Commenting before reading other replies—I’m going to give the boring, sneaky reply that the question isn’t well-specified enough to have an answer; I’d need to know more about what you mean by something to operate solely on a substrate. I mean, clearly there are a lot of cognitive tasks that most people can only do given a pencil and paper, or a computer … is that the sneaky part, that we store information in the environment, and therefore we’re not solely neurons?
Commenting before reading other replies—I’m going to give the boring, sneaky reply that the question isn’t well-specified enough to have an answer; I’d need to know more about what you mean by something to operate solely on a substrate. I mean, clearly there are a lot of cognitive tasks that most people can only do given a pencil and paper, or a computer … is that the sneaky part, that we store information in the environment, and therefore we’re not solely neurons?