A comparative hypothesis examining octopuses, cuttlefish, and jumping spiders as convergent examples of high sensory integration systems.
Abstract
Sleep is widespread across the animal kingdom, yet its functional basis remains unresolved. While prevailing theories emphasize roles in synaptic homeostasis and memory consolidation, these frameworks are largely derived from vertebrate systems. Recent findings demonstrate REM-like sleep states in phylogenetically distant invertebrates, including cephalopods such as the octopus (Octopus vulgaris) and cuttlefish (Sepia officinalis), as well as jumping spiders (family Salticidae). These organisms differ substantially in neural architecture and evolutionary history, but share high sensory bandwidth and real-time integration demands.
Here, it is proposed that REM-like sleep may represent a convergent response to the computational burden imposed by continuous sensory integration. Across independent evolutionary lineages, organisms that must process large volumes of sensory input in real time may require periodic offline processing to maintain functional stability. This perspective suggests that active sleep states may not be lineage-specific adaptations, but functional consequences of complex information processing systems, and proposes a potential relationship between REM-like sleep and sensory integration load that has not been widely considered across taxa.
Keywords
REM sleep; sensory integration; cephalopods; jumping spiders; convergent evolution; sleep function
Introduction
Sleep is a near-universal biological phenomenon, yet its primary function remains incompletely understood. Proposed roles include memory consolidation, metabolic regulation and synaptic homeostasis (Diekelmann and Born, 2010; Tononi and Cirelli, 2014). While these frameworks are supported by substantial evidence, they do not fully explain the persistence of sleep across diverse taxa or the emergence of multiple sleep states, including rapid eye movement (REM) sleep.
These organisms are phylogenetically distant and exhibit fundamentally different neural architectures. However, they share a notable feature: high sensory bandwidth and continuous real-time integration demands. This observation raises the possibility that REM-like sleep may emerge not as a lineage-specific trait, but as a convergent response to a common functional constraint. To date, the relationship between REM-like sleep and sensory integration demands has not been explicitly framed as a unifying cross-taxa principle.
Evolutionary context and divergence
Cephalopods, including octopuses and cuttlefish (which are neither fish nor even vertebrates), share a common ancestor that lived approximately 270–300 million years ago. This ancestor is thought to have been an active, squid-like marine predator possessing a small external shell, a centralized nervous system, and relatively advanced visual capabilities for its time, but lacking the extreme behavioral flexibility and neural specialization seen in modern species (Kröger et al., 2011).
Following divergence, cephalopods underwent substantial evolutionary elaboration. Octopuses lost their external shells and evolved highly flexible bodies, alongside a distributed nervous system in which a large proportion of neurons reside in the arms (Grasso and Basil, 2009). Cuttlefish, by contrast, retained a more centralized neural architecture while developing highly sophisticated chromatophore systems enabling rapid, high-resolution body patterning (Hanlon and Messenger, 2018).
Thus, while octopus and cuttlefish share ancestry, their present-day sensorimotor systems represent distinct evolutionary solutions to complex environmental interaction, both characterized by substantial integration demands.
Table 1: Comparative evolutionary context & REM-like sleep
Sensory integration as a shared constraint
Cephalopods: distributed and centralized integration
In the octopus, neural processing is partially distributed across the arms, each of which is capable of local sensory-motor coordination. This architecture enables parallel processing of tactile, chemical and spatial information, coordinated at the level of the central brain (Grasso and Basil, 2009).
In contrast, other cephalopods, including cuttlefish, rely more heavily on centralized neural processing. However, they exhibit similarly high integration demands through rapid transformation of visual input into coordinated motor output, particularly via chromatophore-driven body patterning (Hanlon and Messenger, 2018).
Additionally, cephalopod skin contains light-sensitive proteins (opsins), suggesting that environmental information may be detected and processed beyond the visual system alone (Ramirez and Oakley, 2015).
Although octopuses lack the cone photoreceptor diversity required for conventional color vision and are therefore considered colorblind, they nonetheless generate precise color-matched camouflage, implying a form of sensory integration that extends beyond standard visual processing (Marshall and Messenger, 1996; Mäthger et al., 2009).
