If we define sleep in terms of brain activity then clams don't sleep because they lack a brain.
That's the challenge. Can that activity be considered sleep or is it just a part of the animal's neural activity that follows a circadian rhythm?
I feel like there is an anthropomorphic element that may be pushing us to label something as "sleep" because we'd like to think gastropods have dreams like we do.
What you suggest is that there may be restful and restorative neurological activities happening. Whether these meet the criteria for sleep, is less clear.
@GLaDTheresCake @dantheclamman
Indeed cephalopods such as octopus, squid, and cuttlefish have a central brain even though it might only be 1/3 of their nerves with the rest being in the limbs. These animals engage in active sleep, analogous to that found in mammals, including dolphins.
That seems quite different from the various clams who have no brain of any kind and might just react to external stimuli.
I imagine there is likely a continuum where at some point dreaming emerges.
@svavar @dantheclamman One definition of sleep which doesn't require a brain (or dreaming or even a nervous system): "a normal, reversible, recurrent state of reduced responsiveness to external stimulation that is accompanied by complex and predictable changes in physiology. "
https://www.britannica.com/science/sleep
By this definition, even a bacterium could sleep.
Sleep, a normal, reversible, recurrent state of reduced responsiveness to external stimulation that is accompanied by complex and predictable changes in physiology. Sleep contrasts with wakefulness, in which state there is an enhanced potential for sensitivity and an efficient responsiveness to external stimuli.
Dr. Dan Killam
Svavar the Neurospicy
Lillian Violet
rsp