Ketamine may reduce the brain's forward prediction, leading to a noisier signal.

“um and there's some work showing that ketamine basically disrupts there's a bit of the tortilla prefrontal cortex so sort of in your prefrontal cortex but a bit back and a bit to the side um that's really associated with this prediction error processing and that's disrupted with ketamine so things that aren't surprising become surprising the things that shouldn't be surprising and are completely predictable and things that aren't predictable are no longer surprising so basically kind of noisy signal”