[Abstract Title]. - Society for Neuroscience

difference exists in the eye-in-head component, is it related to the head velocity produced in HU
trials? Also can this difference be explained by the firing rate of VN neurons (positionvestibular-pause
and eye-head cells) known to project to the ABD? To answer these questions,
the activities of excitatory burst neurons and their inhibitory counterpart, collectively referred to
as burst neurons (BNs), were recorded during HR and HU gaze shifts performed by non human
primates. The burst profile recorded on each HU trial was matched, in a root-mean-squared-error
sense, with a burst measured during HR trials, thus satisfying the assumption that the oculomotor
input to the ABD was the same. Matched trials were found to have similar gaze amplitudes, but
the amplitude and peak velocity of the saccadic eye component was lower for HU movements.
Thus, the difference in the eye velocity waveforms of HR and HU trials reflects the ocular
counter-rotation induced by the head movement. The counter-rotation gain, defined as the ratio
of the difference in the eye velocities and the head velocity, was high (>10) and variable at the
onset of the movement, decreased smoothly during the gaze shift and stabilized at one after gaze
shift offset. Finally a computer simulation was used to check if the difference in the eye
velocities could be explained by VN inputs. The simulation modeled the difference in ABD
firing rate (ΓABD) between HR and HU matched trials as the weighted sum of the difference in
the firing rate of VN (ΓPVPc, ΓPVPi and ΓEHc) input. The oculomotor input was not used in
this model because for matched trials the difference equals zero. Linear regression algorithm was
used to find the optimal set of weights to fit this difference model. The result of this simulation
showed that the weight of EHc cells input was the highest and accounted for most of the
difference in the ABD and consequently the difference in the eye velocities. This leads to the
implication that EHc cells play a major role in reducing the eye velocity during head
unrestrained gaze shifts.
Disclosures: B.P. Bechara, None; N.J. Gandhi, None.
Poster
263. Eye Movements: Eye and Head Control
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 263.11/DD11
Topic: D.06.c. Eye and head control
Support: NSERC (Canada)
Botterell Fund (Queen‟s University, Canada)
Marie Curie (EU)
IAP (Belgium), ARC (UCLouvain, Belgium)