Certain authors claim the deficit in temporal context memory is more significant than the deficit in semantic learning ability (described below). Causes
This disorder is usually acquired in one of four ways: One cause is benzodiazepine drugs such as midazolam, flunitrazepam, lorazepam, temazepam, nitrazepam, triazolam, clonazepam, alprazolam, diazepam, and nimetazepam; all of these are known to have powerful amnesic effects. This has also been recorded in non-benzodiazepine sedatives or "z-drugs" which act on the same set of receptors; such as zolpidem (also known as Ambien), eszopiclone (also known as Lunesta), and zopiclone (also known by brand names Imovane and Zimovane). A second cause is a traumatic brain injury in which damage is usually done to the hippocampus or surrounding cortices. It may also be caused by a PTSD, a shocking event, or an emotional disorder.Illness, though much rarer, can also cause anterograde amnesia if it causes encephalitis, which is the inflammation of brain tissue. There are several types of encephalitis: one such is herpes simplex encephalitis (HSV), which, if left untreated, can lead to neurological deterioration. How HSV gains access to the brain is unknown; the virus shows a distinct predilection for certain parts of the brain. Initially, it is present in the limbic cortices; it may then spread to the adjacent frontal and temporal lobes. Damage to specific areas can result in reduced or eliminated ability to encode new explicit memories, giving rise to anterograde amnesia.
In cases of pure anterograde amnesia, patients have recollections of events prior to the injury, but cannot recall day-to-day information or new facts presented to them after the injury occurred.In most cases of anterograde amnesia, patients lose declarative memory, or the recollection of facts, but they retain nondeclarative memory, often called procedural memory. For instance, they are able to remember and in some cases learn how to do things such as talking on the phone or riding a bicycle, but they may not remember what they had eaten earlier that day for lunch. One extensively studied anterograde amnesiac patient, codenamed H.M., demonstrated that despite his amnesia preventing him from learning new declarative information, procedural memory consolidation was still possible, albeit severely reduced in power. He, along with other patients with anterograde amnesia, were given the same maze to complete day after day. Despite having no memory of having completed the maze the day before, unconscious practice of completing the same maze over and over reduced the amount of time needed to complete it in subsequent trials. From these results, Corkin et al. concluded despite having no declarative memory (i.e. no conscious memory of completing the maze exists), the patients still had a working procedural memory (learning done unconsciously through practice). This supports the notion that declarative and procedural memory are consolidated in different areas of the brain. In addition, patients have a diminished ability to remember the temporal context in which objects were presented.