Anterograde amnesia is a condition in which an individual is unable to form new memories. His old memories still exist and his short-term memory is still functional, but he is unable to commit new information into his long-term memory. Anterograde amnesia is almost always the direct result of some form of brain injury or trauma, but the exact cause of it, as well as the precise mechanism of memory formation and storage, is not fully understood. Conversely, retrograde amnesia is a condition in which an individual loses memories that are formed prior to some incident that causes brain damage.
There are a few different parts of the brain that have been linked to anterograde amnesia. A great deal of new information must pass through the hippocampus before it is committed to permanent memory; as such, damage to the hippocampus can prevent memory formation. The basal forebrain contains structures that produce chemicals important to learning, making it essential to memory formation as well. Other less prominent parts of the brain have also been linked to anterograde amnesia, though the connection between the structures and memory formation is often poorly understood.
The severity of anterograde amnesia can vary from case to case, but it always involves severe forgetfulness. Sometimes amnesia is chemically induced for research purposes; in these cases it is temporary. Often, anterograde amnesia caused by brain damage is permanent. Over time, memory loss can get better or worse; there is no set rule describing the progression of learning impairment.
Not all forms of learning are completely impossible for individuals with anterograde amnesia. While they are often incapable of recalling any facts concerning anything that occurred since they suffered brain damage, individuals suffering from amnesia may still find it possible to learn skills. Studies have shown that while an individual who is not able to form new memories will have no recollection of learning a new skill, he will often be able to perform a new skill without being taught again. This is because his declarative memory is impaired while his procedural memory continues to function.
The human brain is known for its plasticity. Neural plasticity describes the capability of nerves to form new neural pathways to recover lost functionality. In some cases, this involves transferring various neural functions from one side of the brain to the other. Neural plasticity has resulted in the restoration of some neural functionality in some individuals who have suffered brain damage. Scientists are studying ways to apply the property of neural plasticity to treatments for anterograde amnesia and other ailments caused by brain damage.