Andrew's Squid Experiments
    from a Physical Point of View



      The orderly colour changes of cephalopods require an intact brain. When the brain has died, or the nerve supply to the skin has been removed, the colours become chaotic. Such autonomous behaviour highlights a general principle.

      Andrew Packard [1] has observed wave-like excitements flowing through the spots of colour (chromatophores) of squids some days after cutting the nerve to one side of the body. These muscle-operated organs develop supersensitivity and non-nervous communication between them. The different properties can be inspected directly through the transparent surface of the animals' skin.


      Squid with centimeter scale




    Observations

      Waves proceeding in a layered 'neural' wave space show relations within a single layer and between different layers. Black, red and yellow chromatophores act relatively independently of each other, and with different conductivities in the separate layers.

      Besides straight-going waves proceeding from boundaries with innervated skin, we find circular waves radiating from a centre of irritation and spiral waves rotating around a stable core.

      Water temperature influences the waves. Below 6°C they are abolished. Above 10°C, frequency, velocity and numbers of waves differentially increase.

      Deletion of two colliding waves shows, that 1) the conductivity mechanism acts multidirectionally; 2) disappearance of waves behind the points of interference means that the wave space is cleaned during a chromatophore's refractory period.




    Picture sequence

      Fig.1: A black colour wave moves along the denervated side of a squid




    Downloadable Movies



      Experiments done May, 31st 1995:

      Fig.2: Pressure induced waves moving from left (head) to right

      Fig.3: Circular waves coming from center region



      Experiments done October, 27th 1995:

      Fig.4: Straight going waves from left (head) to right

      Fig.5: Circular waves coming from center region

      Fig.6: Clockwise turning spiral waves

      Fig.7: Anti-clockwise turning spiral waves

      Fig.8: Slower wave movement induced by cold water (8°C)

      Fig.9: Externally stimulated circular wave

      Fig.10: Yellow and black colour waves moving independently with only weak influence on each other

      Fig.11: Deleting waves produced by wave collision

      Fig.12: Deleting and diverging waves produced by collision, velocity vector addition



    Conclusion

    In physical terms these findings have some consequences:
    • we find delayed excitement of chromatophore cells,
    • we find comparable time-functions (near Gausian wave) on each chromatophore cell,
    • the mechanism of excitement is delayed (by whatever),
    • we find wave propagation,
    • we find wave-deletion,
    • velocity and direction of interfering excitement can be seen as vector sum of the partial velocities,
    • it is possible to force wave velocities higher then medial velocities (resulting wave vector).
    • the abstraction of mechanism is called "Interference Network" (IN; flowing time-functions on nets),
    • the effect of wave deletion can not be modeled using homogenuous, global, non-cellular circuits,

    Acknowledgement

    Thanks to Andrew Packard for lots of interesting discussions in the special field.

    [AP1995] Packard, A.: Organization of cephalopod chromatophore systems: a neuromuscular image-generator. In: Abbott, N.J., Williamson, R., Maddock, L., Cephalopod Neurobiology, Oxford University Press, 1995, pp. 331-367

    [AP2001] Packard, A 'neural' net that can be seen with the naked eye In : Backhaus. W. (ed) 2001 International School of Biocybernetics (Ischia): Neuronal coding of perceptual systems: pp. 397-402. World Scientific, Singapore, New Jersey, London, Hong Kong, see http://gilly.stanford.edu/APackardneuralnet.pdf

    Additional discussions (March 2005)

    Mail to G. Heinz: heinz@gfai.de
    Mail to A. Packard: andrew@packards.de

    Return to Heinz' homepage: Table of contents: http://www.gfai.de/~heinz

    (c) Copyrights: For the text: G. Heinz; for all pictures and movies: A. Packard
    File created Nov. 24, 1998 gh/ap; upgraded.

    Access no. since aug. 17, 1999