Control of goal-directed and stimulus-driven attention in the brain

We review evidence for partially segregated networks of brain areas that carry out different attentional functions. One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. This ventral frontoparietal network works as a 'circuit breaker' for the dorsal system, directing attention to salient events. Both attentional systems interact during normal vision, and both are disrupted in unilateral spatial neglect.

Psychophysiological and modulatory interactions in neuroimaging

In this paper we introduce the idea of explaining responses, in one cortical area, in terms of an interaction between the influence of another area and some experimental (sensory or task-related) parameter. We refer to these effects as psychophysiological interactions and relate them to interactions based solely on experimental factors (i.e., psychological interactions), in factorial designs, and interactions among neurophysiological measurements (i.e., physiological interactions). We have framed psychophysiological interactions in terms of functional integration by noting that the degree to which the activity in one area can be predicted, on the basis of activity in another, corresponds to the contribution of the second to the first, where this contribution can be related to effective connectivity. A psychophysiological interaction means that the contribution of one area to another changes significantly with the experimental or psychological context. Alternatively these interactions can be thought of as a contribution-dependent change in regional responses to an experimental or psychological factor. In other words the contribution can be thought of as modulating the responses elicited by a particular stimulus or psychological process. The potential importance of this approach lies in (i) conferring a degree of functional specificity on this aspect of effective connectivity and (ii) providing a model of modulation, where the contribution from a distal area can be considered to modulate responses to the psychological or stimulus-specific factor defining the interaction. Although distinct in neurobiological terms, these are equivalent perspectives on the same underlying interaction. We illustrate these points using a functional magnetic resonance imaging study of attention to visual motion and a position emission tomography study of visual priming. We focus on interactions among extrastriate, inferotemporal, and posterior parietal regions during visual processing, under different attentional and perceptual conditions.

Premotor cortex and the recognition of motor actions

In area F5 of the monkey premotor cortex there are neurons that discharge both when the monkey performs an action and when he observes a similar action made by another monkey or by the experimenter. We report here some of the properties of these 'mirror' neurons and we propose that their activity 'represents' the observed action. We posit, then, that this motor representation is at the basis of the understanding of motor events. Finally, on the basis of some recent data showing that, in man, the observation of motor actions activate the posterior part of inferior frontal gyrus, we suggest that the development of the lateral verbal communication system in man derives from a more ancient communication system based on recognition of hand and face gestures.

Looking at pictures: affective, facial, visceral, and behavioral reactions

Colored photographic pictures that varied widely across the affective dimensions of valence (pleasant-unpleasant) and arousal (excited-calm) were each viewed for a 6-s period while facial electromyographic (zygomatic and corrugator muscle activity) and visceral (heart rate and skin conductance) reactions were measured. Judgments relating to pleasure, arousal, interest, and emotional state were measured, as was choice viewing time. Significant covariation was obtained between (a) facial expression and affective valence judgments and (b) skin conductance magnitude and arousal ratings. Interest ratings and viewing time were also associated with arousal. Although differences due to the subject's gender and cognitive style were obtained, affective responses were largely independent of the personality factors investigated. Response specificity, particularly facial expressiveness, supported the view that specific affects have unique patterns of reactivity. The consistency of the dimensional relationships between evaluative judgments (i.e., pleasure and arousal) and physiological response, however, emphasizes that emotion is fundamentally organized by these motivational parameters.

Hemispheric asymmetry reduction in older adults: the HAROLD model

A model of the effects of aging on brain activity during cognitive performance is introduced. The model is called HAROLD (hemispheric asymmetry reduction in older adults), and it states that, under similar circumstances, prefrontal activity during cognitive performances tends to be less lateralized in older adults than in younger adults. The model is supported by functional neuroimaging and other evidence in the domains of episodic memory, semantic memory, working memory, perception, and inhibitory control. Age-related hemispheric asymmetry reductions may have a compensatory function or they may reflect a dedifferentiation process. They may have a cognitive or neural origin, and they may reflect regional or network mechanisms. The HAROLD model is a cognitive neuroscience model that integrates ideas and findings from psychology and neuroscience of aging.

