following surgery showed his hippocampus to be intact except for a specific lesion restricted to the CA1 pyramidal cells. In one instance, transient global amnesia was caused by a hippocampal CA1 lesion. While this was a temporary case of amnesia, it still shows the importance of the CA1 region of the hippocampus in memory. Episodic memory loss is most likely to occur when there has been damage to the hippocampus. There is evidence that damage to the medial temporal lobe correlates to a loss of autobiographical episodic memory. Non-declarative information
Some retrograde and anterograde amnesiacs are capable of non-declarative memory, including implicit learning and procedural learning. For example, some patients show improvement on the pseudorandom sequences experiment just as healthy people; therefore, procedural learning can proceed independently of the brain system required for declarative memory. Some patients with amnesia are able to remember skills that they had learned without being able to consciously recall where they had learned that information. For example, they may learn to do a task and then be able to perform the task later without any recollection of learning the task. According to fMRI studies, the acquisition of procedural memories activates the basal ganglia, the premotor cortex and the supplementary motor area, regions which are not normally associated with the formation of declarative memories. This type of dissociation between declarative and procedural memory can also be found in patients with diencephalic amnesia such as Korsakoffs syndrome. Another example demonstrated by some patients, such as K.C.
The operation of this longer-term consolidation process is seen in the retrograde amnesia of patients with hippocampal damage who can recall memories from childhood relatively normally, but are impaired when recalling experiences that occurred just a few years prior to the time they became amnesic. (Kirwan et al.,2008)In the case of LSJ, her case shows that retrograde amnesia can affect many different parts of knowledge. LSJ was not able to remember things from her child or adult life. She was not able to remember things that most people pick up in everyday life such as logos or the names of common songs. Post-traumatic amnesia is generally due to a head injury (example: a fall, a knock on the head). Traumatic amnesia is often transient, but may be permanent or either anterograde, retrograde, or mixed type. The extent of the period covered by the amnesia is related to the degree of injury and may give an indication of the prognosis for recovery of other functions. Mild trauma, such as a car accident that results in no more than mild whiplash, might cause the occupant of a car to have no memory of the moments just before the accident due to a brief interruption in the short/long-term memory transfer mechanism. The patient may also lose knowledge of who people are. Having longer periods of amnesia or consciousness after an injury may be an indication that recovery from remaining concussion symptoms will take much longer.