Investigating the neural basis of spatial attentional components with probabilistic and reward cueing

Abstract

We are constantly inundated with an abundance of sensory information. “Attention” enables the selection of relevant information and filtering out irrelevant information, to guide adaptive behavior. While attention can be deployed in many forms, in this work, I explored attention that is goal-directed, and based on prior knowledge of task-relevant locations: “endogenous spatial attention”.

Specific locations in the world can become behaviorally relevant for a variety of reasons. First, some locations may manifest a higher probability of the occurrence of task-relevant events, for example, the side of oncoming traffic in a one-way street. Alternatively, events occurring in particular locations could be associated with higher rewards or punishments, for example, the location of an ice cream truck or patrol car in a stream of vehicles. Each of these types of attentional engagement can be studied in the laboratory with probabilistic or reward-based cueing, respectively. Which neural mechanisms mediate each type of attentional cueing remains actively researched.

Second, the behavioral benefits of attention can be mediated by at least one of two mechanistic components: enhanced fidelity of sensory information processing (perceptual sensitivity) or increased weightage during decision-making (choice bias). However, the specific neural mechanisms mediating these two components of attention (sensitivity and bias) are debated. Moreover, how each component of attention is recruited by each type of attention cueing (probabilistic, reward-based) also remains an open question.

In the first two aims of this thesis, I employed a probabilistically cued spatial attention task to explore the neural origins of sensitivity and bias. Specifically, I investigated the causal role of the dorsal posterior parietal cortex (PPC) – a key brain region involved in orienting endogenous attention. In the first aim, I recorded behavioral data from n=26 human participants performing a probabilistically cued attention task while concurrently applying transcranial alternating current stimulation (tACS) at 40 Hz over the right PPC. The results indicate a causal role of rPPC in re-orienting bias – one specific component of attention. In the second aim, I extended these experiments to stimulate the left PPC with 40 Hz tACS in the same cohort of participants. I observed a closely comparable pattern of results, except that lPPC stimulation effects persisted for longer (>30 min) and were more contra-lateralized. Control experiments demonstrated that the tACS effects were stimulation frequency specific.

In the final aim, I employed a reward-cued attention task to explore the neural bases of sensitivity and bias. Specifically, I tested n=24 participants with two different manipulations of reward expectation: across space (space-specific), and across choices (choice-specific). I show that each of these manipulations produced dissociable effects on sensitivity and bias, respectively. Moreover, only space-specific reward cueing evoked neural and physiological signatures of attention, including modulation of event-related potentials (ERPs), alpha-band power lateralization, and oculomotor biases. By contrast, choice-specific reward cueing elicited only neural signatures of biased decision-making. These findings uncover fundamentally dissociable sensory and decisional mechanisms that mediate reward-driven attention, with critical implications for understanding how reward, attention, and choice are linked in the human brain.

Overall, my experiments reveal key neural bases of probabilistic and reward cueing of spatial endogenous attention. In addition, they identify fundamentally dissociable neural underpinnings of key components of attention – sensitivity and bias – recruited by each type of endogenous cueing. These findings advance our understanding of how attention works in the human brain and may enable a deeper understanding of attentional impairments that accompany various neurological and psychiatric disorders like ADHD, autism, and dementia.