November 22, 2008

Deep brain stimulation induces vivid memories

Earlier this year doctors in Toronto reported a strange incident involving a morbidly obese man who was undergoing deep brain stimulation (DBS).

DBS involves implanting electrodes into the brain to treat conditions like Parkinson's and Alzheimer's. In this particular case, the electrodes were implanted into a 50-year old's hypothalamus (an area in the limbic system) in hopes of granting him better control over his appetite.

But a strange thing happened during the procedure.

When the electrodes were stimulated by electrical impulses the man began to experience feelings of deja vu. As the procedure continued, and as surgeons increased the intensity of the electrodes, the patient experienced an influx of memories and feelings of temporal uncertainty.

At one point the patient thought he was in a park with friends. He felt younger and thought that he was 20-years old again. Even his girlfriend of the time was there. According to the patient, he viewed the scene as an observer and experienced the scene in colour. As the surgeons increased the intensity of the stimulation the details became more and more vivid.

Two months later the surgeons repeated the procedure, and the same thing happened again.

This incident, which came as a complete surprise to the surgeons, has given medical researchers cause for hope that DBS may be used to boost memories and better treat neurodegenerative disorders like Alzheimer's.

"We hopefully have found a circuit in the brain which can be modulated by stimulation, and which might provide benefit to patients with memory disorders," said Andres Lozano of Toronto Western Hospital.

In addition, this incident reaffirms a suspicion I've had about the brain and its ability to store memories. I've often thought that the brain does an excellent job recording and storing memories, but that our recall mechanisms are disturbingly weak and highly selective. Our long-term associations with memories are frequently diminished (e.g. some of our more painful memories are often exaggerated, distorted or suppressed).

What this incident with DBS suggests is that our memories are beautifully preserved in our brains. We just lack the recall linkages and cognitive mechanisms to bring those memories back in any kind of detail. Our memories are accessed as fleeting bits of information instead of linear experiences.

Maybe there is a way to tease out the finer details. Looking to the future, perhaps we can use DBS or some other techniques to re-experience our memories in exquisite detail.

I'll get the popcorn.

Citation and photo credit: BBC



I would be highly cautious of leaping to the conclusion that memories are well-preserved in most people. In fact, I don't think they are (except for the few people with photographic memory).

The scene 'recalled' was most probably a mixture of memories and fabrication to fill in the blanks.

This has been seen before. In hyponosis, for example, people can apparently 'recall' their child-hoods in 'perfect detail', but when the these 'memories' are factually checked they turn out to consist of a high degree of fabrication.

George said...

Marc, you may be right to a certain degree, but I believe that the quality and detail of our stored memories greatly exceeds our ability to retrieve them.

Chris said...

The 'memory enhancement' side-effect is interesting but I find it more interesting that they tried and failed to use DBS to treat obesity. If and when they decide to try again, may I suggest they target the reward circuit (lateral hypothalamus, striatum or midbrain dopamine neurons) instead, and make rewarding, stimulating current conditional on the patient engaging in heavy physical exercise? It certainly keeps rats running (Burgess, 1991)..

Stu said...

Hey George,
Love this topic. Did you see this:

It's a bit above my expertise, but it kind of explains how memories are stored so strongly. I agree, it's interesting how our retrieval method is so bad. Certainly a topic I'd like to learn more about.

Anonymous said...

Interesting that the assumption is that the man was "remembering an event", rather than actually "re-experiencing the event". This, "...and feelings of temporal uncertainty", may be the key. Since all events - the entire universe - exists at all points, it may be that his consciousness drifted/focused to the space/time coordinates of the incident, and he was actually there. Temporal Dislocation - it happens all the time. I strive for it...