Prefrontal cortex hemispheric specialization for categorical and coordinate visual spatial memory

Excessive left anterior hippocampal and caudate activation in schizophrenia underlie cognitive underperformance in a virtual navigation task

We used a virtual navigation paradigm in a city environment to assess neuroanatomical correlates of cognitive deficits in schizophrenia spectrum disorders (SSD). We studied a total of N = 36 subjects: 18 with SSD and 18 matched unaffected controls. Participants completed 10 rapid, single-trial navigation tasks within the virtual city while undergoing functional magnetic resonance imaging (fMRI). All trials tested ability to find different targets seen earlier, during the passive viewing of a path around different city blocks. SSD patients had difficulty finding previously-encountered targets, were less likely to find novel shortcuts to targets, and more likely to attempt retracing of the path observed during passive viewing. Based on a priori region-of-interest analyses, SSD participants had hyperactivation of the left hippocampus when passively viewing turns, hyperactivation of the left caudate when finding targets, and hypoactivation of a focal area of the dorsolateral prefrontal cortex when targets were initially shown during passive viewing. We propose that these brain-behaviour relations may bias or reinforce stimulus-response navigation approaches in SSD and underlie impaired performance when allocentric spatial memory is required, such as when forming efficient shortcuts. This pattern may extend to more general cognitive impairments in SSD that could be used to design remediation strategies.

Higher prefrontal activity based on short-term neurofeedback training can prevent working memory decline in acute stroke

This study aimed to clarify whether short-term neurofeedback training during the acute stroke phase led to prefrontal activity self-regulation, providing positive efficacy to working memory. A total of 30 patients with acute stroke performed functional near-infrared spectroscopy-based neurofeedback training for a day to increase their prefrontal activity. A randomized, Sham-controlled, double-blind study protocol was used comparing working memory ability before and after neurofeedback training. Working memory was evaluated using a target-searching task requiring spatial information retention. A decline in spatial working memory performance post-intervention was prevented in patients who displayed a higher task-related right prefrontal activity during neurofeedback training compared with the baseline. Neurofeedback training efficacy was not associated with the patient's clinical background such as Fugl-Meyer Assessment score and time since stroke. These findings demonstrated that even short-term neurofeedback training can strengthen prefrontal activity and help maintain cognitive ability in acute stroke patients, at least immediately after training. However, further studies investigating the influence of individual patient clinical background, especially cognitive impairment, on neurofeedback training is needed. Current findings provide an encouraging option for clinicians to design neurorehabilitation programs, including neurofeedback protocols, for acute stroke patients.

Dissociation of categorical and coordinate spatial relations on dynamic network organization states

Humans can flexibly represent both categorical and coordinate spatial relations. Previous research has mainly focused on hemisphere lateralization in representing these two types of spatial relations, but little is known about how distinct network organization states support representations of the two. Here we used dynamic resting-state functional connectivity (FC) to explore this question. To do this, we separated a meta-identified navigation network into a ventral and two other subnetworks. We revealed a Weak State and a Strong State within the ventral subnetwork and a Negative State and a Positive State between the ventral and other subnetworks. Further, we found the Weak State (i.e., weak but positive FC) within the ventral subnetwork was related to the ability of categorical relation recognition, suggesting that the representation of categorical spatial relations was related to weak integration among focal regions in the navigation network. In contrast, the Negative State (i.e., negative FC) between the ventral and other subnetworks was associated with the ability of coordinate relation processing, suggesting that the representation of coordinate spatial relations may require competitive interactions among widely distributed regions. In sum, our study provides the first empirical evidence revealing different focal and distributed organizations of the navigation network in representing different types of spatial information.

Two-point discrimination assessment of the upper extremities of healthy young Turkish individuals

Objectives

This study aims to measure the two-point discrimination (TPD) values of the upper extremities of healthy young Turkish individuals.

Patients and methods

Between March 2016 and June 2016, a total of 60 healthy students (31 males, 29 females; mean age: 22.0±1.7 years; range, 19 to 27 years) were included. Eleven grand upper limb parts which take innervation from the brachial plexus were measured with an esthesiometer.

Results

The values at the dominant sides were statistically significantly greater than the non-dominant sides at those areas: upper lateral arm (p=0.001), lower lateral arm (p=0.001), mid-posterior arm (p=0.001), mid-lateral forearm (p=0.001), mid-posterior forearm (p=0.012), skin over the first dorsal interossei muscle (p=0.031), and palmar surface of distal phalanx of the thumb (p=0.045). Both dominant and non-dominant lower lateral arm TPD measurement results increased in males compared to females, indicating a statistically significant difference (p=0.005 and p=0.011, respectively). Also, dominant and non-dominant mid-posterior arm measurement scores were found to statistically significantly increase in males compared to females (p=0.019 and p=0.040, respectively).

