When visual inputs are fed into the auditory cortices of infant ferrets, those auditory cortices develop into functional visual systems.
This does not mean the auditory cortex is forming anything like the map the visual cortex would have formed, given “the same” inputs. This is not important for determining whether the cortex is, in some sense, equipotent in quantity compute per surface area, but it is important for determining whether the cortex is uniform.
for example, cats exposed only to horizontal edges early in life don’t have the ability to discern vertical edges later in life. This suggests that our capacities for sensory processing stem from some sort of general-purpose data processing, rather than innate machinery handed to us by evolution.
The brain is very plastic early in life, in the sense that axons which are not receiving feedback from Neuron X can simply physically reroute and terminate on Neuron Y instead—which is why occipital-lobe injuries that would result in large permanent blind spots in adults do not have the same effect on young children. However, I doubt that, e.g., the auditory cortices of the aforementioned ferrets, were simply “reprogrammed” to do the same kind of horizontal/vertical edge detection that infant mammals learn to do natively. In general, if you can block it during infant development and the adult can’t recover it, it’s nature, not nurture.
There’s a man who had the entire left half of his brain removed when he was 5, who has above-average intelligence, and went on to graduate college and maintain steady employment.
Split-brain miracles are up to the aforementioned child plasticity plus the fact that, generally, the cortical hemispheres are symmetrically duplicated in function like the lungs. People can also survive well after the removal of 1 lung, even though the remaining lung can’t change or adapt in any way [ except maybe passively hypertrophying ] to “take over” the function of the missing lung. Removing a child’s entire [ occipital / orbitofrontal / temporal ] cortex—even if you rerouted the relevant sensory input elsewhere—would have devastating effects on cognition/personality that could not be recovered by the remaining cortical areas, just like adult injury.
This does not mean the auditory cortex is forming anything like the map the visual cortex would have formed, given “the same” inputs. This is not important for determining whether the cortex is, in some sense, equipotent in quantity compute per surface area, but it is important for determining whether the cortex is uniform.
The brain is very plastic early in life, in the sense that axons which are not receiving feedback from Neuron X can simply physically reroute and terminate on Neuron Y instead—which is why occipital-lobe injuries that would result in large permanent blind spots in adults do not have the same effect on young children. However, I doubt that, e.g., the auditory cortices of the aforementioned ferrets, were simply “reprogrammed” to do the same kind of horizontal/vertical edge detection that infant mammals learn to do natively. In general, if you can block it during infant development and the adult can’t recover it, it’s nature, not nurture.
Split-brain miracles are up to the aforementioned child plasticity plus the fact that, generally, the cortical hemispheres are symmetrically duplicated in function like the lungs. People can also survive well after the removal of 1 lung, even though the remaining lung can’t change or adapt in any way [ except maybe passively hypertrophying ] to “take over” the function of the missing lung. Removing a child’s entire [ occipital / orbitofrontal / temporal ] cortex—even if you rerouted the relevant sensory input elsewhere—would have devastating effects on cognition/personality that could not be recovered by the remaining cortical areas, just like adult injury.