Fig. 1.

Behavioral state control. Examples of measures of respiration corresponding to major behavioral states: exploration, paradoxical sleep, quiet waking. The pattern of respiration can serve as a reliable marker for each state (Miasnikov et al., 2008b; Weinberger et al., 2006). Shown are the EEGs from the primary auditory cortex (lines 1) and the respiration records (lines 2). (A) During periods of preoccupation with ongoing activity, such as exploration or grooming, while the EEG is fast (A1), respiration is chaotic (A2: AC = 0.06) and the animal may show disproportionate response to tones (startle). (B) During paradoxical (REM) sleep, the EEG is low-voltage fast (B1) and respiration is irregular although less chaotic (B2: AC = 0.31), with many high-frequency shallow breathing movements. (C) During quiet waking, which is the state used for presenting tone during testing and training, the EEG is less desynchronized high-voltage (C1), animals are not moving, respiration is highly regular (C2: AC = 0.95) and the animals are responsive to tones. The respiration autocorrelation function (AC) was continuously calculated on-line over 4-s long epochs. When a randomly-selected inter-trial interval had passed, the software compared the current value of an AC with pre-selected threshold (AC≥0.95) and triggered a stimulus. C3: Quantification of a regular sinusoidal baseline respiration record (first 4 s) disrupted by tone presentation. The “Respiration Change Index” (RCI, Methods) is sensitive to both increases and decreases in signal amplitude and frequency. This example shows a typical response of a Paired animal to the CS tone, recorded while obtaining the behavioral frequency generalization gradient 24 h following completion of the pairing session. The shaded area indicates the first 13-s portion of the respiratory record containing the majority of tone-evoked response. The RCI values found within this epoch were used in the behavior data analysis.