Answer: Korsakoff syndrome is a neurological disorder characterized by memory loss due to a thiamine deficiency.
Patients with Korsakoff syndrome display poor memory, with both retrograde and anterograde amnesia. Korsakoff syndrome is the result of a thiamine (Vitamin B-1) deficiency. It is often observed in severe alcoholics. It may be difficult to diagnose, since there are other neurological factors that may impact the diagnosis, including alcohol withdrawal or traumatic brain injuries.
The memory deficits can be described by the phrase anterograde amnesia. This refers to the inability to form new memories. They may exhibit deficits in explicit memories, and may not be able to state new facts that they had recently learned. They may also forget recent events that took place in their life.
There may also a retrograde amnesia component as well: some patients may forget memories of events that happened in the past, even as far back as childhood memories.
Another symptom that may appear in Korsakoff syndrome is confabulation in speech. Distinct from lying, confabulation is the production of false memories. People believe that they have experienced the confabulation. The reason behind confabulation is still unknown.
Despite the profound memory loss, other cognitive functions may remain intact. For example, many patients with Korsakoff maintain their ability to understand and produce logical speech and can communicate with others. But, the speech is sometimes thin and lacking in real content. They maintain their capacity for learning tasks, also called procedural memory. Some higher order executive functions are maintained, and it is believed that IQ is unaffected by Korsakoff syndrome (Intact memory for implicit contextual information in Korsakoff's amnesia, Oudman et al, 2011)
Korsakoff symptoms can be seen following long term alcohol abuse, but may also occur in patients with AIDS or cancer. In some cases, it can be observed in individuals with poor diets: those suffering from starvation, or those who fast excessively.
Treatments for Korsakoff syndrome are partially effective. Replacement of thiamine with a dietary supplement or injections can alleviate some symptoms. Additionally, cutting alcohol from the diet can help the brain restore its normal function.
Alcohol decreases the levels of thiamine in the blood by interfering with absorption. There are two mechanisms for how thiamine gets from the gut into the blood. Active ATP dependent mechanism is slowed by the presence of alcohol. Passive transport still occurs even when alcohol is present. (Mechanisms of thiamin deficiency in chronic alcoholism.)
Thiamine is important for healthy cell function. Thiamine is an essential coenzyme for the breakdown of carbohydrates. In cases of thiamine deficiency, altered carbohydrate catabolism leads to mitochondrial dysfunction, decreased energy production, and eventual cell death (The Evolution and Treatment of Korsakoff's Syndrome Out of Sight, Out of Mind?)
Although alcohol toxicity affects several parts of the brain, a few regions seem to be particularly vulnerable in Korsakoff syndrome. Specifically, the dorsomedial region of the thalamus and the mammillary bodies of the posterior hypothalamus are heavily damaged. In some cases, the damage to these structures is irreparable, even with thiamine replacement.