Schölvinck, M.L.; (2010) The interplay between spontaneous and evoked brain activity during visual perception. Doctoral thesis , UCL (University College London).

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Abstract

The vast majority of studies in cognitive neuroscience have focused on the brain’s response to a task or stimulus. However, the brain is very active even in the absence of explicit input or output, as its enormous energy consumption at rest suggests. This ongoing brain activity is present at all timescales; as spontaneous neuronal firing measured by electrophysiology, and as slow fluctuations in the BOLD signal measured by functional magnetic resonance imaging (fMRI). Its significance for behaviour is still unclear. This thesis explores the nature of the brain’s spontaneous activity, with an emphasis on its interaction with brain activity devoted to visual perception. Using a theoretical approach, I first show that the amount of energy expended on evoked brain activity related to a perceptual decision is minute compared to the energy expenditure associated with spontaneous activity. I then focus on spontaneous brain activity measured in the fMRI signal, the so-called resting-state fluctuations. Using simultaneous fMRI-electrophysiology in awake monkeys, I demonstrate that these fMRI resting-state fluctuations are strongly correlated to underlying fluctuations in neural activity, and are therefore likely to be neural in origin. A further fMRI study in humans shows that resting-state fluctuations in visual cortex can account for a significant degree to the variability in cortical, and to a lesser degree to the variability in behavioural responses to a visual stimulus at perceptual threshold. Lastly, I use a visual illusion called motion-induced blindness as a model system for studying the effect of spontaneous fluctuations in internal brain state on bistable perception. Using fMRI in humans, I show that while the retinal input remains constant, activity in early visual cortex reflects awareness of the stimulus. In the final, behavioural experiments, I manipulate the brain’s internal state by examining the influence of endogenous attention on the temporal dynamics of motion-induced blindness. Taken together, these studies show that spontaneous brain activity plays an important role in visual perception, and argue that understanding the brain’s internal dynamics is essential to understanding the brain as a whole.

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