In most cases of anterograde amnesia, patients lose declarative memory, or the recollection of facts, but they retain non-declarative memory, often called procedural memory. 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 that were presented to them after the injury occurred. Usually, there remains some capacity for learning although it may be very elementary. In the other case, which has been studied extensively since the early 1970s, patients often have damage that is permanent, although some recovery is possible, depending on the nature of the pathophysiology. In the case that the amnesia is drug-induced, it may be short-lived and patients can recover from it. Some patients with severe cases have a combined form of anterograde and retrograde amnesia, sometimes called global amnesia. Patients who suffer from anterograde amnesic syndromes may present with widely varying degrees of forgetfulness. Damage to any part of this system, including the hippocampus and surrounding cortices results in amnesic syndromes. In addition, patients with tumors who undergo surgery will often sustain damage to these structures, as is described in a case below. Often, patients with seizures which originate in the MTL will have either side or both structures removed (there is one structure per hemisphere). The disease is usually acquired in one of two ways: it is either drug-induced (benzodiazepines such as midazolam, flunitrazepam, temazepam, triazolam, and nimetazepam are known to have powerful amnesic effects ), or it follows a traumatic brain injury in which there is usually damage to the hippocampus or surrounding cortices.Īmnesia is seen in patients who, for the reason of preventing another more serious disorder, have parts of their brain removed that are known to be involved in memory circuits, the most notable of which is known as the medial temporal lobe (MTL) memory system, described below. 6.2 Familiarity and the fractionation of memory.
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