Dorsal Raphe Nucleus Controls Motivational State Transitions in Monkeys

Abstract

The dorsal raphe nucleus (DRN) is an important source of serotonin in the brain but fundamental aspects of its function remain elusive. Here, we present a combination of minimally invasive recording and disruption studies to show that DRN brings about changes in motivation states. We use recently developed methods for identifying temporal patterns in behaviour to show that monkeys change their motivation depending on the availability of rewards in the environment. Distinctive patterns of DRN activity occur when monkeys transition between a high motivation state occupied when rewards are abundant, to a low motivation state engendered by reward scarcity. Disrupting DRN diminishes sensitivity to the reward environment and perturbs transitions in motivational states.

Origins of noise in both improving and degrading decision making

“…From an evolutionary perspective, uncertainty in the representation of value poses significant challenges for humans and animals in making accurate decisions. The uncertainty of an option’s value is an inevitable aspect of decision-making and is due to various factors like the stochasticity inherited from the environment (Drugowitsch et al, 2016), uncertain reward associations (Daw et al, 2005; Schlichting & Preston, 2016; Shohamy & Wagner, 2008; Wimmer & Shohamy, 2012), stochastic memory retrieval (Bakkour et al, 2019; Shadlen & Shohamy, 2016), imprecise inferential reasoning (Barron et al, 2020; Xue et al, 2024), and/or fluctuating motivational states (Priestley et al, 2024; Shen, Chen, et al, 2023). Our findings regarding early noise illustrate a special case where noise can be effectively managed by the brain circuit.…”