The Laboratory of Sensory Systems of Vertebrates has accumulated extensive experience working with marine mammals. Laboratory staff have carried out pioneering studies of dolphin hearing that have become classics, and made discoveries including unihemispheric sleep in dolphins and the determination of the hydrodynamic characteristics of the dolphin body; studies of the visual analyzer of toothed cetaceans have been conducted, and work has been done on mapping the brain of marine mammals (Ladygina, Supin, 1974; Romanenko, 1974; Mukhametov et al., 1976; Supin et al., 1978; Popov, Supin, 2012).
Over the years of the laboratory's existence, new methods for studying the neurophysiology of marine mammals have been developed, and many entirely new concepts have been formulated based on the data obtained. The arrangement of the main sensory areas of the cerebral cortex (visual, auditory, somatosensory), atypical compared with terrestrial mammals, made it possible to propose a new scheme for the evolution of the cerebral cortex in mammals as a whole.
Special mention should be made of research on the physiology of hearing in marine mammals. New methods were developed and unique data obtained. In a number of dolphin species (bottlenose dolphin, beluga whale, Amazon river dolphin, harbor porpoise, false killer whale, common dolphin, and others), electrophysiological methods were used to study such hearing characteristics as response speed, sensitivity and frequency range, frequency and temporal resolution, spatial resolution, mechanisms of sound conduction and binaural hearing, and many others. Data were obtained that changed prevailing views on the hearing of these animals, refuted several false hypotheses, and, in effect, made it possible to create a new approach to the study of mammalian hearing. These results are summarized in the monographs (Supin et al., 2001; Popov, Supin, 2013).
The topographic organization of the retina has been studied in a number of marine mammal species (cetaceans and pinnipeds), and methods have been developed for preparing whole-mount specimens and analyzing the spatial distribution of retinal cells (Cand. Sci. (Biol.) A.M. Mass). Features of the topographic organization of the visual field in cetaceans and pinnipeds have been established, in particular the presence in cetaceans of two areas of best vision (rather than one, as in all other mammals) in the nasal and temporal sectors of the visual field, which provides universal amphibious (aquatic-aerial) vision and a wide field of view. Pinnipeds have a single area of best vision, similar to terrestrial carnivores. Retinal resolving power in the areas of best vision has been measured. A previously unknown mechanism for increasing retinal resolving power through the clustered grouping of ganglion cells has been discovered.
An original hearing-testing method has been developed that allows quantitative assessment of the ability to discriminate complex sound signals. The method is used in both fundamental and applied research on human hearing (Prof. A.Ya. Supin, Cand. Sci. (Biol.) D.I. Nechayev, Research Fellow O.N. Milekhina).
A study of the sleep-wake cycle in dolphins revealed a previously completely unknown mechanism in dolphins — so-called unihemispheric sleep. This study, carried out jointly by A.Ya. Supin and L.M. Mukhametov, was officially recognized as a scientific DISCOVERY, and Professor Supin became a laureate of the USSR State Prize.
Experimental data were obtained on the relationship between functional brain asymmetry (unihemispheric sleep/wakefulness) and the asymmetric state of the eyes in cetaceans (in the beluga whale and bottlenose dolphins). It was established that the eye contralateral to the sleeping hemisphere is closed or half-closed most of the time (more than 90% of the time), while the eye contralateral to the waking hemisphere is more often open (Lyamin et al., 2002a; 2004). Thus, unilateral eye closure can serve as a reliable criterion of sleep in cetaceans.
To date, laboratory staff (Cand. Sci. (Biol.) O.I. Lyamin, Cand. Sci. (Biol.) L.M. Mukhametov) have studied sleep characteristics in more than 25 animal species, including aquatic and semi-aquatic mammals (cetaceans, eared and true seals, walrus, sea otter, Amazonian manatee, hippopotamus, coypu), several species of terrestrial non-laboratory mammals (elephant, blesbok antelope, hyrax, African mole-rat), as well as 3 bird species and 2 turtle species.
As a result of many years of theoretical and experimental study of the biohydrodynamic mechanisms of dolphin swimming, the bioacoustics group has developed a theory of a wing modeling the dolphin's tail fluke. An analytical method for calculating the hydrodynamic characteristics of the wing has been created. Studies of the kinematics and hydrodynamics of Black Sea dolphins have included an estimate of the dolphin's maximum swimming speed, the formulation of a law describing body deformation in an actively swimming dolphin, the study of the elastic properties of the skin, and evidence for the presence of boundary-layer control mechanisms in dolphins.
As a result of many years of observations and experiments, including the use of two-way electroacoustic communication between isolated dolphins, data were obtained on changes in the behavior and vocal signaling of bottlenose dolphins during adaptation to captivity, various stressors, and experimental situations, indicating that signaling parameters can be used to assess the animals' state. Differences in the use of signature whistles by animals of different ages, sexes, and emotional states were studied.
Overall, the laboratory's research has resulted in dozens of publications in both Russian and foreign journals and edited volumes. These publications have high citation indices. The results have also been presented at numerous domestic and international conferences. The laboratory's research is supported by numerous grants.