Integration of what and where in the primate prefrontal cortex

Abnormal amplitude of low-frequency fluctuations associated with rapid-eye movement in chronic primary insomnia patients

Purpose

Chronic primary insomnia (CPI) is the most prevalent sleep disorder worldwide. CPI manifests as difficulties in sleep onset, maintaining sleep, prolonged sleep latency, and daytime impairment and is often accompanied by cognitive problems such as poor academic performance, poor attention, and decreased memory. The most popular explanation of insomnia is hyperarousal or increased activities of neurons. Rapid eye movement (REM) sleep detected by polysomnography (PSG) exhibits a positive relationship with brain homeostasis and can be helpful for optimally preparing an organism for emotional and social function. Limited work has been performed to explore brain function of insomnia patients in combination with PSG analysis.

Results

We observed increased ALFF within areas related to hyperarousal such as the midbrain and bilateral extra-nucleus, whereas decreased ALFF was observed within areas associated with memory and attention involving the parietal and occipital lobule and others. Furthermore, the altered ALFF was associated with the duration of insomnia, sleep efficiency, duration of REM, latency of RME and ratio of REM.

Materials and Methods

In this study, we recruited twenty-five CPI patients and twenty-five normal sleep (NS) volunteers as a control group to investigate the amplitude of low-frequency fluctuations (ALFF) and the correlation between those altered ALFF regions through resting-state fMRI and PSG data.

Conclusions

These findings suggest that hyperarousal reflected by ALFF abnormality within brain areas related to cognition and emotion in insomnia associated with REM sleep.

Thalamic projections sustain prefrontal activity during working memory maintenance

The mediodorsal thalamus (MD) shares reciprocal connectivity with the prefrontal cortex (PFC), and decreased MD-PFC connectivity is observed in schizophrenia patients. Patients also display cognitive deficits including impairments in working memory, but a mechanistic link between thalamo-prefrontal circuit function and working memory is missing. Using pathway-specific inhibition, we found directional interactions between mouse MD and medial PFC (mPFC), with MD-to-mPFC supporting working memory maintenance and mPFC-to-MD supporting subsequent choice. We further identify mPFC neurons that display elevated spiking during the delay, a feature that was absent on error trials and required MD inputs for sustained maintenance. Strikingly, delay-tuned neurons had minimal overlap with spatially tuned neurons, and each mPFC population exhibited mutually exclusive dependence on MD and hippocampal inputs. These findings indicate a role for MD in sustaining prefrontal activity during working memory maintenance. Consistent with this idea, we found that enhancing MD excitability was sufficient to enhance task performance.

Patients with Mild Cognitive Impairment Show Lower Visual Short-Term Memory Performance in Feature Binding Tasks

Background

Early cognitive changes in people at risk of developing dementia may be detected using behavioral tests that examine the performance of typically affected brain areas, such as the hippocampi. An important cognitive function supported by the hippocampi is memory binding, in which object features are associated to create a unified percept.

Aim

To compare visual short-term memory (VSTM) binding performance for object names, locations, and identities between a participant group known to be at higher risk of developing dementia (mild cognitive impairment [MCI]) and healthily aging controls.

Methods

Ten MCI and 10 control participants completed five VSTM tests that differed in their requirement of remembering bound or unbound object names, locations, and identities, along with a standard neuropsychological test (Addenbrooke's Cognitive Examination [ACE]-III).

Results

The performance of the MCI participants was selectively and significantly lower than that of the healthily aging controls for memory tasks that required object-location or name-location binding.

Conclusion

Tasks that measure unimodal (object-location) and crossmodal (name-location) binding performance appear to be particularly effective for the detection of early cognitive changes in those at higher risk of developing dementia due to Alzheimer's disease.

Neural Architecture for Feature Binding in Visual Working Memory

Binding refers to the operation that groups different features together into objects. We propose a neural architecture for feature binding in visual working memory that employs populations of neurons with conjunction responses. We tested this model using cued recall tasks, in which subjects had to memorize object arrays composed of simple visual features (color, orientation, and location). After a brief delay, one feature of one item was given as a cue, and the observer had to report, on a continuous scale, one or two other features of the cued item. Binding failure in this task is associated with swap errors, in which observers report an item other than the one indicated by the cue. We observed that the probability of swapping two items strongly correlated with the items' similarity in the cue feature dimension, and found a strong correlation between swap errors occurring in spatial and nonspatial report. The neural model explains both swap errors and response variability as results of decoding noisy neural activity, and can account for the behavioral results in quantitative detail. We then used the model to compare alternative mechanisms for binding nonspatial features. We found the behavioral results fully consistent with a model in which nonspatial features are bound exclusively via their shared location, with no indication of direct binding between color and orientation. These results provide evidence for a special role of location in feature binding, and the model explains how this special role could be realized in the neural system.SIGNIFICANCE STATEMENT The problem of feature binding is of central importance in understanding the mechanisms of working memory. How do we remember not only that we saw a red and a round object, but that these features belong together to a single object rather than to different objects in our environment? Here we present evidence for a neural mechanism for feature binding in working memory, based on encoding of visual information by neurons that respond to the conjunction of features. We find clear evidence that nonspatial features are bound via space: we memorize directly where a color or an orientation appeared, but we memorize which color belonged with which orientation only indirectly by virtue of their shared location.

Pure optic ataxia and visual hemiagnosia - extending the dual visual hypothesis

Goodale and Milner's two visual system hypothesis is an influential model for the understanding of the primate visual system. Lesions of either the ventral (occipito-temporal) or the dorsal (occipito-parietal) stream produce distinct and dissociated syndromes in humans: visual agnosia is typical for ventral damage, whereas optic ataxia (OA) for dorsal damage. We studied the case of a 59-year-old left-handed woman with a circumscribed lesion around the left posterior occipital sulcus, extending to the underlying white matter. Initially, she presented with a central visual field OA, which regressed to an OA to the right visual hemifield during the 3 months observation period. In addition, tachistoscopic experiments showed visual hemiagnosia to the right visual hemifield. In line with the findings of the neuropsychological experiments, the analysis of the structural MR data by means of a trackwise hodologic probabilistic approach revealed damage to the left superior longitudinal fasciculus and to the left inferior longitudinal fasciculus, indicating an impairment of both the dorsal and the ventral stream. The combination of OA and visual hemiagnosia in the same patient has never been previously described. The present case study thus provides further insights for the understanding of visual processing.