Conclusion

Our study results show that laterality, with lower values on the non-dominant side, but not the sex, has an effect on TPD. The findings of this study may be useful in establishing the normative data for TPD in the upper extremity parts of healthy young Turkish individuals.

Individual Sensory Modality Dominance as an Influential Factor in the Prefrontal Neurofeedback Training for Spatial Processing: A Functional Near-Infrared Spectroscopy Study

Neurofeedback is a neuromodulation technique used to improve brain function by self-regulating brain activity. However, the efficacy of neurofeedback training varies widely between individuals, and some participants fail to self-regulate brain activity. To overcome intersubject variation in neurofeedback training efficacy, it is critical to identify the factors that influence this type of neuromodulation. In this study, we considered that individual differences in cognitive ability may influence neurofeedback training efficacy and aimed to clarify the effect of individual working memory (WM) abilities, as characterized by sensory modality dominance, on neurofeedback training efficacy in healthy young adults. In particular, we focused on the abilities of individuals to retain internal (tactile or somatosensory) or external (visual) body information in their WM. Forty participants performed functional near-infrared spectroscopy-based neurofeedback training aimed at producing efficient and lower-level activity in the bilateral dorsolateral prefrontal cortex and frontopolar cortex. We carried out a randomized, sham-controlled, double-blind study that compared WM ability before and after neurofeedback training. Individual WM ability was quantified using a target searching task that required the participants to retain spatial information presented as vibrotactile or visual stimuli. Participants who received feedback information based on their own prefrontal activity showed gradually decreasing activity in the right prefrontal area during the neurofeedback training and demonstrated superior WM ability during the target searching task with vibrotactile stimuli compared with the participants who performed dummy neurofeedback training. In comparison, left prefrontal activity was not influenced by the neurofeedback training. Furthermore, the efficacy of neurofeedback training (i.e., lower right prefrontal activity and better searching task performance) was higher in participants who exhibited tactile dominance rather than visual dominance in their WM. These findings indicate that sensory modality dominance in WM may be an influential neurophysiological factor in determining the efficacy of neurofeedback training. These results may be useful in the development of neurofeedback training protocols tailored to individual needs.

Two-point discrimination assessment of the lower extremities of healthy young Turkish individuals

OBJECTIVES

To investigate the normative two-point discrimination (TPD) values of the lower extremities of healthy young Turkish individuals.

PATIENTS AND METHODS

Fifty-five healthy, young adults were recruited in this prospective study. Ten lower extremity parts were tested with esthesiometer: proximal thigh, midlateral thigh, midmedial thigh, midposterior thigh, proximal lateral leg, distal lateral leg, medial leg, the tip of great toe, skin over 1-2 metatarsal interspace, skin over 5th metatars at both dominant and non-dominant sides.

RESULTS

There were 27 (49.1%) female and 28 (50.9%) male participants with a mean age of 22.06 ± 1.76 years. The reference values of the TPD of the lower extremities were between 42.4 ± 5.4 mm and 4.0 ± 1.3 mm by females and between 42.6 ± 6.4 mm and 4.4 ± 2.4 mm by males. Test values in the combined group of men and women were statistically greater at the dominant sides than the non-dominant sides at the following areas: proximal lateral leg (p = 0.01), distal lateral leg (p = 0.046), medial leg (p = 0.001), tip of great toe (p = 0.02), skin over 1-2 metatarsal interspace (p = 0.010), skin over 5th metatars (p = 0.002). There was no statistical difference in the test scores of men and women in any of the measured areas, with additional evaluation of both the dominant and the non-dominant sides (p > 0.05).

CONCLUSION

The results of the present study demonstrated that TPD ability varied in different skin areas within the same individual. We found that laterality, though with lower scores on the non-dominant side in some lower extremity parts, but not the gender had an effect on TPD.

Short-Term Audiovisual Spatial Training Enhances Electrophysiological Correlates of Auditory Selective Spatial Attention

Audiovisual cross-modal training has been proposed as a tool to improve human spatial hearing. Here, we investigated training-induced modulations of event-related potential (ERP) components that have been associated with processes of auditory selective spatial attention when a speaker of interest has to be localized in a multiple speaker ("cocktail-party") scenario. Forty-five healthy participants were tested, including younger (19-29 years; n = 21) and older (66-76 years; n = 24) age groups. Three conditions of short-term training (duration 15 min) were compared, requiring localization of non-speech targets under "cocktail-party" conditions with either (1) synchronous presentation of co-localized auditory-target and visual stimuli (audiovisual-congruency training) or (2) immediate visual feedback on correct or incorrect localization responses (visual-feedback training), or (3) presentation of spatially incongruent auditory-target and visual stimuli presented at random positions with synchronous onset (control condition). Prior to and after training, participants were tested in an auditory spatial attention task (15 min), requiring localization of a predefined spoken word out of three distractor words, which were presented with synchronous stimulus onset from different positions. Peaks of ERP components were analyzed with a specific focus on the N2, which is known to be a correlate of auditory selective spatial attention. N2 amplitudes were significantly larger after audiovisual-congruency training compared with the remaining training conditions for younger, but not older, participants. Also, at the time of the N2, distributed source analysis revealed an enhancement of neural activity induced by audiovisual-congruency training in dorsolateral prefrontal cortex (Brodmann area 9) for the younger group. These findings suggest that cross-modal processes induced by audiovisual-congruency training under "cocktail-party" conditions at a short time scale resulted in an enhancement of correlates of auditory selective spatial attention.

