I've only heard of one researcher who believes the brain does something similar to backprop and has gradients, but it sounded extremely handwavy to me. I think

I've only heard of one researcher who believes the brain does something similar to backprop and has gradients, but it sounded extremely handwavy to me. I think it is more likely the brain does something resembling active inference. But I suppose you could say we don't know 100% since we don't fully understand how the brain learns.