Lateral habenula neurons transmit negative value signals to midbrain dopamine neurons

Abstract

Midbrain dopamine neurons are key components of the brain’s reward system. These neurons are excited by reward and sensory stimuli predicting reward, while they are inhibited by reward omission. These excitatory and inhibitory responses have been shown to play important roles in reward learning and positive motivation. However, it was unknown which parts of the brain provide dopamine neurons with reward-related signals necessary for their responses. Recent studies showed evidence that the lateral habenula, part of the structure called the epithalamus, is a good candidate for a source of reward-related signals in dopamine neurons. The lateral habenula projects to midbrain structures such as the substantia nigra pars compacta and ventral tegmental area which contain dopamine neurons. Electrical stimulation of the lateral habenula inhibits dopamine neuron activity. Neurons in the lateral habenula also encode reward-related signals but in an opposite manner to dopamine neurons (i.e., they are inhibited by reward and sensory stimuli predicting reward, and excited by reward omission). These findings suggest that the lateral habenula transmits reward-related signals to dopamine neurons by inhibiting them.