Cortical Structural Connectivity Alterations and Potential Pathogenesis in Mid-Stage Sporadic Parkinson's Disease

Many clinical symptoms of sporadic Parkinson's disease (sPD) cannot be completely explained by a lesion of the simple typical extrapyramidal circuit between the striatum and substantia nigra. Therefore, this study aimed to explore the new potential damaged pathogenesis of other brain regions associated with the multiple and complex clinical symptoms of sPD through magnetic resonance imaging (MRI). A total of 65 patients with mid-stage sPD and 35 healthy controls were recruited in this study. Cortical structural connectivity was assessed by seed-based analysis using the vertex-based morphology of MRI. Seven different clusters in the brain regions of cortical thickness thinning derived from the regression analysis using brain size as covariates between sPD and control were selected as seeds. Results showed that the significant alteration of cortical structural connectivity mainly occurred in the bilateral frontal orbital, opercular, triangular, precentral, rectus, supplementary-motor, temporal pole, angular, Heschl, parietal, supramarginal, postcentral, precuneus, occipital, lingual, cuneus, Rolandic-opercular, cingulum, parahippocampal, calcarine, olfactory, insula, paracentral-lobule, and fusiform regions at the mid-stage of sPD. These findings suggested that the extensive alteration of cortical structural connectivity is one of possible pathogenesis resulting in the multiple and complex clinical symptoms in sPD.

A Functional Near-Infrared Spectroscopy Examination of the Neural Correlates of Cognitive Shifting in Dimensional Change Card Sort Task

This study aims to examine the neural correlates of cognitive shifting during the Dimensional Change Card Sort Task (DCCS) task with functional near-infrared spectroscopy. Altogether 49 children completed the DCCS tasks, and 25 children (Mage = 68.66, SD = 5.3) passing all items were classified into the Switch group. Twenty children (M age = 62.05, SD = 8.13) committing more than one perseverative errors were grouped into the Perseverate group. The Switch group had Brodmann Area (BA) 9 and 10 activated in the pre-switch period and BA 6, 9, 10, 40, and 44 in the post-switch period. In contrast, the Perseverate group had BA 9 and 10 activated in the pre-switch period and BA 8, 9, 10 in the post-switch period. The general linear model results afford strong support to the "V-shape curve" hypothesis by identifying a significant decrease-increase cycle in BA 9 and 44, the neural correlations of cognitive shifting.

Cortical thickness and functional connectivity changes in Chinese chess experts

Background

Repeated practice to acquire expertise could result in the structural and functional changes in relevant brain circuits as a result of long-term potentiation, neurogenesis, glial genesis, and remodeling.

Purpose

The goal of this study is to use surface-based morphology (SBM) to study cortical thickness differences in Chinese chess experts and novices, and to use regions of cortical thickness differences as seeds to guide a resting state connectivity analysis of the same population.

Methods

A raw public dataset from Huaxi MR Research Center consisting of 29 Chinese chess experts and 29 novices was used in this study, with both T1-weighted and resting state functional MRI. Surface based morphometry was performed on the T1 images with the Freesurfur pipeline, with a vertex significance threshold of p<0.05 and a cluster false discovery rate of α < 0.05. Regions with significant differences were used in a seed-based comparison of resting state functional connectivity carried out with Statistical Parameter Mapping (SPM) and the Connectivity Toolbox (CONN). Regions of connectivity differences within groups were computed with a voxel significance threshold of p<0.05 and a cluster false discovery rate of α < 0.01.

Results

Ten regions of the cortex of Chinese chess experts were found to be thinner than chess novices, including regions involved in visual processing, attention, working and episodic memory, and mental imagery, as well as several regions in the prefrontal cortex. There were no regions where experts’ cortices were thicker than novices. Three of the thinner regions exhibited increased functional connectivity to distant brain regions in chess experts.

Conclusions

Brain regions that are structurally affected by chess training are associated with processes that would likely have a high utility in chess expertise. Using a hierarchical control model, we hypothesize that the functional changes linked with some of these structural changes are related to the professionally trained chess players’ ability to perceive and use contextual information, visuospatial perception, and outcome prediction in the domain of chess, all contributing to their exceptional performance.

