Neural and Serotonergic Mechanisms Underlying Time Valuation in Rats (TIMEVALUE)

Time is our scarcest resource. Humans and other animals must decide how to spend their time, choosing from endlessly many activities with distant and uncertain outcomes, thereby assigning value to their time. The neuromodulator serotonin is thought to arbitrate between impulsivity and the patience required to wait for future rewards, suggesting a pivotal function for time valuation. Serotonin-releasing neurons project to frontal cortex, where I have previously identified neurons that predict confidence-guided time investment, but the neural and serotonergic mechanisms for time valuation remain unknown. Here, I aim to identify the cortical control mechanisms that flexibly adjust the value of time to optimize time investment decisions. My central hypothesis is that serotonin sets the value of time dynamically encoded in frontal cortex neural activity.
I will employ a family of decision tasks that allows for model-based quantification of time valuation by requiring rats to invest variable time into choice options with uncertain and delayed outcomes. We will use high-density probes and extracellular single-unit recording devices combined with chemical sensor imaging and optogenetics in freely moving rats, tools that I have developed during my postdoc, to address three main neural mechanisms: (1) What are the dynamic neural signatures of time valuation in orbitofrontal cortex, a frontal cortex area central for valuation? (2) Does serotonin specialize in conveying decision variables that construct time valuation? (3) How does serotonin impact frontal cortex neurons and network dynamics for time valuation? This research will clarify serotonin’s behavioral function and identify principles of serotonergic neuromodulation of cortical information processing. The projects will further characterize the structure of frontal cortex population dynamics underlying time valuation and decision-making.