People thinking about thinking people. The role of the temporo-parietal junction in "theory of mind"

Humans powerfully and flexibly interpret the behaviour of other people based on an understanding of their minds: that is, we use a "theory of mind." In this study we distinguish theory of mind, which represents another person's mental states, from a representation of the simple presence of another person per se. The studies reported here establish for the first time that a region in the human temporo-parietal junction (here called the TPJ-M) is involved specifically in reasoning about the contents of another person's mind. First, the TPJ-M was doubly dissociated from the nearby extrastriate body area (EBA; Downing et al., 2001). Second, the TPJ-M does not respond to false representations in non-social control stories. Third, the BOLD response in the TPJ-M bilaterally was higher when subjects read stories about a character's mental states, compared with stories that described people in physical detail, which did not differ from stories about nonhuman objects. Thus, the role of the TPJ-M in understanding other people appears to be specific to reasoning about the content of mental states.

Beyond mind-reading: multi-voxel pattern analysis of fMRI data

A key challenge for cognitive neuroscience is determining how mental representations map onto patterns of neural activity. Recently, researchers have started to address this question by applying sophisticated pattern-classification algorithms to distributed (multi-voxel) patterns of functional MRI data, with the goal of decoding the information that is represented in the subject's brain at a particular point in time. This multi-voxel pattern analysis (MVPA) approach has led to several impressive feats of mind reading. More importantly, MVPA methods constitute a useful new tool for advancing our understanding of neural information processing. We review how researchers are using MVPA methods to characterize neural coding and information processing in domains ranging from visual perception to memory search.

Neuroimaging studies of working memory: a meta-analysis

We 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 expected dorsal-ventral dissociation between spatial and nonspatial storage in the posterior cortex, but not in the frontal cortex. Some support was found for left frontal dominance in verbal WM, but only for tasks with low executive demand. Executive demand increased right lateralization in the frontal cortex for spatial WM. Tasks requiring executive processing generally produce more dorsal frontal activations than do storage-only tasks, but not all executive processes show this pattern. Brodmann's areas (BAs) 6, 8, and 9, in the superior frontal cortex, respond most when WM must be continuously updated and when memory for temporal order must be maintained. Right BAs 10 and 47, in the ventral frontal cortex, respond more frequently with demand for manipulation (including dual-task requirements or mental operations). BA 7, in the posterior parietal cortex, is involved in all types of executive function. Finally, we consider a potential fourth executive function: selective attention to features of a stimulus to be stored in WM, which leads to increased probability of activating the medial prefrontal cortex (BA 32) in storage tasks.

Aging gracefully: compensatory brain activity in high-performing older adults

Whereas some older adults show significant cognitive deficits, others perform as well as young adults. We investigated the neural basis of these different aging patterns using positron emission tomography (PET). In PET and functional MRI (fMRI) studies, prefrontal cortex (PFC) activity tends to be less asymmetric in older than in younger adults (Hemispheric Asymmetry Reduction in Old Adults or HAROLD). This change may help counteract age-related neurocognitive decline (compensation hypothesis) or it may reflect an age-related difficulty in recruiting specialized neural mechanisms (dedifferentiation hypothesis). To compare these two hypotheses, we measured PFC activity in younger adults, low-performing older adults, and high-performing older adults during recall and source memory of recently studied words. Compared to recall, source memory was associated with right PFC activations in younger adults. Low-performing older adults recruited similar right PFC regions as young adults, but high-performing older adults engaged PFC regions bilaterally. Thus, consistent with the compensation hypothesis and inconsistent with the dedifferentiation hypothesis, a hemispheric asymmetry reduction was found in high-performing but not in low-performing older adults. The results suggest that low-performing older adults recruited a similar network as young adults but used it inefficiently, whereas high-performing older adults counteracted age-related neural decline through a plastic reorganization of neurocognitive networks.

