The human frontal cortex helps mediate working memory, a system that is used for temporary storage and manipulation of information and that is involved in many higher cognitive functions. Working memory includes two components: short-term storage (on the order of seconds) and executive processes that operate on the contents of storage. Recently, these two components have been investigated in functional neuroimaging studies. Studies of storage indicate that different frontal regions are activated for different kinds of information: storage for verbal materials activates Broca's area and left-hemisphere supplementary and premotor areas; storage of spatial information activates the right-hemisphere premotor cortex; and storage of object information activates other areas of the prefrontal cortex. Two of the fundamental executive processes are selective attention and task management. Both processes activate the anterior cingulate and dorsolateral prefrontal cortex.

Working memory (WM), a system for actively maintaining and manipulating information, has been one of the most studied topics in cognitive psychology and cognitive neuroscience. It is fundamental to the performance of many cognitive tasks and day-to-day activities: imagining how an object might look from a different perspective, remembering a phone number while taking something out of the oven, solving a math problem "in your head," or planning the next move in a chess game, to give just a few examples. WM is sometimes conceptualized as an active workspace because it is closely linked with the voluntary allocation of attention. The study of WM is central to understanding how memory and thought work. Models of Working MemoryBaddeley (1992) and colleagues have given one of the clearest conceptualizations of WM. They proposed two basic subsystems for maintaining information-the phonological loop and the visuospatial sketch pad, for remembering verbal and visual information, respectively. These subsystems are further subdivided into passive storage and active rehearsal mechanisms. Manipulation of information held in WM is accomplished by a third, central executive system. Most broad architectures of human cognition incorporate some version of this framework. In this meta-analysis, we are concerned with the neural basis of WM. Controversies on the Organization of the Frontal LobesSome of the earliest neuroimaging studies of WM addressed questions raised in part by Baddeley's (1992) framework-particularly, how the putative components of WM map onto brain systems and whether patterns of brain activation respect the distinctions between types of WM apparent in behavioral studies.Organization by material type. One of the major dimensions along which WM systems may be subdivided is the type of material stored in WM. Three types of material have been most commonly studied: verbal, spatial, and object information. Verbal information includes words, letters, or other material that is primarily coded linguisticallyand is likely to be maintained by a rehearsal process involving a subvocal sequential generation of memory items. Spatial information includes information about the spatial positions of stimuli. Object information includes storage of nonspatial visual features or object identity.We tested three hypotheses about the organization of WM by material type. One organizationalprinciple, based on monkey and human studies (e.g., Funahashi, Chafee, & Goldman- Wilson, 255 Copyright 2003 Psychonomic Society, Inc. Neuroimaging studies of working memory:A meta-analysis TOR D. WAGER and EDWARD E. SMITH University of Michigan, Ann Arbor, MichiganWe performed meta-analyses on 60 neuroimaging (PET and fMRI) studies of working memory (WM), considering three types of storage material (spatial, verbal, and object), three types of executive function (continuous updating of WM, memory for temporal order, and manipulation of information in WM), and interactions between material and executive function. Analyses of material type showed ...

The experience of pain arises from both physiological and psychological factors, including one's beliefs and expectations. Thus, placebo treatments that have no intrinsic pharmacological effects may produce analgesia by altering expectations. However, controversy exists regarding whether placebos alter sensory pain transmission, pain affect, or simply produce compliance with the suggestions of investigators. In two functional magnetic resonance imaging (fMRI) experiments, we found that placebo analgesia was related to decreased brain activity in pain-sensitive brain regions, including the thalamus, insula, and anterior cingulate cortex, and was associated with increased activity during anticipation of pain in the prefrontal cortex, providing evidence that placebos alter the experience of pain.

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Gamma band oscillations participate in the temporal binding needed to synchronize cortical networks, involved in early sensory and short term memory processes. In earlier studies, alterations of these neurophysiological parameters have been found in psychotic disorders. To date no study has explored the temporal dynamics and signal complexity of gamma band oscillations in first episode psychosis (FEP). To address this issue, gamma band analysis was performed in 15 FEP patients and 18 healthy controls who successfully performed an adapted 2-back working memory task. Multiple linear and logistic regression models were computed to explore the relationship between the cognitive status and gamma oscillation changes over time. Based on regression model results, phase diagrams were constructed and their complexity was estimated using fractal dimension, a mathematical tool that describes shapes as numeric values. When adjusted for gamma values at time lags-3 to-4 ms and-15 to-16 ms, FEP patients displayed significantly higher time-dependent changes than controls, independently of the nature of the task. The present results are consistent with a discoordination of the activity of cortical generators engaged by the stimulus apparition in FEP patients, leading to a global binding deficit. In addition, fractal analysis showing higher complexity of gamma signal, confirmed this deficit. Our results provide evidence for recruitment of supplementary cortical generators as compensating mechanisms and yield further understanding for the pathophysiology cognitive impairments in FEP.

A model is proposed to account for recent findings on the time needed to decide that a test instance is a member of a target semantic category. It is assumed that the meaning of a lexical term can be represented by semantic features. Some of these features are essential or defining aspects of a word's meaning (defining features), while others are more accidental or characteristic aspects (characteristic features). This defining versus characteristic distinction is combined with a two-stage processing mechanism in such a way that the first stage determines the similarity between the test instance and target category with respect to both defining and characteristic features, while the second stage considers only agreement between defining features. This model is shown to be consistent with most semantic memory effects, and two new experiments provide further detailed support for it.

An argument is categorical if its premises and conclusion are of the form All members ofC have property F, where C is a natural category like FALCON or BIRD, and P remains the same across premises and conclusion. An example is Grizzly bears love onions. Therefore, all bears love onions. Such an argument is psychologically strong to the extent that belief in its premises engenders belief in its conclusion. A subclass of categorical arguments is examined, and the following hypothesis is advanced: The strength of a categorical argument increases with (a) the degree to which the premise categories are similar to the conclusion category and (b) the degree to which the premise categories are similar to members of the lowest level category that includes both the premise and the conclusion categories. A model based on this hypothesis accounts for 13 qualitative phenomena and the quantitative results of several experiments.

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