| Abstract No.: | C-D3126 |
| Country: | Canada |
| | |
| Title: | FMRI OF THE CAUDATE AND FRONTAL EYE FIELDS WHEN REQUIRED TO INSTANTLY SWITCH A PRO OR ANTISACCADE |
| | |
| Authors/Affiliations: | 1 Ian Cameron*; 1 Brian Coe; 1 Masayuki Watanabe; 1 Patrick Stroman; 1 Douglas Munoz;
1 Queen's University, Kingston, ON, Canada
|
| | |
| Content: | Objectives: The basal ganglia are involved in boosting appropriate neural signals related to a particular action, and suppressing signals related to competing actions. We used functional Magnetic Resonance Imaging (fMRI) to investigate the roles of the caudate nucleus (CN) and the frontal eye fields (FEF) in an oculomotor task switching paradigm. We hypothesized that the CN would show increased activation whenever a planned saccade to one location needed to be cancelled, and a saccade to an alternate location elicited. We also hypothesized that activation in the FEF might parallel activation in the CN, as the FEF inputs saccade generation signals to the CN.
Materials and Methods: Twenty one human subjects participated in an experiment that required them to initiate a saccade towards a stimulus that appeared to the left or right (a prosaccade) or away from the stimulus (an antisaccade). The instruction about which task to perform was given by one of two fixation point colours. Unpredictably on a subset of trials, the instruction switched after stimulus onset. Previous work suggests that this requires the brain to switch a saccade that was programmed based on the initial instruction and stimulus location. For 10 of the subjects, we used 11 slices of 3.3 mm isovoxels to scan the CN in the transverse plane. Next, for 11 subjects, we used 16 slices of 3.3 mm isovoxels to focus on the dorsal CN and FEF in an angled coronal plane. Using an event related design, we compared the response periods of trials in which the instruction switched to those in which it did not.
Results: Analysis of saccade reaction times (SRTs) revealed that regular (non-switch) antisaccades were slower than prosaccades; likewise, subjects made more direction errors on antisaccade trials than on prosaccade trials, demonstrating that prosaccades were more automatic than antisaccades. Even longer SRTs and greater direction errors (‘switch costs’) were found on pro-to-antisaccade and anti-to-prosaccade switch trials, indicating that cancellation and reprogramming processes were involved. fMRI analysis demonstrated significantly greater activation for pro-to-antisaccade switch trials compared to regular prosaccade trials in the oculomotor region of the CN. However, there was not greater CN activation for anti-to-prosaccade switch trials compared to regular antisaccade trials, nor for regular antisaccade trials compared to regular prosaccade trials. The FEF however, showed increased activation for pro-to-antisaccade switch trials and for regular antisaccade trials compared to regular prosaccade trials.
Conclusions: These results suggest that while ‘switch costs’ resulted for switching in either direction, the CN shows increased activation when an automatic response needs to be cancelled and a more complicated volitional response needs to be reprogrammed. The FEF on the other hand shows increased activation for antisaccade generation, a finding that replicates previous studies. |
| | |
| Back |
|
