Frontiers in Aging Neuroscience Aging Neuroscience

Abstract

Mackay et al. (2002) demonstrated that when action and object items are carefully matched for difficulty, the aging process affects the naming of actions and objects equally. Naming difficulty is commonly present in aphasic and demented and imaging studies support the hypothesis of a central role of the left prefrontal and parietal areas in the naming of actions (i.e., verb processing) (Daniele et al., 1994; Perani et al., 1999b). However, studies that establish the role of these areas in older adults are still lacking. Repetitive transcranial magnetic stimulation (rTMS) can induce a brief change in a subject's behavioral performance only if it is applied over an area that is causally engaged in that task being executed. Recent studies reported an improved ability to name pictures after the administration of rTMS over the prefrontal cortex in healthy younger adults and in patients with several types of neurological diseases (Topper et al. reported a selective facilitation in younger adults for action naming when they received rTMS to the left dorsolateral prefrontal cortex (DLPFC). Specifically, they found a shortening in verbal response times compared to sham (i.e., placebo) stimulation. Consistent with these results, Cotelli et al. (2006b, 2008) applied the same protocol in Alzheimer's disease (AD) patients and found that rTMS to the DLPFC improves naming performance in AD patients not only in the early stage (Cotelli et al., 2006b) but also in a more advanced stage of cognitive decline (Cotelli et al., 2008). Importantly, the improvement in AD patients consisted of an increased correctness score after left and right rTMS compared to the sham stimulation condition. Moreover, in patients in the early stages of cognitive