Korsakoff’s Syndrome refers to neuronal damage to the brain caused by a deficiency of the vitamin Thiamine (B1). It is common in long-term alcoholics, because alcohol greatly reduces the ability of the intestines to absorb nutrients (including Thiamine) from food.
Common symptoms are amnesia, confabulation (invented memories that fill in memory gaps caused by the brain damage or by alcoholic blackouts), reduced ability to carry on a conversation, loss of insight (inability to take current information and build on it) and apathy.
In the case of apathy, Korsakoff’s sufferers lose interest in things easily, and are little interested in the things that are happening around them. This could easily be diagnosed or interpreted as depression, but it has different causes from clinical depression.