Grandparents forgets their verbs - Naming ability changes in physiological and pathological aging

Over the last two decades, age-related anatomical and functional brain changes have been characterized by evidence acquired primarily by means of non-invasive functional neuroimaging. These functional changes are believed to favor positive reorganization driven by adaptations to system changes as compensation for cognitive decline. These functional modifications have been linked to residual brain plasticity mechanisms, suggesting that all areas of the brain remain plastic during physiological and pathological aging.

With emerging expertise in functional neuroimaging, multiple studies have shown positive association between age-related brain changes and changes in cognitive and behavioural function.

Studies at the neuronal level have demonstrated that dopaminergic decline and gray matter atrophy are both correlated with specific cognitive changes in older adults. In addition, it has been clearly demonstrated that processing speed, memory, and executive functions depend on the “well-being” of several neuronal substrates. Structural imaging results have also demonstrated widespread gray and white matter tissue atrophy, which largely occurs in the frontal cortex

Evidence has shown namely four hypotheses in explaining the relationship between age-related neuronal activity changes and cognitive performance.

• Overactivation of some cortical areas and a reduction in the hemispheric asymmetry of activation has been documented in older adults as compared to younger adults during cognitive task execution. This leads to episodic memory, working memory, and perceptual tasks. 

• Loss of regional specialization or declining specificity, referred to as dedifferentiation which may lead to reduction of the distinctiveness of within-category representations in the ventral-visual cortex 

• More prevalent higher prefrontal activation during several cognitive tasks. Neuroimaging studies have revealed an age-related reduction in occipito-temporal activity coupled with an increase in frontal activity, a pattern referred to as the posterior-anterior shift in aging. 

• Default network theory – the activity in several regions of the default mode network is altered during the execution of several cognitive tasks; these regions include the medial prefrontal cortex and the medial and lateral parietal cortex. 

All of these physiological-aging-induced structural and functional changes have been linked to residual brain plasticity to counteract neural loss, referred to as “NEURAL STRATEGIES”.

Most recent research suggests that the left frontal and temporal areas are crucial during naming. Moreover, it is suggested that in older adults and patients with dementia, the right prefrontal cortex is also engaged during naming tasks, and naming performance correlates with age and/or the degree of the pathological process.

The age-related changes that were observed in this TMS naming study are consistent with other neuroimaging discoveries and theories of cognitive aging. This study underlines the presence of a facilitatory effect on naming following right or left DLPFC stimulation in older adults; this result is in contrast to the unilateral (i.e., left) effect that was previously observed in young adults. This bilateral frontal effect may be attributed to the presence of a compensatory mechanism that is based on the recruitment of right hemisphere resources to maintain task performance. The same mechanisms could underlie the increased naming accuracy induced by both left and right DLPFC TMS in neurodegenerative patients.

To read the study in detailed please visit:

http://www.frontiersin.org/Journal/FullText.aspx?=55&name=&ART_DOI=10.3389/fnins.2012.00120

Posted in: Clinical discussion,Discussion,Perspective