Cognitive ability has many different dimensions. While all decline with age, it is quite possible for any given individual to find them declining at different rates and at different times, according to the individual distribution of damage and atrophy in the brain. The research noted here illustrates one of many links between a particular cognitive function and a particular location in the brain. In most cases we can look at this sort of evidence and consider that it would be very helpful to have a way to (a) spur greater generation of new cells in the brain, that can integrate into tissues, repair areas of damage, and restore lost function, and (b) clear out the protein aggregates and other forms of metabolic waste associated with the progression towards neurodegenerative disease.
Older adults appear more easily distracted by irrelevant information than younger people when they experience stress or powerful emotions - and a specific network in the brain recently identified as the epicenter for Alzheimer's and dementia may be to blame. A study finds that seniors' attention shortfall is associated with the locus coeruleus, a tiny region of the brainstem that connects to many other parts of the brain. The locus coeruleus helps focus brain activity during periods of stress or excitement.
Increased distractibility is a sign of cognitive aging. The study found that older adults are even more susceptible to distraction under stress or emotional arousal, indicating that the locus coeruleus' ability to intensify focus weakens over time. For instance, if an older adult is taking a memory test in a clinician's office, he or she may be trying hard to focus but will be more easily distracted than a younger adult by other thoughts or noises in the background.
The locus coeruleus appears to be one of the earliest sites of tau pathology, the tangles that are a hallmark of Alzheimer's disease. "Initial signs of this pathology are evident in the locus coeruleus in most people by age 30. Thus, it is critical to better understand how locus coeruleus function changes as we age." The locus coeruleus connects to many parts of the brain and controls the release of the hormone norepinephrine, which influences attention, memory and alertness. Normally, norepinephrine increases the "gain" on neural activity - highly active neurons become more excited, while less active neurons get suppressed.
The researchers recorded physiological arousal and locus coeruleus activity in 28 younger adults and 24 older adults using both brain scans and the measurement of pupil dilation in participants' eyes - an outwardly visible marker for emotional arousal and locus coeruleus activity. During the scans, study participants were shown pairs of photographs. Some trials started with a tone that warned participants that they might receive an electric shock at the end of the trial. Other trials started with a tone indicating that there would be no shock. Participants showed greater pupil dilation and sweat during trials when they might get a shock, indicating greater physiological arousal.
The brain's parahippocampal "place area" becomes active when a person is looking at images of places. In younger adults, expecting a shock amplified activity in the place area when they looked a clear, highlighted image of a building. Pathways in their brains linking the locus coeruleus, the place area, and the frontoparietal network - regions of the brain's cortex that help control what to pay attention to and what to ignore - were uninterrupted. This enabled them to more effectively ignore the information that wasn't important. Older adults, however, showed less activity in the frontoparietal network when anticipating a shock. Their network seemed to no longer effectively respond to signals from the locus coeruleus.