Some multicellular organisms emit light in a conspicuous way. Fireflies carry beacons that shine in the night, and some deep-sea fishes use phosphorescent appendages to attract prey. However, the information content in these light emissions is probably no greater than “I am here”, or possibly “I am moving in a certain direction with a certain velocity”.
A few days ago, a paper appeared in PLoS One showing that the unicellular organism paramecium caudatus uses light signals of a specific wavelength to communicate. These signals influence the proliferation rate of the protozoa and imply that they not only have a sense of vision, but also a signal-generating organ, and an apparatus to translate the visual input into a representation of its environment, which in turn guides the organism’s behaviour.
I found this story through the most interesting Neurotypical blog, written by a neuroscientist who starts off almost apologetically by saying that this has nothing to do with neuroscience. I beg to differ.
Although the paramecium possesses no nervous system, it clearly has all the necessary faculties for information processing of the kind with which neuroscience concerns itself. It is not the substrate that determines the dynamics of an information processing system, but the structure and organisation of the network.