The role of cortical state in perceptual decision-making

Human decision-making behavior is highly variable, even when decisions are based on identical information. This behavioral variability has been attributed to fluctuations in ongoing brain activity, referred to as cortical state. Cortical state is driven by top-down factors (e.g., selective attention) and physiological arousal, which is regulated by the activity of the catecholaminergic and cholinergic neuromodulator systems that globally innervate cortex. In this dissertation, a combination of behavioral experimentation, pharmacological interventions, and electrophysiological recordings of brain activity (EEG) were used to investigate how cortical state affects the computational and neural mechanisms underlying perceptual decision-making in healthy human participants.
Where top-down attention enhanced the encoding of sensory information, pharmacological elevation of baseline catecholaminergic and cholinergic levels did not affect sensory encoding. However, both top-down attention and elevated catecholamine (but not acetylcholine) levels improved perceptual decision-making by increasing the rate at which parietal networks accumulate sensory evidence over time towards a decision threshold. Moreover, top-down attention acted as a bottleneck for the processing of cognitive, but not sensory, types of information. The effects of catecholaminergic neuromodulation on human behavior were rather heterogeneous, as elevated catecholaminergic levels improved the accuracy of perceptual, but not metacognitive decisions. Finally, the effects of top-down behavioral strategies on perceptual decisions were not influenced by elevated baseline neuromodulator levels, but were minimized when task-evoked neuromodulator responses were strong.
Overall, this dissertation furthers our understanding of human behavior by revealing how several factors contributing to cortical state affect the encoding of sensory information and the formation of perceptual decisions.