Brain Implants and Memory Loss


A Conversation with Daniel Schneider, MD

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News reports highlight efforts to build an implantable brain device that will help combat veterans recover lost memories.  Yet, past attempts to create a memory-loss device have failed.    Why the uptick in interest now?

I’m sure there are many factors, but I’ll mention three that quickly come to mind. First, our knowledge of the neuro-anatomy of memory has increased over the past few decades and this generates some optimism. Secondly, there has already been some early success with deep brain stimulation improving memory complaints in another condition. Small studies with DBS probes placed in the fornix of Alzheimer’s patients found promising enough results that this technique is currently being investigated with a large multi-center clinical trial. Finally, and perhaps most importantly, the political climate is ripe for this kind of investment. With all the recent media attention on traumatic brain injury from both military engagements and sports as well as the expected “epidemic of dementia” as baby-boomers age, the political will is there to put more funding into this type of research.

If memory can be recovered, it sounds like it was never lost.    Are memories ever completely lost?  

That is a complicated issue. It may be helpful to think of memory as occurring in three discrete phases: encoding, storage, and retrieval. This is an over simplification, but a useful one. Information gathered through our sense organs must be encoded into a form that can be stored as memory. These memories must then be stored in an adequate storage area. Finally, another process is required to retrieve those memories into a recognizable form. An analogy might be to that of a computer hard drive that needs to encode input into a form that can be stored onto the hard drive and then have the ability to retrieve that data for later use.

Dysfunction can occur within any of these three phases. Much like a computer hard drive, if you have damaged the storage area or if information never actually makes it into storage, it is very unlikely that you will get that information back. However if the problem is with the retrieval system, then it is possible that improvements in that system will help you to retrieve information in a more efficient manner. This is true for memories of facts and events as well as memories for motor tasks like tying a shoe. Generally information like this is not experienced as “lost” per se. It is just harder to access in everyday life without frequent external cues and reminders.

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Is memory loss the same for everyone?   How does memory loss in combat veterans compare to memory loss in people with Alzheimer’s dementia, for example?

Again, the issue is what aspect of memory is being affected. In the classic presentation of Alzheimer’s disease, the initial symptoms come from the degeneration of the hippocampus: the primary memory storage area. This means that over time new memories cannot be stored, whereas much older memories last longer since they are stored in other parts of the brain and it takes longer for those regions to be affected.

In the case of brain injury, the type of memory loss is dependent on the area affected. If someone injures their hippocampus, then they may have symptoms similar to Alzheimer’s disease. However, if they damage another area, like the frontal lobe for instance, they will have different problems. They may have difficulty paying attention, which might limit what memories are formed, or instead have difficulties with retrieval and need cues and reminders to help them recall information.

From a scientific point of view, what would an implantable brain device actually be doing?         

I suppose this depends on the final design of the device. The strategy mentioned in the article is to use deep brain stimulation. To understand this, we have to understand how the brain communicates information. This is through either electric or chemical signaling. Medications try to manipulate chemicals (i.e. neurotransmitters) like Acetylcholine, Dopamine, or Serotonin to improve functioning. Deep brain stimulation is an attempt to use electrical signals directly instead of chemicals to improve functioning of the system. The method of combining interventions strategies at both an electrical and chemical level has been very successful for Parkinson’s disease and that is why researchers are interested in evaluating it’s potential in other brain conditions like memory loss.

Don't memory recovery efforts run the risk of creating false memories? 

This is an interesting question. So-called “false memories” are memories that we experience as real but did not occur as we recall them. The term was made popular in the media in the 80’s when a number of cases of alleged childhood sexual abuse or ritualized satanic cult abuse were found to be impossible as recalled. Blame was placed on psychotherapists who unwittingly created these memories through suggestion, often during episodes of hypnosis. This led to a string of studies by Elizabeth Loftus and others that have helped us over the past decades to better understand this phenomenon.

False memories occur during the retrieval phase of memory. Memory is not retrieved in the same way someone might get a file from a cabinet or a book from a library. It is actually re-formed, and to some degree re-experienced, during the retrieval process. This means that “errors” can creep in during the retrieval and be perpetuated during re-storage and re-retrieval. Since that time, we have learned that false memories are fairly common, though usually in a much more subtle form. For instance, if you try to recall your childhood, many of the memories might involve you seeing yourself from the outside. Obviously this could not be possible since you don’t experience life from outside your own body and is simply a sign that some aspects of that memory may be “false”.

Given that the project they are describing seems to involve stimulating the retrieval system, it is certainly possible that people will be at risk for a greater incidence of false memories, though I suspect they would be subtle if they occurred. It is hard to speculate though until we have a working device that we can test.

We've heard the phrases long term and short term memory.    Do researchers see memory this way or is that just a popular notion?    

These terms were actually coined by researchers in the 1960’s, though the concepts are obviously older. For a researcher, short-term memory (also called “working memory”) is that aspect of memory that is dependent on attention. If I give you a seven digit random number to recall and you keep it in mind by repeating it in your head; that is an example of short-term memory. Once I get you distracted with another task and you are no longer keeping your attention focused on the number, you can only recall it if you actually successfully stored it for later use and can retrieve it. That is long term memory. Note, that this is different from the popular distinction of memory for recent events (like what you ate for dinner last night) as being “short-term” and memory for more remote events (such as an embarrassing episode from childhood) as being “long-term”. For a researcher, both of these would be examples of “long-term memory”.

Michael Hopmeier, a technical advisor and operational consultant to DARPA (the agency funding this project), estimates this project has a 10% - 15% chance of success.   Given all the other issues facing combat veterans,  is this really worth the time and effort?

Sure. I’m not sure where the estimate of 10-15% came from, but even if it is true, I think there is still a tremendous upside to this kind of research, both for military and civilian patients. If it succeeds, we will have a new treatment that can improve the quality of life for thousands of people. If the project fails, we will still learn much about memory and this may help us to be more successful in other projects in the future.



Resources:

Brain Implants hold Promise Restoring Combat Memory Loss


Dr. Daniel Schneider, MD is an Assistant Professor in both the departments of Neurology and Psychiatry and is board certified in both specialties. His areas of expertise are Movement Disorders and Behavioral Neurology and has a particular interest in patients diagnosed with conversion disorders and those with cognitive and behavioral manifestations of movement disorders. In addition to his normal clinic population, he runs a Deep Brain Stimulation clinic within the neurology department and a specialty Dementia clinic that is a joint collaboration between the departments of neurology and psychiatry. He also works with a multidisciplinary team at the state-funded Samuel L. Baily Huntington's Disease center to provide care for patients and families with Huntington's disease.