[Abstract Title]. - Society for Neuroscience

eccentric gaze position. The facilitation of contralateral (agonist) muscles increased for
progressively more contralateral gaze positions (even though the evoked gaze shift was smaller).
In contrast, the suppression of ipsilateral (antagonist) muscles increased for progressively more
ipsilateral gaze positions. Our interpretation of these results is that the cephalomotor command
following FEF stimulation summates with baseline levels of neck EMG activity associated with
different initial gaze positions. Importantly, these evoked patterns of recruitment differ
substantially from those associated with head movements during volitional gaze shifts. These
results suggest that the neural mechanisms that vary eye-head coordination across initial gaze
position are overridden by FEF stimulation (as with SC stimulation), and that observed changes
in eye-head coordination following stimulation results from a straightforward combination of
biomechanical factors with an invariant stimulation-evoked response.
Disclosures: B.B. Chapman , None; J.K. Elsley, None; B.D. Corneil, None.
Poster
263. Eye Movements: Eye and Head Control
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 263.9/DD9
Topic: D.06.c. Eye and head control
Support: CIHR
Title: Neck muscle activation during gaze fixations in the monkey: 3-D postural fields and
relationship to 3-D behavioral constraints
Authors: *F. FARSHADMANESH 1,2 , G. P. KEITH 2,3 , X. YAN 2 , H. WANG 2 , B. D.
CORNEIL 4 , J. D. CRAWFORD 1,2,3 ;
1 Dept Biol., 2 Ctr. for Vision Res., 3 Psychology, York Univ., Toronto, ON, Canada; 4 Physiology,
Pharmacol. and Psychology, Univ. of Western Ontario, London, ON, Canada
Abstract: The head-neck motor system has more muscles than are theoretically required to
specify a particular orientation and velocity. Although some neck muscles are reported to have a
preferred direction (PD) of activation, because of inherent redundancy in the system, and
interaction between muscles, relating the activation for each neck muscle to a given head
movement is difficult. Moreover, the role of neck muscle mechanics in the implementation of
three-dimensional (3-D) postural constraints (i.e., Donders‟ law of the head and the Fick
strategy) are not known. Most previous studies on this topic have been performed in cats or
humans, and generally used various stabilization and/or load-imposing tasks. The current study
investigates the simultaneous activation of several neck muscles in relation to 3-D head posture