Gene expression meta-analysis reveals the up-regulation of CREB1 and CREBBP in Brodmann Area 10 of patients with schizophrenia

Cognitive impairments characterize individuals with schizophrenia, and are correlated to the patients' functional outcome. The transcription factor Cyclic AMP-responsive element-binding protein-1 (CREB1) is involved in learning and memory processes. CREB1 and both CREB-binding protein (CREBBP) and E1A Binding Protein P300 (EP300), co-activators of CREB1, have been associated with schizophrenia. We performed a systematic meta-analysis of CREB1, CREBBP and EP300 differential expression in post mortem Brodmann Area 10 (BA10) samples of patients with schizophrenia vs. healthy controls, following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Two microarray datasets met the inclusion criteria (overall 41 schizophrenia samples and 38 controls were analyzed). We detect up-regulation of CREB1 and CREBBP in BA10 samples of patients with schizophrenia, while EP300 wasn't differentially expressed. The integration of two independent datasets and the positive correlation between the expression patterns of CREB1 and CREBBP increase the validity of the results. The up-regulation of CREB1 and its co-activator CREBBP might relate to BA10 altered activation that has been shown in schizophrenia. As BA10 was shown to be involved in the cognitive impairments associated with schizophrenia, this suggests involvement of CREB1 and CREBBP in the cognitive symptoms that characterize the disease.

Distinct bilateral prefrontal activity patterns associated with the qualitative aspect of working memory characterized by individual sensory modality dominance

In addition to quantitative individual differences in working memory (WM) capacity, qualitative aspects, such as enhanced sensory modality (modality dominance), can characterize individual WM ability. This study aimed to examine the neurological basis underlying the individual modality dominance component of WM using functional near-infrared spectroscopy (fNIRS). To quantify the degree of individual WM modality dominance, 24 participants were required to find seven hidden targets and hold their spatial location and appearance order with vibrotactile or visual stimuli aids. In this searching task, eight participants demonstrated higher performance with the tactile condition (tactile-dominant) whereas sixteen demonstrated visual dominance. We then measured prefrontal activity by fNIRS during memorization of visual stimulus numbers while finger tapping as a cognitive-motor dual-task. Individual modality dominance significantly correlated with bilateral frontopolar and dorsolateral prefrontal activity changes over repeated fNIRS sessions. In particular, individuals with stronger visual dominance showed marked decreases in prefrontal area activity. These results suggest that distinct processing patterns in the prefrontal cortex reflect an individual’s qualitative WM characteristics. Considering the individual modality dominance underlying the prefrontal areas could enhance cognitive or motor performance, possibly by optimizing cognitive resources.

Functional Near-Infrared Spectroscopy Indicates That Asymmetric Right Hemispheric Activation in Mental Rotation of a Jigsaw Puzzle Decreases With Task Difficulty

Mental rotation (MR) is a cognitive skill whose neural dynamics are still a matter of debate as previous neuroimaging studies have produced controversial results. In order to investigate the underlying neurophysiology of MR, hemodynamic responses from the prefrontal cortex of 14 healthy subjects were recorded with functional near-infrared spectroscopy (fNIRS) during a novel MR task that had three categorical difficulty levels. Hemodynamic activity strength (HAS) parameter, which reflects the ratio of brain activation during the task to the baseline activation level, was used to assess the prefrontal cortex activation localization and strength. Behavioral data indicated that the MR requiring conditions are more difficult than the condition that did not require MR. The right dorsolateral prefrontal cortex (DLPFC) was found to be active in all conditions and to be the dominant region in the easiest task while more complex tasks showed widespread bilateral prefrontal activation. A significant increase in left DLPFC activation was observed with increasing task difficulty. Significantly higher right DLPFC activation was observed when the incongruent trials were contrasted against the congruent trials, which implied the possibility of a robust error or conflict-monitoring process during the incongruent trials. Our results showed that the right DLPFC is a core region for the processing of MR tasks regardless of the task complexity and that the left DLPFC is involved to a greater extent with increasing task complexity, which is consistent with the previous neuroimaging literature.

