Abstract
The locus cœruleus (LC) is the primary source of noradrenergic projections to the forebrain, and, in prefrontal cortex, is implicated in decision-making and executive function. LC neurons phase-lock to cortical infra-slow wave oscillations during sleep. Such infra-slow rhythms are rarely reported in awake states, despite their interest, since they correspond to the time scale of behavior. Thus, we investigated LC neuronal synchrony with infra-slow rhythms in awake rats performing an attentional set-shifting task. Local field potential (LFP) oscillation cycles in prefrontal cortex and hippocampus on the order of 0.4 Hz phase-locked to task events at crucial maze locations. Indeed, successive cycles of the infra-slow rhythms showed different wavelengths, and if they are periodic oscillations that can reset phase relative to salient events.
Simultaneously recorded infra-slow rhythms in prefrontal cortex and hippocampus could show different cycle durations as well suggesting independent control. Most LC neurons (including optogenetically identified noradrenergic neurons) recorded here were phase-locked to these infra-slow rhythms, as were hippocampal and prefrontal units recorded on the LFP probes. The infra-slow oscillations also phase-modulated gamma amplitude, linking these rhythms at the time scale of behavior to those coordinating neuronal synchrony. This would provide a potential mechanism where noradrenaline, released by LC neurons in concert with the infra-slow rhythm, would facilitate synchronization or reset of these brain networks, underlying behavioral adaptation.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Tally of phase-locked LC neurons excludes cases with no regular phase-locking of the infra-slow rhythm and sessions with less than 1000 spikes. Figure 2 modified to exclude citation of data from periods without regular phase-locking. Supplementary Table removed (integrated into text, and resultant vector lengths considered uninformative. Reformatted for journal submission.