-
[show abstract]
[hide abstract]
ABSTRACT: The goal of this chapter is to review current knowledge about the effects of normal aging on working memory and its neural underpinnings as revealed by functional neuroimaging. The cognitive neuroscience approach has brought the study of aging to an exciting crossroad with great potential for new discoveries about cognitive aging in general and about working memory in particular. The tools of cognitive neuroscience provide a new source of evidence to test and revise hypotheses about aging that were founded on purely behavioral results. At the same time, neuroimaging studies are raising completely new questions about aging and the potential for lifelong plasticity. Moreover, we believe that a cognitive neuroscience approach to aging can yield new insights into the structure of cognition in the youthful brain. This chapter examines these possibilities as they relate to the structure and function of working memory. We begin with a general overview of working memory, how it is measured by different tasks, and a controversy that pertains to theoretical claims about the organization of working memory. We then review behavioral evidence indicating how working memory changes because of normal aging. This section is organized around three issues central to behavioral studies of aging working memory: (1) the effects of aging on maintenance versus maintenance plus processing tasks; (2) the role of attentional and inhibitory declines in aging working memory; and (3) the effects of aging on verbal versus nonverbal working memory. After an overview of the working memory circuitry in younger adults, we take an in-depth look at neuroimaging studies of aging and working memory published to date, and we examine how this literature can clarify each of the three issues emerging from the behavioral studies. Our conclusions describe what the infusion of neuroimaging has taught us about aging working memory, revisit the controversy about the organization of working memory, and point to directions for future research. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
10/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: fMRI was used to explore age differences in the neural substrate of dual-task processing. Brain activations when there was a 100 ms SOA between tasks, and task overlap was high, were contrasted with activations when there was a 1000 ms SOA, and first task processing was largely complete before the second task began. Younger adults (M=21 yrs) showed activation in dorsolateral prefrontal cortex and in parietal areas as well as in ventral medial frontal cortex and sub-lobar areas. Activations in older adults (M=71 yrs) did not differ significantly from younger adults except for higher activations in occipital and polar prefrontal cortex. The results were well fit by a model with two networks managing dual-task interference, a medial prefrontal network that detects changes in the stimulus situation and maps them to associated changes in the valence of response mappings and a lateral frontal-parietal network that initiates and carries out the shift from one task to the other. The additional activations in older adults as a group and the correlations of individual differences in activation with performance were consistent with recruitment within each of these networks. Alternative explanations such as hemispheric asymmetry reduction and reactive rather than proactive processing in older adults were not supported.
Brain and Cognition 02/2011; 75(3):281-91. · 3.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Work in functional neuroimaging has mapped interference resolution processing onto left inferior frontal regions for both verbal working memory and a variety of semantic processing tasks. The proximity of the identified regions from these different tasks suggests the existence of a common, domain-general interference resolution mechanism. The current research specifically tests this idea in a within-subject design using fMRI to assess the activation associated with variable selection requirements in a semantic retrieval task (verb generation) and a verbal working memory task with a trial-specific proactive interference manipulation (recent-probes). High interference trials on both tasks were associated with activity in the midventrolateral region of the left inferior frontal gyrus, and the regions activated in each task strongly overlapped. The results indicate that an elemental component of executive control associated with interference resolution during retrieval from working memory and from semantic memory can be mapped to a common portion of the left inferior frontal gyrus.
Brain research 01/2009; 1256:92-100. · 2.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The ability to inhibit inappropriate responses is central to cognitive control, but whether the same brain mechanisms mediate inhibition across different tasks is not known. We present evidence for a common set of frontal and parietal regions engaged in response inhibition across three tasks: a go/no-go task, a flanker task, and a stimulus-response compatibility task. Regions included bilateral anterior insula/frontal operculum and anterior prefrontal, right dorsolateral and premotor, and parietal cortices. Insula activity was positively correlated with interference costs in behavioral performance in each task. Principal components analysis showed a coherent pattern of individual differences in these regions that was also positively correlated with performance in all three tasks. However, correlations among tasks were low, for both brain activity and performance. We suggest that common interference detection and/or resolution mechanisms are engaged across tasks, and that inter-task correlations in behavioral performance are low because they conflate measurements of common mechanisms with measurements of individual biases unique to each task.