Brain potentials in affective picture processing: covariation with autonomic arousal and affective report

Emotionally arousing picture stimuli evoked scalp-recorded event-related potentials. A late, slow positive voltage change was observed, which was significantly larger for affective than neutral stimuli. This positive shift began 200-300 ms after picture onset, reached its maximum amplitude approximately 1 s after picture onset, and was sustained for most of a 6-s picture presentation period. The positive increase was not related to local probability of content type, but was accentuated for pictures that prompted increased autonomic responses and reports of greater affective arousal (e.g. erotic or violent content). These results suggest that the late positive wave indicates a selective processing of emotional stimuli, reflecting the activation of motivational systems in the brain.

The neural bases of momentary lapses in attention

Momentary lapses in attention frequently impair goal-directed behavior, sometimes with serious consequences. Nevertheless, we lack an integrated view of the brain mechanisms underlying such lapses. By investigating trial-by-trial relationships between brain activity and response time in humans, we determined that attentional lapses begin with reduced prestimulus activity in anterior cingulate and right prefrontal regions involved in controlling attention. Less efficient stimulus processing during attentional lapses was also characterized by less deactivation of a 'default-mode' network, reduced stimulus-evoked sensory activity, and increased activity in widespread regions of frontal and parietal cortex. Finally, consistent with a mechanism for recovering from attentional lapses, increased stimulus-evoked activity in the right inferior frontal gyrus and the right temporal-parietal junction predicted better performance on the next trial. Our findings provide a new, system-wide understanding of the patterns of brain activity that are associated with brief attentional lapses, which informs both theoretical and clinical models of goal-directed behavior.

Optimizing the use of information: Strategic control of activation of responses

Recent studies indicate that subjects may respond to visual information during either an early parallel phase or a later focused phase and that the selection of the relevant phase is data driven. Using the noise-compatibility paradigm, we tested the hypothesis that this selection may also be strategic and context driven. At least part of the interference effect observed in this paradigm is due to response activation during the parallel-processing phase. We manipulated subjects' expectancies for compatible and incompatible noise in 4 experiments and effectively modulated the interference effect. The results suggest that expectancies about the relative utility of the information extracted during the parallel and focused phases determine which phase is used to activate responses.

Decoding the visual and subjective contents of the human brain

The potential for human neuroimaging to read out the detailed contents of a person's mental state has yet to be fully explored. We investigated whether the perception of edge orientation, a fundamental visual feature, can be decoded from human brain activity measured with functional magnetic resonance imaging (fMRI). Using statistical algorithms to classify brain states, we found that ensemble fMRI signals in early visual areas could reliably predict on individual trials which of eight stimulus orientations the subject was seeing. Moreover, when subjects had to attend to one of two overlapping orthogonal gratings, feature-based attention strongly biased ensemble activity toward the attended orientation. These results demonstrate that fMRI activity patterns in early visual areas, including primary visual cortex (V1), contain detailed orientation information that can reliably predict subjective perception. Our approach provides a framework for the readout of fine-tuned representations in the human brain and their subjective contents.

Language within our grasp

In monkeys, the rostral part of ventral premotor cortex (area F5) contains neurons that discharge, both when the monkey grasps or manipulates objects and when it observes the experimenter making similar actions. These neurons (mirror neurons) appear to represent a system that matches observed events to similar, internally generated actions, and in this way forms a link between the observer and the actor. Transcranial magnetic stimulation and positron emission tomography (PET) experiments suggest that a mirror system for gesture recognition also exists in humans and includes Broca's area. We propose here that such an observation/execution matching system provides a necessary bridge from'doing' to'communicating',as the link between actor and observer becomes a link between the sender and the receiver of each message.

