Psychostimulant Effects on Cognitive Flexibility and Risk-Based Decsion-Making Behavior Following Repetitive Mild Traumatic Brain Injury

This investigation examines how psychostimulant drugs interact with monoaminergic systems to influence cognitive flexibility and risk-based decision-making following repetitive mild traumatic brain injury (TBI). The research builds on the lab's broad, mechanistic focus on central monoaminergic systems, particularly the locus coeruleus, norepinephrine (NE) and dorsal raphe, serotonin pathway and their roles in sensory processing, attention and executive function. Using an established rat model of repetitive mild TBI, the study pairs behavioral assays of flexible attention and decision making with anatomical, electrophysiological, and molecular approaches to link concussion-induced deficits to injury-related pathologies in NE and related neuromodulatory systems.

Methodologically, the project employs a spectrum of techniques described by the laboratory: behavioral paradigms for signal detection, sustained attention, and flexible attention; single- and multi-unit extracellular recordings in both anesthetized and waking animals; simultaneous spike-train recordings from multiple neuronal arrays; and computer-based acquisition and analysis of spike data. Neuroanatomical strategies include mapping monoamine projections using retrograde tracers, immunohistochemistry, and molecular phenotyping such as qRT-PCR of laser-captured monoaminergic neurons. The laboratory's electrophysiological and imaging data highlight how locus coeruleus stimulation modulates sensory neuron responsiveness according to an inverted-U relationship, indicating that NE release dynamically regulates sensitivity to sensory inputs. Complementary analyses focus on the dorsal raphe's role in adaptive and maladaptive behaviors mediated by serotonin and interacting transmitters.

A central element of the study is the examination of psychostimulant drug actions, exemplified by methylphenidate (MPH, Ritalin) and their capacity to modulate sensory and cognitive responses. Prior laboratory observations in normal rats show that MPH administration can enhance thalamic neuronal responsiveness to sensory-driven synaptic inputs, suggesting potential rescuing or modulatory effects on attention and sensory processing. The current work evaluates whether such psychostimulant effects can influence cognitive flexibility and risk-based decision-making after repetitive mild TBI, and whether these effects interact with TBI-induced alterations in NE circuitry.

Clinically relevant outcomes of this research include improved mechanistic understanding of how synaptically released norepinephrine and serotonin regulate prefrontal cortical circuit physiology and executive functions such as planning, attention, and decision-making. The project aims to clarify how repetitive concussive events impair flexible attention through injury-related NE system pathologies, as evidenced by altered NE fiber density in prefrontal cortical layers observed in the rat model. By integrating behavioral, anatomical, electrophysiological, and molecular data, the research seeks to inform therapeutic considerations for cognitive deficits following mild TBI, as well as inform how psychostimulant drugs may alter these outcomes. The work advances knowledge of monoaminergic contributions to executive function and offers a translational framework linking basic neurobiology to potential clinical strategies for TBI-related cognitive impairment.