[Abstract Title]. - Society for Neuroscience

Authors: *S. P. MAHAFFY 1,2 , R. J. KRAUZLIS 1 ;
1 Systems Neurobio. Lab., Salk Inst., La Jolla, CA; 2 Neurosciences Grad. Program, UCSD, La
Jolla, CA
Abstract: Primates are adept at selecting moving targets for smooth pursuit eye movements,
even in the presence of competing distracter motion. The superior colliculus has been implicated
recently in the spatial selection of targets for smooth pursuit, but the neural mechanism for
selecting the direction of pursuit motion is unknown. Based on its connectivity and previously
documented role in pursuit gain control, the frontal pursuit area is a reasonable candidate for the
site that helps determine the direction of pursuit. In particular, the frontal pursuit area contains
directionally selective cells that respond during the acceleration and maintenance of smooth
pursuit. To test his idea, we have recorded in the frontal pursuit area during a target selection
task to determine whether neurons in this area discriminate pursuit targets in time to underlie
pursuit selection.
The task was a two-alternative forced choice match-to-sample selection of isoluminant colored
dots moving in a step-ramp towards fixation. The monkey‟s task was to smoothly pursue the
stimulus whose color matched the cue presented earlier in the trial. Dots always moved parallel
and opposite to each other slightly offset from fixation, and their angle was adjusted to match the
preferred direction of the neuron under study. Pursuit latencies were measured for each trial with
a hinge model. Neural discrimination latencies, identifying when the cell‟s firing rate
discriminated the direction of pursuit, were measured with an ROC analysis with a precision of
one millisecond.
We have recorded from 34 pursuit-related cells in the frontal pursuit area of one monkey. Pursuit
in the preferred direction typically evoked a vigorous and sustained response during the target
selection task, with some cells exhibiting a burst of activity during the initiation of pursuit.
Pursuit in the non-preferred direction left the firing rate unchanged or suppressed, although some
cells showed a transitory increase in activity before pursuit onset regardless of pursuit direction.
We found that 15 out of the 34 (44%) cells discriminated target from distracter before pursuit
onset. For these cells, the mean lead time for neural discrimination was 13 ms +/- 12ms (S.D.).
These results show that a substantial minority of cells in the frontal pursuit area discriminate
target from distracter prior to the onset of pursuit. This suggests that the frontal pursuit area may
be involved in the process of determining the direction of pursuit eye movements when the target
is selected in the presence of distracters.
Disclosures: S.P. Mahaffy , None; R.J. Krauzlis, None.
Poster
264. Eye Movements: Smooth Pursuit
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 264.8/DD25