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Cephalopods have arguably the largest and most complex nervous systems amongst the invertebrates; but despite the squid giant axon being one of the best studied nerve cells in neuroscience, and the availability of superb information on the morphology of some cephalopod brains, there is surprisingly little known about the operation of the neural networks that underlie the sophisticated range of behaviour these animals display. This review focuses on a few of the best studied neural networks: the giant fiber system, the chromatophore system, the statocyst system, the visual system and the learning and memory system, with a view to summarizing our current knowledge and stimulating new studies, particularly on the activities of identified central neurons, to provide a more complete understanding of networks within the cephalopod nervous system.

This paper provides the first detailed description of the time courses of light-evoked pupillary constriction for two species of cephalopods, Sepia officinalis (a cuttlefish) and Eledone cirrhosa (an octopus). The responses are much faster than hitherto reported, full contraction in Sepia taking less than 1·s, indicating it is among the most rapid pupillary responses in the animal kingdom. We also describe the dependence of the degree of pupil constriction on the level of ambient illumination and show considerable variability between animals. Furthermore, both Sepia and Eledone lack a consensual light-evoked pupil response. Pupil dilation following darkness in Sepia is shown to be very variable, often occurring within a second but at other times taking considerably longer. This may be the result of extensive light-independent variations in pupil diameter in low levels of illumination.

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For many organisms vision is of fundamental importance to many aspects of their lives. Here we present the first study to examine the effects of ontogeny and light intensity on the vision of a cephalopod. We measured the visual acuity of four size classes of Sepia officinalis L., 1758 (common cuttlefish) under four light intensities. We used an optomotor testing system in which we recorded the unconditioned whole-body movements exhibited by individuals when placed inside a rotating cylinder lined with vertical black and white stripes. By varying the width of these stripes to determine the minimum width associated with a positive response, we were able to estimate the visual acuity angle or minimum separable angle (MSA). We found a significant effect of both body size and light intensity; larger animals had greater visual acuity, while individuals of all size classes discriminated more detail at higher light intensities. The minimum recorded MSA for S. officinalis was 34′ of arc (0.57°) for the largest animals (80 mm) at the highest light intensity used (15 µW·cm -2 ). Decreasing light intensity from 15 to 4.5 µW·cm -2 affected animals of all sizes to approximately the same degree, reducing their visual acuity by approximately 55%.Résumé : La vision joue un rôle fondamental dans plusieurs aspects de la vie de nombreux organismes. Nous présen-tons ici, pour la première fois, une étude des effets de l'ontogénie et de l'intensité lumineuse sur la vision d'un cépha-lopode. Nous avons mesuré l'acuité visuelle chez quatre classes de taille de la seiche commune (Sepia officinalis L., 1758) sous quatre conditions d'intensité lumineuse. Nous avons utilisé un système d'évaluation optomotrice qui permet d'enregistrer les mouvements du corps entier, sans conditionnement préalable, chez des individus placés à l'intérieur d'un cylindre rotatif marqué de bandes verticales noires et blanches. En variant la largeur des bandes afin de détermi-ner la largeur minimale qui provoque une réaction positive, nous avons pu estimer l'angle d'acuité visuelle ou l'angle minimal de séparation (MSA). Il y a un effet significatif à la fois de la taille et de l'intensité lumineuse; les animaux plus grands ont une meilleure acuité visuelle et les individus de toutes les classes de taille peuvent distinguer plus de détails aux intensités lumineuses plus élevées. Le MSA minimal observé chez S. officinalis est de 34′ d'arc (0,57°) chez les animaux les plus grands (80 mm) à l'intensité lumineuse la plus forte (15 µW·cm -2 ). La réduction de l'intensité lumineuse de 15 à 4,5 µW·cm -2 affecte les animaux de façon semblable sans égard à leur taille, en diminuant leur acuité visuelle d'environ 55 %.[Traduit par la Rédaction] Groeger et al. 279