I recall reading in On Intelligence that brain activity when someone is imagining something is identical to actually perceiving/performing it. For example, imagining oneself playing piano causes the motor cortex to light up as though it was actually playing piano, and imagining a scene causes V1 to light up.
However, I haven’t seen any mention of a mechanism for this in discussion around HTM. It seems as though you’d need proximal feedback from higher level regions for this to work. Digging through some neuroscience texts, here’s what I’ve found so far:
Layers 5/6 project to Layers 1/6 in lower-level regions
There seems to be evidence of neurons in L6 that project to L2/3, but no mention of whether this is to proximal or distal dendrites.
It also seems necessary for some kind of recurrent proximal feedback somewhere. After all, if that wasn’t the case, shutting off sensory input would mean sensory regions would shut off, meaning no input to higher level regions, which would shut off too, eventually leading to the entire brain shutting off. Sensory deprivation chambers evidently aren’t a death sentence and seem as though they might even increase activity in some sense.
There’s also the possibility that this problem is solved by thalamic feedback too. I know Numenta is looking into the thalamus now, so any ideas from that research is welcome here too.