Additionally, anterograde amnesics without combined retrograde disorders (localized damage to the MTL system) have memories prior to the traumatic event. For this reason, the MTL is not the storage place of all memories; other regions in the brain also store memories. The key is the MTL is responsible for the learning of new materials. Other memory systems
A limited number of cases have been described in which patients with damage to other parts of the brain acquired anterograde amnesia. Easton and Parker observed damage to either the hippocampus or the surrounding cortices does not seem to result in severe amnesia in primate models. They suggested damage to the hippocampus and surrounding structures alone does not explain the amnesia they saw in patients, or increasing damage does not correlate with the degree of impairment. Furthermore, the data do not explain the dichotomy that exists in the MTL memory system between episodic and semantic memory. To demonstrate their hypothesis, they used a primate model with damage to the basal forebrain. They proposed that the disruption of neurons that project from the basal forebrain to the MTL are responsible for some of the impairment in anterograde amnesia. Easton and Parker also reported MRI scans of patients with severe anterograde amnesia showed damage beyond to cortical areas around the hippocampus and amygdala (a region of brain involved in emotions) and to surrounding white matter (white matter in the brain consists of axons, long projections of neuronal cell bodies).
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.