John S. Duncan

Common regions of the human frontal lobe recruited by diverse cognitive demands.

Though many neuroscientific methods have been brought to bear in the search for functional specializations within prefrontal cortex, little consensus has emerged. To assess the contribution of functional neuroimaging, this article reviews patterns of frontal-lobe activation associated with a broad range of different cognitive demands, including aspects of perception, response selection, executive control, working memory, episodic memory and problem solving. The results show a striking regularity: for many demands, there is a similar recruitment of mid-dorsolateral, mid-ventrolateral and dorsal anterior cingulate cortex. Much of the remainder of frontal cortex, including most of the medial and orbital surfaces, is largely insensitive to these demands. Undoubtedly, these results provide strong evidence for regional specialization of function within prefrontal cortex. This specialization, however, takes an unexpected form: a specific frontal-lobe network that is consistently recruited for solution of diverse cognitive problems.

Selective Attention and the Organization of Visual Information

Medical Research Council, Applied Psychology Unit, Cambridge, England Theories of visual attention deal with the limit on our ability to see (and later report) several things at once. These theories fall into three broad classes. Objectbased theories propose a limit on the number of separate objects :that can be perceived simultaneously. Discrimination-based theories propose a limit on the number of separate discriminations that can be made. Space-based theories propose a limit on the spatial area from which information can be taken up. To distinguish these views, the present experiments used small (< 1 °), brief, foveal displays, each consisting of two overlapping objects (a box with a line struck through it). It was found that two judgments that concern the same object can be made simultaneously without loss of accuracy, whereas two judgments that concern different objects cannot. Neither the similarity nor the difficulty of required discriminations, nor the spatial distribution of information, could account for the results. The experiments support a view in which parallel, preattentive processes serve to segment the field into separate objects, followed by a pfocess of focal attention that deals with only one object at a time. This view is also able to account for results taken to support both discrimination-based and space-based theories. Object-Based Theories of Visual Attention Theories of visual attention are concerned with the limit on our ability to see (and later report) several things at once. This article deals with what I call object-based theories (e.g., Neisser, 1967), which propose that this limit concerns the number of separate objects that can be seen. Here some predictions of this view are tested, and object-based theories are contrasted with discrimination-based theories (e.g., Allport, 1971, 1980) and with spaced-based theories (e.g., Hoffman & Nelson, 1981; Posner, Snyder, & Davidson, 1980). The work of Neisser (1967) illustrates the object-based approach. Neisser (1967) proposed that perceptual analysis of the visual world takes place in two successive stages. The first, preattentive, stage segments the field into separate objects on the basis of such Gestalt properties as spatial proximity, continuity of contour, shared color or movement, and so on. The second stage, focal attention, analyzes a particular object in more detail. Neisser (1967) supposed that, whereas preat

The clinicopathologic spectrum of focal cortical dysplasias: A consensus classification proposed by an ad hoc Task Force of the ILAE Diagnostic Methods Commission†

Purpose:  Focal cortical dysplasias (FCD) are localized regions of malformed cerebral cortex and are very frequently associated with epilepsy in both children and adults. A broad spectrum of histopathology has been included in the diagnosis of FCD. An ILAE task force proposes an international consensus classification system to better characterize specific clinicopathological FCD entities.

Prefrontal cortical function and anxiety: controlling attention to threat-related stimuli

Threat-related stimuli are strong competitors for attention, particularly in anxious individuals. We used functional magnetic resonance imaging (fMRI) with healthy human volunteers to study how the processing of threat-related distractors is controlled and whether this alters as anxiety levels increase. Our work builds upon prior analyses of the cognitive control functions of lateral prefrontal cortex (lateral PFC) and anterior cingulate cortex (ACC). We found that rostral ACC was strongly activated by infrequent threat-related distractors, consistent with a role for this area in responding to unexpected processing conflict caused by salient emotional stimuli. Participants with higher anxiety levels showed both less rostral ACC activity overall and reduced recruitment of lateral PFC as expectancy of threat-related distractors was established. This supports the proposal that anxiety is associated with reduced top-down control over threat-related distractors. Our results suggest distinct roles for rostral ACC and lateral PFC in governing the processing of task-irrelevant, threat-related stimuli, and indicate reduced recruitment of this circuitry in anxiety.

