Modulation of the Startle Response During Human Gait

Abstract

While many studies have shown that there is a phase-dependent modulation of proprioceptive and exteroceptive reflexes during gait, little is known about such modulation for auditory reflexes. To examine how startle reactions are incorporated in an ongoing gait pattern, unexpected auditory stimuli were presented to eight healthy subjects in six phases of the step cycle during walking on a treadmill at 4 km/h. For both legs, electromyographic activity (EMG) was recorded in the biceps femoris (BF), the rectus femoris (RF), the tibialis anterior (TA), and the soleus (SO). In addition, stance and swing phases of both legs, along with knee angles of both legs and the left ankle angle, were measured. All subjects showed various response peaks. Responses with latencies of approximately 60 ms (F1), approximately 85 ms (F2), and approximately 145 ms (F3) were found. The amplitude of the reflex responses was dependent on the timing of the startle stimulus in the step cycle. Although the startle response habituated rapidly, the phase-dependent modulation pattern generally remained the same. The phase-dependent amplitude modulations were not strictly correlated with the modulation of the background activity. The TA even showed a transition from facilitatory F2 responses during stance to suppressive responses during midswing. Responses were observed in both flexors and extensors, often in coactivation, especially during stance. Furthermore the gait characteristics showed a shortening of the subsequent step cycle and a small decrease in the range of motion of ankle and knees. These results suggest that the responses are adapted to achieve extra stability dependent on the phase of the step cycle. However, even in the first trials, the changes in kinematics were small allowing a smooth progression of gait.

The Differential Role of Motor Cortex in Stretch Reflex Modulation Induced by Changes in Environmental Mechanics and Verbal Instruction

“…In contrast, TMS resulted in an average shortening of the long-latency onset of 16±30 ms in Experiment 1, with a maximum of 39.6 ms. The increased variability in long-latency onset for Experiments 1 and 2 is consistent with an auditory startle (Nieuwenhuijzen et al, 2000). The reduced variability in Experiment 3 further suggests that the auditory click was not triggering the subjects’ reactions in this final experiment.…”

Speeding up gait initiation and gait-pattern with a startling stimulus

“…In contrast, startle does not have direct access to these spinal centres and this may explain why the basic gait-pattern is little affected. Nieuwenhuijzen et al [26] reported that startle was well integrated during gait, with only discrete kinematic changes that did not modify its course. In the same line, the results of Schepens and Delwaide [18] indicated that the step cycle was not modified when an unexpected loud sound was applied.…”

Cervicolumbar Coordination in Mammalian Quadrupedal Locomotion: Role of Spinal Thoracic Circuitry and Limb Sensory Inputs

“…A possible explanation for this unexpected, albeit consistent, alteration in the relative timing of lumbar flexor and extensor motor bursts in response to cervical afferent pathway activation was that it resulted from the unilateral mode of DR stimulation. Because peripheral sensory inputs from the left and right limb pairs are activated in phase opposition during actual stepping (Nieuwenhuijzen et al, 2000;Pearson, 2000), an additional series of experiments was conducted in which low-threshold DR afferents to both sides of the lumbar or cervical cord were stimulated alternately to more accurately reproduce the bilateral patterning of proprioceptive information input that occurs in vivo. However, in close correspondence with the effects of solitary DR activation (Fig, 5 B, C), a strictly antiphase relationship or an overall tendency toward coincident bursting continued to be expressed by homolateral flexor L2 and extensor L5 ventral roots in activity patterns elicited by alternating electrical stimulation of left and right L2 ( Fig.…”