Given the dramatic changes in neuronal excitability and the emergence of different brain rhythms across states of vigilance, we further hypothesized that respiration-gamma coupling is modulated by brain state. We thus hypothesized that respiratory signals relayed through Reu organize gamma synchrony in the prefrontal network. It has been shown that Reu mediates long-range gamma synchrony between the PFC and hippocampus 29 and appears to be necessary for the emergence of slow potentials in the PFC 30 that are likely respiration-related 31, 32. How respiration organizes gamma synchrony in the prefrontal network is unknown. In the rodent 21, 25, 26 and cat cerebral cortex 27, respiration modulates gamma amplitude and elicits a respiration-related cortical rhythm (RR), which tends to be more prominent in frontal regions 20, 21, 28. There has been a recent accumulation of evidence showing that respiration is a potent modulator of cortical and hippocampal activity 20, 21, 22, 23, 24. The ability of gamma to organize cortical activity is closely related to its 25 ms cycle which provides an optimal window for the co-activation of multiple neurons within successive cycles, facilitating the formation of local neuronal assemblies 18, 19. It has been consistently linked to higher-level functions such as consciousness 13, attention 14 and memory 15, 16, which denotes its fundamental role in prefrontal cortical functions 11, 17. The gamma rhythm (30–80 Hz), which is prominent in the aroused brain 10, plays an important role in the normal physiology 11 and pathophysiology 12 of the prefrontal network. Precise, inter-regional synchronization in this network is essential for memory processes and is largely facilitated by oscillations that emerge during different states of consciousness 7, 8, 9. The nucleus reuniens (Reu), a midline thalamic structure, provides a crucial link between the PFC and the hippocampus, forming a functional network that mediates multiple cognitive operations 4, 5, 6. Much of PFC output is reciprocated 1 with the notable exception of hippocampal afferents 2, 3 for which no direct prefrontal feedback projections have been found. The prefrontal cortex (PFC) is an anatomical hub that integrates inputs from a diverse set of cortical and subcortical structures 1.
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