Planning of Ballistic Movement following Stroke: Insights from the Startle Reflex

Abstract

Following stroke, reaching movements are slow, segmented, and variable. It is unclear if these deficits result from a poorly constructed movement plan or an inability to voluntarily execute an appropriate plan. The acoustic startle reflex provides a means to initiate a motor plan involuntarily. In the presence of a movement plan, startling acoustic stimulus triggers non-voluntary early execution of planned movement, a phenomenon known as the startReact response. In unimpaired individuals, the startReact response is identical to a voluntarily initiated movement, except that it is elicited 30–40 ms. As the startReact response is thought to be mediated by brainstem pathways, we hypothesized that the startReact response is intact in stroke subjects. If startReact is intact, it may be possible to elicit more task-appropriate patterns of muscle activation than can be elicited voluntarily. We found that startReact responses were intact following stroke. Responses were initiated as rapidly as those in unimpaired subjects, and with muscle coordination patterns resembling those seen during unimpaired volitional movements. Results were striking for elbow flexion movements, which demonstrated no significant differences between the startReact responses elicited in our stroke and unimpaired subject groups. The results during planned extension movements were less straightforward for stroke subjects, since the startReact response exhibited task inappropriate activity in the flexors. This inappropriate activity diminished over time. This adaptation suggests that the inappropriate activity was transient in nature and not related to the underlying movement plan. We hypothesize that the task-inappropriate flexor activity during extension results from an inability to suppress the classic startle reflex, which primarily influences flexor muscles and adapts rapidly with successive stimuli. These results indicate that stroke subjects are capable of planning ballistic elbow movements, and that when these planned movements are involuntarily executed they can be as rapid and appropriate as those in unimpaired individuals.

A startling acoustic stimulus facilitates voluntary lower extremity movements and automatic postural responses in people with chronic stroke

“…This observation is different from the complete normalization of ankle dorsiflexion reaction times in HSP patients [25], and of paretic hand extension [14] and elbow flexion and extension movements [13] in people with stroke. It must be mentioned, though, that the SAS-induced acceleration was highly variable across stroke participants (as can be seen in Fig.…”

Cortical involvement in the StartReact effect

“…In line with the conclusions of previous authors, it is possible that both systems are involved in the rapid triggering of prepared movements in response to a SAS (Marinovic et al, 2014, Nonnekes et al, 2014) and further research is necessary to determine the specific pathways involved in the StartReact effect. This knowledge may have important ramifications as use of a SAS is becoming more popular as a methodology used to investigate various aspects of movement control in special populations such as Parkinson’s disease (Carlsen et al, 2013, Fernandez-Del-Olmo et al, 2013) and stroke patients (Honeycutt and Perreault, 2012), with conclusions drawn about whether specific neural circuitry is intact or damaged.…”

A broadband acoustic stimulus is more likely than a pure tone to elicit a startle reflex and prepared movements

“…2007; Maslovat et al. 2009, 2014; Carlsen and Mackinnon 2010; Honeycutt and Perreault 2012; Drummond et al. 2013).…”

“…), that RTs in trials where SCM activity is detected are different than those where no SCM is detected (Carlsen et al. 2007; Honeycutt and Perreault 2012; Honeycutt et al. 2013; Tresch et al.…”

“…2007) in both healthy controls and various motor disordered populations, such as patients with Parkinson’s disease (Carlsen et al. 2013) and stroke (Honeycutt and Perreault 2012). …”