[Abstract Title]. - Society for Neuroscience

Topic: D.16.d. Kinematics and Muscle Activity
Support: NIH grant R37-AG006457
the Swedish Brain Foundation
Title: Hand haptic touch modifies postural hip tone
Authors: *E. FRANZEN 1,2 , V. S. GURFINKEL 1 , W. G. WRIGHT 3 , P. J. CORDO 1 , F. B.
HORAK 1 ;
1 Neurolog. Sci. Inst., Oregon Hlth. & Sci. Univ., Portland, OR; 2 Karolinska Instituet, Stockholm,
Sweden; 3 PT Dept., Temple Univ., Philadelphia, PA
Abstract: Axial muscle tone provides a stable reference frame for the execution of limb
movements and stabilizes the torso during gait and stance. It has been proposed that tonic muscle
activity for stance posture is supported, if not generated, by the resting discharge of sensory
afferents from over the entire body. Earlier studies have shown that manual contact with a
surface, perceived to be fixed in space, increases postural stability, even though light haptic
touch results in a purely sensory interaction between the body and the floor (Lackner, et al,1999).
This enhanced stability from hand haptic input may be a result from alterations in postural tone.
To investigate why the body is stabilized by light touch we explored the influence of heavy and
light haptic touch on postural tone in 14 healthy adults (20-55 and 85 yrs of age). We measured
hip torsional torque and the position of the center of pressure under the feet of subjects standing
on a slowly rotating force plate (Gurfinkel et al, 2006). This unique device twisted the hips by
virtue of rotating the feet with the pelvis fixed to a solid external frame and was not giving
information concerning the reference. Normal sway was not restricted by the pelvis fixation so
the subjects remained in a state of active postural control during the three tested stability
conditions: 1) quiet standing with the arms at the sides, 2) firmly gripping a rigid bar, or 3)
lightly touching a rigid bar. The subjects stood quietly with eyes closed as a platform rotated for
±10 deg at 1deg/s. As expected, the RMS of the center of pressure decreased during gripping and
touching the bar (p