Age-related prefrontal cortex activation in associative memory: an fNIRS pilot study.

Older adults typically perform more poorly than younger adults in free recall memory tests. This age-related deficit has been linked to decline of brain activation and brain prefrontal lateralization, which may be the result of compensatory mechanisms. In the present pilot study, we investigated the effect of age on prefrontal cortex (PFC) activation during performance of a task that requires memory associations (temporal vs. spatial clustering), using functional Near-Infrared Spectroscopy (fNIRS). Ten younger adults, ten cognitively high-performing older individuals, and ten low-performing older individuals completed a free recall task, where either a temporal or spatial strategy (but not both simultaneously) could be employed to retrieve groups of same-category stimuli, whilst changes in PFC haemodynamics were recorded by means of a 12-channel fNIRS system. The results suggest PFC activation, and right lateralization specific to younger adults. Moreover, age did not affect use of memory organization, given that temporal clustering was preferred over spatial clustering in all groups. These findings are in line with previous literature on the aging brain and on temporal organization of memory. Our results also suggest that the PFC may be specifically involved in memory for temporal associations. Future research may consider whether age-related deficits in temporal organization may be an early sign of PFC pathology and possible neurodegeneration

Perspective taking and systematic biases in object location memory.

The aim of the current study was to develop a novel task that allows for the quick assessment of spatial memory precision with minimal technical and training requirements. In this task, participants memorized the position of an object in a virtual room and then judged from a different perspective, whether the object has moved to the left or to the right. Results revealed that participants exhibited a systematic bias in their responses that we termed the reversed congruency effect. Specifically, they performed worse when the camera and the object moved in the same direction than when they moved in opposite directions. Notably, participants responded correctly in almost 100% of the incongruent trials, regardless of the distance by which the object was displaced. In Experiment 2, we showed that this effect cannot be explained by the movement of the object on the screen, but that it relates to the perspective shift and the movement of the object in the virtual world. We also showed that the presence of additional objects in the environment reduces the reversed congruency effect such that it no longer predicts performance. In Experiment 3, we showed that the reversed congruency effect is greater in older adults, suggesting that the quality of spatial memory and perspective-taking abilities are critical. Overall, our results suggest that this effect is driven by difficulties in the precise encoding of object locations in the environment and in understanding how perspective shifts affect the projected positions of the objects in the two-dimensional image

Spatial working memory in normal aging: a new perspective on cognitive decline

Le vieillissement normal est associé à une variété de changements des capacités cognitives, incluant un déclin général des performances de mémoire de travail. La mémoire de travail est le système cérébral sous-tendant le stockage temporaire et la manipulation simultanée d'une quantité d'information limitée. La littérature reporte que la mémoire de travail visuo-spatiale montre un plus grand déclin lié à l'âge que la mémoire de travail verbale. Cependant, ce plus grand déclin des performances de mémoire de travail visuo-spatiale n'a pas été démontré en-dehors d'expériences neuropsychologiques effectuées sur écrans d'ordinateur. Le travail décrit ici fournit les premières données obtenues dans un environnement réel en laboratoire, comparant la mémoire de travail spatiale allocentrique avec la mémoire de travail des couleurs. Mes données expérimentales ne suggèrent pas de plus grand déclin lié à l'âge de la mémoire de travail spatiale allocentrique. Dans une première étude publiée, j'ai montré qu'une évaluation de la capacité de mémoire (comme le nombre de choix corrects avant une erreur) suggérerait que la mémoire de travail spatiale est plus affectée que la mémoire des couleurs. En revanche, l'évaluation des performances de la mémoire parfaite (basée sur le nombre d'essais sans erreur) suggère que les mémoires de travail spatiale et des couleurs sont affectées similairement par l'âge. Dans une deuxième étude publiée, dans laquelle j'ai spécifiquement testé l'effet de la charge mnésique sur les performances de mémoire de travail, je n'ai trouvé aucune évidence que la mémoire de travail spatiale était plus affectée par l'âge que la mémoire de travail des couleurs. Somme toute, ces découvertes suggèrent que le déclin lié à l'âge dans les performances de mémoire pourrait être lié à la demande représentationnelle de la tâche et non pas au type d'information à mémoriser. Dans une troisième étude sur les corrélats électro-encéphalographiques (EEG) des performances mnésiques, j'ai évalué si une activité EEG au repos corrèle avec le déclin des performances de mémoire observés chez les personnes âgées. J'ai trouvé des changements liés à l'âge consistants avec les résultats décrits antérieurement dans la littérature, comme une diminution de la fréquence moyenne du pic alpha. De plus, la fréquence du pic alpha au repos corrèle avec la performance en mémoire de travail spatiale à travers les groupes d'âge. En revanche, je n'ai trouvé aucun paramètre EEG au repos qui corrèle avec les performances de mémoire pour le groupe de personnes âgées considéré séparément. Dans ma thèse, je discute les nouvelles perspectives que mes données fournissent sur les bases cognitive et neurobiologique de la mémoire de travail. Mon travail ouvre de nouvelles directions pour la recherche de marqueurs neurobiologiques du déclin mnésique dans le vieillissement normal pour donner in fine de nouvelles indications pour la pratique clinique. -- Normal aging is associated with a variety of changes in cognitive capacities, including an overall décliné in working memory performance. Working memory is the brain system supporting the temporary storage and simultaneous manipulation of a limited amount of information. Interestingly, visuo-spatial working memory has been reported to exhibit a greater age-related décliné than verbal working memory. However, this greater age-related décliné in visuo-spatial working memory performance has not been demonstrated outside neuropsychological experiments performed on computer screens. The work described here provides the first data, obtained in a real-world laboratory environment, comparing allocentric spatial working memory with color working memory. My experimental data suggest no greater age-related décliné in allocentric spatial working memory. In a first published study, I have shown that an estimate of memory capacity (such as the number of correct choices before erring) may suggest that spatial working memory is more affected than color working memory. In contrast, the évaluation of perfect memory performance (based on the number of errorless trials) suggests that spatial and color working memory are equally affected by âge. In a second published study, in which I specifically tested the effect of memory load on working memory performance, I found no evidence that spatial working memory was more affected by âge than color working memory. Altogether, these findings suggest that the age-related décliné in memory performance may be linked to the representational demand of the task and not to the type of information to be remembered. In a third study of the electroencephalographic (EEG) correlates of memory performance, I evaluated whether some resting-state EEG activity may correlate with the décliné of memory performance observed in older adults. I found some age-related changes consistent with previous findings reported in the literature, such as a decrease of alpha averaged peak frequency. In addition, resting-state alpha averaged peak frequency correlated with spatial working memory performance across âge groups. In contrast, I did not find any resting-state EEG parameter that correlated with memory performance for the group of older adults considered separately. In my thesis, I discuss the new perspectives that my findings provide on the cognitive and neurobiological bases of working memory. My work opens new directions in the search for neurobiological markers of memory décliné in normal aging to provide in fine new approaches in clinical practice

