By Jonny Lupsha, Wondrium Staff Writer
Some aspects of sleep science are studied through animal sleep habits. This is because learning about things like memory consolidation during sleep can only go so far with human study. Can we really learn from animal sleep studies?
Octopuses may be able to dream. Their colors often flicker while they doze, suggesting something similar to REM sleep. Although that’s a curious fact, it may not seem too important to our everyday lives, aside from maybe winning a question at trivia night—but it is.
Sleep studies in humans can only tell us so much. Sleep science shows how we store memories for long-term storage—or delete them—while we sleep, but those studies are limited to phenomenological or philosophical realms. How do we get a better and more neurophysiological view of the relationship between sleep and memory? Animal sleep studies.
In his video series Secrets of Sleep Science: From Dreams to Disorders, Dr. H. Craig Heller, the Lorry I. Lokey/Business Wire Professor of Biological Sciences and Human Biology at Stanford University, explained how it works using a study of sleepy kittens.
Three Groups of Sleepy Kittens
Learning any motor skill comes with practice, but progress is seen in the brain during periods of both wake and sleep. Dr. Heller noted that in a visual discrimination task, improvement was “limited to the region of the visual field that was used in the training” and not shown in regions of the system not needed in the visual discrimination task.
“That means that the improvement was not in the visual system as a whole, but only in the specific visual circuits that were involved in the training,” he said. “Could the improvement be due to structural changes in those circuits?”
To learn this, scientist Marcos Frank tested binocular vision in kittens. The visual cortex on each side of the brain receives information from both eyes, which is how we have depth perception. So Frank took three groups of kittens and in the first group, he closed one eye of each kitten during the last six hours of light for the day. In the second group, he did the same but allowed the kittens to sleep for the next six hours in the dark. In the third group, he closed one eye in each kitten again, then put them in the dark but prevented them from sleeping.
A Cat’s Eye
“In each kitten, he then measured the amount of input to the visual cortical neurons from the left and right eyes,” Dr. Heller said. “He found that even six hours of monocular deprivation in the light caused there to be more input to the visual cortex from the open eye.
“This shift was amplified during the next six hours in the dark if the kitten slept, but if not, if the kitten was sleep deprived, this rewiring did not occur.”
Aside from making us ask ourselves how we’d feel keeping sleepy kittens awake for science, what were the outcomes of this study?
“Only six hours of asymmetry in visual stimulation was sufficient to induce structural changes in the visual system, and these changes were largely dependent on sleep,” Dr. Heller said. “It is therefore likely that the changes resulting from training in the visual discrimination task were also due to synaptic structural changes in the specific pathways that were used, and these changes were dependent on sleep.”
Animal sleep studies can teach us about structural changes in the body and brain that human sleep studies can’t. Despite branching off from an evolutionary standpoint 500 million years ago, we may yet learn something about ourselves from octopus sleep states.