[Abstract Title]. - Society for Neuroscience

was that eye position would dominate the response via the gain field.
Neural activity was recorded in areas 7a and DP contralateral to the reaching arm. The monkey
was required to fixate one of 9 positions on a touch screen while a visual stimulus (expansion
optic flow, radius 6º) appeared behind the fixation point. The change from structured to
unstructured motion cued the monkey to make a ballistic hand movement towards the target and
hold his hand in place. A binocular Fresnel prism introduced a 10º shift in the same direction or
the opposite direction as the spatial gain field of the unit; the monkey had to reach to the physical
location of the target which did not match the perceived location. The trained monkey correctly
reached to the target within a few trials demonstrating swift adaptation to the distortion. Changes
in firing rate were assessed across 3 events of the task: (1) fixation onset, (2) visual stimulus
onset (“visual signal”), and (3) lifting of hand from rest (“reach signal”). Linear regressions with
categorical variables denoting the presence or absence of the prism distortion quantified changes
in spatial tuning.
Spatial tuning of single unit activity was compared during the “pre-prism” block, the “prism”
block, and the “post-prism” block (33/60); the remainder were not tested “post prism”. The
spatial tuning typically returned to pre-prism levels once the prism was removed. Alteration of
the spatial tuning with insertion of the prisms to at least one event was found in 26/33 units. If
the cells merely responded to the shift in eye position in the prism block, the firing rate would be
expected to vary in proportion to the slope of the gain field. This did not occur indicating more
complex interactions between the prism and neuronal activity.
In many cases, the prism distortion altered the slope of the reach field. For some cells, the change
in the shape of the reach field acted in a manner to correct for the prisms (10/24). In others, there
was no clear relation between the prism and the change in the reach field.
Similar variations in spatial tuning were observed for the fixation onset and the visual signal.
These dramatic changes in spatial tuning across all measured neural events suggest that there is a
range of remapping of the sensorimotor transformations that guide reaching.
Disclosures: A. Karnik, None; B. Heider, None; R.M. Siegel, None.
Poster
262. Visually-Guided Reaching II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 262.11/CC25
Topic: D.05.d. Visually guided reaching
Support: Natural Sciences and Engineering Research Council of Canada
National Institutes of Health