Tag: Marjorie Woollacott

Inaccurate Grip Predictions for Congenital Amputees’ Absent Hand: Evidence of Sensory-dependent Construction of Accurate Internal Models for Motor Planning

Presenter: Samantha Ross

Mentor: Marjorie Woollacott

AM Poster Presentation

Poster 41

To what extent does accurate internal model construction, for motor planning, depend on sensory experience? A previous study showed preserved accuracy of models for traumatic amputees’ absent hand (Philip & Frey, 2011). We investigated whether accurate internal models depend on initial limb presence. Five congenital upper limb amputees and matched controls performed two grip selection tasks: overt grip selection (OGS), where participants explicitly grasped a presented stimulus with their intact hand; and prospective grip selection (PGS), where judgments were made for either hand while remaining stationary. Predictive accuracy was calculated by comparing PGS directly to OGS for intact hand, and to the inversed OGS for absent hand. Amputees did not signifi- cantly differ in overall accuracy from controls [F(1,4)=4.49, p=0.10], or between hands [F(1,4)=0.13, p=0.74]. However, a significant accuracy-orientation pattern for amputees’ absent hand, [F(1,4)=7.908, p=0.048] was found. This suggests amputee’s directly use their intact hand for decisions about absent hand, supporting sensory-dependent construction of internal hand models for motor planning.

Vestibular Modulation of the abductor hallucis and abductor digiti minimi Muscles in Response to Changes in Head Position and Visual Cues

Presenter: Jonathan Wallace

Faculty Mentor: Brain Dalton, Marjorie Woollacott

Presentation Type: Oral

Primary Research Area: Science

Major: Human Physiology

Maintaining standing balance involves processing of vestibular, visual, and somatosensory information to produce dynamic motor responses. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and if the medium-latency responses are altered by changes in head position and visual cues. Indwelling electromyography (EMG) of the abductor hallucis (AH) and abductor digiti minimi (ADM) were sampled while bilateral electrical vestibular stimulation (EVS) was administered to quietly standing participants. Vestibular stimulation delivered on the mastoid processes is interpreted as a true head acceleration which creates a medium- latency vestibular-evoked balance response. A cumulant density function (i.e. cross-correlation) was used to analyze EVS input and the muscle activity (output). When the head was positioned 90◦ to the left with the eyes closed, the medium-latency response amplitude was -0.122 ± 0.027 in the AH and 0.130 ± 0.048 in the ADM. Visual cues reduced the medium-latency amplitude by 14 and 23% in the AH and ADM, respectively (p < 0.05). When the head was oriented 90◦ to the right, the medium-latency response was opposite for the AH (0.101 ± 0.042) and ADM (0.065 ± 0.026, p < 0.05). The inversion and reduction of the medium-latency response with changes to head position and visual input indicate that the vestibular system is modulating activity in the ADM and AH. These results may suggest that the ADM and AH muscles are important contributors to standing balance control.