I remember reading in Scientific American, years ago, about evolved circuits. (Here’s some background from Wikipedia: Evolvable hardware.) I believe the circuit described in SA is the “tone discriminator” mentioned in Wikipedia.
The most intriguing element of that circuit was an element that did … nothing. The path to this part of this circuit was, as I remember, a dead end, with no output. Or perhaps, that part of the circuit simply passed the signal through unchanged. What I DO remember, because it was so striking, was that if that element were removed, the circuit did not work at all.
Obviously, that element was doing something. But it was nowhere near obvious what it was doing. I always felt that the circuit must have been responding NOT its inputs but to the electric field in which it found itself.
Which brings me to this article from Science Daily:
The brain — awake and sleeping — is awash in electrical activity, and not just from the individual pings of single neurons communicating with each other. In fact, the brain is enveloped in countless overlapping electric fields, generated by the neural circuits of scores of communicating neurons. …
New work by [Costas] Anastassiou and his colleagues, however, suggests that the fields do much more — and that they may, in fact, represent an additional form of neural communication.
“In other words,” says Anastassiou, … “while active neurons give rise to extracellular fields, the same fields feed back to the neurons and alter their behavior,” even though the neurons are not physically connected — a phenomenon known as ephaptic coupling. “So far, neural communication has been thought to occur at localized machines, termed synapses. Our work suggests an additional means of neural communication through the extracellular space independent of synapses.”
The takeaway: we cannot reverse-engineer that one evolved, well-defined circuit. We will never reverse-engineer the human brain.