Frontal lobes and aging: Deterioration and Compensation

Until the mid 1990s, available evidence regarding neurocognitive aging could be summarized in a simple statement: cognitive deficits in healthy older adults are largest for tasks that are highly dependent on executive control processes because these processes are mediated by the prefrontal cortex (PFC), which is the region most disrupted by healthy aging. This view, known as the frontal lobe hypothesis, rested on the assumption that both cognitive and cerebral aging occurred mainly in one direction: a decline in function. This simple version of the frontal lobe hypothesis was challenged by the first crop of positron emotion tomography (PET) studies, which clearly showed that aging can have two opposing effects on brain activity: compared to young adults, older adults showed reduced activity in some brain regions but increased activity in other brain regions (e.g, Grady et al., 1994; Cabeza et al., 1997b). Age-related increases in neural activity were prominent within PFC, where they often involved regions that were not reliably recruited by younger adults. These findings challenged the standard assumption that aging is associated with a simple pattern of cognitive and neural decline, and supported the notion that cognitive processing in the aging brain is not just a weaker version of cognitive processing in the young brain, it is different.