Brain Metabolism but Not Gray Matter Volume Underlies the Presence of Language Function in the Minimally Conscious State (MCS): MCS+ Versus MCS- Neuroimaging Differences

Background. The minimally conscious state (MCS) is subcategorized into MCS- and MCS+, depending on the absence or presence, respectively, of high-level behavioral responses such as command-following. Objective. We aim to investigate the functional and structural neuroanatomy underlying the presence of these responses in MCS- and MCS+ patients. Methods. In this cross-sectional retrospective study, chronic MCS patients were diagnosed using repeated Coma Recovery Scale-Revised assessments. Fluorodeoxyglucose-positron emission tomography data were acquired on 57 patients (16 MCS-; 41 MCS+) and magnetic resonance imaging with voxel-based morphometry analysis was performed on 66 patients (17 MCS-; 49 MCS+). Brain glucose metabolism and gray matter integrity were compared between patient groups and control groups. A metabolic functional connectivity analysis testing the hypothesis of preserved language network in MCS+ compared with MCS- was also done. Results. Patients in MCS+ presented higher metabolism mainly in the left middle temporal cortex, known to be important for semantic processing, compared with the MCS- group. The left angular gyrus was also functionally disconnected from the left prefrontal cortex in MCS- compared with MCS+ group. No significant differences were found in gray matter volume between patient groups. Conclusions. The clinical subcategorization of MCS is supported by differences in brain metabolism but not in gray matter structure, suggesting that brain function in the language network is the main support for recovery of command-following, intelligible verbalization and/or intentional communication in the MCS. Better characterizing the neural correlates of residual cognitive abilities of MCS patients contributes to reduce their misdiagnosis and to adapt therapeutic approaches.

Age-related differences in brain activations during spatial memory formation in a well-learned virtual Morris water maze (vMWM) task

The current study applied a rodent-based virtual Morris water maze (vMWM) protocol to an investigation of differences in search performance and brain activations between young and older male human adults. All participants completed in-lab practice and testing before performing the task in the fMRI scanner. Behavioral performance during fMRI scanning - measured in terms of corrected cumulative proximity (CCProx) to the goal - showed that a subgroup of older good performers attained comparable levels of search accuracy to the young while another subgroup of older poor performers exhibited consistently lower levels of search accuracy than both older good performers and the young. With regard to brain activations, young adults exhibited greater activations in the cerebellum and cuneus than all older adults, as well as older poor performers. Older good performers exhibited higher activation than older poor performers in the orbitofrontal cortex (BA 10/11), as well as in the cuneus and cerebellum. Brain-behavior correlations further showed that activations in regions involved in visuomotor control (cerebellum, lingual gyrus) and egocentric spatial processing (premotor cortex, precuneus) correlated positively with search accuracy (i.e., closer proximity to goal) in all participants. Notably, activations in the anterior hippocampus correlated positively with search accuracy (CCProx inversed) in the young but not in the old. Taken together, these findings implicated the orbitofrontal cortex and the cerebellum as playing crucial roles in executive and visuospatial processing in older adults, supporting the proposal of an age-related compensatory shift in spatial memory functions away from the hippocampus toward the prefrontal cortex.

Cortical Functional Domains Show Distinctive Oscillatory Dynamic in Bimanual and Mirror Visual Feedback Tasks

It is believed that Mirror Visual Feedback (MVF) increases the interlimb transfer but the exact mechanism is still a matter of debate. The aim of this study was to compare between a bimanual task (BM) and a MVF task, within functionally rather than geometrically defined cortical domains. Measure Projection Analysis (MPA) approach was applied to compare the dynamic oscillatory activity (event-related synchronization/desynchronization ERS/ERD) between and within domains. EEG was recorded in 14 healthy participants performing a BM and an MVF task with the right hand. The MPA was applied on fitted equivalent current dipoles based on independent components to define domains containing functionally similar areas. The measure of intradomain similarity was a "signed mutual information," a parameter based on the coherence. Domain analysis was performed for joint tasks (BM and MVF) and for each task separately. MVF created 9 functional domains while MB task had only 4 functionally distinctive domains, two over the left hemispheres and two bilateraly. For all domains identified for BM task alone, similar domains could be identified in MVF and joint tasks analysis. In addition MVF had domains related to motor planning on the right hemisphere and to self-recognition of action. For joint tasks analysis, seven domains were identified, with similar functions for the left and the right hand with exception of a domain covering BA32 (self-recognition of action) of the left hand only. In joint task domain analysis, the ERD/ERS showed a larger difference between domains than between tasks. All domains which involved the sensory cortex had a visible beta ERS at the onset of movement, and post movement beta ERS. The frequency of ERD varied between domains. Largest difference between tasks existed in domains responsible for the awareness of action. In conclusion, functionally distinctive domains have different ERD/ERS patterns, similar for both tasks. MVF activates contralateral hemisphere in similar manner to BM movements, while at the same time also activating the ipsilateral hemisphere. Significance: Following stroke cortical activation and interhemispheric inhibition from the contralesional side is reduced. MVF creates stronger ipsilateral activity than BM, which is highly relevant of neurorehabilitation of movements.

