Memory Loss from a Silent Source

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Memory loss (a.k.a. amnesia) involves episodes of unusual forgetfulness that typically refers to an inability to remember new events, an inability to recall one or more memories from the past, or both. Signs and symptoms of memory loss are medically significant because they can be one of the first indications that you may have been or currently are suffering from a brain disorder. In a recent study, researchers have determined that in a select group of individuals, as many as 1 in 4 may be affected by memory loss from a silent source.

Memory loss can result from numerous causes such as alcohol and drug abuse, brain tumors, trauma to the head such as repeated blows from boxing or football, certain medications, migraine headaches and depression. However, memory loss is also often a normal part of aging where a person may find it increasingly difficult to learn new things or that it takes more time to remember things that have already been learned. In its most severe form, memory loss can be due to age-associated neurodegenerative conditions, such as Alzheimer's disease.

With neurodegenerative disease, the part of the brain that is most commonly affected and associated with memory loss is the hippocampus. The hippocampus is a horseshoe shaped paired structure that lies deep within the brain below the cortical surface, with its two “horns” located one each in both hemispheres of the brain.

The hippocampus plays an important role in consolidating and processing information from short-term memory to long-term memory. It is sometimes described as being likened to an index card system where memories can be stored, ordered and accessed when needed.

Damage to the hippocampus can result from hypoxia, encephalitis and epilepsy. In Alzheimer’s disease it is one of the first parts of the brain to suffer damage, which can manifest with memory loss and disorientation. However, in individuals 60 and above, not all cases of memory loss are attributable to Alzheimer’s disease, but to other regions of the brain outside of the hippocampus where brain infarcts (strokes) can be responsible for memory loss.

A stoke is when the blood supply to a part of the brain is interrupted or when a blood vessel in the brain bursts, spilling blood into the spaces surrounding brain cells, which then causes brain cell death. Symptoms of a stroke typically include sudden numbness or weakness, especially on one side of the body; sudden confusion or trouble speaking or understanding speech; or, a sudden severe headache of unknown etiology. However, not all strokes are so obvious.

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One type of non-obvious stroke is a “silent stroke” where minimal brain damage has occurred. Silent strokes are common in individuals 60 and above who have high blood pressure. Various degrees of memory loss can be the result of a silent stroke, which is often missed by an individual and his family or attributed to as normal “forgetfulness,” but could in fact be linked to dementia outside of Alzheimer’s disease and/or damage to the hippocampus.

Memory loss Columbia University study

To address the potential connection of memory loss between damage to the hippocampus and silent strokes, researchers from the Taub Institute for Research on Alzheimer’s Disease and the Aging Brain at Columbia University Medical Center in New York, published their findings in the January 2012 issue of the journal Neurology, examining both silent strokes and hippocampal shrinkage simultaneously in elderly volunteers.

In the study, 658 volunteers aged 65 and older and free of dementia were given MRI brain scans and underwent a battery of tests that measured their memory, language, speed at processing information and visual perception.

What they determined was that a total of 174 of the volunteers—who had experienced a silent stroke—scored worse on memory tests than those who had not experienced a silent stroke. This was true whether or not they had a small hippocampus, which is an indication that the hippocampus had experienced a stroke or some other damage at some time in the participant’s life. In other words, their results showed that silent strokes independent of the hippocampus can contribute to memory loss.

The conclusion by the researchers of study was that both hippocampal size and brain infarcts independently contribute to memory performance in elderly individuals without dementia, and that stroke prevention measures can prevent memory loss.

According to study author Adam M. Brickman, PhD, “Given that conditions like Alzheimer’s disease are defined mainly by memory problems, our results may lead to further insight into what causes symptoms and the development of new interventions for prevention. Since silent strokes and the volume of the hippocampus appeared to be associated with memory loss separately in our study, our results also support stroke prevention as a means for staving off memory problems,” says Doctor Brickman.

Image source: Flickr: Used under Creative Commons License

Source: Neurology January 3, 2012 vol. 78 no. 1

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