The two main classes of amnesia are retrograde and anterograde. With retrograde amnesia a person is unable to recall details that were learned before the event that caused the amnesia. An example of this would be a concussion. The person would have difficulty remembering what happened to them during the minutes or hours preceding the head injury. However, with anterograde amnesia, the person is unable to learn any new information following the brain trauma. By assessing learning and memory skills of amnesiacs versus normal people, we find that there are many differences. .
Removal or severe damage to the hippocampus causes amnesiac syndrome. People with this syndrome know they have a memory problem. Procedural learning is preserved as well. It is a form of anterograde amnesia. Usually, their basic knowledge is unaffected. Their main loss is a deficit in episodic and semantic memory. A normal person has both the primacy and recency effect along the serial position curve, while someone with amnesic syndrome would only show a recency effect.
Korsakoff's Syndrome many times comes from alcoholism. Alcoholism eventually causes brain damage and niacin deficiency. It results in anterograde amnesia, however, there is a more gradual onset compared to amnesiac syndrome. A Korsakoff's patient will also begin to have retrograde amnesia, and their old memories will begin to disappear. A test done on Korsakoff's and control subjects showed that amnesiac subjects rely more on familiarity, while the control subjects were quite accurate, replicating other judgments of frequency. This study by Huppert and Piercy showed a qualitative rather than just a quantitative difference between amnesiacs and control subjects. .
Electroconvulsive shock or EC Therapy began in the 1040's to help with severe depression. It sets off all the neurons in the head. Some side effects have been retrograde forgetting and consolidation blockage.