One of the clearest aspects of cognitive ageing is decline in ‘fluid intelligence’, measured with simple tests of novel problem solving. Evidence from functional brain imaging and study of brain-damaged patients links fluid intelligence to a specific, distributed brain system, encompassing parts of lateral frontal, dorsomedial frontal and parietal lobes (‘multiple-demand’ or MD system). The MD system is linked to cognitive or attentional control, creating and combining the component fragments of complex, goal-directed thought and behaviour. We know that impaired MD function, linked to loss of fluid intelligence, will compromise performance across cognitive domains, including perception, memory, language and emotional control. Our research addresses a series of interrelated hypotheses.
- In healthy ageing, a major variable in cognitive change is the function of the MD system.
- In specific cognitive domains, age-related change reflects interaction between the general-purpose MD system and content-specific systems of posterior cerebral cortex.
- In part, cognitive decline vs preservation depends on decline or preservation in such interactive networks, assessed by structural and functional measures of integrity in participating nodes and their connections.
- The possibility exists for compensatory reorganization of function between distinct components of the MD system, primarily specialized for somewhat separate aspects of cognitive and attentional control.
Current analyses focus on the role of frontal lobes for supporting systems that are differentially affected by age. Our recent work on patients with focal brain lesions (Roca et al.,2010) suggests important dissociations between different aspects of frontal lobe function. A posterior frontal network is critical in fluid intelligence, closely associated with many standard tests of ‘executive’ function. A separate test of time allocation -perhaps measuring ability to keep ‘the big picture’ while focusing on individual task details – is dependent on more anterior frontal regions, and perhaps to a higher level of cognitive control.
Our preliminary data show that, as usual, there is a substantial decline in fluid intelligence with advancing age (figure below, left). Meanwhile, time allocation or keeping hold of the big picture shows only very small changes (figure below, right).