1Authors MPS and JAS contributed equally to this work.
Received: May 5, 2014; Received in revised form: October 16, 2014; Accepted: October 30, 2014; Published Online: November 13, 2014
To make appropriate choices, organisms must weigh the costs and benefits of potential valuable outcomes, a process known to involve the nucleus accumbens (NAc) and its dopaminergic input. However, it is currently unknown if dopamine dynamically tracks alterations in expected reward value online as behavioral preferences change and if so, if it is causally linked to specific components of value such as reward magnitude and/or delay to reinforcement.
Electrochemical methods were used to measure subsecond NAc dopamine release during a delay discounting task where magnitude was fixed but delay varied across blocks (n = 7 rats). Next, to assess whether this dopamine signaling was causally related to specific components of choice behavior, we employed selective optogenetic stimulation of dopamine terminals in the NAc using a modified delay discounting task in which both delay and magnitude varied independently (n = 23 rats).
Cues predictive of available choices evoked dopamine release that scaled with the rat’s preferred choices and dynamically shifted as delay to reinforcement for the large reward increased. In the second experiment, dopamine signaling was causally related to features of decision making, as optogenetically enhanced dopamine release within the NAc during predictive cue presentation was sufficient to alter subsequent value-related choices. Importantly, this dopamine-mediated shift in choice was limited to delay-based, but not magnitude-based, decisions.
These findings indicate that NAc dopamine dynamically tracks delay discounting and establishes a causal role for this signaling in a subset of value-based associative strategies.