Be sure to visit The Cognitive Axon tomorrow for symptom 4!
Symptom 3: Long term memory loss
Why is it that it only takes you a few seconds to hide from zombies before they get distracted, forget their prey, and move on after some other helpless chap? Yet they flock in droves to places like malls and churches that they remember from their pre-zombie past?
We contend that zombies are incapable of storing long-term memories as a result of a disorder called anterograde amnesia. Anyone who's seen the movie Momento will know the symptoms well. Immediate events are available for only a few minutes at a time, at most, before their flow of conscious memories is disrupted.
Once distracted, someone afflicted with anterograde amnesia will lose those memories as if they never existed at all. However, memories that were gained before the amnesia-inducing brain damage will be retained as clearly as if they had happened yesterday.
This phenomenon arises from damage to a very specific area of the brain called the hippocampus. This region sits right behind the amygdala (which we talked about earlier) and is nestled deep within the temporal lobe. For such severe amnestic symptoms, our hypothetical zombie subjects would have to lose both their left and right hippocampuses.
This is a rare condition that has so far really only come about for surgical reasons and doesn't really tend to happen naturally. However, there are cases in which severe vitamin deficiency can lead to memory issues and anterograde amnesia. This is due to the susceptibility of the mamillary bodies, a brain region that is heavily interconnected with the hippocampus, to vitamin deficiency degeneration.
This leads to a disorder referred to as Wernicke-Korsakoff’s syndrome, characterized by memory disruptions, which may be involved in regulation of the hippocampus. Whether a virus has destroyed the hippocampus, or zombies are simply suffering from a severe vitamin deficiency, it's safe to say that somehow they've lost their hippocampuses for good, as well as any ability to form memories of the new un-life.