Cephalopod behaviour.

Underlying all animal behaviors, from the simplest reflexive reactions to the more complex cognitive reasoning and social interaction, are nervous systems uniquely adapted to bodies, environments, and challenges of different animal species. Coleoid cephalopods - octopuses, squid, and cuttlefish - are widely recognized as the most behaviorally complex invertebrates and provide exciting opportunities for studying the neural control of behaviour. These unusual molluscs evolved over 400 million years ago from slow-moving armored forms to active predators of coastal and open ocean ecosystems. In this primer we will discuss how, during cephalopod evolution, the relatively simple ganglion-based molluscan nervous system has been extensively transformed to control the complex bodies and process extensive visual, tactile, and chemical sensory inputs, and summarize some recent findings about their fascinating behaviors.

Recording electrical activity from the brain of behaving octopus.

Octopuses, which are among the most intelligent invertebrates,1,2,3,4 have no skeleton and eight flexible arms whose sensory and motor activities are at once autonomous and coordinated by a complex central nervous system.5,6,7,8 The octopus brain contains a very large number of neurons, organized into numerous distinct lobes, the functions of which have been proposed based largely on the results of lesioning experiments.9,10,11,12,13 In other species, linking brain activity to behavior is done by implanting electrodes and directly correlating electrical activity with observed animal behavior. However, because the octopus lacks any hard structure to which recording equipment can be anchored, and because it uses its eight flexible arms to remove any foreign object attached to the outside of its body, in vivo recording of electrical activity from untethered, behaving octopuses has thus far not been possible. Here, we describe a novel technique for inserting a portable data logger into the octopus and implanting electrodes into the vertical lobe system, such that brain activity can be recorded for up to 12 h from unanesthetized, untethered octopuses and can be synchronized with simultaneous video recordings of behavior. In the brain activity, we identified several distinct patterns that appeared consistently in all animals. While some resemble activity patterns in mammalian neural tissue, others, such as episodes of 2 Hz, large amplitude oscillations, have not been reported. By providing an experimental platform for recording brain activity in behaving octopuses, our study is a critical step toward understanding how the brain controls behavior in these remarkable animals.

Protocol for controlled behavioral testing of octopuses using a single-arm tactile discrimination two-choice task.

Due to their unique body, standard behavioral testing protocols are often hard to apply to octopuses. Our protocol enables controlled behavioral testing of the sensory systems in single arms while allowing observation of the arm motion. The protocol allows the researcher to exclude the sense of vision without surgical manipulation and selectively test peripheral sensory input-derived learning and motor behavior. Applying the protocol requires systematic and multistage training of octopuses to associate correct maze interaction with food reward. For complete details on the use and execution of this profile, please refer to Gutnick et al. (2020).

Squid adjust their body color according to substrate.

Coleoid cephalopods camouflage on timescales of seconds to match their visual surroundings. To date, studies of cephalopod camouflage-to-substrate have been focused primarily on benthic cuttlefish and octopus, because they are readily found sitting on the substrate. In contrast to benthic cephalopods, oval squid (Sepioteuthis lessoniana species complex) are semi-pelagic animals that spend most of their time in the water column. In this study, we demonstrate that in captivity, S. lessoniana Sp.2 (Shiro-ika, white-squid) from the Okinawa archipelago, Japan, adapts the coloration of their skin using their chromatophores according to the background substrate. We show that if the animal moves between substrates of different reflectivity, the body patterning is changed to match. Chromatophore matching to substrate has not been reported in any loliginid cephalopod under laboratory conditions. Adaptation of the chromatophore system to the bottom substrate in the laboratory is a novel experimental finding that establishes oval squid as laboratory model animals for further research on camouflage.

Neuroecology: Forces that shape the octopus brain.

Octopuses inhabit almost all seas in the world. A new study on tropical species suggests that, as in vertebrates, folding in the brain and visual system might be linked to habitat and lifestyle.

Use of Peripheral Sensory Information for Central Nervous Control of Arm Movement by Octopus vulgaris.

Octopuses are active predators with highly flexible bodies and rich behavioral repertoires [1-3]. They display advanced cognitive abilities, and the size of their large nervous system rivals that of many mammals. However, only one third of the neurons constitute the CNS, while the rest are located in an elaborate PNS, including eight arms, each containing myriad sensory receptors of various modalities [2-4]. This led early workers to question the extent to which the CNS is privy to non-visual sensory input from the periphery and to suggest that it has limited capacity to finely control arm movement [3-5]. This conclusion seemed reasonable considering the size of the PNS and the results of early behavioral tests [3, 6-8]. We recently demonstrated that octopuses use visual information to control goal-directed complex single arm movements [9]. However, that study did not establish whether animals use information from the arm itself [9-12]. We here report on development of two-choice, single-arm mazes that test the ability of octopuses to perform operant learning tasks that mimic normal tactile exploration behavior and require the non-peripheral neural circuitry to use focal sensory information originating in single arms [1, 10]. We show that the CNS of the octopus uses peripheral information about arm motion as well as tactile input to accomplish learning tasks that entail directed control of movement. We conclude that although octopus arms have a great capacity to act independently, they are also subject to central control, allowing well-organized, purposeful behavior of the organism as a whole.