Tracking multiple independent targets: evidence for a parallel tracking mechanism

There is considerable evidence that visual attention is concentrated at a single locus in the visual field, and that this locus can be moved independent of eye movements. Two studies are reported which suggest that, while certain aspects of attention require that locations be scanned serially, at least one operation may be carried out in parallel across several independent loci in the visual field. That is the operation of indexing features and tracking their identity. The studies show that: (a) subjects are able to track a subset of up to 5 objects in a field of 10 identical randomly-moving objects in order to distinguish a change in a target from a change in a distractor; and (b) when the speed and distance parameters of the display are designed so that, on the basis of some very conservative assumptions about the speed of attention movement and encoding times, the predicted performance of a serial scanning and updating algorithm would not exceed about 40% accuracy, subjects still manage to do the task with 87% accuracy. These findings are discussed in relation to an earlier, and independently motivated model of feature-binding--called the FINST model--which posits a primitive identity maintenance mechanism that indexes and tracks a limited number of visual objects in parallel. These indexes are hypothesized to serve the function of binding visual features prior to subsequent pattern recognition.

Electrophysiological correlates of feature analysis during visual search

Event-related brain potentials (ERPs) were recorded from normal young adults during visual search tasks in which the stimulus arrays contained either eight identical items (homogeneous arrays) or seven identical items and one deviant item (pop-out arrays). Four experiments were conducted in which different classes of stimulus arrays were designated targets and the remaining stimulus arrays were designated nontargets. In Experiments 1 and 2, both target and nontarget pop-out stimuli elicited an enhanced anterior N2 wave and a contralaterally larger posterior P1 wave, but Experiments 3 and 4 demonstrated that these components do not reflect fully automatic pop-out detection processes. In all four experiments, target pop-outs elicited enlarged anterior P2, posterior N2, occipital P3, and parietal P3 waves. The target-elicited posterior N2 wave contained a contralateral subcomponent (N2pc) that exhibited a focus over occipital cortex in maps of current source density. The overall pattern of results was consistent with guided search models in which preattentive stimulus information is used to guide attention to task-relevant stimuli.

Resolving emotional conflict: a role for the rostral anterior cingulate cortex in modulating activity in the amygdala

Effective mental functioning requires that cognition be protected from emotional conflict due to interference by task-irrelevant emotionally salient stimuli. The neural mechanisms by which the brain detects and resolves emotional conflict are still largely unknown, however. Drawing on the classic Stroop conflict task, we developed a protocol that allowed us to dissociate the generation and monitoring of emotional conflict from its resolution. Using functional magnetic resonance imaging (fMRI), we find that activity in the amygdala and dorsomedial and dorsolateral prefrontal cortices reflects the amount of emotional conflict. By contrast, the resolution of emotional conflict is associated with activation of the rostral anterior cingulate cortex. Activation of the rostral cingulate is predicted by the amount of previous-trial conflict-related neural activity and is accompanied by a simultaneous and correlated reduction of amygdalar activity. These data suggest that emotional conflict is resolved through top-down inhibition of amygdalar activity by the rostral cingulate cortex.

Chromatic mechanisms in lateral geniculate nucleus of macaque

This paper introduces a new technique for the analysis of the chromatic properties of neurones, and applies it to cells in the lateral geniculate nucleus (l.g.n.) of macaque. The method exploits the fact that for any cell that combines linearly the signals from cones there is a restricted set of lights to which it is equally sensitive, and whose members can be exchanged for one another without evoking a response. Stimuli are represented in a three-dimensional space defined by an axis along which only luminance varies, without change in chromaticity, a 'constant B' axis along which chromaticity varies without changing the excitation of blue-sensitive (B) cones, a 'constant R & G' axis along which chromaticity varies without change in the excitation of red-sensitive (R) or green-sensitive (G) cones. The orthogonal axes intersect at a white point. The isoluminant plane defined by the intersection of the 'constant B' and 'constant R & G' axes contains lights that vary only in chromaticity. In polar coordinates the constant B axis is assigned the azimuth 0-180 deg, and the constant R & G axis the azimuth 90-270 deg. Luminance is expressed as elevation above or below the isoluminant plane (-90 to +90 deg). For any cell that combines cone signals linearly, there is one plane in this space, passing through the white point, that contains all lights that can be exchanged silently. The position of this 'null plane' provides the 'signature' of the cell, and is specified by its azimuth (the direction in which it intersects the isoluminant plane of the stimulus space) and its elevation (its angle of inclination to the isoluminant plane). A colour television receiver was used to produce sinusoidal gratings whose chromaticity and luminance could be modulated along any vector passing through the white point in the space described. The spatial and temporal frequencies of modulation could be varied over a large range. When stimulated by patterns of low spatial and low temporal frequency, two groups of cells in the parvocellular laminae of the l.g.n. were distinguished by the locations of their null planes. The null planes of the larger group were narrowly distributed about an azimuth of 92.6 deg and more broadly about an elevation of 51.5 deg, which suggests that they receive opposed, but not equally balanced, inputs from only R and G cones. These we call R-G cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Gaze fixation and the neural circuitry of face processing in autism

