The dissociative effects of ketamine are likely caused by an uncoupling of neocortical brain circuits from subcortical regions, leading to a different dominant rhythm in the brain.

“in so far as we know it has to do with an uncoupling of certain brain circuits in particular neocortical brain circuits the neocortex is the part of the brain the lumpy outside part of the brain that's associated with action planning it does a lot of things really it's involved in sensory perception it's involved in speech generation many many things but the neocortex has connections to other regions which are called subcortical regions and it seems that when people take ketamine or fenine PCP there's an uncoupling of those networks a quieting of those networks that starts to create a different dominant rhythm in the brain”