On the relative role of inhibition in age-related working memory decline

In this cross-sectional study, the mediating role of inhibition relative to speed in age-related working memory decline on different tasks was investigated. It was hypothesized that the role of inhibition is marginal or absent in a relatively "passive" or simple working memory task, but present in a relatively "active" or complex task in which the processing, rather than the storage capacity of working memory, is addressed. This hypothesis was tested with a structural equation model that was fitted on a subsample (N = 213) of the Maastricht Aging Study (MAAS). The first trial of the Verbal Learning Test (VLT) served as the passive test and the Self-Paced Auditory Serial Addition Task (SPASAT) as the active test. Results showed that the role of inhibition was absent in predicting VLT performance, whereas it was comparable to the role of speed in predicting SPASAT performance. These findings suggest a relative, task-dependent role of inhibition in explaining age-related memory decline.     

Differences in feedback- and inhibition-related neural activity in adult ADHD

The objective of this study was to examine response inhibition- and feedback-related neural activity in adults with attention deficit hyperactivity disorder (ADHD) using event-related functional MRI. Sixteen male adults with ADHD and 13 healthy/normal controls participated in this study and performed a modified Go/NoGo task. Behaviourally, attention and inhibition problems in the ADHD group were observed; no feedback-related differences between the groups were detected. The neuroimaging data showed that the ADHD group displayed more activation in the inferior frontal gyrus and putamen during response inhibition. During feedback-related processes, the ADHD group displayed less activation in the inferior frontal/orbitofrontal cortex, hippocampus/nucleus accumbens, and caudate nucleus, but more activity in the inferior frontal gyrus. These results indicate that at least two distinguishable underlying brain networks related to response inhibition and feedback are altered in adults with ADHD.     

The use of faces as stimuli in neuroimaging and psychological experiments: A procedure to standardize stimulus features

In psychological experiments involving facial stimuli, it is of great importance that the basic perceptual or psychological characteristics that are investigated are not confounded by factors such as brightness and contrast, head size, hair cut and color, skin color, and the presence of glasses and earrings. Standardization of facial stimulus materials reduces the effect of these confounding factors. We therefore employed a set of basic image processing techniques to deal with this issue. The processed images depict the faces in gray-scale, all at the same size, brightness, and contrast, and confined to an oval mask revealing only the basic features such as the eyes, nose, and mouth. The standardization was successfully applied to four different face databases, consisting of male and female faces and including neutral as well as happy facial expressions. An important advantage of the proposed standardization is that featural as well as configurational information is retained. We also consider the procedure to be a major contribution to the development of a de facto standard for the use of facial stimuli in psychological experiments. Such methodological standardization would allow a better comparison of the results of these studies.     

Atrophy of the parietal lobe in preclinical dementia

Cortical grey matter atrophy patterns have been reported in healthy ageing and Alzheimer disease (AD), but less consistently in the parietal regions of the brain. We investigated cortical grey matter volume patterns in parietal areas. The grey matter of the somatosensory cortex, superior and inferior parietal lobule was measured in 75 older adults (38 cognitively stable and 37 individuals with cognitive decline after 3 years). Dementia screening 6 years after scanning resulted in nine AD cases from the cognitively stable (n=3) and cognitive decline group (n=6), who were assigned to a third group, the preclinical AD group. When regional differences in cortical volume in the parietal lobe areas were compared between groups, significant differences were found between either the cognitive decline or stable group on the one hand and preclinical AD individuals on the other hand in the inferior parietal lobule. Group membership was best predicted by the grey matter volume of the inferior parietal lobule, compared to the other parietal lobe areas. The parietal lobe was characterised by a differential atrophy pattern based on cognitive status, which is in agreement with the 'last-developed-first-atrophied' principle. Future studies should investigate the surplus value of the inferior parietal lobe as a potential marker for the diagnosis of AD compared to other brain regions, such as the medial temporal lobe and the prefrontal lobe.     

Developmental differences in prefrontal activation during working memory maintenance and manipulation for different memory loads

The ability to keep information active in working memory is one of the cornerstones of cognitive development. Prior studies have demonstrated that regions which are important for working memory performance in adults, such as dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), and superior parietal cortex, become increasingly engaged across school-aged development. The primary goal of the present functional MRI study was to investigate the involvement of these regions in the development of working memory manipulation relative to maintenance functions under different loads. We measured activation in DLPFC, VLPFC, and superior parietal cortex during the delay period of a verbal working memory task in 11-13-year-old children and young adults. We found evidence for age-related behavioral improvements in working memory and functional changes within DLPFC and VLPFC activation patterns. Although activation profiles of DLPFC and VLPFC were similar, group differences were most pronounced for right DLPFC. Consistent with prior studies, right DLPFC showed an interaction between age and condition (i.e. manipulation versus maintenance), specifically at the lower loads. This interaction was characterized by increased activation for manipulation relative to maintenance trials in adults compared to children. In contrast, we did not observe a significant age-dependent load sensitivity. These results suggest that age-related differences in the right DLPFC are specific to working memory manipulation and are not related to task difficulty and/or differences in short-term memory capacity.     

