The Neurobiology of Memory and Aging
"I lost my keys again," my mother exclaimed at dinner a few nights ago, "I really am getting old." This use of old age as a justification for memory deficits is extremely common. Many people relate old age with loss of memory and other neurobiological functions. Why is it that aging seems to go hand in hand with losing and forgetting things? Is there a neurobiological explanation for this phenomenon?
It is clear to neurobiologists that aging results in a decrease in brain size as well as a decrease in the efficiency of brain functions. It has been a widely held belief that aging causes neurons to die and for the overall number of neurons to decrease as one reaches old age. Studies conducted by Dr. David Merrill refute this idea, sighting a lack of neuronal loss in the entohinal cortex after running an MRI on a healthy subject. Instead, Merill indicates that loss of neurons may occur in degenerative disorders, such as Alzheimers, but not in healthy brains. However, it remains true that some aspects of cognition do decline as age increases, such as short term and long term memory. Since these effects are not caused by a decrease in the number of neurons present, there must be another neurobiological explanation.
In order to understand memory loss it is necessary to understand how memory works in a normal brain without any cognitive deficits. Memory can be separated into three distinct parts: working memory, declarative memory, and procedural memory (1). Working memory is the most short term, and it involves repeating something that someone has just said in conversation or remembering something you had just seen briefly. This part of memory does not ever become fully stored in the brain, does not become permanent memory, and can be erased once something new is put into the same part of the brain. (1). Therefore, once one sees something else or takes part in a new conversation is it difficult to remember all of the details from the one before. Declarative memory includes remembering facts one has used effort to learn in the past, and things one has tried to remember. The last part of memory, procedural memory, consists of everything one has learned by repetition, such as playing an instrument or sport, driving a car, or walking.
The brain is dividing into several sections, including the cerebellum, the frontal lobe, and the temporal lobe, among others. The temporal lobe exists in two parts, one on each side of the brain close to the ears. It is largely responsible for the memory system (2). On the medial surface of the temporal lobe there are three important structure that are essential for human functioning. These structures are named, in order from rostral to caudal, the olfactory cortex, the amygdala, and the hippocampus. Together these three structures are referred to as the "limbic system" (1). Their functions became understood after studying how the brain functions upon...