Nasal inhalations and exhalations evoke distinct prefrontal-cortex responses with constant latency

Neuronal activity synchronous to breathing is salient across the mammalian brain. These modulations are typically characterized as oscillating signals phase-locked to the ongoing breathing rhythm and treated as evidence for respiratory 'entrainment' of cortical and subcortical oscillations. Since activation of the olfactory circuitry has been identified as their preponderant source, we wondered whether respiratory brain signals could be better understood as sequences of evoked sensory potentials. To help distinguish between these scenarios, we set out to quantify the detailed alignment of prefrontal cortex local field potentials (LFPs) to the nasal airflow cycle across the natural repertoire of rat breathing. We found that, while LFP and breathing show salient synchrony for all breathing modes, the phase of their locking is a strict linear function of respiratory rate. We explain this by showing that LFPs align to nasal airflow with a constant time lag of 100 ms, irrespective of breathing rate. Segmenting by breathing cycles revealed that LFP peaks and fast-gamma bursts are time-locked to inhalations, while LFP troughs and slow-gamma activity time-lock to exhalations. Our results support the view that respiratory signals across the frontal brain of rodents are sensory potentials evoked by cyclic ortho- and retronasal airflow.