It is further speculated that the distributed control of octopus appendages may constitute a rudimentary form of multi-agent coordination, increasing integration demands and contributing to observed problem-solving behaviors such as object manipulation and escape, behaviors that have been extensively documented in this species.
Jumping spiders: visual integration and behavioral specialization
Spiders as a group possess multiple sensory modalities, including mechanosensory hairs that detect vibration and air movement, as well as multiple eyes. However, most spider species rely primarily on vibration-based sensing and web-mediated environmental extension, with relatively limited visual acuity.
In contrast, jumping spiders (family Salticidae) represent a marked departure from this pattern. They possess highly specialized forward-facing principal eyes capable of high-resolution vision, alongside additional eyes that detect motion and provide spatial awareness. This creates a modular visual system requiring integration across multiple streams of input (Land and Nilsson, 2012).
Jumping spiders are active hunters rather than passive web users. They stalk prey, evaluate distances and execute targeted jumps, often employing detours and route planning that indicate internal modelling of their environment (Cross and Jackson, 2016).
REM-like sleep states have been identified in jumping spiders, including retinal movement and periodic motor activity during rest (Rößler et al., 2022). Such states have not been broadly documented across other spider taxa, suggesting that REM-like phenomena may emerge in subgroups with elevated integration demands, rather than being a universal feature of the clade.
REM-like sleep as a convergent phenomenon
Figure 1: REM-like sleep has been observed in phylogenetically distant organisms that differ in neural architecture but share high sensory integration demands. Octopuses exhibit distributed processing across semi-autonomous appendages, cuttlefish rely on rapid visual-to-motor transformations, and jumping spiders integrate multiple visual streams for active predation. Despite these differences, all three systems exhibit REM-like states, suggesting a convergent response to integration load. This framework proposes that high-bandwidth, continuously updating systems may require structured periods of offline processing.
Across these systems, REM-like states share several features:
- internally generated neural activity
- motor output decoupled from external stimuli
- cyclic alternation with quiescent states
These states occur in organisms with differing neural architectures—distributed in octopuses, more centralized in cuttlefish and jumping spiders—but converge in their requirement for continuous integration of high-volume sensory input.
Notably, not all organisms that exhibit sleep display REM-like states. Crustaceans such as crayfish demonstrate sleep-like quiescence and neural state changes but lack clear evidence of REM-like activity (Ramón et al., 2004).
It is also striking that these organisms are broadly solitary and semelparous (one big reproduction event followed by death). This co-occurrence is unlikely to be explanatory on its own, but its repetition alongside REM-like states in otherwise distant lineages is difficult to ignore.
Taken together, these observations suggest that REM-like sleep may not be a universal feature of sleep, but may instead emerge under specific computational constraints.
Comparative features of organisms exhibiting REM-like sleep
A proposed framework: integration load and offline processing
Existing models, such as the synaptic homeostasis hypothesis, propose that sleep serves to regulate synaptic strength accumulated during wakefulness (Tononi and Cirelli, 2014). Extending this framework, organisms that continuously integrate large volumes of sensory data may accumulate a greater degree of unresolved neural activity during active states.
REM-like states may represent periods in which this processing becomes internally active and structured, rather than passive.
This perspective suggests that sleep—particularly active sleep—may not function solely as an adaptive enhancement, but as a functional consequence of system-level complexity.
Conclusion
The presence of REM-like sleep in phylogenetically distant organisms with high sensory integration demands suggests a possible convergent response to a shared constraint.
This perspective does not establish causation, nor does it resolve the function of sleep. Rather, it identifies a pattern: that systems operating under substantial integration demands may require structured periods of offline activity.
Whether this relationship generalizes across taxa remains an open question.
References
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Acknowledgements
The author used ChatGPT (OpenAI) to assist with drafting, editing and figure generation. All content was reviewed and verified by the author. Concepts, hypotheses and interpretations originated entirely with the author.
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