The underestimated giants: operant conditioning, visual discrimination and long-term memory in giant tortoises.

Relatively little is known about cognition in turtles, and most studies have focused on aquatic animals. Almost nothing is known about the giant land tortoises. These are visual animals that travel large distances in the wild, interact with each other and with their environment, and live extremely long lives. Here, we show that Galapagos and Seychelle tortoises, housed in a zoo environment, readily underwent operant conditioning and we provide evidence that they learned faster when trained in the presence of a group rather than individually. The animals readily learned to distinguish colors in a two-choice discrimination task. However, since each animal was assigned its own individual colour for this task, the presence of the group had no obvious effect on the speed of learning. When tested 95 days after the initial training, all animals remembered the operant task. When tested in the discrimination task, most animals relearned the task up to three times faster than naïve animals. Remarkably, animals that were tested 9 years after the initial training still retained the operant conditioning. As animals remembered the operant task, but needed to relearn the discrimination task constitutes the first evidence for a differentiation between implicit and explicit memory in tortoises. Our study is a first step towards a wider appreciation of the cognitive abilities of these unique animals.

Animal Behavior: Socializing Octopus.

Building on the recently published Octopus bimaculoides genome, a new study identifies an evolutionarily conserved neural mechanism for serotonergic regulation of social behaviors.

Behavioral analysis of cuttlefish traveling waves and its implications for neural control.

Traveling waves (from action potential propagation to swimming body motions or intestinal peristalsis) are ubiquitous phenomena in biological systems and yet are diverse in form, function, and mechanism. An interesting such phenomenon occurs in cephalopod skin, in the form of moving pigmentation patterns called "passing clouds". These dynamic pigmentation patterns result from the coordinated activation of large chromatophore arrays. Here, we introduce a new model system for the study of passing clouds, Metasepia tullbergi, in which wave displays are very frequent and thus amenable to laboratory investigations. The mantle of Metasepia contains four main regions of wave travel, each supporting a different propagation direction. The four regions are not always active simultaneously, but those that are show synchronized activity and maintain a constant wavelength and a period-independent duty cycle, despite a large range of possible periods (from 1.5 s to 10 s). The wave patterns can be superposed on a variety of other ongoing textural and chromatic patterns of the skin. Finally, a traveling wave can even disappear transiently and reappear in a different position ("blink"), revealing ongoing but invisible propagation. Our findings provide useful clues about classes of likely mechanisms for the generation and propagation of these traveling waves. They rule out wave propagation mechanisms based on delayed excitation from a pacemaker but are consistent with two other alternatives, such as coupled arrays of central pattern generators and dynamic attractors on a network with circular topology.

Social learning in Cartilaginous fish (stingrays Potamotrygon falkneri).

Social learning is considered one of the hallmarks of cognition. Observers learn from demonstrators that a particular behavior pattern leads to a specific consequence or outcome, which may be either positive or negative. In the last few years, social learning has been studied in a variety of taxa including birds and bony fish. To date, there are few studies demonstrating learning processes in cartilaginous fish. Our study shows that the cartilaginous fish freshwater stingrays (Potamotrygon falkneri) are capable of social learning and isolates the processes involved. Using a task that required animals to learn to remove a food reward from a tube, we found that observers needed significantly (P < 0.01) fewer trials to learn to extract the reward than demonstrators. Furthermore, observers immediately showed a significantly (P < 0.05) higher frequency of the most efficient "suck and undulation" strategy exhibited by the experienced demonstrators, suggesting imitation. Shedding light on social learning processes in cartilaginous fish advances the systematic comparison of cognition between aquatic and terrestrial vertebrates and helps unravel the evolutionary origins of social cognition.

Octopus vulgaris uses visual information to determine the location of its arm.

Octopuses are intelligent, soft-bodied animals with keen senses that perform reliably in a variety of visual and tactile learning tasks. However, researchers have found them disappointing in that they consistently fail in operant tasks that require them to combine central nervous system reward information with visual and peripheral knowledge of the location of their arms. Wells claimed that in order to filter and integrate an abundance of multisensory inputs that might inform the animal of the position of a single arm, octopuses would need an exceptional computing mechanism, and "There is no evidence that such a system exists in Octopus, or in any other soft bodied animal." Recent electrophysiological experiments, which found no clear somatotopic organization in the higher motor centers, support this claim. We developed a three-choice maze that required an octopus to use a single arm to reach a visually marked goal compartment. Using this operant task, we show for the first time that Octopus vulgaris is capable of guiding a single arm in a complex movement to a location. Thus, we claim that octopuses can combine peripheral arm location information with visual input to control goal-directed complex movements.