Jacobs, Elina Alexandra Katariina; (2018) Cortical state dynamics during sensory decision-making. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Cortical states, defined as the dynamics of cortical neural activity on the timescale of seconds or more, vary during different behavioural states. Originally associated mainly with the sleep-wake cycle, it is now recognised that cortical states present subtle changes during waking that reflect the cognitive and behavioural demands an individual is pursuing. Therefore, it has been suggested that attention leads to a desynchronised cortical state, characterised by the absence of low frequency oscillations, which is thought to improve the information processing of the object of interest and thereby improve performance in attention demanding tasks. To maximise the beneficial effects of desynchronisation, it has been proposed that this state should occur locally, as this may spot-light the attended feature. I investigated this hypothesis by asking whether attending to a specific sensory modality leads to local desynchronisation of the sensory cortex of the modality being used. I trained mice to perform visual and auditory decision making tasks, and assessed cortical state through spectral analysis of widefield calcium signals. Genetically encoded calcium indicators were expressed in cortical excitatory neurons, and their activity was imaged simultaneously across cortex while the animals were performing the different tasks. Cortical states correlated with task engagement rather than with task performance, and this effect was global. Unexpectedly, the biggest desynchronisation was seen in somatosensory cortex in all tasks, and there was along lasting effect of reward. These effects could not be explained by movement or pupil diameter, a commonly used measure of arousal. Furthermore, desynchronisation correlated with reaction time. Thus, variations in cortical state closely relate to changes in task engagement, demands and outcome. This suggests that desynchronization is not a causal effect of attention that improves performance, but instead may be a cognitive state related to preparing rapid and coordinated responses to sensory stimuli.

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