NeuroImage 09/2005; 27(2):323-40. · 5.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Age-related differences in cognitive performance are well documented. These differences are most pronounced during tasks with high demands on cognitive control, and it has been proposed that selective alteration of prefrontal activity is associated with cognitive changes in old age. Here, differences in the neural systems underlying selection requirements for older and younger adults were investigated using functional magnetic resonance imaging (fMRI). A verb generation task was used, and selection requirements were varied with regard to whether each noun could be associated with either few (scissors-cut) or many (ball-bounce, kick, throw...) competing alternatives. The two age groups showed statistically equivalent behavioral performance across the task conditions but marked differences in activation. Across both age groups, high selection demands activated several regions including bilateral frontal, left anterior frontal, left inferior temporal regions, and the dorsal anterior cingulate cortex (ACC). Between-group comparisons using region-of-interest analyses revealed less activation for senior adults in left inferior frontal gyrus (IFG), left inferior temporal gyrus, and the anterior cingulate and higher activation in right inferior frontal gyrus compared to young adults. These findings indicate age-related changes in multiple regions contributing to aspects of selection requirements during verb generation.
NeuroImage 01/2005; 23(4):1382-90. · 5.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Cognitive control requires the resolution of interference among competing and potentially conflicting representations. Such conflict can emerge at different points between stimulus input and response generation, with the net effect being that of compromising performance. The goal of this article was to dissociate the neural mechanisms underlying different sources of conflict to elucidate the architecture of the neural systems that implement cognitive control. By using functional magnetic resonance imaging and a verbal working memory task (item recognition), we examined brain activity related to two kinds of conflict with comparable behavioral consequences. In a trial of our item-recognition task, participants saw four letters, followed by a retention interval, and a probe letter that did or did not match one of the letters held in working memory (positive probe and negative probe, respectively). On some trials, conflict arose solely because of the current negative probe having a high familiarity, due to its membership in the immediately preceding trial's target set. On other trials, additional conflict arose because of the current negative probe having also been a positive probe on the immediately preceding trial, producing response-level conflict. Consistent with previous work, conflict due to high familiarity was associated with left prefrontal activation, but not with anterior cingulate activation. The response-conflict condition, when compared with high-familiarity conflict trials, was associated with anterior cingulate cortex activation, but with no additional left prefrontal activation. This double dissociation points to differing contributions of specific cortical areas to cognitive control, which are based on the source of conflict.
Proceedings of the National Academy of Sciences 10/2003; 100(19):11171-5. · 9.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Is there a single executive process or are there multiple executive processes that work together towards the same goal in some task? In these experiments, we use counter switching and response inhibition tasks to examine the neural underpinnings of two cognitive processes that have often been identified as potential executive processes: the switching of attention between tasks, and the resolution of interference between competing task responses. Using functional magnetic resonance imaging (fMRI), for both event-related and blocked design tasks, we find evidence for common neural areas across both tasks in bilateral parietal cortex (BA 40), left dorsolateral prefrontal cortex (DLPFC; BA 9), premotor cortex (BA 6) and medial frontal cortex (BA 6/32). However, we also find areas preferentially involved in the switching of attention between mental counts (BA 7, BA 18) and the inhibition of a prepotent motor response (BA 6, BA 10), respectively. These findings provide evidence for the separability of cognitive processes underlying executive control.
Neuropsychologia 02/2003; 41(3):357-70. · 3.64 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Patients with frontal lobe lesions and control participants were assessed on 2 tests of semantic knowledge. In the triadic comparison task, participants were shown all possible triplets of 12 animal names and judged which 2 of each triplet were most alike. In the ordered similarity task, participants rank ordered animals in terms of their similarity to a target animal. For both tasks, semantic structure--derived from multidimensional scaling techniques--revealed similar representations in patients with frontal lobe lesions and control participants. Additional pathfinder analyses also produced networks that did not differ between groups. These patients exhibited intact semantic knowledge despite deficits on tests of free recall and verbal fluency that involved the same semantic category and exemplars. Thus, intact representation of semantic knowledge in frontal patients stands in contrast to their marked deficits in strategic retrieval of semantic knowledge.
Neuropsychology 05/2002; 16(2):197-207. · 3.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Is there a single executive process or are there multiple executive processes that work together towards the same goal in some task? In these experiments, we use counter switching and response inhibition tasks to examine the neural underpinnings of two cognitive processes that have often been identified as potential executive processes: the switching of attention between tasks, and the resolution of interference between competing task responses. Using functional magnetic resonance imaging (fMRI), for both event-related and blocked design tasks, we find evidence for common neural areas across both tasks in bilateral parietal cortex (BA 40), left dorsolateral prefrontal cortex (DLPFC; BA 9), premotor cortex (BA 6) and medial frontal cortex (BA 6/32). However, we also find areas preferentially involved in the switching of attention between mental counts (BA 7, BA 18) and the inhibition of a prepotent motor response (BA 6, BA 10), respectively. These findings provide evidence for the separability of cognitive processes underlying executive control.
Neuropsychologia 41(3):357-370. · 3.64 Impact Factor