Prefrontal activity predicts individual differences in optimal attentional strategy for preventing motor performance decline: a functional near-infrared spectroscopy study

Directing attention to movement outcomes (external focus; EF), not body movements (internal focus; IF), is a better cognitive strategy for motor performance. However, EF is not effective in some healthy individuals or stroke patients. We aimed to identify the neurological basis reflecting the individual optimal attentional strategy using functional near-infrared spectroscopy. Sixty-four participants (23 healthy young, 23 healthy elderly, and 18 acute stroke) performed a reaching movement task under IF and EF conditions. Of these, 13 healthy young participants, 11 healthy elderly participants, and 6 stroke patients showed better motor performance under EF conditions (EF-dominant), whereas the others showed IF-dominance. We then measured prefrontal activity during rhythmic hand movements under both attentional conditions. IF-dominant participants showed significantly higher left prefrontal activity than EF-dominant participants under IF condition. In addition, receiver operating characteristic analysis supported that the higher activity in the left frontopolar and dorsolateral prefrontal cortices could detect IF-dominance as an individual's optimal attentional strategy for preventing motor performance decline. Taken together, these results suggest that prefrontal activity during motor tasks reflects an individual's ability to process internal body information, thereby conferring IF-dominance. These findings could be applied for the development of individually optimized rehabilitation programs.

Shared and Distinct Neural Bases of Large- and Small-Scale Spatial Ability: A Coordinate-Based Activation Likelihood Estimation Meta-Analysis

Background: Spatial ability is vital for human survival and development. However, the relationship between large-scale and small-scale spatial ability remains poorly understood. To address this issue from a novel perspective, we performed an activation likelihood estimation (ALE) meta-analysis of neuroimaging studies to determine the shared and distinct neural bases of these two forms of spatial ability. Methods: We searched Web of Science, PubMed, PsycINFO, and Google Scholar for studies regarding "spatial ability" published within the last 20 years (January 1988 through June 2018). A final total of 103 studies (Table 1) involving 2,085 participants (male = 1,116) and 2,586 foci were incorporated into the meta-analysis. Results: Large-scale spatial ability was associated with activation in the limbic lobe, posterior lobe, occipital lobe, parietal lobe, right anterior lobe, frontal lobe, and right sub-lobar area. Small-scale spatial ability was associated with activation in the parietal lobe, occipital lobe, frontal lobe, right posterior lobe, and left sub-lobar area. Furthermore, conjunction analysis revealed overlapping regions in the sub-gyrus, right superior frontal gyrus, right superior parietal lobule, right middle occipital gyrus, right superior occipital gyrus, left inferior occipital gyrus, and precuneus. The contrast analysis demonstrated that the parahippocampal gyrus, left lingual gyrus, culmen, right middle temporal gyrus, left declive, left superior occipital gyrus, and right lentiform nucleus were more strongly activated during large-scale spatial tasks. In contrast, the precuneus, right inferior frontal gyrus, right precentral gyrus, left inferior parietal lobule, left supramarginal gyrus, left superior parietal lobule, right inferior occipital gyrus, and left middle frontal gyrus were more strongly activated during small-scale spatial tasks. Our results further indicated that there is no absolute difference in the cognitive strategies associated with the two forms of spatial ability (egocentric/allocentric). Conclusion: The results of the present study verify and expand upon the theoretical model of spatial ability proposed by Hegarty et al. Our analysis revealed a shared neural basis between large- and small-scale spatial abilities, as well as specific yet independent neural bases underlying each. Based on these findings, we proposed a more comprehensive version of the behavioral model.

Functional Magnetic Resonance Imaging and Oculomotor Dysfunction in Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is a significant cause of disability, especially when symptoms become chronic. This chronicity is often linked to oculomotor dysfunction (OMD). To our knowledge, this is the first prospective study to localize aberrations in brain function between mTBI cohorts, by comparing patients with mTBI with OMD with an mTBI control group without OMD, using task and resting-state functional magnetic resonance imaging (fMRI). Ten subjects with mTBI who had OMD (OMD group) were compared with nine subjects with mTBI who had no findings of OMD (control group). These groups were determined by a developmental optometrist using objective testing for OMD. The (convergence) task fMRI data demonstrated significantly decreased brain activity, measured as decreases in the blood oxygen level dependent (BOLD) signal, in the OMD group compared with the control group in three brain regions: the left posterior lingual gyrus, the bilateral anterior lingual gyrus and cuneus, and the parahippocampal gyrus. When doing a seed-based resting state fMRI analysis in the lingual/parahippocampal region, a large cluster covering the left middle frontal gyrus and the dorsolateral pre-frontal cortex (Brodmann areas 9 and 10), with decreased functional correlation in the OMD group, was identified. Together these observations provide evidence for neural networks of interactions involving the control of eye movement for visual processing, reading comprehension, spatial localization and navigation, and spatial working memory that appear to be decreased in mTBI patients with OMD compared with mTBI patients without OMD. The clinical symptomatology associated with post-traumatic OMD correlates well with these MRI findings.