Diminished gaze fixation is one of the core features of autism and has been proposed to be associated with abnormalities in the neural circuitry of affect. We tested this hypothesis in two separate studies using eye tracking while measuring functional brain activity during facial discrimination tasks in individuals with autism and in typically developing individuals. Activation in the fusiform gyrus and amygdala was strongly and positively correlated with the time spent fixating the eyes in the autistic group in both studies, suggesting that diminished gaze fixation may account for the fusiform hypoactivation to faces commonly reported in autism. In addition, variation in eye fixation within autistic individuals was strongly and positively associated with amygdala activation across both studies, suggesting a heightened emotional response associated with gaze fixation in autism.

Invariant visual representation by single neurons in the human brain

It takes a fraction of a second to recognize a person or an object even when seen under strikingly different conditions. How such a robust, high-level representation is achieved by neurons in the human brain is still unclear. In monkeys, neurons in the upper stages of the ventral visual pathway respond to complex images such as faces and objects and show some degree of invariance to metric properties such as the stimulus size, position and viewing angle. We have previously shown that neurons in the human medial temporal lobe (MTL) fire selectively to images of faces, animals, objects or scenes. Here we report on a remarkable subset of MTL neurons that are selectively activated by strikingly different pictures of given individuals, landmarks or objects and in some cases even by letter strings with their names. These results suggest an invariant, sparse and explicit code, which might be important in the transformation of complex visual percepts into long-term and more abstract memories.

The representation of object concepts in the brain

Evidence from functional neuroimaging of the human brain indicates that information about salient properties of an object-such as what it looks like, how it moves, and how it is used-is stored in sensory and motor systems active when that information was acquired. As a result, object concepts belonging to different categories like animals and tools are represented in partially distinct, sensory- and motor property-based neural networks. This suggests that object concepts are not explicitly represented, but rather emerge from weighted activity within property-based brain regions. However, some property-based regions seem to show a categorical organization, thus providing evidence consistent with category-based, domain-specific formulations as well.

Contour integration by the human visual system: evidence for a local "association field"

The Gestalt law of "good continuation" has been used to describe a variety of phenomena demonstrating the importance of continuity in human perception. In this study, we consider how continuity may be represented by a visual system that filters spatial data using arrays of cells selective for orientation and spatial frequency. Many structures (e.g. fractal contours) show a form of redundancy which is well represented by the continuity of features as they vary across space and frequency. We suggest that it is possible to take advantage of the redundancy in continuous, but non-aligned features by associating the outputs of filters with similar tuning. Five experiments were performed, to determine the rules that govern the perception of continuity. Observers were presented with arrays of oriented, band-pass elements (Gabor patches) in which a subset of the elements was aligned along a "jagged" path. Using a forced-choice procedure, observers were found to be capable of identifying the path within a field of randomly-oriented elements even when the spacing between the elements was considerably larger than the size of any of the individual elements. Furthermore, when the elements were oriented at angles up to +/- 60 deg relative to one another, the path was reliably identified. Alignment of the elements along the path was found to play a large role in the ability to detect the path. Small variations in the alignment or aligning the elements orthogonally (i.e. "side-to-side" as opposed to "end-to-end") significantly reduced the observer's ability to detect the presence of a path. The results are discussed in terms of an "association field" which integrates information across neighboring filters tuned to similar orientations. We suggest that some of the processes involved in texture segregation may have a similar explanation.