Selection requirements during verb generation: differential recruitment in older and younger adults Jonas Persson, Ching-Yune C. Sylvester, James K. Nelson, Kathryn M. Welsh, John Jonides, and Patricia A. Reuter-Lorenz * Department of Psychology, University of Michigan, Ann Arbor, MI 48109-1109, USA Received 31 March 2004; revised 21 July 2004; accepted 4 August 2004 Age-related differences in cognitive performance are well documented. These differences are most pronounced during tasks with high demands on cognitive control, and it has been proposed that selective alteration of prefrontal activity is associated with cognitive changes in old age. Here, differences in the neural systems underlying selection requirements for older and younger adults were investigated using functional magnetic resonance imaging (fMRI). A verb generation task was used, and selection requirements were varied with regard to whether each noun could be associated with either few (scissors—cut) or many (ball— bounce, kick, throw...) competing alternatives. The two age groups showed statistically equivalent behavioral performance across the task conditions but marked differences in activation. Across both age groups, high selection demands activated several regions including bilateral frontal, left anterior frontal, left inferior temporal regions, and the dorsal anterior cingulate cortex (ACC). Between-group comparisons using region-of-interest analyses revealed less activation for senior adults in left inferior frontal gyrus (IFG), left inferior temporal gyrus, and the anterior cingulate and higher activation in right inferior frontal gyrus compared to young adults. These findings indicate age-related changes in multiple regions contributing to aspects of selection require- ments during verb generation. D 2004 Elsevier Inc. All rights reserved. Keywords: Aging; Prefrontal; Selection; fMRI; Semantic; Memory; Executive function Introduction Age-related decline in various cognitive domains such as memory is well documented (Craik and Salthouse, 1999). In particular, senior adults often experience more difficulties than younger adults on memory tasks with high demands on control processes (Craik, 1977; Moscovitch and Winocur, 1995). There is a growing consensus that the prefrontal cortex (PFC) undergoes anatomical and functional deterioration as a function of normal aging, and it has been proposed that dysfunction of frontal systems may underlie age-related cognitive decline (Raz et al., 1997; West, 1996). Here, we test this hypothesis using functional magnetic resonance imaging (fMRI), focusing on the role of prefrontal regions, and more specifically, the left inferior frontal gyrus (IFG). Substantial research has shown that left IFG is activated when tasks are complex and the demands on cognitive resources are high. A common interpretation of this result is that this specific region is activated when novel or weakly associated representa- tions are temporarily assembled to solve the task at hand and at the same time suppress other potential, but context-inappropriate, representations (Buckner, 2003; Duncan and Owen, 2000; Miller, 2000; Nolde et al., 1998; Thompson-Schill et al., 1997). Tasks in which responses are based on a straightforward match between a cue and a specific representation does not appear to engage these prefrontal regions. In a long-term memory framework, however, left IFG seems to play a role in the active selection of representations, possibly by means of interacting with posterior regions in temporal and parietal cortex that operate as storage sites. In one study (Thompson-Schill et al., 1997), subjects were asked to generate an appropriate verb in response to a visually presented noun. Two different generation tasks were used, one where the nouns had multiple alternative responses (high selection demands), and one task in which there was a clear dominant response to the noun (low selection demands). It was found that higher activity in left IFG was associated with the former task, in which there were several valid responses to a noun (i.e., higher demands on selection). These results suggest that, as a cognitive task gets more complex, the demand for top-down control of behavior increases and left inferior prefrontal regions are recruited. As previously discussed, senior adults are selectively impaired in tasks with high demands on effortful processing and cognitive control (Hasher et al., 1991; Moscovitch and Winocur, 1995; Salthouse, 1996). Therefore, it is reasonable to believe that left IFG 1053-8119/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2004.08.004 * Corresponding author. Department of Psychology, University of Michigan, 525 East Hall, Ann Arbor, MI 48109-1109. Fax: +1 734 763 7480. E-mail address: parl@umich.edu (P.A. Reuter-Lorenz). Available online on ScienceDirect (www.sciencedirect.com.) www.elsevier.com/locate/ynimg NeuroImage 23 (2004) 1382 – 1390