Failure of Crosstalk in Brain Underlies Cognition Loss in Old Age


BOSTON, Dec. 5 -- A brain-wide failure to swap information can cloud cognition in the aging brain, even in the absence of Alzheimer's disease, according to researchers here.
Action Points --->
Explain to interested patients that this study suggests that age-related declines in communication among widely separated brain regions may be responsible for the decline in cognition common to many older people.
In a study of 93 adults, reduced correlation between systems at the front and back of the brains of older volunteers was associated with lower performance on cognitive tests, Randy L. Buckner, Ph.D., of Harvard's Center for Brain Science, and colleagues reported in the Dec. 6 issue of Neuron.
The reduced communications appeared to be associated with age-related degradation of the white matter linking elements of the brain's so-called default network, they wrote.
The default network is associated with functions such as remembering and planning, but the researchers found age-related changes also affect the dorsal attention network, which is active when a person is engaged in a cognitive task.
Using functional MRI techniques, "we may have caught the failure of communication in the act," Dr. Buckner said.
The researchers divided the 93 adults into a young group of 38 volunteers ages 18 to 34 and an older group of 55 volunteers ages 60 to 93.
Dr. Buckner and colleagues measured functional correlations between the medial prefrontal cortex and the posterior cingulate/retrosplenial cortex, two parts of the default network that are widely separated and connected by conduits of white matter.
They found "a dramatic reduction in correlation between the two groups" that was significant on an independent samples t test at P<0.001. What's more, they also found significant differences (at P<0.001) within the older group, with the older volunteers having lower correlations than the younger members of the group.
Using PET scans, nine members of the older group were shown to be free of amyloid deposition, a hallmark of Alzheimer's, the researchers reported.
But they had only slightly better correlation between the two brain areas than did the older group as a whole, and it was still significantly lower than in the younger group (P<0.001).
Findings were similar for the dorsal attention system, which includes brain regions used for tasks that require directed attention, the researchers said.
Interestingly, not all widely separated brain systems are impaired, the researchers said. In particular, they showed that there was no significant difference between the younger and older volunteers in correlations between elements of the visual system.
The researchers said a consequence of the lack of communication between brain regions is significantly poorer performance (P<0.05) on a range of cognitive tasks falling into three areas -- executive function, memory, and processing speed.
"Those individuals exhibiting the lowest functional correlations also exhibited the poorest cognitive test scores," Dr. Buckner and colleagues reported, although they cautioned that other factors -- such as lower levels of neurotransmitters in the older volunteers -- might also play role.
The research "may help explain why some people are just as sharp in their 90s as they were in their 40s," said lead author Jessica Andrews-Hanna, a graduate student in Dr. Buckner's lab. "We all age differently and cognitive abilities vary considerably among individuals."
The study was supported by the NIH, the Alzheimer's Association, and the Howard Hughes Medical Institute. The researchers reported no conflicts.
Primary source: NeuronSource reference:Andrews-Hanna JR, et al "Disruption of large-scale brain systems in advanced aging" Neuron 2007; 56: 924-35.