Preparatory attention in visual cortex

Top-down attention is the mechanism that allows us to selectively process goal-relevant aspects of a scene while ignoring irrelevant aspects. A large body of research has characterized the effects of attention on neural activity evoked by a visual stimulus. However, attention also includes a preparatory phase before stimulus onset in which the attended dimension is internally represented. Here, we review neurophysiological, functional magnetic resonance imaging, magnetoencephalography, electroencephalography, and transcranial magnetic stimulation (TMS) studies investigating the neural basis of preparatory attention, both when attention is directed to a location in space and when it is directed to nonspatial stimulus attributes (content-based attention) ranging from low-level features to object categories. Results show that both spatial and content-based attention lead to increased baseline activity in neural populations that selectively code for the attended attribute. TMS studies provide evidence that this preparatory activity is causally related to subsequent attentional selection and behavioral performance. Attention thus acts by preactivating selective neurons in the visual cortex before stimulus onset. This appears to be a general mechanism that can operate on multiple levels of representation. We discuss the functional relevance of this mechanism, its limitations, and its relation to working memory, imagery, and expectation. We conclude by outlining open questions and future directions.

The Distributed Nature of Working Memory

Studies in humans and non-human primates have provided evidence for storage of working memory contents in multiple regions ranging from sensory to parietal and prefrontal cortex. We discuss potential explanations for these distributed representations: (i) features in sensory regions versus prefrontal cortex differ in the level of abstractness and generalizability; and (ii) features in prefrontal cortex reflect representations that are transformed for guidance of upcoming behavioral actions. We propose that the propensity to produce persistent activity is a general feature of cortical networks. Future studies may have to shift focus from asking where working memory can be observed in the brain to how a range of specialized brain areas together transform sensory information into a delayed behavioral response.

A boy named Sue

One major lesson learned in the cognitive sciences is that even basic human cognitive capacities are extraordinarily complicated and elusive to mechanistic explanations. This is definitely the case for naming and identity. Nothing seems simpler than using a proper name to refer to a unique individual object in the world. But psychological research has shown that the criteria and mechanisms by which humans establish and use names are unclear and seemingly contradictory. Children only develop the necessary knowledge and skills after years of development and naming degenerates in unusual selective ways with strokes, schizophrenia, or Alzheimer disease. Here we present an operational model of social interaction patterns and cognitive functions to explain how naming can be achieved and acquired. We study the Grounded Naming Game as a particular example of a symbolic interaction that requires naming and present mechanisms that build up and use the semiotic networks necessary for performance in the game. We demonstrate in experiments with autonomous physical robots that the proposed dynamical systems indeed lead to the formation of an effective naming system and that the model hence explains how naming and identity can get socially constructed and shared by a population of embodied agents.

Feature-location binding in 3D: Feature judgments are biased by 2D location but not position-in-depth

A fundamental aspect of human visual perception is the ability to recognize and locate objects in the environment. Importantly, our environment is predominantly three-dimensional (3D), but while there is considerable research exploring the binding of object features and location, it is unknown how depth information interacts with features in the object binding process. A recent paradigm called the spatial congruency bias demonstrated that 2D location is fundamentally bound to object features, such that irrelevant location information biases judgments of object features, but irrelevant feature information does not bias judgments of location or other features. Here, using the spatial congruency bias paradigm, we asked whether depth is processed as another type of location, or more like other features. We initially found that depth cued by binocular disparity biased judgments of object color. However, this result seemed to be driven more by the disparity differences than the depth percept: Depth cued by occlusion and size did not bias color judgments, whereas vertical disparity information (with no depth percept) did bias color judgments. Our results suggest that despite the 3D nature of our visual environment, only 2D location information - not position-in-depth - seems to be automatically bound to object features, with depth information processed more similarly to other features than to 2D location.

Rethinking Cortical Organization

One way to understand the topography of the cerebral cortex is that “like attracts like.” The cortex is organized to maximize nearest neighbor similarity. This principle can explain the separation of the cortex into discrete areas that emphasize different information domains. It can also explain the maps that form within cortical areas. However, because the cortex is two-dimensional, when a parameter space of much higher dimensionality is reduced onto the cortical sheet while optimizing nearest neighbor relationships, the result may lack an obvious global ordering into separate areas. Instead, the topography may consist of partial gradients, fractures, swirls, regions that resemble separate areas in some ways but not others, and in not a lack of topographic maps but an excess of maps overlaid on each other, no one of which seems to be entirely correct. Like a canvas in a gallery of modern art that no two observers interpret the same way, this lack of obvious ordering of high-dimensional spaces onto the cortex might then result in some scientific controversy over the true organization. In this review, the authors suggest that at least some sectors of the cortex do not have a simple global ordering and are better understood as a result of a reduction of a high-dimensional space onto the cortical sheet. The cortical motor system may be an example of this phenomenon. The authors discuss a model of the lateral motor cortex in which a reduction of many parameters onto a simulated cortical sheet results in a complex topographic pattern that matches the actual monkey motor cortex in surprising detail. Some of the ambiguities of topography and areal boundaries that have plagued the attempt to systematize the lateral motor cortex are explained by the model. NEUROSCIENTIST the attempt to syste 13(2):138—147, 2007.

Coding of Visual, Auditory, Rule, and Response Information in the Brain: 10 Years of Multivoxel Pattern Analysis

How is the processing of task information organized in the brain? Many views of brain function emphasize modularity, with different regions specialized for processing different types of information. However, recent accounts also highlight flexibility, pointing especially to the highly consistent pattern of frontoparietal activation across many tasks. Although early insights from functional imaging were based on overall activation levels during different cognitive operations, in the last decade many researchers have used multivoxel pattern analyses to interrogate the representational content of activations, mapping out the brain regions that make particular stimulus, rule, or response distinctions. Here, we drew on 100 searchlight decoding analyses from 57 published papers to characterize the information coded in different brain networks. The outcome was highly structured. Visual, auditory, and motor networks predominantly (but not exclusively) coded visual, auditory, and motor information, respectively. By contrast, the frontoparietal multiple-demand network was characterized by domain generality, coding visual, auditory, motor, and rule information. The contribution of the default mode network and voxels elsewhere was minor. The data suggest a balanced picture of brain organization in which sensory and motor networks are relatively specialized for information in their own domain, whereas a specific frontoparietal network acts as a domain-general "core" with the capacity to code many different aspects of a task.

Auditory Processing in the Posterior Parietal Cortex

Goal-directed behavior can be characterized as a dynamic link between a sensory stimulus and a motor act. Neural correlates of many of the intermediate events of goal-directed behavior are found in the posterior parietal cortex. Although the parietal cortex’s role in guiding visual behaviors has received considerable attention, relatively little is known about its role in mediating auditory behaviors. Here, the authors review recent studies that have focused on how neurons in the lateral intraparietal area (area LIP) differentially process auditory and visual stimuli. These studies suggest that area LIP contains a modality-dependent representation that is highly dependent on behavioral context.

