Isolated cortical computations during delta waves support memory consolidation


Delta waves have been described as periods of generalized silence across the cortex, and their alternation with periods of endogenous activity results in the slow oscillation of slow-wave sleep. Despite evidence that delta waves are instrumental for memory consolidation, their specific role in reshaping cortical functional circuits remains puzzling. In a rat model, we found that delta waves are not periods of complete silence and that the residual activity is not mere neuronal noise. Instead, cortical cells involved in learning a spatial memory task subsequently formed cell assemblies during delta waves in response to transient reactivation of hippocampal ensembles during ripples. This process occurred selectively during endogenous or induced memory consolidation. Thus, delta waves represent isolated cortical computations tightly related to ongoing information processing underlying memory consolidation.

R. Todorova, M. Zugaro (2019). Science 366(6463):377-381.

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.