An adaptive coding model of neural function in prefrontal cortex

Key Points The prefrontal cortex is crucial for effective, organized behaviour. On the basis of data from functional neuroimaging in humans and single-cell electrophysiology in the behaving monkey, this paper proposes an adaptive coding model of prefrontal function. Functional imaging data show some specific associations between particular cognitive functions and local prefrontal activations. However, there is also strong evidence for common regions of recruitment in response to a wide range of different cognitive demands. These regions include the cortex in and around the posterior part of the inferior frontal sulcus, the frontal operculum/anterior insula and the dorsal part of the anterior cingulate. Converging data come from electrophysiology in the monkey. Over large regions of the lateral frontal cortex, many cells show activity related to whatever arbitrary task a monkey has been trained to perform. These cells code many aspects of task events, including information relevant to stimuli, responses, working memory delays, response rules and reward states. Cells of many different types are found closely intermingled and widely distributed across the lateral surface. Even individual cells show evidence for adaptability of function, coding different information in different task contexts. In the adaptive coding model, the central idea is that neurons throughout large regions of prefrontal cortex have the capacity to code many different types of information. In any given task context, neurons adapt to preserve only information of relevance to current behaviour. At the same time, they support the representation of related information elsewhere in the brain, including coding of relevant stimuli, responses, representations in semantic memory and reward states. This view links previous accounts of prefrontal function that are based on concepts of working memory, selective attention and control. The model implies that, within the prefrontal cortex, regional specializations will be statistical rather than absolute. Neurons with the capacity to contribute to any given function might be widely distributed across the prefrontal cortex, although possibly with different distributions for different functions. This view of quantitative rather than qualitative specialization is consistent with data from electrophysiological, imaging and lesion studies. It suggests that conclusions concerning regional specialization will depend on criteria for assessing selectivity and, in imaging experiments, on experimental demand and power. The adaptive coding model points to several key issues and approaches for future work. These include an assessment of long- and short-term adaptability, a quantitative comparison of cell properties between different prefrontal regions, and an investigation of how prefrontal adaptability differs from that in other cortical regions. AbstractThe prefrontal cortex has a vital role in effective, organized behaviour. Both functional neuroimaging in humans and electrophysiology in awake monkeys indicate that a fundamental principle of prefrontal function might be adaptive neural coding — in large regions of the prefrontal cortex, neurons adapt their properties to carry specifically information that is relevant to current concerns, producing a dense, distributed representation of related inputs, actions, rewards and other information. A model based on such adaptive coding integrates the role of the prefrontal cortex in working memory, attention and control. Adaptive coding points to new perspectives on several basic questions, including mapping of cognitive to neurophysiological functions, the influences of task content and difficulty, and the nature of frontal lobe specializations.

The multiple-demand (MD) system of the primate brain: mental programs for intelligent behaviour

A common or multiple-demand (MD) pattern of frontal and parietal activity is associated with diverse cognitive demands, and with standard tests of fluid intelligence. In intelligent behaviour, goals are achieved by assembling a series of sub-tasks, creating structured mental programs. Single cell and functional magnetic resonance imaging (fMRI) data indicate a key role for MD cortex in defining and controlling the parts of such programs, with focus on the specific content of a current cognitive operation, rapid reorganization as mental focus is changed, and robust separation of successive task steps. Resembling the structured problem-solving of symbolic artificial intelligence, the mental programs of MD cortex appear central to intelligent thought and action.

