Perceptual decision making is a critical component of human cognition by which the brain processes raw sensory evidence from its environment to guide actions that best suit goals. However, the evidence that the environment provides is often ambiguous and requires the brain to evaluate it in an optimal way to maximize decision success. Although the extensive study has been conducted to understand how the brain evaluates noisy sensory evidence over time to guide perceptual decisions, it is unclear how different regions of the brain contribute to this evidence evaluation, and how these regions evaluate evidence differently demanding on the demands of a given situation.
One area of the brain, posterior parietal cortex (PPC), has long been a target of this study. PPC lies at the junction of brain regions canonically associated with sensory and motor processes, and neurons in PPC exhibit activity that scales with incoming sensory evidence during formation of perceptual decisions and reflects the time of decision commitment across multiple sensory modalities and species. Thus far, these studies have largely neglected the temporal component of evidence evaluation: In situations in which some epochs of evidence are more relevant than others, how do the dynamics of neural activity accommodate the different task demands to account for the animal’s behavioral strategy? Also, do the distinct processing dynamics of PPC emerge locally or simply inherited from upstream sensory regions?
In this dissertation, I describe three studies involving human and rat subjects performing auditory perceptual decision making tasks involving varying timescales of evidence evaluation in which different epochs of evidence are relevant for the decision. In the first study, I show that humans are capable of employing multiple timescales of evidence evaluation for different purposes during a multi-stage change detection task, and these timescales are selectively recruited depending on how circumstances progress regardless of the subject’s expectations. In the second study, I use neuropixel probes to record single unit activity in the PPC of rats performing the same change detection task to examine a neural mechanism for how the brain can flexibly adapt timescales of decision making for different purposes. Finally, I describe a study in which the primary auditory cortex of rats is inactivated during an auditory discrimination task, with results suggesting that primary auditory cortex is not necessary for evaluation of evidence over time for auditory decisions and that this function emerges later in downstream brain regions.
