Changes in the Hippocampus Underlie Memory Changes with Age
The hippocampus is a region of the brain located in the medial temporal lobe, which is that area located on each side of person's head. If you look at your head and take the region where your ears are located, and pass an imaginary line into your skull from your ear region inward, you would pass through the hippocampal formation where the hippocampus is located. The derivation of the name, hippocampus, comes from its seahorse appearance that early neuroscientists noted during anatomical investigations of the brain.
The hippocampus has been known for some type to be instrumental in memory. For a number of years it was thought of as being the key anatomical site in the brain for memory. However, more current research has found that it is far from being the only part of the brain involved in memory. The hippocampus is still understood to be a very important part of the brain instrumental in memory. However, in reality, the hippocampus is one part of a large circuit in the brain that is important for memory.
Recent research has found that as memories age, different parts of the brain become involved in memory, working in a compensatory manner to apparently take the burden off of the hippocampus. In an article in the September/October 2009 edition American Scientific-Mind, the research findings of Larry Squire of the University of California at San Diego are discussed. Using functional MRI studies, Squire and his team were able to examine the changes in the neurophysiology of the brain and how these changes were related to memory.
What Squire and his team found was that activity in the hippocampus area declined when the study's participants had to recall information for progressively longer periods of time, ranging from more immediate information up to many years. The team found that activity in the hippocampus region continued to decline up to about 12 years. However, participants that had to recall information that was over 12 years old appeared to demonstrate hippocampal activity that stabilized after the 12-year period. Therefore, it appears that memory components connected to the hippocampus demonstrate progressively less neurological investment by the hippocampus in the energy it uses. Furthermore, it also appears that the hippocampus becomes less and less responsible for maintaining the currency of memory.
However, this is not the end of the story. With the plasticity that the brain has it appears to shift responsibility to for recalling those memories for that 12-year period to other areas of the brain. In particular, activity appears to increase in the frontal, temporal and parietal areas for recalling information for that period of time when the hippocampus is reducing its activity.
What is interesting is that many memory diseases of old age, such as Alzheimer's disease, start at the subcortical level, or the more evolutionarily primitive allocortical region. The hippocampus is one of the important brain areas that make up part of the deep inner allocortex. This can be another reason why many older adults with Alzheimer's disease often face shorter-term memory deficits at the start of the disease, with many of their long-term memories being preserved until later in the disease. I say "another reason" becomes we do know that Alzheimer's disease also influences a closely associated neural pathway that connects with the hippocampal region called the entorhinal cortex.
The new research results by Squire, although not specifically addressing memory and the aging adult, does have implications for this age group. Although memory is a very important part for human existence, as we age memory becomes a more sensitive topic. Having greater knowledge of the inner workings of memory is essential for all professionals working with older adults. Squire's research does raise some interesting questions for this age group.
First, are many of the normal forms of forgetfulness that we attribute to aging, often quite stereotypically, part of the same processes that are found among all ages? In other words, if this process of a progressive reduction in activity found in the hippocampus is found among all age groups, are many of the supposed memory tests for more short and immediate term memory given to older adults demonstrating any appreciably different results than would be found among other age groups and if so, what is the quantifiable difference?
A second question that the new research raises is if, during the hippocampal reduction, there is a compensatory increase in activity in other areas of the brain, especially the frontal, temporal and parietal lobes, is this activity increase equipotent for all ages? Does the compensatory neurological enhancement found among these areas for recalling information during this period of time exist on equally quantifiable levels for all ages? Or is a neurological enhancement in activity also found to exist among older adults but at an activity gradient that is much lower than that found among younger individuals. Hence, are the roadways for travel of information still found to exist among older adults, but with a much narrower road carrying less information?
I find the current information very interesting, possibly leading to many answers to questions that have been posed in neuroscience, especially related to the aging brain. However, I also find the research posing other questions as they relate to the elderly that can as yet not be answered. Good research often answers many questions while raising many more. In particular in dealing with the brain, an organ we still know so little about, the questions continue to arise. As an organ, the brain is far from being static and the changes that can exist with age are numerous. We know that the brain has a level of plasticity that continues to exist even as we age. Therefore, it becomes important to understand the impact of Squire's research and how it can be used to help understand the aging brain.