Article

Human gait involves a repetitive leg motor pattern that emerges after gait
initiation. While the automatic maintenance of the gait-pattern may be under the
control of subcortical motor centres, gait initiation requires the voluntary
launching of a different motor program. In this study, we sought to examine how
the two motor programmes respond to an experimental manipulation of the timing of
gait initiation. Subjects were instructed to start walking as soon as possible at
the perception of an imperative signal (IS) that, in some interspersed trials was
accompanied by a startling auditory stimulus (SAS). This method is known to
shorten the latency for execution of the motor task under preparation. We
reasoned that, if the two motor programmes were launched together, the
gait-pattern sequence would respond to SAS in the same way as gait initiation. We
recorded the gait phases and the electromyographic (EMG) activity of four muscles
from the leg that initiates gait. In trials with SAS, latency of all gait
initiation-related events showed a significant shortening and the bursts of EMG
activity had higher amplitude and shorter duration than in trials without SAS.
The events related to gait-pattern were also advanced but otherwise unchanged.
The fact that all the effects of SAS were limited to gait initiation suggests
that startle selectively can affect the neural structures involved in gait
initiation. Additionally, the proportional advancement of the gait-pattern
sequence to the end of gait initiation supports the view that gait initiation may
actually trigger the inputs necessary for generating the gait-pattern sequence.
CI - Copyright 2009 Elsevier B.V. All rights reserved.

Langue : ANGLAIS