Modality-Independent Coding of Scene Categories in Prefrontal Cortex

Natural environments convey information through multiple sensory modalities, all of which contribute to people's percepts. Although it has been shown that visual or auditory content of scene categories can be decoded from brain activity, it remains unclear how humans represent scene information beyond a specific sensory modality domain. To address this question, we investigated how categories of scene images and sounds are represented in several brain regions. A group of healthy human subjects (both sexes) participated in the present study, where their brain activity was measured with fMRI while viewing images or listening to sounds of different real-world environments. We found that both visual and auditory scene categories can be decoded not only from modality-specific areas, but also from several brain regions in the temporal, parietal, and prefrontal cortex (PFC). Intriguingly, only in the PFC, but not in any other regions, categories of scene images and sounds appear to be represented in similar activation patterns, suggesting that scene representations in PFC are modality-independent. Furthermore, the error patterns of neural decoders indicate that category-specific neural activity patterns in the middle and superior frontal gyri are tightly linked to categorization behavior. Our findings demonstrate that complex scene information is represented at an abstract level in the PFC, regardless of the sensory modality of the stimulus.SIGNIFICANCE STATEMENT Our experience in daily life includes multiple sensory inputs, such as images, sounds, or scents from the surroundings, which all contribute to our understanding of the environment. Here, for the first time, we investigated where and how in the brain information about the natural environment from multiple senses is merged to form modality-independent representations of scene categories. We show direct decoding of scene categories across sensory modalities from patterns of neural activity in the prefrontal cortex (PFC). We also conclusively tie these neural representations to human categorization behavior by comparing patterns of errors between a neural decoder and behavior. Our findings suggest that PFC is a central hub for integrating sensory information and computing modality-independent representations of scene categories.

Abnormal Intrinsic Functional Hubs in Severe Male Obstructive Sleep Apnea: Evidence from a Voxel-Wise Degree Centrality Analysis

Purpose

Obstructive sleep apnea (OSA) has been associated with changes in brain structure and regional function in certain brain areas. However, the functional features of network organization in the whole brain remain largely uncertain. The purpose of this study was to identify the OSA-related spatial centrality distribution of the whole brain functional network and to investigate the potential altered intrinsic functional hubs.

Methods

Forty male patients with newly confirmed severe OSA on polysomnography, and well-matched good sleepers, participated in this study. All participants underwent a resting-state functional MRI scan and clinical and cognitive evaluation. Voxel-wise degree centrality (DC) was measured across the whole brain, and group difference in DC was compared. The relationship between the abnormal DC value and clinical variables was assessed using a linear correlation analysis.

Results

Remarkably similar spatial distributions of the functional hubs (high DC) were found in both groups. However, OSA patients exhibited a pattern of significantly reduced regional DC in the left middle occipital gyrus, posterior cingulate cortex, left superior frontal gyrus, and bilateral inferior parietal lobule, and DC was increased in the right orbital frontal cortex, bilateral cerebellum posterior lobes, and bilateral lentiform nucleus, including the putamen, extending to the hippocampus, and the inferior temporal gyrus, which overlapped with the functional hubs. Furthermore, a linear correlation analysis revealed that the DC value in the posterior cingulate cortex and left superior frontal gyrus were positively correlated with Montreal cognitive assessment scores, The DC value in the left middle occipital gyrus and bilateral inferior parietal lobule were negatively correlated with apnea-hypopnea index and arousal index in OSA patients.

Conclusion

Our findings suggest that OSA patients exhibited specific abnormal intrinsic functional hubs including relatively reduced and increased DC. This expands our understanding of the functional characteristics of OSA, which may provide new insights into understanding the dysfunction and pathophysiology of OSA patients.

Bilingualism as a Contributor to Cognitive Reserve? Evidence from Cerebral Glucose Metabolism in Mild Cognitive Impairment and Alzheimer's Disease

OBJECTIVE

Bilingualism is discussed as one factor contributing to "cognitive reserve" (CR), as it enhances executive control functions. To elucidate the underlying cerebral correlates, regional glucose uptake was compared between bilinguals and monolinguals with mild cognitive impairment (MCI) and beginning-stage Alzheimer's disease (AD) by using [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET).

METHODS

Thirty patients (73.2 ± 7.4) diagnosed with MCI or probable AD received physical and neuropsychological examinations, blood tests, and FDG-PET scans. Sixteen patients were classified as lifelong bilinguals, following the criterion of Bialystok et al., and groups were matched for age, sex, and mini mental state examination scores. Analyses were conducted using statistical parametric mapping version 8. The whole brain was used as reference region for intensity normalization and years of education were controlled for.

RESULTS

Bilingual patient groups showed substantially greater impairment of glucose uptake in frontotemporal and parietal regions [including Brodmann areas (BAs) 9, 47, 40, and 21] and in the left cerebellum relative to monolingual patients.

