The Connection Between Sleep and Memory in Older Adults
The importance of sleep among older adults has often been minimized. It has frequently been stated that older adults do not need as much sleep as individuals who are younger. It has been known that older adults are often more susceptible to being awaken and experience less time in deep sleep. However, new research is also showing that beyond the regenerative importance of sleep, reduced periods of time spent in deep sleep may also contribute to memory problems as we age.
Neuroscience researchers at the University of California, Berkeley have found that periods of deep sleep appear to be critical for transferring memories from the hippocampal region of the brain to areas of the prefrontal cortex, the area of the brain that appears to be critical for long-term memory storage. The study demonstrated a strong relationship between the quality of deep sleep and the amount of memory disturbance. Generally speaking, it appears that the greater amount of time spent in deep sleep, the less disturbance found to exist in memory. Younger individuals tend to spend more time in deeper periods of sleep. However, as one ages, time spent in stages of deep sleep are lessened and with this reduction in deep sleep, there is a concomitant increase in memory issues.
Memories work their way through the hippocampus. As memories are encoded and consolidated, they move from the hippocampus to parts of the prefrontal cortex of the brain, an area of the brain that is responsible for planning, reasoning, and ultimately controlling our behavior. The researchers found that the hippocampus is influenced by a reduction in slow wave deep sleep patterns. This reduction allows the memory information to more or less get stuck in the hippocampus of many older adults. When the memory information gets stuck in the hippocampus, other information coming into the hippocampus interferes with the original memories that have not been transferred, and the new information overwrites the previous memories that were never transferred to the long-term memory storage area. This in turn leads to a disruption and even and eradication of the original memory.
Deep sleep, marked by slow waves, appears to be critical for the consolidation of information learned during the day. Healthy individuals spend approximately a quarter of their sleep time in deep sleep. The slow wave pattern of deep sleep appears to emanate from the middle frontal lobe region of the brain. However, it appears that as we age, this area of the brain deteriorates, leading to a reduction in time spent in deep sleep. Subsequently, with less time spent in deep sleep, a reduction in memory consolidation exists, with many memories being held up in the limbic region, failing to transfer over to the frontal brain region responsible for long-term memory storage.
In the current University of California, Berkeley study, 18 healthy young adults and 15 healthy older adults had their memory tested on a word pairs task. They were introduced to the word pairs prior to going to sleep. They were then subsequently tested the next morning on their memory of the word pairs. During sleep, all the participants were connected EEG's to measure their brain waves. Upon waking and attempting to remember the paired words, their brains were imaged using both structural and functional magnetic resonance imaging.
What the research found was that there was an association between the level of deterioration within the middle frontal lobe and the level of reduction in slow wave sleep. As the middle frontal lobe deteriorated, this in turn led to a greater reduction in slow wave sleep and with it, impaired long-term memory storage. Conversely, in those with more intact middle frontal lobe regions, a greater level of slow wave sleep existed and with it a greater level of memory transfer from the limbic region to the frontal region of the brain. As was evident, older age was commonly associated with greater levels of deterioration in the frontal lobe region. The greater level of deterioration within the middle frontal lobe region that existed among older adults lead to a 75 percent reduction in the quality of deep sleep among older adults, and furthermore, the reduction in deep sleep was associated with a 55 percent worse performance on the memory task for older adults.
The research has important implications for possible future work on enhancing memory among older adults. Given that deep sleep patterns appear to be associated with memory, future research on enhancing deep sleep patterns may be critical in seeking if this will in turn enhance memory among older adults. Furthermore, since structural areas are now being targeted as the loci for apparent problems in sleep and subsequent memory issues, targeting these areas therapeutically may also help to enhance brain health among older adults.
Poor Sleep in Old Age Prevents the Brain from Storing Memories (2013, Jan 27). Science Daily: http://www.sciencedaily.com/releases/2013/01/130127134212.htm