Older adults reallocate neural resources, increasing activity in prefrontal cortex to perform cognitive tasks, presumably to compensate for declining neural processing in posterior brain regions. Davis et al. show: 1). that this reflects the effects of aging rather than differences in task difficulty (i.e. not due to the same cognitive tasks tending to be more demanding for older adults than for younger adults); 2). that the shift in fact reflects compensation (the age-related increase in PFC activation is positively correlated with cognitive performance and negatively correlated with the age-related decrease in occipitotemporal activity.); and 3). that the deactivation of the midline "default network" associated with conscious rest processes, which must be suppressed for successful cognitive performance, is reduced in posterior midline cortex but increased in medial frontal cortex.
The experiments were performed on 12 younger (mean age = 22.2 years) and 12 older adults (mean age = 69.2 years), presumably referenced by the Y and O prefixes in this figure from the paper (I'm not clear from the text on what distinguishes YM and YP, but I think they refer to the two different tasks, episodic retrieval and visual discrimination).
Figure (click to enlarge) - The posterio-anterior shift pattern for activations: across 2 different tasks and 2 levels of confidence, the occipital cortex showed greater activity in younger than in older adults A, whereas PFC showed the opposite pattern (B). The PASA pattern for deactivations: across 2 different tasks and 2 levels of confidence, posterior midline cortex (precuneus, C) showed greater deactivations in younger than older adults, whereas the anterior midline cortex (medial PFC, D) showed the opposite pattern. Notes: Activation bars represent effect size for each modeled effect, and error bars represent standard error for peak activity across participants.
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