Abstract
Large variability between individual response times, even in identical conditions, is a ubiquitous property of animal behavior. However, the origins of this stochasticity and its relation to action decisions remain unclear. Here we focus on the state of the perception–action network in the pre-stimulus period and its influence on subsequent saccadic response time and choice in humans. We employ magnetoencephalography (MEG) and a correlational source reconstruction approach to identify the brain areas where pre-stimulus oscillatory activity predicted saccadic response time to visual targets. We find a relationship between future response time and pre-stimulus power, but not phase, in occipital (including V1), parietal, posterior cingulate and superior frontal cortices, consistently across alpha, beta and low gamma frequencies, each accounting for between 1 and 4% of the RT variance. Importantly, these correlations were not explained by deterministic sources of variance, such as experimental factors and trial history. Our results further suggest that occipital areas mainly reflect short-term (trial to trial) stochastic fluctuations, while the frontal contribution largely reflects longer-term effects such as fatigue or practice. Parietal areas reflect fluctuations at both time scales. We found no evidence of lateralization: these effects were indistinguishable in both hemispheres and for both saccade directions, and non-predictive of choice — a finding with fundamental consequences for models of action decision, where independent, not coupled, noise is normally assumed.
Highlights
The extent to which apparently random fluctuations in behavior are predictable is of fundamental theoretical and practical interest
3) oscillatory amplitude is highly correlated between V1 and the rest of the network, parietal and frontal areas still make independent contributions: While correlations in occipital areas capture mainly short-term fluctuations, frontal and parietal contributions appear partly driven by longer-term sources of variance
5) We found no clear evidence for a relationship between latency and the phase of baseline oscillations
Summary
The extent to which apparently random fluctuations in behavior are predictable is of fundamental theoretical and practical interest. The time taken to initiate even the most basic responses to highly salient stimulations typically varies four- to five-fold (Fig. 1A). It remains largely unknown why and when this variability occurs: how much is related to the experimental design (experimental factors, trial history, fatigue, practice etc.) and how much is stochastic; and to what extent it is predicted by pre-stimulus brain states. Evidence for predicting response time variability from pre-stimulus neural markers is much less consistent, even though this time-period is increasingly thought to contain the seeds of the variance in electrophysiological responses to a stimulus (Arieli et al, 1996; Nikulin et al, 2007)
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