Abstract
Semantic verbal fluency is among the most employed tasks in cognitive aging research and substantial work is devoted to understanding the underlying mechanisms behind age-related differences at the neural and behavioral levels. The present investigation aimed to evaluate the role of moderating variables, such as age, sex, MMSE, and proxies of cognitive reserve (CR) on the hemodynamic response evoked by semantic verbal fluency in healthy young and healthy older adults. So far, no study has been conducted to this end. To elucidate the exclusive effect of the mentioned variables on brain activation during semantic fluency, finger tapping was included as a control task. Results showed that disregarding adjustments for age, older adults displayed important parietal activations during semantic fluency as well as during finger-tapping. Specifically, the anterior intra-parietal sulcus (IPS) and left inferior parietal lobule (IPL) were areas activated in both tasks in the older group. Younger adults, only displayed parietal activations related to age and sex when these demographics were employed as predictors. Concerning proxies of CR in semantic fluency, the only vocabulary was an important moderator in both age groups. Higher vocabulary scores were associated with lesser activation in occipital areas. Education did not show significant correlations with brain activity during semantic fluency in any of the groups. However, both CR proxies were significantly correlated to brain activations of older adults during finger tapping. Specifically, vocabulary was associated with frontal regions, while education correlated with parietal lobe and cingulate gyrus. Finally, the effects of MMSE were mostly observed on brain activation of older adults in both tasks. These findings demonstrate that the effects of moderating variables on shaping brain activation are intricate and not exclusive of complex verbal tasks. Thus, before adjusting for “nuisance variables,” their importance needs to be established. This is especially true for samples including older adults for whom a motor task may be a demanding operation due to normal age-related processes of dedifferentiation.
Highlights
Verbal fluency tasks are among the neuropsychological tests most widely employed in both experimental and clinical aging studies
Semantic Fluency Condition Assessment of the hemodynamic response of the young group during the verbal fluency condition contrasted against the resting condition and controlled by age and Mini-Mental State Examination (MMSE) scores showed activations in the right hemisphere in cerebellar crus I and VI, visual cortex (BA 17, BA 18, and V4), lateral occipital cortex, optic radiation and fornix; and bilaterally in the thalamus, anterior thalamic radiation and caudate
We examined the role of different demographic variables as well as proxies of cognitive reserve on the hemodynamic brain response during the execution of semantic fluency as compared to a simple motor task i.e., finger tapping
Summary
Verbal fluency tasks are among the neuropsychological tests most widely employed in both experimental and clinical aging studies These tasks assess the capacity to accurately and quickly produce words matching either a letter of the alphabet (phonemic fluency) or a semantic category (semantic fluency) within a limited time. The literature proposes that semantic fluency is influenced by increasing age (e.g., Tallberg et al, 2008; Stolwyk et al, 2015) and by sex (Capitani et al, 1999; Lanting et al, 2009), education (da Silva et al, 2004; Tallberg et al, 2008), vocabulary (Shao et al, 2014) and global mental status (Obeso et al, 2012) The importance of these factors has been evaluated at the behavioral level (van Hooren et al, 2007), while their relationship with brain activity is still largely unknown. The number of correct words per category, errors, and perseverations were registered and scored afterward
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