Activity of Interneurones in the Arm of Octopus in Response to Tactile Stimulation

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Abstract
1. A method for recording nervous activity from the nervous system of the arm of Octopus is given. Difficulties of mobility and vasoconstriction are reduced by brain lesions. 2. Three areas were recorded: afferent sucker nerves, axial ganglia, and the dorsolateral axial cord. 3. The sucker nerves include large tactile units corresponding to discrete parts of the sucker rim. These are fast-adapting, phasic, not very sensitive, and are located in the area of motor innervation of the same nerve. 4. Two types of interneurones were found in the axial ganglia, responding to either tactile stimulation of their own or neighbouring suckers, or to proprioceptive input from their own sucker. Motor units to the sucker musculature were also found. 5. Almost all recorded units in the dorsolateral axial cord were interneurones receiving tactile input. They have the following characteristics: (a) they are rapidly adapting, often phasic, and show little or no ‘spontaneous’ activity. (b) they habituate rapidly to even complex patterns of stimulation and discriminate between them, behaving as ‘novelty units’. (c) different sites of stimulation are discriminated by change in both the number of active units and their temporal patterning. The smallest area shown to be separately represented is the rim of one sucker. (d) prolonged activity can be initiated by a brief initial stimulus, which is without apparent correlated motor output. (e) stimulation of areas outside a unit's sensory field can lead to activity in that unit or to dehabituation in a previously active unit. No proprioceptive representation was found.