Researchers can measure the level of noise in the signals of neural circuits in the brain, and see that it is higher in older brains. The proximate cause of this noise is an open question. With an eye to finding out more about the mechanisms involved, it would be interesting to see if there is any correlation of magnitude with measures such as epigenetic dysregulation or the low level of demyelination of nerves that occurs in aging.
Researchers found that background noise in key cortical regions of the brain responsible for higher functions was associated with poorer memorization of visual information, and that this noise also was associated with age. They concluded that neural noise might be the mechanism behind aging-associated loss of cognitive ability, slowing of behavioral responses, uncertain memories and wavering concentration. The noise measured in the studies was random signaling that did not fit the pattern of the brain's natural oscillations. These oscillations are rhythmic patterns of electrical activity generated by nerve cells, or neurons, linked within the brain's circuitry. This activity occurs in addition to electrical signals generated by individual neurons.
In recent years brain oscillations have become an intense focus of research by scientists seeking to discover any functional roles they might play. Emerging evidence suggests that oscillations might prime nerve circuits to respond more efficiently to stimuli. "Imagine that individual neurons are like surfers. Nearby surfers experience the same waves, which are like the oscillations linking neurons in the brain. But like noise, additional interfering factors often disrupt the perfect wave at different times and different spots along the beach."
Researchers flashed one, two or three colored squares for less than one-fifth of a second, gave the subjects almost one second to memorize the colors, and then flashed a second display and asked the participants if the colors matched. The researchers used mathematical algorithms to extract measures of noise in the oscillations from EEG data collected during the interval when the subjects were trying to memorize the colors. On average, older subjects performed worse than younger subjects. The scientists determined that this poorer performance was due to additional noise in nerve circuits in the visual cortex; neurons did not appear to coordinate as well in generating lower-frequency oscillations. When the researchers accounted for the noise, age was no longer an independent, significant factor in performance in this experiment.
"Instead of having a normal conversation, the neurons that make up the memory networks in older adults seemed to be talking over one another, leading to a communication breakdown and degrading their memory performance. I think these types of experiments will allow neuroscientists to explore the neural underpinnings of cognitive changes across normal aging and in a variety of disease states, including autism, Parkinson's and schizophrenia, each of which is associated with breakdowns in neural oscillations."