Title: Trial-to-trial Variability of Spike Response of V1 and Saccadic Response Time 2 3 4

32 33 Single neurons in the primary visual cortex (V1) show variability in spike activity in response to 34 an identical visual stimulus. In the current study, we examined the behavioral consequences of 35 the variability in spike activity of V1 neurons for visually-guided saccades. We recorded single 36 cell activity from V1 of monkeys trained to detect and make saccades toward visual targets of 37 varying contrast, and analyzed trial-to-trial covariation between the onset time or firing rate of 38 neural response and saccadic response time (RT). Neural latency (NL, the time of the first 39 spike of neural response) was correlated with RT, whereas firing rate (FR) was not. When FR 40 was computed with respect to target onset ignoring NL, a ‘false’ correlation between FR and RT 41 emerged. Multiple regression and partial correlation analyses on NL and FR for predictability of 42 RT variability, as well as a simulation with artificial Poisson spike trains, supported the 43 conclusion that the correlation between FR with respect to target onset and RT was mediated 44 by a correlation between NL and RT, emphasizing the role of trial-to-trial variability of NL for 45 extracting RT-related signals. We attempted to examine laminar differences in RT-related 46 activity. Neurons recorded in the superficial layers tended to show a higher sensitivity to 47 stimulus contrast and a lower correlation with RT compared to those in the lower layers, 48 suggesting a sensory-to-motor transformation within V1 that follows the order of known 49 anatomical connections. These results demonstrate that the trial-to-trial variability of neural 50 response in V1 propagates to the stage of saccade execution, resulting in trial-to-trial variability 51 of RT of a visually-guided saccade. 52