Startle-evoked changes in diaphragmatic activity during wakefulness and sleep

Area of Science:

• Neuroscience
• Sleep Science
• Respiratory Physiology

Background:

• Generalized muscle atonia characterizes rapid-eye-movement sleep (REMS).
• Diaphragm inhibition during REMS includes fractionations, brief electromyogram (EMG) pauses linked to phasic events.
• Motor inhibition is also a component of the startle response, and REMS involves high brain activation.

Purpose of the Study:

• To investigate the hypothesis that the neural basis of diaphragm fractionations during REMS is the activation of a startle network.
• To compare the effects of auditory stimuli on diaphragm activity during REMS, non-rapid-eye-movement sleep (NREMS), and wakefulness.

Main Methods:

• Auditory tone bursts (100 dB, 20 ms) were administered to cats during REMS, NREMS, and wakefulness at a fixed inspiratory level.
• Diaphragmatic EMG (DIA EMG) activity was measured and averaged over 100 ms post-stimulus.
• Parameters analyzed included latency to peak/nadir, activity change, and peak/nadir duration. Sham studies were conducted concurrently.

Main Results:

• Auditory stimuli induced profound suppression of DIA EMG activity in all cats during REMS (latency 42.4 ± 10.0 ms, duration 35.9 ± 17.6 ms).
• Similar suppression of DIA activity was observed during NREMS (latency 40.9 ± 13.3 ms, duration 23.9 ± 13.4 ms).
• An excitatory DIA EMG response occurred in only two cats during NREMS and wakefulness.

Conclusions:

• The startle-induced suppression of diaphragm activity during sleep shares similarities with spontaneous fractionations observed during REMS.
• These findings suggest that diaphragm fractionations during REMS may originate from the activation of a central startle system.