Fig. 7

Illustration of respiratory rhythm reset and evidence that seizure-associated central apneic episodes result from a partial activation of the diving reflex brainstem circuitry. Taken from [88] with permission. Raw data record shows two events, the first associated with a flat head-out plethysmogram and the second showing a small ripple present in the plethysmogram. Both events are similarly associated with brief bursts in the EEG that can be isolated by high-pass filtering (top sweep). When non-flat plethysmogram periods are superimposed using the brief bursts to align the records, the plethysmograms superimpose, indicating a reset of the respiratory rhythm with each burst. The periods of no air movement are consistent with activation of the diving reflex efferent pathways and resemble responses induced by actual activation of the diving reflex with nasopharyngeal mist or irrigation with water (data not shown). a Example record of two events, one event that includes complete cessation of breathing effort as evidenced by flatline plethysmograph, and a later event where respiratory effort did not stop. Records from top to bottom are high-pass filtered EEG (top EEG channel was filtered), plethysmograph, ECG, and two EEG recordings, one from each hemisphere over dorsal hippocampus. The pronounced artifacts evident on the filtered EEG trace are associated with the central apneic episode lasting about 1.5 s (onset indicated by arrow), and a later event that does not include cessation of airflow. High-frequency events are evident in the full bandpass EEG records. Segment of raw data is taken from a longer seizure episode; the onset and offset of the seizure itself are not illustrated. Calibrations are 0.025 mV filtered EEG, 0.2 ml plethysmograph, 0.05 mV ECG, and 0.2 mV for both EEG channels. Time calibration is 2 s. b Twenty superimposed sequential non-apneic events from a single animal to highlight the complete alignment of the pre- and post-artifact plethysmograph records. This alignment, given the broader range of phases leading up to the event onset, indicates a resetting of the respiratory rhythm, but the rhythm after about 1–1.5 s becomes highly variable. Calibrations are 0.05 mV filtered EEG and 0.2 ml plethysmograph. Time calibration is 1 s