Rostrocaudal functional gradient among the pre-dorsal premotor cortex, dorsal premotor cortex and primary motor cortex in goal-directed motor behaviour

The dorsal premotor cortex residing in the dorsolateral aspect of area 6 is a rostrocaudally elongated area that is rostral to the primary motor cortex (M1) and caudal to the prefrontal cortex. This region, which is subdivided into rostral [pre-dorsal premotor cortex (pre-PMd)] and caudal [dorsal premotor cortex proper (PMd)] components, probably plays a central role in planning and executing actions to achieve a behavioural goal. In the present study, we investigated the functional specializations of the pre-PMd, PMd, and M1, because the synthesis of the specific functions performed by each area is considered to be essential. Neurons were recorded while monkeys performed a conditional visuo-goal task designed to include separate processes for determining a behavioural goal (reaching towards a right or left potential target) on the basis of visual object instructions, specifying actions (direction of reaching) to be performed on the basis of the goal, and preparing and executing the action. Neurons in the pre-PMd and PMd retrieved and maintained behavioural goals without encoding the visual features of the visual object instructions, and subsequently specified the actions by multiplexing the goals with the locations of the targets. Furthermore, PMd and M1 neurons played a major role in representing the action during movement preparation and execution, whereas the contribution of the pre-PMd progressively decreased as the time of the actual execution of the movement approached. These findings revealed that the multiple processing stages necessary for the realization of an action to accomplish a goal were implemented in an area-specific manner across a functional gradient from the pre-PMd to M1 that included the PMd as an intermediary.

Hyperactivity of caudate, parahippocampal, and prefrontal regions during working memory in never-medicated persons at clinical high-risk for psychosis

BACKGROUND

Deficits in working memory (WM) are a core feature of schizophrenia (SZ) and other psychotic disorders. We examined brain activity during WM in persons at clinical high risk (CHR) for psychosis.

METHODS

Thirty-seven CHR and 34 healthy control participants underwent functional MRI (fMRI) on a 3.0T scanner while performing an N-back WM task. The sample included a sub-sample of CHR participants who had no lifetime history of treatment with psychotropic medications (n=11). Data were analyzed using SPM8 (2-back>0-back contrast). Pearson correlations between brain activity, symptoms, and WM performance were examined.

RESULTS

The total CHR group and medication-naive CHR sub-sample were comparable to controls in most demographic features and in N-back WM performance, but had significantly lower IQ. Relative to controls, medication-naïve CHR showed hyperactivity in the left parahippocampus (PHP) and the left caudate during performance of the N-back WM task. Relative to medication-exposed CHR, medication naïve CHR exhibited hyperactivity in the left caudate and the right dorsolateral prefrontal cortex (DLPFC). DLPFC activity was significantly negatively correlated with WM performance. PHP, caudate and DLPFC activity correlated strongly with symptoms, but results did not withstand FDR-correction for multiple comparisons. When all CHR participants were combined (regardless of medication status), only trend-level PHP hyperactivity was observed in CHR relative to controls.

CONCLUSIONS

Medication-naïve CHR exhibit hyperactivity in regions that subserve WM. These regions are implicated in studies of schizophrenia and risk for psychosis. Results emphasize the importance of medication status in the interpretation of task - induced brain activity.

Role of Prefrontal Persistent Activity in Working Memory

The prefrontal cortex is activated during working memory, as evidenced by fMRI results in human studies and neurophysiological recordings in animal models. Persistent activity during the delay period of working memory tasks, after the offset of stimuli that subjects are required to remember, has traditionally been thought of as the neural correlate of working memory. In the last few years several findings have cast doubt on the role of this activity. By some accounts, activity in other brain areas, such as the primary visual and posterior parietal cortex, is a better predictor of information maintained in visual working memory and working memory performance; dynamic patterns of activity may convey information without requiring persistent activity at all; and prefrontal neurons may be ill-suited to represent non-spatial information about the features and identity of remembered stimuli. Alternative interpretations about the role of the prefrontal cortex have thus been suggested, such as that it provides a top-down control of information represented in other brain areas, rather than maintaining a working memory trace itself. Here we review evidence for and against the role of prefrontal persistent activity, with a focus on visual neurophysiology. We show that persistent activity predicts behavioral parameters precisely in working memory tasks. We illustrate that prefrontal cortex represents features of stimuli other than their spatial location, and that this information is largely absent from early cortical areas during working memory. We examine memory models not dependent on persistent activity, and conclude that each of those models could mediate only a limited range of memory-dependent behaviors. We review activity decoded from brain areas other than the prefrontal cortex during working memory and demonstrate that these areas alone cannot mediate working memory maintenance, particularly in the presence of distractors. We finally discuss the discrepancy between BOLD activation and spiking activity findings, and point out that fMRI methods do not currently have the spatial resolution necessary to decode information within the prefrontal cortex, which is likely organized at the micrometer scale. Therefore, we make the case that prefrontal persistent activity is both necessary and sufficient for the maintenance of information in working memory.

Working Memory in the Service of Executive Control Functions

Working memory is a type of short-term memory which has a crucial cognitive function that supports ongoing and upcoming behaviors, allowing storage of information across delay periods. The content of this memory may typically include tangible information about features such as the shape, color or texture of an object, and its location and motion relative to the body, as well as phonological information. The neural correlate of working memory has been found in different brain areas that are involved in organizing perceptual or motor functions. In particular, neuronal activity in prefrontal areas encodes task-related information corresponding to working memory across delay periods, and lesions in the prefrontal cortex severely affect the ability to retain this type of memory. Recent studies have further expanded the scope and possible role of working memory by showing that information of a more abstract nature (including a behavior-guiding rule, or the occurrence of a conflict in information processing) can also be maintained in short-term memory, and used for adjusting the allocation of executive control in dynamic environments. It has also been shown that neuronal activity in the prefrontal cortex encodes and maintains information about such abstract entities. These findings suggest that the prefrontal cortex plays crucial roles in the organization of goal-directed behavior by supporting many different mnemonic processes, which maintain a wide range of information required for the executive control of ongoing and upcoming behaviors.

