Where are memories stored?
Memories aren’t stored in just one part of the brain—different types of memories are stored in different and interconnected brain regions.
In the 1950s, a patient named Henry Molaison (HM) had his hippocampus and part of the medial temporal lobe surgically removed to treat his epilepsy. As a result, HM was only able to remember recent events for a few minutes, and was unable to permanently remember new information.
HM’s case suggested that the hippocampus is required for forming and storing new episodic memories, but not for motor learning. HM was able to improve his performance on motor tasks over days or weeks, yet had no memory of having ever encountered or practised those tasks.
After the surgery, HM’s memory became limited almost only to events that occurred years before his surgery, in the distant past. This indicated the hippocampus and medial temporal region are not the sites of permanent memory storage, but that long-term memories seem to at some stage migrate to other region(s).
Subsequent research suggests these long-term memories may be stored in parts of the cerebral cortex, which overlies the hippocampus. Certain areas in the cortex are important for storing semantic memory—factual knowledge—and knowledge about how this is used from day to day.
Another important memory structure is the amygdala. Whereas the hippocampus appears to be necessary for forming and storing explicit memories, and parts of the cerebral cortex are the long-term repository of learned information, the amygdala is important for attaching emotional significance to memories.
Strongly emotional memories are difficult to forget—the permanence of these memories suggests that interactions between the amygdala, hippocampus and neocortex crucially determine how “stable” a memory is; that is, how likely it is to be retained over time.
In addition to modulating memories, the amygdala also appears to be the brain region where memories for fear are stored. For this reason, researchers including Professor Pankaj Sah and Dr Timothy Bredy believe that understanding how fear memories are formed in the amygdala may help in treating conditions such as post-traumatic stress disorder.
source : The University of Queensland Australia