Chunking in Backward Recall of Digits: An fMRI study

Working memory is the mind’s sketchpad for mental storage and manipulation of information (Miller et al., 2018). It is crucial to everyday tasks such as recalling PINs and passwords, mental mathematical manipulations, and learning new sequences of action. Dysfunction of this executive function is detrimental to these everyday tasks and significantly lowers the quality of life, as seen in patients living with schizophrenia, multiple sclerosis, and traumatic brain injury (Forbes et al., 2008; Litvan et al, 1988; McDowell et al., 1997). Therefore, understanding the mechanisms underlying working memory is crucial to having a better understanding of these disorders. In most working memory applications, the order of recall is important. When memory content is recalled, it can be recalled in the same order it was presented (forward recall) or the reverse order (backward recall). Backward recall, despite being uncommon in everyday life, is widely used in research and clinical settings. For instance, backward digit span (backward recall of digits) has been used in psychological research as a measure of working memory for children, adults, and the elderly populations (Elliott et al., 1990; Wechsler, 2014). It has strong correlations with current and future academic performance for children and has shown strong sensitivity to age-related cognitive decline (Bull et al., 2008; Bopp & Verhaeghen, 2005). Thus, it has been an area of interest to determine the mechanism behind backward recall

Age-Related Changes in Neural Activity During Performance Matched Working Memory Manipulation

A long-standing assumption in the cognitive aging literature is that performance on working memory (WM) tasks involving serial recall is relatively unaffected by aging, whereas tasks that require the rearrangement of items prior to recall are more age-sensitive. Previous neuroimaging studies of WM have found age-related increases in neural activity in frontoparietal brain regions during simple maintenance tasks, but few have examined whether there are age-related differences that are specific to rearranging WM items. In the current study, older and younger adults' brain activity was monitored using functional magnetic resonance imaging (fMRI) as they performed WM tasks involving either maintenance or manipulation (letter–number sequencing). The paradigm was developed so that performance was equivalent across age groups in both tasks, and the manipulation condition was not more difficult than the maintenance condition. In younger adults, manipulation-related increases in activation occurred within a very focal set of regions within the canonical brain WM network, including left posterior prefrontal cortex and bilateral inferior parietal cortex. In contrast, older adults showed a much wider extent of manipulation-related activation within this WM network, with significantly increased activity relative to younger adults found within bilateral PFC. The results suggest that activation and age-differences in lateral PFC engagement during WM manipulation conditions may reflect strategy use and controlled processing demands rather than reflect the act of manipulation per se

The Neuronal Correlates of Digits Backward Are Revealed by Voxel-Based Morphometry and Resting-State Functional Connectivity Analyses

Digits backward (DB) is a widely used neuropsychological measure that is believed to be a simple and effective index of the capacity of the verbal working memory. However, its neural correlates remain elusive. The aim of this study is to investigate the neural correlates of DB in 299 healthy young adults by combining voxel-based morphometry (VBM) and resting-state functional connectivity (rsFC) analyses. The VBM analysis showed positive correlations between the DB scores and the gray matter volumes in the right anterior superior temporal gyrus (STG), the right posterior STG, the left inferior frontal gyrus and the left Rolandic operculum, which are four critical areas in the auditory phonological loop of the verbal working memory. Voxel-based correlation analysis was then performed between the positive rsFCs of these four clusters and the DB scores. We found that the DB scores were positively correlated with the rsFCs within the salience network (SN), that is, between the right anterior STG, the dorsal anterior cingulate cortex and the right fronto-insular cortex. We also found that the DB scores were negatively correlated with the rsFC within an anti-correlation network of the SN, between the right posterior STG and the left posterior insula. Our findings suggest that DB performance is related to the structural and functional organizations of the brain areas that are involved in the auditory phonological loop and the SN

Cognitive tests used in chronic adult human randomised controlled trial micronutrient and phytochemical intervention studies

In recent years there has been a rapid growth of interest in exploring the relationship between nutritional therapies and the maintenance of cognitive function in adulthood. Emerging evidence reveals an increasingly complex picture with respect to the benefits of various food constituents on learning, memory and psychomotor function in adults. However, to date, there has been little consensus in human studies on the range of cognitive domains to be tested or the particular tests to be employed. To illustrate the potential difficulties that this poses, we conducted a systematic review of existing human adult randomised controlled trial (RCT) studies that have investigated the effects of 24 d to 36 months of supplementation with flavonoids and micronutrients on cognitive performance. There were thirty-nine studies employing a total of 121 different cognitive tasks that met the criteria for inclusion. Results showed that less than half of these studies reported positive effects of treatment, with some important cognitive domains either under-represented or not explored at all. Although there was some evidence of sensitivity to nutritional supplementation in a number of domains (for example, executive function, spatial working memory), interpretation is currently difficult given the prevailing 'scattergun approach' for selecting cognitive tests. Specifically, the practice means that it is often difficult to distinguish between a boundary condition for a particular nutrient and a lack of task sensitivity. We argue that for significant future progress to be made, researchers need to pay much closer attention to existing human RCT and animal data, as well as to more basic issues surrounding task sensitivity, statistical power and type I error

Neural underpinnings of working memory in adult survivors of childhood brain tumors

Objective: Adult survivors of childhood brain tumors are at risk for cognitive performance deficits that require the core cognitive skill of working memory. Our goal was to examine the neural mechanisms underlying working memory performance in survivors. Method: We studied the working memory of adult survivors of pediatric posterior fossa brain tumors using a letter n-back paradigm with varying cognitive workload (0-, 1-, 2-, and 3-back) and functional magnetic resonance imaging as well as neuropsychological measures. Results: Survivors of childhood brain tumors evidenced lower working memory performance than demographically-matched healthy controls. Whole-brain analyses revealed significantly greater blood-oxygen level dependent (BOLD) activation in the left superior / middle frontal gyri and left parietal lobe during working memory (2-back versus 0-back contrast) in survivors. Left frontal BOLD response negatively correlated with 2- and 3-back working memory performance, Auditory Consonant Trigrams (ACT), and Digit Span Backwards. In contrast, parietal lobe BOLD response negatively correlated with 0-back (vigilance task) and ACT. Conclusions: The results revealed that adult survivors of childhood posterior fossa brain tumors recruited additional cognitive control resources in the prefrontal lobe during increased working memory demands. This increased prefrontal activation is associated with lower working memory performance and is consistent with the allocation of latent resources theory

The Development and Relation of Working Memory and Fluid Intelligence in Middle and Late Childhood: A Neurocognitive Developmental Perspective

Working memory (WM) und fluid intelligence (Gf) are both key abilities in many cognitive development areas. Previous studies showed that both constructs are substantially related. However, WM consists of different aspects and it is not clear which of these aspects underlies this relation. Moreover, previous studies investigating the development of the neural basis of verbal WM have neglected the fact that WM and Gf are related. Accordingly, the main goal of the two studies presented in this dissertation was to gain a deeper understanding of the relation between WM and Gf. In addition, we aimed to investigate how age and Gf combine to affect WM performance and WM-related brain activity in middle and late childhood. The main question addressed in this umbrella paper was driven by the question of how Gf and WM develop, which was incorporated in both studies. The results revealed that WM and Gf improve with increasing age. Moreover, results showed that different WM aspects promote the development of WM as well as of Gf. However, also individual differences in Gf seem to foster the development in WM. Hence, the relation between WM and Gf seems to go in both directions. In addition, neural results revealed an age-by-Gf interaction effect on WM-related brain activation, indicating that also functional brain differences contribute to the development of WM and Gf. The results are discussed in terms of neural efficiency and in terms of theoretical and practical implications