The Role of the Parietal Cortex in the Representation of Task-Reward Associations

Rewards obtained from specific behaviors can and do change across time. To adapt to such conditions, humans need to represent and update associations between behaviors and their outcomes. Much previous work focused on how rewards affect the processing of specific tasks. However, abstract associations between multiple potential behaviors and multiple rewards are an important basis for adaptation as well. In this experiment, we directly investigated which brain areas represent associations between multiple tasks and rewards, using time-resolved multivariate pattern analysis of functional magnetic resonance imaging data. Importantly, we were able to dissociate neural signals reflecting task-reward associations from those related to task preparation and reward expectation processes, variables that were often correlated in previous research. We hypothesized that brain regions involved in processing tasks and/or rewards will be involved in processing associations between them. Candidate areas included the dorsal anterior cingulate cortex, which is involved in associating simple actions and rewards, and the parietal cortex, which has been shown to represent task rules and action values. Our results indicate that local spatial activation patterns in the inferior parietal cortex indeed represent task-reward associations. Interestingly, the parietal cortex flexibly changes its content of representation within trials. It first represents task-reward associations, later switching to process tasks and rewards directly. These findings highlight the importance of the inferior parietal cortex in associating behaviors with their outcomes and further show that it can flexibly reconfigure its function within single trials. Significance statement: Rewards obtained from specific behaviors rarely remain constant over time. To adapt to changing conditions, humans need to continuously update and represent the current association between behavior and its outcomes. However, little is known about the neural representation of behavior-outcome associations. Here, we used multivariate pattern analysis of functional magnetic resonance imaging data to investigate the neural correlates of such associations. Our results demonstrate that the parietal cortex plays a central role in representing associations between multiple behaviors and their outcomes. They further highlight the flexibility of the parietal cortex, because we find it to adapt its function to changing task demands within trials on relatively short timescales.

Short-Term Memory for Space and Time Flexibly Recruit Complementary Sensory-Biased Frontal Lobe Attention Networks

The frontal lobes control wide-ranging cognitive functions; however, functional subdivisions of human frontal cortex are only coarsely mapped. Here, functional magnetic resonance imaging reveals two distinct visual-biased attention regions in lateral frontal cortex, superior precentral sulcus (sPCS) and inferior precentral sulcus (iPCS), anatomically interdigitated with two auditory-biased attention regions, transverse gyrus intersecting precentral sulcus (tgPCS) and caudal inferior frontal sulcus (cIFS). Intrinsic functional connectivity analysis demonstrates that sPCS and iPCS fall within a broad visual-attention network, while tgPCS and cIFS fall within a broad auditory-attention network. Interestingly, we observe that spatial and temporal short-term memory (STM), respectively, recruit visual and auditory attention networks in the frontal lobe, independent of sensory modality. These findings not only demonstrate that both sensory modality and information domain influence frontal lobe functional organization, they also demonstrate that spatial processing co-localizes with visual processing and that temporal processing co-localizes with auditory processing in lateral frontal cortex.

A Source for Feature-Based Attention in the Prefrontal Cortex

In cluttered scenes, we can use feature-based attention to quickly locate a target object. To understand how feature attention is used to find and select objects for action, we focused on the ventral prearcuate (VPA) region of prefrontal cortex. In a visual search task, VPA cells responded selectively to search cues, maintained their feature selectivity throughout the delay and subsequent saccades, and discriminated the search target in their receptive fields with a time course earlier than in FEF or IT cortex. Inactivation of VPA impaired the animals' ability to find targets, and simultaneous recordings in FEF revealed that the effects of feature attention were eliminated while leaving the effects of spatial attention in FEF intact. Altogether, the results suggest that VPA neurons compute the locations of objects with the features sought and send this information to FEF to guide eye movements to those relevant stimuli.

Many neighbors are not silent. fMRI evidence for global lexical activity in visual word recognition

Many neurocognitive studies investigated the neural correlates of visual word recognition, some of which manipulated the orthographic neighborhood density of words and nonwords believed to influence the activation of orthographically similar representations in a hypothetical mental lexicon. Previous neuroimaging research failed to find evidence for such global lexical activity associated with neighborhood density. Rather, effects were interpreted to reflect semantic or domain general processing. The present fMRI study revealed effects of lexicality, orthographic neighborhood density and a lexicality by orthographic neighborhood density interaction in a silent reading task. For the first time we found greater activity for words and nonwords with a high number of neighbors. We propose that this activity in the dorsomedial prefrontal cortex reflects activation of orthographically similar codes in verbal working memory thus providing evidence for global lexical activity as the basis of the neighborhood density effect. The interaction of lexicality by neighborhood density in the ventromedial prefrontal cortex showed lower activity in response to words with a high number compared to nonwords with a high number of neighbors. In the light of these results the facilitatory effect for words and inhibitory effect for nonwords with many neighbors observed in previous studies can be understood as being due to the operation of a fast-guess mechanism for words and a temporal deadline mechanism for nonwords as predicted by models of visual word recognition. Furthermore, we propose that the lexicality effect with higher activity for words compared to nonwords in inferior parietal and middle temporal cortex reflects the operation of an identification mechanism based on local lexico-semantic activity.

There's Waldo! A Normalization Model of Visual Search Predicts Single-Trial Human Fixations in an Object Search Task

When searching for an object in a scene, how does the brain decide where to look next? Visual search theories suggest the existence of a global "priority map" that integrates bottom-up visual information with top-down, target-specific signals. We propose a mechanistic model of visual search that is consistent with recent neurophysiological evidence, can localize targets in cluttered images, and predicts single-trial behavior in a search task. This model posits that a high-level retinotopic area selective for shape features receives global, target-specific modulation and implements local normalization through divisive inhibition. The normalization step is critical to prevent highly salient bottom-up features from monopolizing attention. The resulting activity pattern constitues a priority map that tracks the correlation between local input and target features. The maximum of this priority map is selected as the locus of attention. The visual input is then spatially enhanced around the selected location, allowing object-selective visual areas to determine whether the target is present at this location. This model can localize objects both in array images and when objects are pasted in natural scenes. The model can also predict single-trial human fixations, including those in error and target-absent trials, in a search task involving complex objects.

How to learn places without spatial concepts: Does the what-and-where reaction time system in children regulate learning during stimulus repetition?

We investigated the role of repetition for place learning in children although the acquisition of organizing spatial concepts is often seen as more essential. In a reaction-time accuracy task, 7- and 9-year-old children were presented with a randomized sequence of objects-in-places. In a novelty condition (NC), memory sets in different colors were presented, while in a repetition condition (RC), the identical memory set was tested several times. Shape memory deteriorated more than place memory in the NC, but also stayed superior to place memory when both improved in the RC. False alarms occurred for objects and places in the same way in 7-year-olds in the NC, but were negligible for 9-year-olds. In contrast, false alarms in the RC occurred in both age groups mainly for place memory. The Common Region Test (CRT) predicted reaction times only in the novelty condition, indicating use of spatial concepts. Importantly, reaction times for shapes were faster than for places at the beginning of the experiment but slowed down thereafter, while reaction times for places were slow at the beginning of the experiment but accelerated considerably thereafter. False alarms and regulation of reaction times indicated that repetition facilitated true abstraction of information leading to place learning without spatial concepts.

