Physiological concomitants of diving in the caiman, Caiman sclerops

Epidural EEG recordings were made from the olfactory bulbs and from the cerebral hemispheres of Caiman sclerops while floating on the surface of a shallow tank and during submersion. Manual analysis of the olfactory bulb data failed to reveal obvious differences in background activity between surface and underwater records, but, of course, there were no olfactory spindles underwater. Manual analysis of the cerebral EEG's indicated two peculiarities existing while the caiman was submerged. The first was frequent bursts of high voltage spikes and spindles; the second was a periodic lowering in amplitude of higher frequencies. This underwater EEG activity began promptly after the animal submerged; it always disappeared before the animal gave any external evidence of movement or surfacing; and it was never seen in a moving animal or in an animal on the surface. Power spectral density analysis of caiman olfactory bulb EEG's revealed statistically significant differences between surface and underwater olfactory background activity. Caimans exhibited a classical episode of bradycardia upon submersion, however, when threatened they were capable of initiation of bradycardia before diving. When threatened underwater, bradycardia deepened and they could maintain the bradycardia for long periods after surfacing. Bradycardial response before diving and the continued maintenance of the bradycardia after surfacing suggests that caimans voluntarily control vagal tone. A paper on the method used for statistical comparison of power spectra is included.