS) during the reaction time (RT) interval to induce a cortical silent period in the contralateral primary motor cortex (M1). Thirteen participants performed 20° wrist extension movements as fast as possible in response to either a control stimulus (82dB) or SAS (124 dB). PMTs for startle trials were faster than control trials, while TMS significantly delayed movement onset compared to No TMS or Sham TMS conditions. In Experiment 2, we examined the StartReact effect in a highly cortically represented action involving speech of a consonant-vowel (CV) syllable. Similar to previous work examining limb movements, a robust StartReact effect was found. Collectively, these experiments provide evidence for cortical (M1) involvement in the StartReact effect.

Pitch planning in English and Taiwanese Mandarin: Evidence from startle-elicited responses

“…Together with the findings in Stevenson et al (2014), the observations we have made here reveal a good deal of similarity between speech plans and other SASinduced (e.g., upper limb) movements. In SAS-induced speech, overall trajectories for a prepared response are generally maintained, whether relating to vowel formants, pitch, or lip movements.…”

“…Except as described here, apparatus and procedures for the present experiment were exactly as described for experiment 2 in Stevenson et al (2014).…”

“…In English syllables thus triggered, lip kinematics and vowel F1 and F2 are unaffected by the presentation of a SAS, indicating that these parameters are encoded in the speech plan and are not dependent on afferent feedback. However, results for parameters relating to pitch control, such as pitch level and contour, are not reported by Stevenson et al (2014). This leaves an important gap, as previous research shows that vowel formants may not be bound by a fixed relationship with pitch during vowel production (Li enard and Di Benedetto, 1999;Traunm€ uller and Eriksson, 2000), suggesting that these parameters may be dissociated in speech plans.…”

“…When elicited by a SAS, a previously prepared upper limb movement (e.g., flexion or extension) can be released at a short latency (muscle pre-motor reaction time <70 ms) while the kinematics and accuracy of the movement remain largely unaffected; this latency has been claimed to be too short to allow somatosensory feedback correction in arm movements (Carlsen et al, 2012). Stevenson et al (2014) extend the SAS experimental paradigm to speech production, showing that prepared English CV syllables elicited by SAS are initiated at shortened latencies, with lower-lip movements for [ba] initiated earlier in SAS-elicited responses (Mean ¼ 75 ms) than in control responses (Mean ¼ 116 ms). In English syllables thus triggered, lip kinematics and vowel F1 and F2 are unaffected by the presentation of a SAS, indicating that these parameters are encoded in the speech plan and are not dependent on afferent feedback.…”

Startling speech: eliciting prepared speech using startling auditory stimulus

“…However, recent transcranial magnetic stimulation (TMS) studies show that the StartReact effect may not be limited to subcortically stored programs, but can also be observed in cortically dependent processes (Alibiglou and MacKinnon, 2012; Stevenson et al, 2014). These studies found that, when a cortical silent period was induced by applying TMS to motor cortex, the StartReact response was delayed in startle trials.…”