Preparation and Control of Movement

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Many of our actions are triggered by changes in the environment and most of these actions can be prepared in advance of the anticipated change. When skillful human action is observed in these reactive situations one may be oblivious to the fine synchronization that is required between movement preparation, initiation and execution and yet each is vital to the effective control of action. Success and failure of these processes can be seen in many situations in everyday life, from the Olympic sprinter who prepares for a fast start out of the blocks in elegant smooth pursuit of their goal, to the Parkinson's disease patient who fails to initiate a seemingly simple step over a roadside curb and freezes despite what appears to be maximum cognitive effort. This proposal will examine how people prepare, initiate and control their actions in various environmental contexts using a variety of methodologies. One method we have used to good effect in the past is to probe the processes of movement preparation by delivering a startling stimulus along with the "go" command. This brief loud sound causes a startle reflex but also appears to trigger and release any voluntary movement that is planned, stored and ready to initiate. Indeed when we consider the two examples mentioned earlier it has been shown that very fast reaction times of the sprinter (less than 100 milliseconds) may be the result of a startle like trigger and not a false start. We have also shown that startle can trigger prepared movements quite smoothly and effortlessly in patients with Parkinson's disease. Because we have an understanding of the pathways responsible for the startle reflex, it then becomes possible to map movement preparation and initiation as it interacts with this reflex. This proposal is designed to continue our research efforts into the investigation of motor preparation and initiation using techniques such as startle. The first series of experiments will investigate how a group of muscles are prepared to produce fast, accurate and smooth movements. Although we easily and effectively interact with our environment by moving our limbs to targets in space, the programming and control of muscle synergies across a single joint is still not clearly understood. Recently we suggested that agonist/antagonist coordinated activity may be controlled by both cortical and subcortical brain structures. Here we propose to investigate whether the cerebellum is involved in modulating the amplitudes and/or timing of such coordinated actions as a simple triphasic (agonist-antagonist-agonist) muscle burst of activity. A second series of experiments explores response preparation for complex movements. Most of our previous studies used startle to probe movement preparation with simple, single component movements of either wrist or elbow extension. However, the process of preparing, timing and sequencing of multi-component movements requires high levels of coordination, which will also be studied using a startling stimulus. Our third series of experiments will examine the processes involved when a startling sound triggers a prepared response. Specifically we will examine experimental protocols that can differentiate between the various explanations that have been put forward to account for this triggering of intended responses known as the StartReact effect. Finally we will investigate the experimental indicators of startle. Many studies conducted in our lab have successfully used a loud acoustic stimulus to examine the process of response preparation under a variety of circumstances. However, we are constantly evaluating our experimental methodology to ensure our results are valid and reproducible.