The role of the right inferior frontal gyrus: inhibition and attentional control

There is growing interest regarding the role of the right inferior frontal gyrus (RIFG) during a particular form of executive control referred to as response inhibition. However, tasks used to examine neural activity at the point of response inhibition have rarely controlled for the potentially confounding effects of attentional demand. In particular, it is unclear whether the RIFG is specifically involved in inhibitory control, or is involved more generally in the detection of salient or task relevant cues. The current fMRI study sought to clarify the role of the RIFG in executive control by holding the stimulus conditions of one of the most popular response inhibition tasks–the Stop Signal Task–constant, whilst varying the response that was required on reception of the stop signal cue. Our results reveal that the RIFG is recruited when important cues are detected, regardless of whether that detection is followed by the inhibition of a motor response, the generation of a motor response, or no external response at all.

Three-dimensional maximum probability atlas of the human brain, with particular reference to the temporal lobe

Probabilistic atlases of neuroanatomy are more representative of population anatomy than single brain atlases. They allow anatomical labeling of the results of group studies in stereotaxic space, automated anatomical labeling of individual brain imaging datasets, and the statistical assessment of normal ranges for structure volumes and extents. No such manually constructed atlas is currently available for the frequently studied group of young adults. We studied 20 normal subjects (10 women, median age 31 years) with high‐resolution magnetic resonance imaging (MRI) scanning. Images were nonuniformity corrected and reoriented along both the anterior‐posterior commissure (AC–PC) line horizontally and the midsagittal plane sagittally. Building on our previous work, we have expanded and refined existing algorithms for the subdivision of MRI datasets into anatomical structures. The resulting algorithm is presented in the Appendix . Forty‐nine structures were interactively defined as three‐dimensional volumes‐of‐interest (VOIs). The resulting 20 individual atlases were spatially transformed (normalized) into standard stereotaxic space, using SPM99 software and the MNI/ICBM 152 template. We evaluated volume data for all structures both in native space and after spatial normalization, and used the normalized superimposed atlases to create a maximum probability map in stereotaxic space, which retains quantitative information regarding inter‐subject variability. Its potential applications range from the automatic labeling of new scans to the detection of anatomical abnormalities in patients. Further data can be extracted from the atlas for the detailed analysis of individual structures. Hum. Brain Mapping 19:224–247,2003. ©2003 Wiley‐Liss,Inc.

Competitive brain activity in visual attention.

Visual attention can be considered from the perspective of distributed brain activity engendered by visual input. We propose that visual objects compete for representation in multiple brain systems, sensory and motor, cortical and subcortical. Competition is integrated, however, such that multiple systems converge, working on the different properties and action implications of a selected object. Top-down priming biases competition towards objects relevant to current behaviour. Recent single-unit studies have shown widespread suppression of ignored-object representations in extrastriate cortex, and patterns of spatial and nonspatial priming by task relevance. Human and monkey lesion studies have demonstrated the strong integration tendency of different spatial and nonspatial systems, also revealed in recent studies of normal behaviour. In many cases, no unitary brain system may be responsible for unitary cognitive events such as attention. Such events may emerge as distinct systems converge to work on common cognitive problems.

Rehabilitation of executive functioning: An experimental–clinical validation of Goal Management Training

Two studies assessed the effects of a training procedure (Goal Management Training, GMT), derived from Duncans theory of goal neglect, on disorganized behavior following TBI. In Study 1, patients with traumatic brain injury (TBI) were randomly assigned to brief trials of GMT or motor skills training. GMT, but not motor skills training, was associated with significant gains on everyday paper-and-pencil tasks designed to mimic tasks that are problematic for patients with goal neglect. In Study 2, GMT was applied in a postencephalitic patient seeking to improve her meal-preparation abilities. Both naturalistic observation and self-report measures revealed improved meal preparation performance following GMT. These studies provide both experimental and clinical support for the efficacy of GMT toward the treatment of executive functioning deficits that compromise independence in patients with brain damage.