How brain encodes magnitude and delay of rewards

Washington, July 10 : Anticipation may be best when expecting something good, but humans and animals would rather not wait, preferring an immediate reward. Now, researchers have found how a decision-making region of the brain encodes information associated with the magnitude and delay of rewards.

The preference for immediate reward is called temporal discounting, and the value of reward depreciated according to its delay is referred to as temporally discounted value.

Previous animal studies aimed at studying the neural signals associated with the impact of reward magnitude and delay on choice behavior have been difficult to interpret.

"Despite the fundamental role of time in decision making, how the brain encodes the temporally discounted values to guide the animal's choice during intertemporal choice remains poorly understood," says lead author Dr. Daeyeol Lee from Yale University School of Medicine.

Published in the journal Neuron, the scientists examined whether the dorsolateral prefrontal cortex (DLPFC), a part of the brain implicated in decision-making and contextual control of behaviors, is involved in temporal discounting and intertemporal choice.

The researchers studied the brains and behaviors of animals trained in an intertemporal choice task where reward delays were indicated by clocks. Importantly, the positions of targets associated with small or large rewards and their corresponding delays were randomly varied.

"We demonstrated that the neural signals in the DLPFC related to temporally discounted values did not simply reflect reward magnitude or reward delay," Lee said.

"In many DLPFC neurons, signals related to reward magnitude and delay were combined such that neurons tended to change their activity similarly when the reward from a particular choice becomes larger and when it becomes available more immediately," Lee added.

The results suggest that activity related to temporally discounted values in the prefrontal cortex might determine the animal's behavior during intertemporal choice.

The authors caution that their findings likely reveal only a part of the process, as results from previous studies have suggested that the prefrontal cortex might be one of many brain regions involved in intertemporal choice.

ANI