Flexible Coding of Task Rules in Frontoparietal Cortex: An Adaptive System for Flexible Cognitive Control

How do our brains achieve the cognitive control that is required for flexible behavior? Several models of cognitive control propose a role for frontoparietal cortex in the structure and representation of task sets or rules. For behavior to be flexible, however, the system must also rapidly reorganize as mental focus changes. Here we used multivoxel pattern analysis of fMRI data to demonstrate adaptive reorganization of frontoparietal activity patterns following a change in the complexity of the task rules. When task rules were relatively simple, frontoparietal cortex did not hold detectable information about these rules. In contrast, when the rules were more complex, frontoparietal cortex showed clear and decodable rule discrimination. Our data demonstrate that frontoparietal activity adjusts to task complexity, with better discrimination of rules that are behaviorally more confusable. The change in coding was specific to the rule element of the task and was not mirrored in more specialized cortex (early visual cortex) where coding was independent of difficulty. In line with an adaptive view of frontoparietal function, the data suggest a system that rapidly reconfigures in accordance with the difficulty of a behavioral task. This system may provide a neural basis for the flexible control of human behavior.

Shape and spatial working memory capacities are mostly independent

Whether visual working memory (WM) consists of a common storage resource or of multiple subsystems has been a controversial issue. Logie (1995) suggested that it can be divided into visual (for color, shape, objects, etc.) and spatial WM (for location). However, a recent study reported evidence against this hypothesis. Using a dual task paradigm, Wood (2011) showed interference between shape and spatial WM capacities, suggesting that they share a common resource limitation. We re-examined this finding controlling possible confounding factors, including the way to present spatial location cues, task order, and type of WM load to be manipulated. The same pattern of results was successfully reproduced, but only in a highly powered experiment (N = 90), and therefore the size of interference was estimated to be quite small (d = 0.24). Thus, these data offer a way to reconcile seemingly contradicting previous findings. On the one hand, some part of the storage system is genuinely shared by shape and spatial WM systems, confirming the report of Wood (2011). On the other hand, the amount of the overlap is only minimal, and therefore the two systems should be regarded as mostly independent from each other, supporting the classical visuo-spatial separation hypothesis.

End effects and cross-dimensional interference in identification of time and length: Evidence for a common memory mechanism

Memory plays a critical role in time estimation, yet detailed mechanisms underlying temporal memory have not been fully understood. The current functional magnetic resonance imaging (fMRI) study investigated memory phenomena in absolute identification of time durations and line lengths. In both time and length identification, participants responded faster to end-of-range stimuli (e.g., the shortest or longest items of the stimulus set) than to middle stimuli. Participants performed worse in the incongruent condition (mismatch between time and length in the stimulus position) than in the congruent condition, indicating cross-dimensional interference between time and length. Both phenomena reflect increased difficulty of retrieving information relevant to the current context in the presence of context-irrelevant information. A region in the lateral inferior prefrontal cortex showed a greater response to the middle stimuli and in the incongruent condition suggesting greater demands for controlled memory retrieval. A cognitive model based on the ACT-R (Adaptive Control of Thought - Rational) declarative memory mechanisms accounted for the major behavioral and imaging results. The results suggest that contextual effects in temporal memory can be understood in terms of domain-general memory principles established outside the time estimation domain.

Prefrontal neuronal responses during audiovisual mnemonic processing

During communication we combine auditory and visual information. Neurophysiological research in nonhuman primates has shown that single neurons in ventrolateral prefrontal cortex (VLPFC) exhibit multisensory responses to faces and vocalizations presented simultaneously. However, whether VLPFC is also involved in maintaining those communication stimuli in working memory or combining stored information across different modalities is unknown, although its human homolog, the inferior frontal gyrus, is known to be important in integrating verbal information from auditory and visual working memory. To address this question, we recorded from VLPFC while rhesus macaques (Macaca mulatta) performed an audiovisual working memory task. Unlike traditional match-to-sample/nonmatch-to-sample paradigms, which use unimodal memoranda, our nonmatch-to-sample task used dynamic movies consisting of both facial gestures and the accompanying vocalizations. For the nonmatch conditions, a change in the auditory component (vocalization), the visual component (face), or both components was detected. Our results show that VLPFC neurons are activated by stimulus and task factors: while some neurons simply responded to a particular face or a vocalization regardless of the task period, others exhibited activity patterns typically related to working memory such as sustained delay activity and match enhancement/suppression. In addition, we found neurons that detected the component change during the nonmatch period. Interestingly, some of these neurons were sensitive to the change of both components and therefore combined information from auditory and visual working memory. These results suggest that VLPFC is not only involved in the perceptual processing of faces and vocalizations but also in their mnemonic processing.

The ecology of human fear: survival optimization and the nervous system

We propose a Survival Optimization System (SOS) to account for the strategies that humans and other animals use to defend against recurring and novel threats. The SOS attempts to merge ecological models that define a repertoire of contextually relevant threat induced survival behaviors with contemporary approaches to human affective science. We first propose that the goal of the nervous system is to reduce surprise and optimize actions by (i) predicting the sensory landscape by simulating possible encounters with threat and selecting the appropriate pre-encounter action and (ii) prevention strategies in which the organism manufactures safe environments. When a potential threat is encountered the (iii) threat orienting system is engaged to determine whether the organism ignores the stimulus or switches into a process of (iv) threat assessment, where the organism monitors the stimulus, weighs the threat value, predicts the actions of the threat, searches for safety, and guides behavioral actions crucial to directed escape. When under imminent attack, (v) defensive systems evoke fast reflexive indirect escape behaviors (i.e., fight or flight). This cascade of responses to threat of increasing magnitude are underwritten by an interconnected neural architecture that extends from cortical and hippocampal circuits, to attention, action and threat systems including the amygdala, striatum, and hard-wired defensive systems in the midbrain. The SOS also includes a modulatory feature consisting of cognitive appraisal systems that flexibly guide perception, risk and action. Moreover, personal and vicarious threat encounters fine-tune avoidance behaviors via model-based learning, with higher organisms bridging data to reduce face-to-face encounters with predators. Our model attempts to unify the divergent field of human affective science, proposing a highly integrated nervous system that has evolved to increase the organism's chances of survival.

