Do attentional capacities and processing speed mediate the effect of age on executive functioning?

The executive processes are well known to decline with age, and similar data also exists for attentional capacities and processing speed. Therefore, we investigated whether these two last nonexecutive variables would mediate the effect of age on executive functions (inhibition, shifting, updating, and dual-task coordination). We administered a large battery of executive, attentional and processing speed tasks to 104 young and 71 older people, and we performed mediation analyses with variables showing a significant age effect. All executive and processing speed measures showed age-related effects while only the visual scanning task performance (selective attention) was explained by age when controlled for gender and educational level. Regarding mediation analyses, visual scanning partially mediated the age effect on updating while processing speed partially mediated the age effect on shifting, updating and dual-task coordination. In a more exploratory way, inhibition was also found to partially mediate the effect of age on the three other executive functions. Attention did not greatly influence executive functioning in aging while, in agreement with the literature, processing speed seems to be a major mediator of the age effect on these processes. Interestingly, the global pattern of results seems also to indicate an influence of inhibition but further studies are needed to confirm the role of that variable as a mediator and its relative importance by comparison with processing speed.

Inhibitory control of memory in normal ageing: dissociation between impaired intentional and preserved unintentional processes.

The aim of this study was to compare the performance of elderly and young participants on a series of memory tasks involving either intentional or unintentional inhibitory control of memory content. Intentional inhibition processes in working and episodic memory were explored with directed forgetting tasks and in semantic memory with the Hayling task. Unintentional inhibitory processes in working memory, long-term memory, and semantic memory were explored with an interference resolution task, the retrieval practice paradigm, and the flanker task, respectively. The results indicate that elderly participants' performance on the two directed forgetting tasks and the Hayling task is lower than that of young ones, and that this impairment is not related to their initial memory capacity. This suggests that there is a specific dysfunction affecting intentional inhibitory control of memory contents in normal ageing.

Directed forgetting and aging: the role of retrieval processes, processing speed, and proactive interference.

The directed forgetting effect obtained with the item method is supposed to depend on both selective rehearsal of to-be-remembered (TBR) items and attentional inhibition of to-be-forgotten (TBF) items. In this study, we investigated the locus of the directed forgetting deficit in older adults by exploring the influence of recollection and familiarity-based retrieval processes on age-related differences in directed forgetting. Moreover, we explored the influence of processing speed, short-term memory capacity, thought suppression tendencies, and sensitivity to proactive interference on performance. The results indicated that older adults' directed forgetting difficulties are due to decreased recollection of TBR items, associated with increased automatic retrieval of TBF items. Moreover, processing speed and proactive interference appeared to be responsible for the decreased recall of TBR items.

Retrieval-induced forgetting in normal ageing.

The retrieval-induced forgetting (RIF) paradigm was used to assess the integrity of Unintentional inhibitory functioning in normal ageing. The paradigm was adapted to explore the RIF effect under conditions that allow us to differentiate the contribution of intentional and automatic retrieval processes to performance. The results showed the presence of equivalent and significant RIF effects in young and older adults, for both the intentional and automatic retrieval performance. These results suggest that unintentional inhibitory processes are spared in normal ageing and confirm that RIF effect is independent of the kind of memory processes involved in task performance.

Comparison of inhibitory functioning in mild Alzheimer's disease and frontotemporal dementia.

Executive dysfunction is frequently reported in Alzheimer's disease (AD) and the frontal variant of frontotemporal dementia (FTD). More specifically, inhibitory dysfunction is observed early in AD and inhibitory deficits are also prominent in patients with FTD. However, few studies have simultaneously explored and compared inhibitory abilities in both degenerative diseases. Consequently, the aim of this study was to compare verbal and motor inhibitory processes in the initial stages of AD and the frontal variant of FTD. Stroop and Go/No-go tasks were administered. The results demonstrate that, on the Go/No-go task, AD and FTD patients do not produce more errors than control subjects. However, both groups are impaired on the Stroop task (mainly with regard to the error score) but do not differ from each other. These results indicate that AD and FTD patients do not present a general impairment of their inhibitory abilities. Moreover, these two kinds of dementia present similar quantitative and qualitative inhibitory impairments on the two tasks, although their patterns of structural and functional cerebral impairments are known to be different. The presence of similar inhibitory deficits despite very different patterns of brain damage is in agreement with the hypothesis that inhibitory dysfunction in the two groups of patients depends on a disconnection process between anterior and posterior cerebral areas, rather than on the presence of focal metabolism decreases in different regions.

Social mind representation: where does it fail in frontotemporal dementia?

We aimed at investigating social disability and its cerebral correlates in frontotemporal dementia (FTD). To do so, we contrasted answers of patients with early-stage FTD and of their relatives on personality trait judgment and on behavior prediction in social and emotional situations. Such contrasts were compared to control contrasts calculated with answers of matched controls tested with their relatives. In addition, brain metabolism was measured in patients with positron emission tomography and the [(18)F]fluorodeoxyglucose method. Patients turned out to be as accurate as controls in describing their relative's personality, but they failed to predict their relative's behavior in social and emotional circumstances. Concerning the self, patients were impaired both in current personality assessment and in prediction of their own behavior. Those two self-evaluation measures did not correlate. Only patients' anosognosia for social behavioral disability was found to be related to decreased metabolic activity in the left temporal pole. Such results suggest that anosognosia for social disability in FTD originates in impaired processing of emotional autobiographical information, leading to a self-representation that does not match current behavior. Moreover, we propose that perspective-taking disability participates in anosognosia, preventing patients from correcting their inaccurate self-representation based on their relative's perspective.