Prefrontal-based cognitive processing and exploratory behavior
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Exploration (performing actions to obtain information) is a critical cognitive function necessary for learning and decision-making. Effective decision-making requires finding the right balance between exploration and exploitation (taking action to obtain immediate reward). We can distinguish two types of learning and decision-making that differ crucially in how they approach exploratory behavior that are thought to be served by partially distinct neural systems. Reflexive decision-making is thought to be more habitual or automatic, computationally cheap, and mediated largely by processing in the striatum. Reflective decision-making is more goal-directed, relatively computationally expensive, depends on executive processing, and is thought to crucially depend on the prefrontal cortex. Reflective learning involves building a rich mental representation of the environment. This representation can allow the learner to use uncertainty in the environment to direct exploratory choices when they will be most valuable. To be most effective, one should explore when and where there is more uncertainty in the environment in order to gain more information to guide future choices. In contrast, reflexive strategies lead to “random” exploration. In a series of studies I examined the involvement of prefrontal cortex in reflective learning and the role of reflective processing in exploratory decision-making. In two studies, I investigated the contribution of prefrontal cortex to reflective and reflexive learning by examining the effects of prefrontal transcranial infrared laser stimulation on category learning. Reflective, but not reflexive, category learning was improved by laser stimulation. In three studies, I investigated factors influencing reflective and reflexive processing in exploratory decision-making. Study 3 found that greater levels of depression symptoms were associated with less frequent reflective strategy use. Study 4 found that genotype on a gene modulating prefrontal dopamine levels (COMT) was associated with reflective strategy use under cognitive load. Study 5 investigated reflective exploratory behavior in older (>60 years) and younger (<30 years) populations, finding that rather than a reflective processing deficit, older adults’ performance suffered (relative to younger adults) due to applying the wrong reflective strategy. These findings advance our understanding of the mechanisms of exploratory behavior and suggest a critical role for the prefrontal-based learning system.