Memory – what is memory? Most of us take it for granted, but stop and ask yourself: how would you define memory? Dr. Larry R. Squire, head of the Memory Research Laboratory at UCSD, defined memory during his lecture, “Conscious and Unconscious Memory Systems of the Mammalian Brain,” part of the monthly “Grey Matters Lecture Series,” held at the Natural History Museum in Balboa Park. According to Dr. Squire, “Memory is a large topic, built on the fundamental idea that the experiences we have can change the nervous system so that later on our mental life and our behavior can be different as a result of what’s happened in the past.”
Dr. Squire has devoted his life to understanding memory. Specifically, he has been trying to figure out how memory is structured and organized, what brain systems it involves and how those systems work together to form memories. Since memory is a broad, complicated topic, a broad approach is required to understand it, ranging from experiments on a molecular level (determining how neurons connect to each to other) to experiments on a “systems” scale (determining how information flows through different parts of the brain).
The focus of the talk was on a part of the brain called the medial temporal lobe, which is required to transform perceptions into memory. This part of the brain is not required for long-term maintenance or recall of memories, only for the initial formation of memories. In the words of Dr. Squire, “This is a system that has a time-limited role in the formation of memory. After sufficient time has passed, this system is not needed for either storage or retrieval.”
The function of the medial temporal lobe is strikingly illustrated by a patient, referred to by his initials, E.P., who contracted viral encephalitis at the age of 70. By chance, the virus specifically destroyed his entire medial temporal lobe but left the rest of his brain untouched. E.P. could remember intricate details from his childhood, including the best route to take from his house to the movie theater, but could not form any new memories. Said Dr. Squire, “The immediate memory, the amount of material that can be held in mind, is available, but once some time elapses, all of that information is lost and he is not able to reach back into the past and recover anything that’s happened recently.”
The reason E.P. could suffer from such a specific form of memory loss is that memory is actually composed of several different memory systems. Memory systems can be divided into two types, conscious and unconscious. The conscious memory is what we normally think of as memory, when we make conscious recollections of past experiences.
The concept of unconscious memory is a little harder to grasp. Dr. Squire describes unconscious memory as ¦where performance changes as a result of experience, and in that sense deserves the term memory, but it changes without requiring any conscious memory content, in many cases without ever requiring the realization that memory is being drawn on.” One example of unconscious memory is the formation of habits, if you have ever decided to stop by the store on the way home from work, but then zoned out during the drive and wound up at home, you’ve experienced your unconscious memory taking over. This type of memory often forms as the result of extensive repetition. The brain becomes conditioned to perform certain tasks, and they can be done on “autopilot,” requiring minimal conscious effort.
Unconscious memory is again illustrated by E.P.’s performance on a memory test. In this test, E.P. was presented with eight pairs of objects, and one object of each pair was labeled “correct” on the underside. During a trial, E.P. was asked to select the correct object from each pair. After one session of 40 trials, a normal subject was able to memorize which object was correct and pick the correct one every time. Surprisingly, even though E.P. never remembered taking the test, after 36 sessions of 40 trials, he was able to pick the correct object every time. “You have to picture him, repeatedly reaching out for the object, turning it over and finding it was correct. After several trials, he said, ‘How am I doing this?’ The technician asked him, ‘Are you doing it because you remember from the past which object is correct?’ and he said ‘No, it just goes from here [pointing at his head] to here [pointing at his hand],’ which we thought must be the perfect way of talking about a habit.”
This memory test with E.P. demonstrates how our unconscious memory is separate from conscious memory and can substitute for it. Dr. Squire’s fascinating research reveals that there is more going on with our memory than we realize.
For more information on the Grey Matters Lecture Series, including future lecture dates, please visit: http://greymatters.ucsd.edu.