While imaging brain studies can’t show us what we’re thinking, they can show us comparatively how two brains are performing from two different groups. Neuroscientists use such comparisons to form hypothesis about brain behavior. Using neuroimaging techniques to study aging — techniques such as MRI, fMRI and PET scans — is still a relatively new science: it’s only been around since the mid 1990s.
One finding from this research is that older adults tend to engage in overactivation of certain areas of their brain. What this means that in order to perform the same cognitive tasks in the experiment, an older brain will light up in different regions and with greater intensity (suggesting greater “work” by the brain) than their younger counterparts.
Some researchers have interpreted such overactivation as a sign of impairment (especially when paired with poor performance on the task). But in an article just published in Current Directions in Psychological Science Reuter-Lorenz and Cappell suggest that overactivation serves “a beneficial, compensatory function without which performance decrements would result.” In other words, if an older brain didn’t overcompensate, older people wouldn’t perform as well on cognitive tasks as younger people. It’s a healthy adaptation of the brain.
Why would an aging brain need to compensate in the first place? The researchers has some theories, suggesting it might have to work harder to make up for its own declining efficiency or for processing deficiencies elsewhere in our brains. Or it may be a result of degraded input signals — our failing sensations and perceptions — into the brain in the first place.
Are older brains simply younger brains working harder? The researchers suggest that, by and large, the answer is “yes:”
In our lab, […] we found that older adult activated regions of the dorsolateral prefrontal cortex at lower loads, whereas younger adults activated these same sites only at higher loads. Importantly, at the lower loads, age differences in performance were minimal. At the higher loads [as the task became increasingly more difficult], activation in the younger group exceeded that observed in the older group, and elderly performance was relatively deficient as well.
The researchers found that for some tasks, both young and old activate the same regions of the brain, older adults just do it a little bit sooner. When the tasks are easy, older people overactivate certain brain regions in an apparent compensatory behavior in order to provide good, equivalent performance on the task. But as the task gets harder, older brains just can’t always keep up, and no amount of compensatory brain activation is going to help, resulting in decreased performance relative to the younger group. Researchers like their acronyms, so they call this series of observations “CRUNCH” — compensation-related utilization of neural circuits hypothesis.
Keep in mind, this is just a series of hypotheses that the researchers propose, based upon their current observations in their research on these topics. It’s an interesting set of hypotheses, though, suggesting that while we may be able to try and keep our brains “healthy” through regular exercise and such, there may be “hard” limits to what the brain can naturally do as it ages.
Reuter-Lorenz, P.A. & Cappell, K.A. (2008). Neurocognitive aging and the compensation hypothesis. Current Directions in Psychological Science, 17(3), 177-182.