Neural responses to light stimulation in the octopus arm.

Octopus are known to be visual animals. Beyond functions of the eyes, recent investigations have documented the importance of extraocular photoreception in behavior. Octopus arms have been shown to respond behaviorally to local light exposure with negative phototaxis. Moreover, light-activated chromatophore expansion (LACE) in octopus arms indicates that skin-based photoreception may contribute to light detection. In this study, we used electrophysiological recordings to investigate the neural activity of the arm's axial nerve cord in response to light on the arm. We tested the hypothesis that light stimulates activity of neurons in the arm's axial nerve cord. We also aimed to determine sensitivities to different wavelengths of light. The results showed that the axial nerve cord was strongly responsive to light stimulation of the arm and that the response travels along the length of the axial nerve cord. Blue light generated the strongest neural activity while red and green light also induced responses. Light induced neural activity was mediated through the aboral arm skin and by the oral-side skin and suckers. These findings reveal the role of the skin in the sensory abilities of octopuses and provide insights into the neural mechanisms underlying their response to light. The study underscores the importance of extraocular photoreception in future investigations of cephalopod sensory and behavioral biology.