One of the most well-known of such cases is of a man we call H.M. Surgeons had cut out his hippocampus in an attempt to reduce his epileptic seizures. They were successful at getting rid of his seizures, but there was a severe side effect: He was unable to form any new memories.

Another way this used to be done was by severing what’s called the “Corpus Callosum”. This part of the brain connects the left and right hemispheres of the brain. We call those who underwent this process “Split Brain Patients”

One popular explanation is that healthy people actually confabulate all the time. It’s what our left hemisphere just naturally -- it creates stories to explain our actions and feelings to ourselves. This is why the patients don’t feel any different -- our conscious perception of a self that makes decisions is mostly an illusion anyways.