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let's talk about the memistor. no, not the MEMRISTOR, which is a resistor that changes resistance depending on the past current that has flowed through it. this is the MEMISTOR, which is like a transistor that remembers its conductive state! here is its symbol. (THREAD) 
in this 1960 paper (www-isl.stanford.edu/~widrow/papers…), they made the first memistor with a pencil lead in a bath of copper sulfate/sulfuric acid. by forcing current in and out of a 3rd wire placed in the bath, they electroplated/removed copper from the pencil lead, changing its resistance
this is what it looked like.
so what can a memistor be used for? the 1960 paper uses it to build an electrical model of a neuron! this model has several inputs and one output. each input is weighted and summed to form the output, but the weights change depending on the inputs.
the paper gives a tantalizing hint at a possible future direction!
and now, almost 60 years later, there's a new paper that does exactly that: onlinelibrary.wiley.com/doi/full/10.10…
this paper uses a conductive polymer (but not the one you might be thinking of, PEDOT) and a salt water solution to create a memistor without all the nasty chemicals. it's also much smaller, which is very important for building brains!
to make this sort of brain, you could, perhaps, use a modified inkjet printer, or even an OLED production line.
so that means that within the next few years, we'll have robots with highly advanced brains, but unlike our rotund, wrinkly lumps, theirs will be very flat, wafer thin, and very salty! 😂
