SfN XXXIVth Annual Meeting Abstract, San Diego, 2004.

PREPARATORY DELAY ACTIVITY IN THE MONKEY POSTERIOR PARIETAL CORTEX

PREDICTS REACH, BUT NOT SACCADE REACTION TIMES.

T.R. Dickinson & L.H. Snyder

Activity in the monkey parietal reach region (PRR) and the lateral intraparietal area (LIP) reflects both spatial information and the effector (i.e., arm or eye) that will be used in an upcoming reach or saccade task. To obtain evidence for an effector-specific functional role of these regions in sensory to motor transformations, we tested the hypothesis that increased neuronal activity during a preparatory delay period would lead specifically to faster reach (PRR) or saccade (LIP) reaction times (RTs) in visually-guided movement tasks. We found that PRR activity was correlated with reach but not saccadic RT when the type of movement, but not the spatial goal of that movement, was prepared in advance.

Each additional spike of PRR activity during the preparation period was associated with a 1.23 ms decrease in reach RT (p<0.01), and a 0.47 ms increase in saccade RT (p>0.8). The relationship was even stronger in PRR cells that showed significantly more activity on reach compared to saccade trials. The effect was largely independent of the actual movement direction and cannot, therefore, reflect spatial prediction. No significant correlations were found between preparatory activity and either reach or saccade reaction times within LIP or in area 5, outside of PRR.

The data from PRR provide evidence for neuronal activity predictive of a behavioural efficiency not previously demonstrated in the posterior parietal cortex, and support the claim for an effector-specific role for PRR in providing spatial information for an upcoming reach.

Support contributed by: NIH & EJLB