Patients with anterograde amnesia may have episodic, semantic, or both types of explicit memory impaired for events after the trauma that caused the amnesia. This suggests that memory consolidation for different types of memory takes place in different regions of the brain. Despite this, current knowledge on human memory is still insufficient to "map out" the wiring of a human brain to discover which parts of which lobe are responsible for the various episodic and semantic knowledge within a persons memory. Amnesia is seen in patients who, for the reason of preventing another more serious disorder, have parts of their brains known to be involved in memory circuits removed, the most notable of which is known as the medial temporal lobe (MTL) memory system, described below. Patients with seizures originating in the MTL may have either side or both structures removed (there is one structure per hemisphere). In addition, patients with tumors who undergo surgery will often sustain damage to these structures, as is described in a case below. Damage to any part of this system, including the hippocampus and surrounding cortices, results in amnesic syndromes. This is why after a stroke people have a chance of developing cognitive deficits that result in anterograde amnesia, since strokes can involve the temporal lobe in the temporal cortex, and the temporal cortex houses the hippocampus. Finally, anterograde amnesia can be the first clinical sign that Alzheimers disease develops in within the brain.
In neurology, anterograde amnesia is the inability to create new memories after the event that caused amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories created prior to the event are lost while new memories can still be created. Both can occur together in the same patient. To a large degree, anterograde amnesia remains a mysterious ailment because the precise mechanism of storing memories is not yet well understood, although it is known that the regions of the brain involved are certain sites in the temporal cortex, especially in the hippocampus and nearby subcortical regions. Signs and symptoms
People with anterograde amnesic syndromes may present with widely varying degrees of forgetfulness. Some with severe cases have a combined form of anterograde and retrograde amnesia, sometimes called global amnesia. In the case of drug-induced amnesia, it may be short-lived and patients can recover from it. In the other case, which has been studied extensively since the early 1970s, patients often have permanent damage, although some recovery is possible, depending on the nature of the pathophysiology. Usually, some capacity for learning remains, although it may be very elementary.