Figure 2.

The rat hippocampus displays a low-frequency respiration-coupled oscillation (HRR), which coexists with faster theta oscillations during activated states. A, Example raw traces of simultaneous recordings of air pressure in the nasal cavity (nasal) along with LFPs from the OB and hippocampus of a urethane-anesthetized rat (DG; CA1, region 1 of cornu ammonis). B, Power spectrum of the nasal pressure signal, revealing a respiratory rate of ∼1.5 Hz (Resp. Freq., blue dashed line). C, OB, DG, and CA1 power spectra. There are prominent power peaks in OB and DG at the respiratory frequency (blue dashed lines); CA1 has a prominent power peak at the theta frequency range (∼4.5 Hz). D, Coherence spectra between nasal respiration and LFP signals (blue lines). Light gray lines reproduce the power spectra depicted in C. There are coherence peaks at the exact same frequency as respiration and its harmonics, along with lack of coherence at the peak frequency of CA1 theta. Results in B–D were obtained from a 60 s representative data segment of activated state, which included the raw signals depicted in A. E, Mean respiratory and theta peak frequencies across animals (n = 6 rats). *p < 0.001 (paired t test). F, Mean nasal-LFP coherence at respiratory and theta peak frequencies (n = 6 rats). *p < 0.001 (paired t tests). Error bars indicate SEM.