Many people are increasingly using their mobile phones as mental prostheses to extend the capacity of their brains [see ‘Science fiction becomes reality‘ on October 12th, 2016]. This does not just include tracking their appointments in a calender app or using a search engine to track down a piece of information that they have temporarily forgotten; but also recording their activities and preferences via social media apps. Many of us are happy to share our thoughts with those close to us but we take it for granted that we are in complete control of what is shared and with whom. So, unexpected or unauthorised sharing of our personal information via these mental prostheses can cause shock and embarrassment. Now, spare a thought for the giant cuttlefish whose neurons are directly connected to about ten million chromatophores in its skin. Each chromatophore is sack of pigment that can be shrunk or expanded to show its particular colour. In giant cuttlefish the chromatophores are red, yellow and black/brown. Beneath the chromatophores is a layer of iridophores, which manipulate the wavelengths of light using layers of plates to produce blues and greens and below these cells are leucophores that reflect light outwards through the iridophores and chromatophores. In effect, the cuttlefish is wearing an Ultra-High Definition TV screen with about 10 million pixels directly connected to its brain. Even when resting calmly, a cuttlefish’s skin can be pulsing with complex patterns of colour; perhaps this is similar to the way our minds can be teeming with activity even when we are sitting quietly apparently doing nothing. Imagine what it would be like if all of those thoughts were displayed on a giant television screen. It would give a whole new meaning to the phrase ‘to wear your heart on your sleeve’.
Peter Godfrey-Smith, Other Minds: The Octopus and the Evolution of Intelligent Life, London: William Collins, 2018.