Functions of delay-period activity in the prefrontal cortex and mnemonic scotomas revisited

Working memory (WM) is one of key concepts to understand functions of the prefrontal cortex. Delay-period activity is an important neural correlate to understand the role of WM in prefrontal functions. The importance of delay-period activity is that this activity can encode not only visuospatial information but also a variety of information including non-spatial visual features, auditory and tactile stimuli, task rules, expected reward, and numerical quantity. This activity also participates in a variety of information processing including sensory-to-motor information transformation. These mnemonic features of delay-period activity enable to perform various important operations that the prefrontal cortex participates in, such as executive controls, and therefore, support the notion that WM is an important function to understand prefrontal functions. On the other hand, although experiments using manual versions of the delayed-response task had revealed many important findings, an oculomotor version of this task enabled us to use multiple cue positions, exclude postural orientation during the delay period, and further prove the importance of mnemonic functions of the prefrontal cortex. In addition, monkeys with unilateral lesions exhibited specific impairment only in the performance of memory-guided saccades directed toward visual cues in the visual field contralateral to the lesioned hemisphere. This result indicates that memories for visuospatial coordinates in each hemifield are processed primarily in the contralateral prefrontal cortex. This result further strengthened the idea of mnemonic functions of the prefrontal cortex. Thus, the mnemonic functions of the prefrontal cortex and delay-period activity may not need to be reconsidered, but should be emphasized.

Spatial patterns of persistent neural activity vary with the behavioral context of short-term memory

A short-term memory can be evoked by different inputs and control separate targets in different behavioral contexts. To address the circuit mechanisms underlying context-dependent memory function, we determined through optical imaging how memory is encoded at the whole-network level in two behavioral settings. Persistent neural activity maintaining a memory of desired eye position was imaged throughout the oculomotor integrator after saccadic or optokinetic stimulation. While eye position was encoded by the amplitude of network activity, the spatial patterns of firing were context dependent: cells located caudally generally were most persistent following saccadic input, whereas cells located rostrally were most persistent following optokinetic input. To explain these data, we computationally identified four independent modes of network activity and found these were differentially accessed by saccadic and optokinetic inputs. These results show how a circuit can simultaneously encode memory value and behavioral context, respectively, in its amplitude and spatial pattern of persistent firing.

Dynamic routing of task-relevant signals for decision making in dorsolateral prefrontal cortex

Neurons in the dorsolateral prefrontal cortex (DLPFC) encode a diverse array of sensory and mnemonic signals, but little is known about how this information is dynamically routed during decision making. We analyzed the neuronal activity in the DLPFC of monkeys performing a probabilistic reversal task where information about the probability and magnitude of reward was provided by the target color and numerical cues, respectively. The location of the target of a given color was randomized across trials and therefore was not relevant for subsequent choices. DLPFC neurons encoded signals related to both task-relevant and irrelevant features, but only task-relevant mnemonic signals were encoded congruently with choice signals. Furthermore, only the task-relevant signals related to previous events were more robustly encoded following rewarded outcomes. Thus, multiple types of neural signals are flexibly routed in the DLPFC so as to favor actions that maximize reward.

Spatial and temporal distribution of visual information coding in lateral prefrontal cortex

Prefrontal neurons code many kinds of behaviourally relevant visual information. In behaving monkeys, we used a cued target detection task to address coding of objects, behavioural categories and spatial locations, examining the temporal evolution of neural activity across dorsal and ventral regions of the lateral prefrontal cortex (encompassing parts of areas 9, 46, 45A and 8A), and across the two cerebral hemispheres. Within each hemisphere there was little evidence for regional specialisation, with neurons in dorsal and ventral regions showing closely similar patterns of selectivity for objects, categories and locations. For a stimulus in either visual field, however, there was a strong and temporally specific difference in response in the two cerebral hemispheres. In the first part of the visual response (50-250 ms from stimulus onset), processing in each hemisphere was largely restricted to contralateral stimuli, with strong responses to such stimuli, and selectivity for both object and category. Later (300-500 ms), responses to ipsilateral stimuli also appeared, many cells now responding more strongly to ipsilateral than to contralateral stimuli, and many showing selectivity for category. Activity on error trials showed that late activity in both hemispheres reflected the animal's final decision. As information is processed towards a behavioural decision, its encoding spreads to encompass large, bilateral regions of prefrontal cortex.

Differential roles of delay-period neural activity in the monkey dorsolateral prefrontal cortex in visual-haptic crossmodal working memory

Previous studies have shown that neurons of monkey dorsolateral prefrontal cortex (DLPFC) integrate information across modalities and maintain it throughout the delay period of working-memory (WM) tasks. However, the mechanisms of this temporal integration in the DLPFC are still poorly understood. In the present study, to further elucidate the role of the DLPFC in crossmodal WM, we trained monkeys to perform visuo-haptic (VH) crossmodal and haptic-haptic (HH) unimodal WM tasks. The neuronal activity recorded in the DLPFC in the delay period of both tasks indicates that the early-delay differential activity probably is related to the encoding of sample information with different strengths depending on task modality, that the late-delay differential activity reflects the associated (modality-independent) action component of haptic choice in both tasks (that is, the anticipation of the behavioral choice and/or active recall and maintenance of sample information for subsequent action), and that the sustained whole-delay differential activity likely bridges and integrates the sensory and action components. In addition, the VH late-delay differential activity was significantly diminished when the haptic choice was not required. Taken together, the results show that, in addition to the whole-delay differential activity, DLPFC neurons also show early- and late-delay differential activities. These previously unidentified findings indicate that DLPFC is capable of (i) holding the coded sample information (e.g., visual or tactile information) in the early-delay activity, (ii) retrieving the abstract information (orientations) of the sample (whether the sample has been haptic or visual) and holding it in the late-delay activity, and (iii) preparing for behavioral choice acting on that abstract information.

A rostro-caudal axis for language in the frontal lobe: the role of executive control in speech production

The present article promotes a formal executive model of frontal functions underlying speech production, bringing together hierarchical theories of adaptive behavior in the (pre-)frontal cortex (pFC) and psycho- and neurolinguistic approaches to spoken language within an information-theoretic framework. Its biological plausibility is revealed through two Activation Likelihood Estimation meta-analyses carried out on a total of 41 hemodynamic studies of overt word and continuous speech production respectively. Their principal findings, considered in light of neuropsychological evidence and earlier models of speech-related frontal functions, support the engagement of a caudal-to-rostral gradient of pFC activity operationalized by the nature and quantity of speech-related information conveyed by task-related external cues (i.e., cue codability) on the one hand, and the total informational content of generated utterances on the other. In particular, overt reading or repetition and picture naming recruit primarily caudal motor-premotor regions involved in the sensorimotor and phonological aspects of speech; word and sentence generation engage mid- ventro- and dorsolateral areas supporting its basic predicative and syntactic functions; finally, rostral- and fronto-polar cortices subsume domain-general strategic processes of discourse generation for creative speech. These different levels interact in a top-down fashion, ranging representationally and temporally from the most general and extended to the most specific and immediate. The end-result is an integrative theory of pFC as the main executive component of the language cortical network, which supports the existence of areas specialized for speech communication and articulation and regions subsuming internal reasoning and planning. Prospective avenues of research pertaining to this model's principal predictions are discussed.

