Ataxic Neurodegenerative Satiety Deficiency Syndrome (ANSDS) is the neurological dysfunction that "zombies" possess.
The frontal lobe is the part of the brain involved with "executive functioning" - enabling people to think carefully and solve problems in an abstract way. Zombies only possess just enough frontal lobe activity to "listen" to the thalamus, through which sensory input is processed. However, absent a properly functioning frontal lobe, a zombie is driven entirely by base emotions - such as rage - that are housed in the primitive parts of our brain, notably the amygdala. The anterior cingulate cortex modulates and dampens the excitability of the amygdala. A zombie has a dysfunctional anterior cingulate cortex, rendering it unable to modulate feelings of anger. The result is hyper-aggression.
Zombies suffer from cerebellar and basal ganglia dysfunction. Those are the parts of the brain that make fluidity of motion possible. The basal ganglia helps with coordinated movement. The cerebellum helps with balance. As a result of the dysfunctions, zombies are incapable of running, jumping, climbing and quickly changing direction. They possess a wide-legged, unsteady, lurching walk, usually accompanied by a back and forth tremor in the trunk of the body.
Zombies are always hungry because they don't have a properly functioning ventromedial hypothalamus: the region of the brain that lets a person know whether they've eaten enough. The result is hyperphagia. Zombies will eat and eat and eat, but never feel satiated.