The brain structure of a feral ghoul indicates that the regenerative ability of the neurological system that affords "normal" 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," according to the ghoul physician Barrows. Despite the apparent lack of the higher reasoning they once had as humans, some are capable of semi-intelligible speech, as the Vault 34 security officers will occasionally growl out understandable phrases similar to the trogs of The Pitt, indicating that their vocal chords and their brain's speech centers are still relatively intact.
As the reasoning and critical thinking portions of a ghoul's brain deteriorate, the ghoul subject becomes increasingly hostile, giving in to a carnal need to feed. It remains unclear exactly what precipitates this change in neurobiology and psychology, but anecdotal evidence seems to indicate that non-social ghouls, or those in isolation, are more prone to the condition.
It is possible that this is a gradual process, meaning that eventually all ghouls will succumb to this condition. However, considering the existence of ghouls that have been born prior to the Great War two centuries ago, it is quite possible that this theory is inaccurate, or that the rate of degeneration is dependent on the individual affected and surrounding environmental factors.
As with normal ghouls, ferals are not only extremely resistant to radiation, they are actually healed by it, as can be seen when a glowing one uses its radiation blast nearby other ghouls. M.A.R.Go.T. also states that feral ghouls have no internal body heat.
Similar to ghouls, a maddened ghoul's body has been ravaged by necrosis, and as such look like nothing more than shambling corpses. Differentiating them from normal ghouls, though, is the equally ravaged mind of mindless ghoul; they have long since lost their sense of reason or higher thought and as such follow basic animal instinct.
As mindless ghouls have long since lost their ability to reason or think in-depth, they have relatively underdeveloped tactics when in combat. They simply shuffle towards their closest enemy, and the player often has little to fear when engaging in combat with isolated individuals. Mindless ghouls often travel in groups, though, and as such can pose a threat when greatly outnumbering their foes. As fighters they are meager at best.