[Abstract Title]. - Society for Neuroscience

Authors: *G. P. KEITH 1 , J. F. X. DESOUZA 2 , X. YAN 4 , H. WANG 4 , J. D. CRAWFORD 3 ;
1 Dept Psychol, 2 Psychology, 3 Psychology, Biol. and Kinesiology, York Univ., Toronto, ON,
Canada; 4 Ctr. for Vision Res., Toronto, ON, Canada
Abstract: We developed a method for determining the intrinsic reference frame of neuronal
activity associated with head-unrestrained gaze shifts. The use of head-unrestrained animals
allows for more natural behavior and distinguishing between head and space/body frames.
However, it also necessitates the measurement of three-dimensional gaze and head orientations,
which are torsionally noisy and enter the range of motion where non-linear effects become
significant. To develop our method we used a data set (see accompanying abstract) where
monkeys made head-unrestrained gaze shifts from a central home target to a variety of secondary
targets throughout the general receptive field of units recorded in the superior colliculus. Rather
than training the animal to dissociate eye, head, and body, we allowed the animal to dissociate
these through the natural variability of its behavior. We developed our technique and explored its
limitations using simulations of other possible conditions. Real and simulated unit activity were
plotted as a function of both target location and gaze saccade metrics in eye, head, and
body/space frames using mathematically correct 3-D transformations that accounted for
variabilities in torsional as well as horizontal and vertical initial and final eye and head position.
Simulations of known but noisy receptive fields in various frames showed that a neuron‟s
intrinsic reference frame was identifiable by the greater coherence of that neuron's activity for
trials plotted in this frame. The statistical determination of this coherence was made using the
PRESS statistic of nonparametric regression (used since position values were continuous rather
than discrete), which measured the predictability of the fit relative to the data. If the reference
frame showing the best fit was significantly better than that made in the other reference frames,
then it was identified as the candidate for that neuron's intrinsic reference frame. Further
simulations showed that this method was robust for different receptive field shapes and sizes,
and pointed toward various possible improvements in the experimental methodology. We further
showed how these statistics can be combined across units and how this method can be used to
analyze intermediate reference frames or units having gain-field-like activity modulations. The
application of this data to our current data set is shown in the accompanying abstract, but the
method can be applied to essentially any spatially-related unit activity.
Disclosures: G.P. Keith, None; J.F.X. DeSouza, None; X. Yan, None; H. Wang, None; J.D.
Crawford, None.
Poster
263. Eye Movements: Eye and Head Control
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 263.6/DD6