The brain structure of a feral ghoul indicates that the regenerative ability of the neurological systems that affords typical necrotic post-humans their longevity does not extend into the higher reasoning functions of the brain itself. This condition is referred to as "ferocious post-necrotic dystrophy".

As the reasoning and high order thinking portions of the brain deteriorate, the ghoul subject becomes increasingly hostile, giving into a carnal need to feed as opposed to the capacity for thinking and reasoning that a non-feral ghoul retains. It remains unclear exactly what precipitates this change in biology and psychology, but anecdotal evidence seems to indicate that non-social ghouls, or those in isolation, are more prone to the condition.

So the isolation makes them go crazy?