Memory Loss & the Brain

Consolidation refers to a presumed process by which new information is placed into long-term memory storage.

Incoming information is often placed into short-term memory, where it can survive for several minutes, or into working memory, where it can survive for an hour or longer. However, these forms of memory are essentially transient. At some point, the information must be established in long-term memory to survive.

There appears to be a consolidation period, during which this transition occurs, and during which memory is still unstable. There are two main reasons to assume that consolidation is not instantaneous. The first is interference: if subjects are asked to learn a list of words, and then asked to learn a second list of words, this later learning interferes with recall of the first list of words. This suggests that newly-formed memories can be disrupted by later incoming information.

The second reason to assume that consolidation is not instantaneous comes from patients who have sustained brain injury which causes retrograde amnesia, a loss of memory for events occurring before the injury. Typically, retrograde amnesia is time-graded, meaning that there may be near total loss of memory for the events immediately before the injury, partial loss of events occurring somewhat before the injury, and little or no loss of memory for events from the distant past. For example, someone who sustains a blow to the head in the course of a car accident may have no memory of the accident itself, sketchy memory of the drive which led to the crash, and normal memory for events before the day of the crash. In other cases, memory disruptions may occur which stretch as far back as several years before the injury.

These findings suggest that new memories are vulnerable, and that brain damage can disrupt them before they are fully stabilized in memory; older memories become progressively more stable and are more likely to survive.

The biological mechanisms of consolidation are poorly understood, although long-term potentiation has been implicated in causing anatomical changes in the brain which may underlie long-term memory formation.