Other studies show animals with similar injuries can recognize objects with which they are familiar, but, when the objects are presented in an unexpected context, they do not score well on recognition tests. Islands of memory
Patients with anterograde amnesia have trouble recalling new information and new autobiographical events, but the data are less consistent in regard to the latter. Medveds and Hirst recorded the presence of islands of memory – detailed accounts – that were described by such patients. The island memories were a combination of semantic and episodic memories. The researchers recorded patients giving long narratives with a fair amount of detail that resembled memories that the patients had prior to the trauma. The appearance of islands of memory could have something to do with the functioning of adjacent cortical areas and the neocortex. In addition, the researchers suspect that the amygdala played a role in the narratives. Notable cases
The most famous case reported is that of patient Henry Molaison, known as H.M., in March 1953. Molaisons chief complaint was the persistence of severe seizures and therefore had a bilateral lobectomy (both of his medial temporal lobes were removed). As a result, Molaison had bilateral damage to both the hippocampal formation and the perirhinal cortex. Molaison had average intelligence and perceptual ability and a decent vocabulary. However, he could not learn new words or remember things that had happened more than a few minutes earlier. He could remember anything from his childhood.
Although later the complications can be much more widespread and strongly impair cognitive processes, at the initial stage of Alzheimers the changes observed can be restricted to anterograde amnesia and a mild deficit in retaining newly learnt sequences. This is explained by the fact that the disease is initiated within the medial temporal lobe and first affacts the entorhinal cortex that directly sends and receives information from the hippocampal formation. Alcohol intoxication
Anterograde amnesia can also be caused by alcohol intoxication, a phenomenon commonly known as a blackout. Studies show rapid rises in blood alcohol concentration over a short period of time severely impair or in some cases completely block the brains ability to transfer short-term memories created during the period of intoxication to long-term memory for storage and later retrieval. Such rapid rises are caused by drinking large amounts of alcohol in short periods of time, especially on an empty stomach, as the dilution of alcohol by food slows the absorption of alcohol. Alcohol-related anterograde amnesia is directly related to the rate of consumption of alcohol (and is often associated with binge drinking), and not just the total amount of alcohol consumed in a drinking episode. Test subjects have been found not to experience amnesia when drinking slowly, despite being heavily intoxicated by the end of the experiment.