Octopus vulgaris has about half a billion neurons, roughly six times more than a mouse. Unlike in mammals, most of these neurons – about three fifths – are in its arms rather than in its central brain, a brain which nonetheless boasts about forty anatomically distinct lobes. Also unusual is that octopus brains lack myelin – the insulating material that in mammalian brains helps long-range neural connections develop and function. The octopus nervous system is therefore more distributed and less integrated than mammalian nervous systems of similar size and complexity. Octopus consciousness –
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