The unity and diversity of executive functions and their contributions to complex "Frontal Lobe" tasks: a latent variable analysis.

▪ Abstract The prefrontal cortex has long been suspected to play an important role in cognitive control, in the ability to orchestrate thought and action in accordance with internal goals. Its neural basis, however, has remained a mystery. Here, we propose that cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represent goals and the means to achieve them. They provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task. We review neurophysiological, neurobiological, neuroimaging, and computational studies that support this theory and discuss its implications as well as further issues to be addressed

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An integrative theory of prefrontal cortex function

Publisher Summary This chapter focuses on the modern notion of short-term memory, called working memory. Working memory refers to the temporary maintenance of information that was just experienced or just retrieved from long-term memory but no longer exists in the external environment. These internal representations are short-lived, but can be maintained for longer periods of time through active rehearsal strategies, and can be subjected to various operations that manipulate the information in such a way that makes it useful for goal-directed behavior. Working memory is a system that is critically important in cognition and seems necessary in the course of performing many other cognitive functions, such as reasoning, language comprehension, planning, and spatial processing. This chapter demonstrates the functional importance of dopamine to working memory function in several ways. Elucidation of the cognitive and neural mechanisms underlying human working memory is an important focus of cognitive neuroscience and neurology for much of the past decade. One conclusion that arises from research is that working memory, a faculty that enables temporary storage and manipulation of information in the service of behavioral goals, can be viewed as neither a unitary, nor a dedicated system. Data from numerous neuropsychological and neurophysiological studies in animals and humans demonstrates that a network of brain regions, including the prefrontal cortex, is critical for the active maintenance of internal representations.

Chapter 11 Working memory

Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

Despite the concern that has been expressed about potential method biases, and the pervasiveness of research settings with the potential to produce them, there is disagreement about whether they really are a problem for researchers in the behavioral sciences. Therefore, the purpose of this review is to explore the current state of knowledge about method biases. First, we explore the meaning of the terms “method” and “method bias” and then we examine whether method biases influence all measures equally. Next, we review the evidence of the effects that method biases have on individual measures and on the covariation between different constructs. Following this, we evaluate the procedural and statistical remedies that have been used to control method biases and provide recommendations for minimizing method bias.

Sources of Method Bias in Social Science Research and Recommendations on How to Control It

This article describes how fMRI can be used to examine the large-scale networks of cortical areas that subserve high-level cognition, such as sentence comprehension and visual thinking. The findings from a number of studies show that the qualitative and quantitative nature of the cognitive processes determines which cortical areas are activated (the network constituency) and the degree to which each network member is activated. For example, during sentence comprehension, activation in the left posterior temporal region and the inferior frontal gyrus, as well as their right hemisphere homologs, increases as a function of the linguistic complexity of the sentence. Such findings indicate that cognition emerges from the collaboration among the multiple cortical areas that compose the large-scale networks, rather than from the aggregate of autonomously functioning modules. The patterns of activation also show systematic shifts in the activity of a network during the spontaneous recovery of function by stroke patients, demonstrating cortical plasticity in adults. Finally, the article describes some simulation models that relate the information processing activity of a computational system to its resource consumption. This construct enables a mapping from the functional properties of the cognitive systems to the biological substrate that is reflected in fMRI.

Modeling the mind: very-high-field functional magnetic resonance imaging activation during cognition.

A Comparison of Aphasic and Normal Adults in a Sentence-Verification Task

The present paper compared the processing of complex embedded sentences in Chinese, Norwegian, and English to determine if the underlying mental operations are similar in these diverse languages. The task involved reading a sentence likeIt’s true that the dots aren’t red and deciding whether it was true or false according to an accompanying picture. The verification latencies were analyzed in terms of a model based on one central mental operation. The results for all three languages conformed to the predictions of the model and showed similar processing rates. Moreover, the Norwegian study expanded the analysis to include quantification in sentences likeIt’s true that many of the dots aren’t red. These studies suggest that certain fundamental operations may be universally implicated in language processing.

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Comparative studies of comprehension: An investigation of Chinese, Norwegian, and English.

: One purpose of the research is to develop models of cognitive processes in understanding mechanical systems. A particular focus was on the processes in mentally animating the representation of a mechanical system, and the contribution of animation graphics in comprehension. Several studies, involving eye fixations, verbal protocols and process tracing, indicated that mental animation was difficult for individuals who were not knowledgeable about mechanics. Animation did help them determine the motion of individual components, but animation alone did not entirely compensate for the subject's difficulty in identifying relevant features and ignoring irrelevant features. A second goal of the research was to analyze the differences among individuals who are performing analytic reasoning tasks. The cognitive processes in a widely used, nonverbal test of analytic intelligence, the Raven Progressive Matrices Test were analyzed using experimental and modelling techniques. The processes that distinguish average and superior performance are the ability to induce abstract relations and the ability to dynamically manage a large set of problem solving goals in working memory. Mechanical reasoning, Intelligence testing, Individual differences in problem solving.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA251556&Location=U2&doc=GetTRDoc.pdf

Understanding Mechanical Systems Through Computer Animation and Kinematic Imagery

Magnetic resonance imaging (MRI) technology at field strengths up to 1.5 T is mature after many years of experience by manufacturers in providing a clinically acceptable level of performance. The MRI technique is the accepted modality of choice for neuroimaging when the question of structural abnormality is raised. The development of functional MRI (fMRI) offers potential for developing clinical applications in which brain function as well as anatomy are examined [1]. The presumed mechanism on which most current fMRI is based is the increased MR signal that arises from the increased blood flow that occurs with increased neuronal activity. The increased flow, out of proportion to the tissue oxygen utilization, increases the net tissue blood oxygenation [2] thereby decreasing the magnetic susceptibility-induced transverse relaxation caused by deoxygenated blood. This has been termed blood oxygenation level dependent (BOLD) contrast [3]. Such signal changes in the microvasculature are small (1–5%), and therefore always limited by the available signal-to-noise ratio (SNR). Strategies to improve the reliability of such measurements for clinical applications would be useful.

Patricia A. Carpenter

Papers

Modeling the mind: very-high-field functional magnetic resonance imaging activation during cognition.

A Comparison of Aphasic and Normal Adults in a Sentence-Verification Task

Comparative studies of comprehension: An investigation of Chinese, Norwegian, and English.

Understanding Mechanical Systems Through Computer Animation and Kinematic Imagery

High Field Functional MRI in Humans: Applications to Cognitive Function