It has been determined that there are multiple memory systems within the brain, each devoted to different functions. For example, one memory system allows a person to learn to hit a baseball. Other systems cause a person to remember trying to hit a baseball and not succeeding. Another memory system will make that same person tense when he comes to the plate after having been hit in the head by the pitcher the last time he was at bat. These memories are orchestrated by different networks.
Dr. LeDoux tells the story of a French physician named Edouard Claparede. The good French doctor examined a female patient who had brain damage and seemed to have lost all abilities to create new memories. Every time Claparede walked into this patient’s room he had to re-introduce himself, even if he left and returned just moments later. One day Dr. Claparede decided to attempt something new. He entered the room as normal and held out his hand to greet the female patient. She reached to shake his hand. When their hands met, however, she immediately pulled her hand back. Claparede had hidden a tack in his palm and pricked the patient with it. Interestingly, the next time Claparede entered the room she had no recollection of him, but would not shake his hand. She was unable to tell him why she would not shake his hand, only that she wouldn’t do it.
Claparede concluded that he had come to signify danger. He was no longer just a man but a
stimulus with a specific emotional meaning. Although the patient did not have a conscious memory of the situation, subconsciously she learned that shaking Claparede’s hand could cause her harm, and her brain used this stored information, this memory, to prevent the unpleasantness from occurring again…the patient’s ability to protect herself from a situation of potential danger by refusing to shake hands reflects a different kind of memory system. This system forms implicit or nondeclarative memories about dangerous or otherwise threatening situations. Memories of this type…are created through the mechanism of fear conditioning – because of its association with the painful pinprick, the sight of Claparede had become a learned trigger of defensive behavior (a conditioned fear stimulus).
Two important discoveries have resulted from Claparede’s experiment. The first is that learning is not completely dependant on conscious awareness. The other is that once learning has taken place, the stimulus does not have to be consciously known to generate the emotional response. Humans, therefore, have an implicit emotional system of memory interdependent of an explicit conscious memory. This is called the emotional memory.
A way to illustrate the impact of both the explicit and implicit memory systems can be through the description of an accident. A person is driving down the road and has a terrible accident. In the midst of this accident, the horn is stuck and blares for what seems like eternity. The person is in pain and is traumatized by the accident. Later, the person is riding with a friend and hears the horn of another car. The person has physical reactions such as muscle tension, increased perspiration, blood pressure and heart rate and other bodily reactions. These are implicit bodily responses. The sound of the horn also travels to another memory system, which holds explicit memories. That person is now reminded of the facts of the accident. Emotional arousal occurred through the implicit memory causing bodily reactions. Without this, the person’s conscious memory would be flat. The two memories are now unified into a potentially new area of long-term memory.
However, suppose that the accident happened so long ago that the explicit memory system has forgotten details of the event, or even the event itself. If the implicit, emotional memory has not forgotten the accident, when a horn sounds, an emotional reaction could be triggered. The person would then be in an emotional state for which they have no understanding. For this to happen, the emotional memory would have to be less forgetful than the explicit memory system. This, according to research, appears to be the case.
Two facts support this idea. First, the explicit memory system is incredibly forgetful and inaccurate. Second, conditioned fear responses diminish very little over time. They actually increase potency as time goes on.
Adapted from Joseph E. LeDoux, The Emotional Brain : The Mysterious Underpinnings of Emotional Life (New York: Simon & Schuster, 1996)