Do Octopuses Dream?
The Basis of Dreaming
Dreaming has been the focus of scientific studies for a long time now, particularly in vertebrates like mammals and birds, and some of the most widely accepted theories suggest that dreams have purposes related to memory consolidation, neurla plasticity, threat simulation, and cognitive problem-solving. In humans, dreaming predominantly occurs during the rapid eye movement (REM) stage of sleep, characterised by high brain activity and intense neural replay of our waking moments.
The Synaptic Homeostasis Hypothesis (Tononi & Cirelli, 2003) introduces the idea that sleep, particularly REM sleep, helps 'prune' unnecessary synaptic connections formed during waking hours, strengthening important neural pathways and eliminating any redundant ones. Another theory, the Activation-Synthesis model (Hobson & McCarley, 1977), suggests that dreams are the brain’s way of making sense of random activity during sleep: the brainstem sends out random bursts of signals and the forebrain, responsible for higher thinking, tries to interpret these signals by weaving them into narrative – what we might experience as dreams .
Recent comparisons of human and animal sleep have displayed that species with advanced cognition – such as rats, birds and now cephalopods – show signs of REM-like states, similar to that of humans, indicating that dreaming may serve a fundamental role in intelligence and survival.
Octopus Brains and the Sleep Cycle
Octopuses (yes octopuses – not octopi) are extremely neurologically advanced invertebrates with about 500 million neurones, three-fifths of which are located in the arm nervous system (the rest distributed between the brain and optic lobes). Unlike vertebrates, they have no centralised neocortex but have a vertical lobe – memory and learning – and optic lobes – complex visual and processing -, structures which suggest a sophisticated system for perception and possible dreaming.
By performing electrophysiological recordings from the central brain to examine neural activity during octopus sleep, a technique developed through studies by Medeiros et al., 2021, two distinct sleep states in octopuses were revealed:
'Quiet sleep' is characterised by prolonged stillness, reduced neural activity and minimal chromatophore engagement. During 'active sleep', occurring every 30-40 minutes, is marked by rapid chromatophore activation, eye movements and motor twitches (like those seen while awake), remarkably similar to that of REM sleep in vertebrates.
Brain recordings show the active sleep closely resembles wakefulness, especially in areas linked to learning and memory, suggesting that they process information during their sleep. This similarity between humans and octopus active vs REM sleep states raises questions about whether they might experience dreams in a comparable manner to vertebrates.
Evidence for Dreaming
Neural Activity During Active Sleep
Neuroscientific studies have shown certain traits during active sleep: Elevated activity in the vertical lobe, similar to our hippocampal activation, suggests memory consolidation; fluctuating activation of the optic lobes implies internal visual processing, corresponding to mental imagery; spontaneous limb movement resembling behavioural replay which has been previously observed in mammals during REM sleep.
In other studies on various non-human primates, using calcium imaging (tracks neurone activity by detecting changes in calcium levels which correlate with neuronal firing) and electrode recordings (insertion of tiny electrodes into the brain to measure electrical signals), have helped us study this neural activity and may help broaden our knowledge regarding these octopus dreams in the future.
Chromatophore Expression
Chromatophores are pigment cells responsible for colour changes in cephalopods such as squid, cuttlefish, and octopuses. During active sleep, they displayed rapid and seemingly coordinated colour shifts, mirroring patterns seen during waking activities such as hunting and camouflage. This strongly suggests that octopuses, like humans, may be experiencing internally generated dream-like states in which they relive past events or simulate potential future scenarios, displaying their very complex cognition.
What Could They Dream About?
Hunting Sequences
As ambush predators, octopuses use sophisticated hunting tactics. This can be seen reflected in their chromatophore changes during sleep which suggests that they may replay or refine past hunting experiences in order to strengthen their predatory skills through neural reinforcement.
Defensive Strategies
Octopuses are constantly under pressure to survive between being both predator and prey. Their sleep characteristics suggest that their dreams may involve simulated escape behaviours, such as inking, jet propulsion or rapid colour shifts to reinforce and perfect their defensive responses.
Problem Solving
In general, through observation, octopuses are seen to excel at complex tasks like maze navigation and escaping from enclosures. There is a possibility that active sleep could help them mentally map their surroundings, similar to how human dreams replay difficult experiences and assist in problem-solving.
Social and Reproductive Behaviours
Even though they are primarily solitary, octopuses engage in intricate mating behaviours involving body language and chromatophore changes which are visually reflected during their active sleep. Dreaming may allow reinforcement of such interactions in order to ensure reproductive success.
Evolutionary Significance
Convergence of REM-like sleep
Despite their evolutionary divergence from vertebrates over 500 million years ago, the fact that octopuses exhibit REM-like sleep could suggests that sleep-dependant memory processing is essential for intelligent organisms and in their survival for so long.
Adaptive Mechanism
Dreams may help enhance survival in octopuses by refining behaviours through neural replay which reinforces their cognitive flexibility, mirroring how REM sleep in vertebrates strengthens synaptic connections thus enhancing their adaptive learning.
Conclusion
Octopuses have a structured sleep cycle, including active sleep, which closely resembles REM sleep in humans. Brain recordings and body movements suggest they may dream about real experiences. While we cannot know exactly what they dream of, evidence indicates they use sleep for memory and learning, just like humans. This research helps us understand why dreaming matters across species and challenges the idea that only some animals experience complex mental states.