Abstract
When engaged in a repetitive task our performance fluctuates from trial-to-trial. In particular, inter-trial reaction time variability has been the subject of considerable research. It has been claimed to be a strong biomarker of attention deficits, increases with frontal dysfunction, and predicts age-related cognitive decline. Thus, rather than being just a consequence of noise in the system, it appears to be under the control of a mechanism that breaks down under certain pathological conditions. Although the underlying mechanism is still an open question, consensual hypotheses are emerging regarding the neural correlates of reaction time inter-trial intra-individual variability. Sensory processing, in particular, has been shown to covary with reaction time, yet the spatio-temporal profile of the moment-to-moment variability in sensory processing is still poorly characterized. The goal of this study was to characterize the intra-individual variability in the time course of single-trial visual evoked potentials and its relationship with inter-trial reaction time variability. For this, we chose to take advantage of the high temporal resolution of the electroencephalogram (EEG) acquired while participants were engaged in a 2-choice reaction time task. We studied the link between single trial event-related potentials (ERPs) and reaction time using two different analyses: (1) time point by time point correlation analyses thereby identifying time windows of interest; and (2) correlation analyses between single trial measures of peak latency and amplitude and reaction time. To improve extraction of single trial ERP measures related with activation of the visual cortex, we used an independent component analysis (ICA) procedure. Our ERP analysis revealed a relationship between the N1 visual evoked potential and reaction time. The earliest time point presenting a significant correlation of its respective amplitude with reaction time occurred 175 ms after stimulus onset, just after the onset of the N1 peak. Interestingly, single trial N1 latency correlated significantly with reaction time, while N1 amplitude did not. In conclusion, our findings suggest that inter-trial variability in the timing of extrastriate visual processing contributes to reaction time variability.
Highlights
Transient and rapid fluctuations in behavioral performance are a characteristic of human behavior, even when task characteristics are maintained constant (MacDonald et al, 2006)
Inter-trial reaction time variability is significantly related to variability in sensory cortex responses
We investigated the relationship between reaction time and visual evoked responses, using EEG recordings acquired while participants were engaged in a 2-choice reaction time task, and two different analyses
Summary
Transient and rapid fluctuations in behavioral performance are a characteristic of human behavior, even when task characteristics are maintained constant (MacDonald et al, 2006). In spite of its lower temporal resolution, this has mostly been studied in functional magnetic resonance imaging (fMRI) studies using tasks requiring visual selective attention (Weissman et al, 2006, 2009) Under these conditions, moments of slower reaction times are associated with brain activity patterns characterized by reduced pre-stimulus activity levels in frontal control regions including the anterior cingulate cortex and dorsolateral prefrontal cortex, reduced stimulus-evoked responses in the visual cortex, increased activity in the default-mode network (DMN), and increased post-stimulus activity in the anterior cingulate cortex (Weissman et al, 2006; Prado et al, 2011). The moment-to-moment fluctuations in brain state that underlie inter-trial reaction time variability affect the way the sensory cortices process incoming stimuli
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