Single Unit Recordings of Rat Lateral Habenula during a Navigation-based Spatial Memory Task

Abstract

In recent years, the lateral habenula (LHb) has become an area of great interest, as in vivo electrophysiological studies in head-fixed primates revealed the presence of neurons that respond differentially to rewards, punishment, and their cues-- in a manner opposite to the well-characterized dopaminergic neurons in the ventral tegmental area (VTA). Furthermore, these responses encode reward/punishment magnitude and are dependent on the outcomes of previous trials. Thus the LHb may be a generator of error prediction signals (Hikosaka, 2010). The lateral habenula is a point of convergence for basal ganglia and limbic circuits, which then projects to midbrain neuromodulatory systems. One functional connection of great interest includes inhibitory connections between LHb and VTA. LHb may also be part of action selection neural circuitry that is guided by motivation. We studied the role of the LHb in motivated behaviors in a semi naturalistic form. In particular, we conducted single unit recordings in LHb as Long Evans rats performed a navigation-based spatial memory task on a radial arm maze. Analyses of neural data confirm the existence of RPE encoding cells; however, the majority of LHb neurons recorded contain movement, particularly velocity, related correlates. Although the habenula has been found to be involved in many behaviors, Hikosaka has also proposed that the primary function of the lateral habenula is to suppress motor function under unfavorable conditions. The movement related cells found here may be involved in monitoring overall activity levels or encode specific aspects of behavior for action-specific learning.