Working memory decline in normal aging: Is it really worse in space than in color?

Aging is associated with a variety of changes in cognitive capacities, including a declinein working memory performance. Nevertheless, visuo-spatial working memory has beenshown to exhibit a greater age-related decline than verbal working memory. Here, weassessed age-related changes in allocentric spatial working memory and color workingmemory. We tested 20–30-year-old and 65–75-year-old adults on four memory tasksrequiring participants to learn, on a repeated-trial basis (i.e., reference memory) or a trial-unique basis (i.e., working memory), the locations or colors of three pads among 18 padsdistributed in a real-world laboratory environment. Older adults performed worse thanyoung adults on all memory tasks, but especially on working memory tasks. Some mea-sures, including the older adults’ relative decrease in the number of correct choices beforeerring (CBE), as compared to young adults, and the number of trials with the first or first twochoices correct, may suggest a greater age-related decline in allocentric spatial than colorworking memory. In contrast, the total number of disks visited to find the goals, the abso-lute decrease in CBE in older adults, the number of errorless trials and the number of trialswith the first three choices correct revealed no age-related differences in working memoryperformance for spatial versus color information. We discuss how, depending on the mea-sures used to evaluate memory performance, age-related declines in working memory mayappear greater for spatial information because allocentric spatial memory may have quan-titatively greater representational demands (i.e., require more bits of information) thancolor memory

Working memory decline in normal aging: Memory load and representational demands affect performance

Normal aging is associated with numerous changes in cognitive capacities, including an overall decline in working memory performance. Nevertheless, whereas some neuropsychological evaluations have suggested that visuo-spatial working memory may exhibit a greater age-related decline than verbal working memory, other assessments made in real-world tasks, or in tasks with higher memory loads, have suggested that age-related declines in working memory performance may be similar for spatial, visual and verbal information. Here, we tested young (20–30 years) and older (64–73 years) healthy adults in real-world laboratory memory tasks designed to assess the impact of memory load (one, two or three items to remember) on age-related changes in working memory performance for color and allocentric spatial information. We used several measures to characterize working memory performance: the total number of choices to find the goal(s), a measure of overall task performance; the number of correct choices before erring, an estimate of memory capacity; and the number of errorless trials, a measure of perfect memory. All measures revealed: (1) an overall decline of working memory performance with age; (2) a greater age-related decline of working memory performance with higher memory loads, regardless of the type of information; (3) no evidence that spatial working memory was more affected by age than color working memory. We discuss how age-related declines in working memory performance may be most influenced by memory load, the representational demands of the task and its dependence on hippocampal function, and not by the type of information to be remembered

Distinct effects of beta-amyloid and tau on cortical thickness in cognitively healthy older adults.

IntroductionPublished reports of associations between β-amyloid (Aβ) and cortical integrity conflict. Tau biomarkers may help elucidate the complex relationship between pathology and neurodegeneration in aging.MethodsWe measured cortical thickness using magnetic resonance imaging, Aβ using Pittsburgh compound B positron emission tomography (PiB-PET), and tau using flortaucipir (FTP)-PET in 125 cognitively normal older adults. We examined relationships among PET measures, cortical thickness, and cognition.ResultsCortical thickness was reduced in PiB+/FTP+ participants compared to the PiB+/FTP- and PiB-/FTP- groups. Continuous PiB associations with cortical thickness were weak but positive in FTP- participants and negative in FTP+. FTP strongly negatively predicted thickness regardless of PiB status. FTP was associated with memory and cortical thickness, and mediated the association of PiB with memory.DiscussionPast findings linking Aβ and cortical thickness are likely weak due to opposing effects of Aβ on cortical thickness relative to tau burden. Tau, in contrast to Aβ, is strongly related to cortical thickness and memory