[Abstract Title]. - Society for Neuroscience

Topic: D.06.c. Eye and head control
Support: CIHR (Canada)
JDC holds a Canada Research Chair
Title: Intrinsic reference frames for visuomotor receptive fields in head-free gaze shifts II:
Superior colliculus units in the monkey
Authors: *J. F. DESOUZA 1 , G. P. KEITH 1 , X. YAN 1 , H. WANG 1 , J. D. CRAWFORD 1,2 ;
1 Psychology, Ctr. Vision Res., Toronto, ON, Canada; 2 Biol., York Univ., Toronto, ON, Canada
Abstract: We trained two macaque monkeys to make gaze shifts to visual targets in a headunrestrained
condition and where the targets were projected onto a tangent screen in front of the
monkey. Three dimensional (3-D) eye and head orientations were recorded. A vertical recording
chamber was placed at streotaxic centre to provide electrode access to the midbrain. Animals
were trained to fixate a central target in the dark and then make gaze saccades toward briefly
presented targets, with no memory delay, and with no constraints on their natural patterns of eye
head coordination. Gaze-related activity of intermediate and deep layer superior colliculus (SC)
neurons was identified using single-unit recording. The visuomotor receptive fields of 10 units
were fully characterized using these methods, requiring animals to make gaze shifts toward at
least 9 to a maximum of 16 targets with a repetition of approximately 10 trials per target. A
standard analysis of gaze-related activity in space coordinates showed a variety of units with
both „closed‟ and „open‟ receptive fields, with „hot spots‟ ranging from 14 to 44.7º amplitude.
The activation for a given unit was highly variable for a given target. However, the initial
combinations of eye and head position at centre fixation during viewing were highly variable,
with 9.9º variation in horizontal-vertical head orientation and 11.3º variation in head torsion, and
7.7º variation in eye-in-space torsion. A 3-D kinematic analysis was used to rotate both the
saccade target positions and the gaze saccade trajectories themselves into space and head
coordinates, and unit activity was re-plotted in all 6 combinations (gaze trajectory and target vs.
three frames). The fit coherence of the units in these different plots was then compared using the
non-parametric fit/PRESS statistic method described in the companion abstract (Keith et al.
2008). Not every unit has been analyzed at this time, but preliminary results suggest that the
receptive field activity of most units fit best to target position in eye coordinates, and at this time,
at the population level these fits are statistically better than fits in head or space coordinates.
These preliminary findings agree with our previous investigation of SC frames using electrical
microstimulation (Klier et al. 2001).
Disclosures: J.F. DeSouza, None; G.P. Keith, None; X. Yan, None; H. Wang, None; J.D.
Crawford, None.
Poster