Behavioral correlates of activity of optogenetically identified locus coeruleus noradrenergic neurons in rats performing t-maze tasks

Norepinephrine, a neuromodulator released during times of stress and arousal, is implicated in neuronal plasticity, memory consolidation and cognitive functions, including decision-making and behavioral flexibility. The brainstem nucleus locus coeruleus (LC) is the major source of forebrain norepinephrine. We recorded optogenetically identified LC neuronal activity in rats performing at their own pace in a fully automated T-maze for liquid rewards. First they had to choose the reward arm on the basis of visual cues, then new spatial reward contingencies were imposed. In the session where the animal shifted tasks the first time, the LC firing rate after VC onset increased significantly, even as the animal adhered to the previous rule. Firing rate also increased prior to crossing photodetectors that controlled stimulus onset and offset, and this was positively correlated with accelerations, consistent with a role in mobilizing effort. The results contribute to the growing evidence that the LC is essential for behavioral adaptation by promoting cognitive flexibility and mobilizing effort in face of changing environmental contingencies.

L. Xiang, A. Harel, HY. Gao, AE. Pickering, SJ. Sara, SI. Wiener (2019). Scientific Reports 9:1361.

Nested sequences of hippocampal assemblies during behavior support subsequent sleep replay

During exploration, hippocampal place cells activate one after the other forming sequences that represent the ongoing trajectory at the behavioral timescale. During subsequent slow wave sleep, the same sequences are endogenously replayed at a highly accelerated pace, contributing to memory consolidation. How is this sequential organization maintained across two different time scales, expressed at disjoint moments in time and during different brain states? We show that this requires faster sequences at the theta (~150 ms) time scale, nested within the slow, behavioral time scale sequences.

C. Drieu, R. Todorova, M. Zugaro (2018). Science 362(6415):675-679.