Distractor Interference in Selective Reaching: Dissociating Distance and Grouping Effects

In the present experiment, the authors sought to differentiate between a distance and a grouping explanation for the symmetric versus asymmetric patterns of distractor interference in selective reaching. Participants (N = 16) pointed to a green target that appeared either with or without a red distractor. Target-distractor separation was manipulated within an array of 5 closely grouped stimulus boxes, and distractor interference (difference in performance between trials with and trials without a distractor) was measured in reaction time, movement time, percentage errors, and movement endpoints. Small distances (5 mm) between target and distractor yielded a symmetric pattern of interference, whereas large distances (20 mm) yielded an asymmetric pattern, with more interference from near than from far distractors. Those findings support the distance account of distractor interference and refute the grouping account.     

Serial and subjective clustering on a verbal learning test (VLT) in children aged 5–15: The nature of subjective clustering

This study investigated which strategies children aged 5–15 years (N?=?408) employ while performing a multitrial free recall test of semantically unrelated words. Serial clustering (i.e., a relatively passive strategy) is an index of the sequential consistency of recall order. Subjective clustering (i.e., a more active strategy) is based on similar word groupings in successive trials. Previously, Meijs et al. (2009 Meijs, C. J. C., Hurks, P. P. M., Kalff, A. C., Slaats-Willemse, D. I. E., Rozendaal, N. and Jolles, J. 2009. Differential development of learning strategies on a Pictorial Verbal Learning Test (PVLT) in primary school children. Child Neuropsychology, 15: 247–261. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) found that the level of (serial and subjective) clustering increases with age. At all ages, the level of serial clustering correlates positively with the ability to recall information on VLT trials. However, subjective clustering is more predictive of VLT performance than serial clustering after ≥ 3 trials, but only in children aged 8+. Knowledge on how children organize words (based on, for example, sound or meaning) and how this relates to developmental stage is still lacking. This study revealed that the level of subjective clustering is primarily determined by the position of words in a VLT list. More specifically, primacy (i.e., recall of words 1–3 of the VLT list — whether recalled in the same order or reversed) and recency (i.e., recall of words 14–15) effects primarily determine level subjective organization over successive trials. Thus, older children still organize words based on the serial position of the VLT list and are much less likely to organize them based on any other feature of the words, for example, sound or meaning. This indicates that the most important information to be learned needs to be presented first or last, even in older children and even with repeated presentations.     

Learning and retrieval rate of words presented auditorily and visually

Mode of presentation (visual or auditory) of a multitrial free recall test is stressed as an important factor in improving the diagnosis of certain neurological patients. For further use in neuropsychological research, an experiment was carried out using normal subjects, in which the effects of presentation mode and order of modality were investigated. There were no differential effects of these variables on several parameters, such as the number of words recalled and the learning curve. The time needed for the responses in immediate recall was the same in both auditory and visual conditions. In delayed recall, however, the interresponse times were significantly shorter when words had been presented auditorily than when presented visually. The results are discussed in light of further application in the field of neuropsychology.     

Inter-individual differences in how presentation modality affects verbal learning performance in children aged 5 to 16

This study examines inter-individual differences in how presentation modality affects verbal learning performance. Children aged 5 to 16 performed a verbal learning test within one of three presentation modalities: pictorial, auditory, or textual. The results indicated that a beneficial effect of pictures exists over auditory and textual presentation modalities and that this effect increases with age. However, this effect is only found if the information to be learned is presented once (or at most twice) and only in children above the age of 7. The results may be explained in terms of single or dual coding of information in which the phonological loop is involved. Development of the (sub)vocal rehearsal system in the phonological loop is believed to be a gradual process that begins developing around the age of 7. The developmental trajectories are similar for boys and girls. Additionally, auditory information and textual information both seemed to be processed in a similar manner, namely without labeling or recoding, leading to single coding. In contrast, pictures are assumed to be processed by the dual coding of both the visual information and a (verbal) labeling of the pictures.     

Education does not protect against age-related decline of switching focal attention in working memory

In this experimental study, effects of age and education on switching focal attention in working memory were investigated among 44 young (20-30 years) and 40 middle-aged individuals (50-60 years). To this end, a numeric n-back task comprising two lag conditions (1- and 2-back) was administered within groups. The results revealed a comparable increase of reaction time as a function of lag across age groups, but a disproportionate decrease of accuracy in the middle-aged relative to the young group. The latter effect did not interact with education, which challenges the cognitive reserve hypothesis. Moreover, the high-educated middle-aged participants showed a greater increase of reaction time as a function of lag than their low-educated counterparts. Apparently, they were not able to sustain their relatively high response speed across conditions. These results suggest that education does not protect against age-related decline of switching focal attention in working memory.