Opportunity cost determines free-operant action initiation latency and predicts apathy

Area of Science:

• Neuroscience
• Computational Psychiatry
• Behavioral Economics

Background:

• Apathy is a poorly understood neuropsychiatric symptom characterized by impaired self-initiated behavior.
• The opportunity cost of time (OCT) is hypothesized to link self-initiated behavior with motivational status.
• OCT quantifies the reward foregone per unit of time when no action is taken.

Purpose of the Study:

• To investigate the relationship between OCT, self-initiation, and apathy.
• To test the hypothesis that higher OCT leads to shorter action latencies.
• To determine if individuals with greater OCT sensitivity exhibit higher apathy.

Main Methods:

• A novel behavioral task, the 'Fisherman Game', was used to modulate OCT.
• Participants self-initiated actions to collect rewards or perform non-rewarding tasks.
• Computational modeling using 'average-reward' reinforcement learning analyzed action latencies and apathy across two studies (n=21 lab, n=90 online).

Main Results:

• Action initiation latency was significantly driven by changes in OCT.
• Individuals with higher apathy demonstrated increased sensitivity to OCT variations, particularly younger adults.
• Computational modeling indicated that apathetic individuals perceived a greater change in subjective OCT due to heightened reward sensitivity.

Conclusions:

• OCT is a crucial variable in understanding free-operant action initiation.
• The findings provide novel insights into the computational mechanisms underlying apathy.
• This research highlights the role of OCT in motivational deficits and self-initiated behavior.