Dyslexia: the Role of Vision and Visual Attention

Dyslexia is more than just difficulty with translating letters into sounds. Many dyslexics have problems with clearly seeing letters and their order. These difficulties may be caused by abnormal development of their visual “magnocellular” (M) nerve cells; these mediate the ability to rapidly identify letters and their order because they control visual guidance of attention and of eye fixations. Evidence for M cell impairment has been demonstrated at all levels of the visual system: in the retina, in the lateral geniculate nucleus, in the primary visual cortex and throughout the dorsal visuomotor “where” pathway forward from the visual cortex to the posterior parietal and prefrontal cortices. This abnormality destabilises visual perception; hence, its severity in individuals correlates with their reading deficit. Treatments that facilitate M function, such as viewing text through yellow or blue filters, can greatly increase reading progress in children with visual reading problems. M weakness may be caused by genetic vulnerability, which can disturb orderly migration of cortical neurones during development or possibly reduce uptake of omega-3 fatty acids, which are usually obtained from fish oils in the diet. For example, M cell membranes require replenishment of the omega-3 docosahexaenoic acid to maintain their rapid responses. Hence, supplementing some dyslexics’ diets with DHA can greatly improve their M function and their reading.

WORKING MEMORY IMPAIRMENT AS AN ENDOPHENOTYPIC MARKER OF A SCHIZOPHRENIA DIATHESIS

This chapter focuses on the viability of working memory impairment as an endophenotypic marker of a schizophrenia diathesis. It begins with an introduction of the construct of working memory. It follows with a review of the operational criteria for defining an endophenotype. Research findings regarding the working memory performance of schizophrenia and schizophrenia-spectrum patients, first-degree relatives of schizophrenia patients and healthy controls, are reviewed in terms of the criteria for being considered an endophenotypic marker. Special attention is paid to specific components of the working memory deficit (namely, encoding, maintenance, and manipulation), in terms of which aspects are likely to be the best candidates for endophenotypes. We consider the extant literature regarding working memory performance in bipolar disorder and major depression in order to address the issue of relative specificity to schizophrenia. Despite some unresolved issues, it appears that working memory impairment is a very promising candidate for an endophenotypic marker of a schizophrenia diathesis but not for mood disorders. Throughout this chapter, we identify future directions for research in this exciting and dynamic area of research and evaluate the contribution of working memory research to our understanding of schizophrenia.

Functional connectivity changes between parietal and prefrontal cortices in primary insomnia patients: evidence from resting-state fMRI

Background

Primary insomnia can severely impair daytime function by disrupting attention and working memory and imposes a danger to self and others by increasing the risk of accidents. We speculated that the neurobiological changes impeding working memory in primary insomnia patients would be revealed by resting-state functional MRI (R-fMRI), which estimates the strength of cortical pathways by measuring local and regional correlations in blood oxygen level dependent (BOLD) signs independent of specific task demands.

Methods

We compared the R-fMRI activity patterns of 15 healthy controls to 15 primary insomnia patients (all 30 participants were right-handed) using a 3.0 T MRI scanner. The SPM8 and REST1.7 software packages were used for preprocessing and analysis. Activity was expressed relative to the superior parietal lobe (SPL, the seed region) to reveal differences in functional connectivity to other cortical regions implicated in spatial working memory.

Result

In healthy controls, bilateral SPL activity was associated with activity in the posterior cingulate gyrus, precuneus, ventromedial prefrontal cortex, and superior frontal gyrus, indicating functional connectivity between these regions. Strong functional connectivity between the SPL and bilateral pre-motor cortex, bilateral supplementary motor cortex, and left dorsolateral prefrontal cortex was observed in both the control group and the primary insomnia group. However, the strength of several other functional connectivity pathways to the SPL exhibited significant group differences. Compared to healthy controls, connectivity in the primary insomnia group was stronger between the bilateral SPL and the right ventral anterior cingulate cortex, left ventral posterior cingulate cortex, right splenium of the corpus callosum, right pars triangularis (right inferior frontal gyrus/Broca’s area), and right insular lobe, while connectivity was weaker between the SPL and right superior frontal gyrus (dorsolateral prefrontal cortex).

Conclusion

Primary insomnia appears to alter the functional connectivity between the parietal and frontal lobes, cortical structures critical for spatial and verbal working memory.

Visual-spatial attention aids the maintenance of object representations in visual working memory

Theories have proposed that the maintenance of object representations in visual working memory is aided by a spatial rehearsal mechanism. In this study, we used two different approaches to test the hypothesis that overt and covert visual-spatial attention mechanisms contribute to the maintenance of object representations in visual working memory. First, we tracked observers' eye movements while they remembered a variable number of objects during change-detection tasks. We observed that during the blank retention interval, participants spontaneously shifted gaze to the locations that the objects had occupied in the memory array. Next, we hypothesized that if attention mechanisms contribute to the maintenance of object representations, then drawing attention away from the object locations during the retention interval should impair object memory during these change-detection tasks. Supporting this prediction, we found that attending to the fixation point in anticipation of a brief probe stimulus during the retention interval reduced change-detection accuracy, even on the trials in which no probe occurred. These findings support models of working memory in which visual-spatial selection mechanisms contribute to the maintenance of object representations.

Executive control processes underlying multi-item working memory

A dominant view of prefrontal cortex (PFC) function is that it stores task-relevant information in working memory. To examine this and determine how it applies when multiple pieces of information must be stored, we trained two macaque monkeys to perform a multi-item color change-detection task and recorded activity of neurons in PFC. Few neurons encoded the color of the items. Instead, the predominant encoding was spatial: a static signal reflecting the item's position and a dynamic signal reflecting the animal's covert attention. These findings challenge the notion that PFC stores task-relevant information. Instead, we suggest that the contribution of PFC is in controlling the allocation of resources to support working memory. In support of this, we found that increased power in the alpha and theta bands of PFC local field potentials, which are thought to reflect long-range communication with other brain areas, was correlated with more precise color representations.

Attention in the real world: toward understanding its neural basis

The efficient selection of behaviorally relevant objects from cluttered environments supports our everyday goals. Attentional selection has typically been studied in search tasks involving artificial and simplified displays. Although these studies have revealed important basic principles of attention, they do not explain how the brain efficiently selects familiar objects in complex and meaningful real-world scenes. Findings from recent neuroimaging studies indicate that real-world search is mediated by 'what' and 'where' attentional templates that are implemented in high-level visual cortex. These templates represent target-diagnostic properties and likely target locations, respectively, and are shaped by object familiarity, scene context, and memory. We propose a framework for real-world search that incorporates these recent findings and specifies directions for future study.

