The interaction effect between dopamine and task difficulty: Spontaneous eye blink rates diversely relate with Nogo-N2 across various task difficulties.

Nogo- N2 and P3 are the two major components in the neural time course of response inhibition (RI) and are both related, albeit differently, to dopamine (DA). However, contradictory results from previous studies imply that there may be an interaction effect between DA and task difficulty on the neural time course of RI. To investigate this, we assessed the correlation between spontaneous eye blink rate (EBR) and N2/P3 elicited by the Go/Nogo tasks across various task difficulties, manipulated by the Nogo-stimuli probability (NP) and Go-stimuli response deadline (RTD). In experiment 1, there were two conditions, low (20%) and high (40%) NP, both of which were fixed on an RTD of 1000 ms. We found that higher EBR was significantly related to a more negative Nogo-N2 amplitude. In experiment 2, there were also two conditions, long (1000 ms) and short (300 ms) RTD, both of which were fixed on an NP of 20%. We found that higher EBR was significantly related to more negative Nogo-N2 amplitude in both conditions, however, there was no significant correlation between EBR and P3 in both of the experiments. These results confirmed the interaction effect between DA and task difficulty on the neural course of the Go/Nogo task. This suggests that task difficulty should be considered in future studies that investigate the influence of DA on RI.