The relationship between executive functions and fluid intelligence in schizophrenia

An enduring question is unity vs. separability of executive deficits resulting from impaired frontal lobe function. In previous studies, we have asked how executive deficits link to a conventional measure of fluid intelligence, obtained either by standard tests of novel problem-solving, or by averaging performance in a battery of novel tasks. For some classical executive tasks, such as the Wisconsin Card Sorting Test (WCST), Verbal Fluency, and Trail Making Test B (TMTB), frontal deficits are entirely explained by fluid intelligence. However, on a second set of executive tasks, including tests of multitasking and decision making, deficits exceed those predicted by fluid intelligence loss. In this paper we discuss how these results shed light on the diverse clinical phenomenology observed in frontal dysfunction, and present new data on a group of 15 schizophrenic patients and 14 controls. Subjects were assessed with a range of executive tests and with a general cognitive battery used to derive a measure of fluid intelligence. Group performance was compared and fluid intelligence was introduced as a covariate. In line with our previous results, significant patient-control differences in classical executive tests were removed when fluid intelligence was introduced as a covariate. However, for tests of multitasking and decision making, deficits remained. We relate our findings to those of previous factor analytic studies describing a single principal component, which accounts for much of the variance of schizophrenic patients' cognitive performance. We propose that this general factor reflects low fluid intelligence capacity, which accounts for much but not all cognitive impairment in this patient group. Partialling out the general effects of fluid intelligence, we propose, may clarify the role of additional, more specific cognitive impairments in conditions such as schizophrenia.

Prefrontal cortical microcircuits bind perception to executive control

During the perception-to-action cycle, our cerebral cortex mediates the interactions between the environment and the perceptual-executive systems of the brain. At the top of the executive hierarchy, prefrontal cortical microcircuits are assumed to bind perceptual and executive control information to guide goal-driven behavior. Here, we tested this hypothesis by comparing simultaneously recorded neuron firing in prefrontal cortical layers and the caudate-putamen of rhesus monkeys, trained in a spatial-versus-object, rule-based match-to-sample task. We found that during the perception and executive selection phases, cell firing in the localized prefrontal layers and caudate-putamen region exhibited similar location preferences on spatial-trials, but less on object- trials. Then, we facilitated the perceptual-executive circuit by stimulating the prefrontal infra-granular-layers with patterns previously derived from supra-granular-layers, and produced stimulation-induced spatial preference in percent correct performance on spatial trials, similar to neural tuning. These results show that inter-laminar prefrontal microcircuits play causal roles to the perception-to-action cycle.

The Rostro-Caudal Axis of Frontal Cortex Is Sensitive to the Domain of Stimulus Information

Evidence suggests that lateral frontal cortex implements cognitive control processing along its rostro-caudal axis, yet other evidence supports a dorsal-ventral functional organization for processes engaged by different stimulus domains (e.g., spatial vs. nonspatial). This functional magnetic resonance imaging study investigated whether separable dorsolateral and ventrolateral rostro-caudal gradients exist in humans, while participants performed tasks requiring cognitive control at 3 levels of abstraction with language or spatial stimuli. Abstraction was manipulated by using 3 different task sets that varied in relational complexity. Relational complexity refers to the process of manipulating the relationship between task components (e.g., to associate a particular cue with a task) and drawing inferences about that relationship. Tasks using different stimulus domains engaged distinct posterior regions, but within the lateral frontal cortex, we found evidence for a single rostro-caudal gradient that was organized according to the level of abstraction and was independent of processing of the stimulus domain. However, a pattern of dorsal/ventral segregation of processing engaged by domain-specific information was evident in each separable frontal region only within the most rostral region recruited by task demands. These results suggest that increasingly abstract information is represented in the frontal cortex along distinct rostro-caudal gradients that also segregate along a dorsal-ventral axis dependent on task demands.

Transfer of the nonmatch-to-goal rule in monkeys across cognitive domains

To solve novel problems, it is advantageous to abstract relevant information from past experience to transfer on related problems. To study whether macaque monkeys were able to transfer an abstract rule across cognitive domains, we trained two monkeys on a nonmatch-to-goal (NMTG) task. In the object version of the task (O-NMTG), the monkeys were required to choose between two object-like stimuli, which differed either only in shape or in shape and color. For each choice, they were required to switch from their previously chosen object-goal to a different one. After they reached a performance level of over 90% correct on the O-NMTG task, the monkeys were tested for rule transfer on a spatial version of the task (S-NMTG). To receive a reward, the monkeys had to switch from their previously chosen location to a different one. In both the O-NMTG and S-NMTG tasks, there were four potential choices, presented in pairs from trial-to-trial. We found that both monkeys transferred successfully the NMTG rule within the first testing session, showing effective transfer of the learned rule between two cognitive domains.

Separable sustained and selective attention factors are apparent in 5-year-old children

In adults and older children, evidence consistent with relative separation between selective and sustained attention, superimposed upon generally positive inter-test correlations, has been reported. Here we examine whether this pattern is detectable in 5-year-old children from the healthy population. A new test battery (TEA-Ch^J) was adapted from measures previously used with adults and older children and administered to 172 5-year-olds. Test-retest reliability was assessed in 60 children. Ninety-eight percent of the children managed to complete all measures. Discrimination of visual and auditory stimuli were good. In a factor analysis, the two TEA-Ch^J selective attention tasks (one visual, one auditory) loaded onto a common factor and diverged from the two sustained attention tasks (one auditory, one motor), which shared a common loading on the second factor. This pattern, which suggests that the tests are indeed sensitive to underlying attentional capacities, was supported by the relationships between the TEA-Ch^J factors and Test of Everyday Attention for Children subtests in the older children in the sample. It is possible to gain convincing performance-based estimates of attention at the age of 5 with the results reflecting a similar factor structure to that obtained in older children and adults. The results are discussed in light of contemporary models of attention function. Given the potential advantages of early intervention for attention difficulties, the findings are of clinical as well as theoretical interest.

The what, where and how of auditory-object perception

The fundamental perceptual unit in hearing is the 'auditory object'. Similar to visual objects, auditory objects are the computational result of the auditory system's capacity to detect, extract, segregate and group spectrotemporal regularities in the acoustic environment; the multitude of acoustic stimuli around us together form the auditory scene. However, unlike the visual scene, resolving the component objects within the auditory scene crucially depends on their temporal structure. Neural correlates of auditory objects are found throughout the auditory system. However, neural responses do not become correlated with a listener's perceptual reports until the level of the cortex. The roles of different neural structures and the contribution of different cognitive states to the perception of auditory objects are not yet fully understood.