CONCLUSION

Bilingualism is likely to contribute to CR, given that bilingual patients showed more severe brain changes than monolinguals when adjusting for severity of cognitive impairment. The latter did not only comprise BAs relevant to speech and language but also structures typically involved in AD pathology, such as the temporal and the parietal cortices.

Hemispheric lateralization in top-down attention during spatial relation processing: a Granger causal model approach

Magnetoencephalography was recorded during a matching-to-sample plus cueing paradigm, in which participants judged the occurrence of changes in either categorical (CAT) or coordinate (COO) spatial relations. Previously, parietal and frontal lobes were identified as key areas in processing spatial relations and it was shown that each hemisphere was differently involved and modulated by the scope of the attention window (e.g. a large and small cue). In this study, Granger analysis highlighted the patterns of causality among involved brain areas--the direction of information transfer ran from the frontal to the visual cortex in the right hemisphere, whereas it ran in the opposite direction in the left side. Thus, the right frontal area seems to exert top-down influence, supporting the idea that, in this task, top-down signals are selectively related to the right side. Additionally, for CAT change preceded by a small cue, the right frontal gyrus was not involved in the information transfer, indicating a selective specialization of the left hemisphere for this condition. The present findings strengthen the conclusion of the presence of a remarkable hemispheric specialization for spatial relation processing and illustrate the complex interactions between the lateralized parts of the neural network. Moreover, they illustrate how focusing attention over large or small regions of the visual field engages these lateralized networks differently, particularly in the frontal regions of each hemisphere, consistent with the theory that spatial relation judgements require a fronto-parietal network in the left hemisphere for categorical relations and on the right hemisphere for coordinate spatial processing.

Categorical encoding of color in the brain

The areas of the brain that encode color categorically have not yet been reliably identified. Here, we used functional MRI adaptation to identify neuronal populations that represent color categories irrespective of metric differences in color. Two colors were successively presented within a block of trials. The two colors were either from the same or different categories (e.g., "blue 1 and blue 2" or "blue 1 and green 1"), and the size of the hue difference was varied. Participants performed a target detection task unrelated to the difference in color. In the middle frontal gyrus of both hemispheres and to a lesser extent, the cerebellum, blood-oxygen level-dependent response was greater for colors from different categories relative to colors from the same category. Importantly, activation in these regions was not modulated by the size of the hue difference, suggesting that neurons in these regions represent color categorically, regardless of metric color difference. Representational similarity analyses, which investigated the similarity of the pattern of activity across local groups of voxels, identified other regions of the brain (including the visual cortex), which responded to metric but not categorical color differences. Therefore, categorical and metric hue differences appear to be coded in qualitatively different ways and in different brain regions. These findings have implications for the long-standing debate on the origin and nature of color categories, and also further our understanding of how color is processed by the brain.

Dissociable roles of the hippocampus and parietal cortex in processing of coordinate and categorical spatial information

It is generally accepted that spatial relationships and spatial information are critically involved in the formation of cognitive maps. It remains unclear, however, which properties of the world are explicitly encoded and how these properties might contribute to the formation of such maps. It has been proposed that spatial relations are encoded either categorically, such that the relative positions of objects are defined in prepositional terms; or as visual coordinates, such that the precise distances between objects are represented. Emerging evidence from human and animal studies suggests that distinct neural circuits might underlie categorical and coordinate representations of object locations during active spatial navigation. Here we review evidence for the hypothesis that the hippocampal formation is crucial for encoding coordinate information, whereas the parietal cortex is crucial for encoding categorical spatial information. Our short review provides a novel view regarding the functions and potential interactions of these two regions during active spatial navigation.

Visual-spatial working memory performance and temporal gray matter volume predict schizotypal personality disorder group membership

BACKGROUND

Prior work shows individuals with schizotypal personality disorder (SPD) evince temporal lobe volume abnormalities similar to schizophrenia but sparing of prefrontal cortex, which may mitigate psychosis and the severe neurocognitive impairments observed in schizophrenia. This study examined the extent to which frontal-temporal gray matter volume and neurocognitive performance predict: (1) SPD group membership in a demographically-balanced sample of 51 patients and 37 healthy controls; and (2) symptom severity in SPD.

METHODS

Dimensional gray-matter volume (left frontal-temporal regions (Brodmann area (BA) 10, 21, 22)) and neurocognitive performance on key memory tasks (California Verbal Learning Test (CVLT), Dot Test, Paced Auditory Serial Addition Test (PASAT)), all salient to schizophrenia-spectrum disorders were examined in a multi-variable model.

RESULTS

Middle temporal gyrus (BA21) volume and spatial-working memory (Dot Test) performance were significant predictors of SPD group membership likelihood, with poorer working-memory performance indicating increased probability of SPD membership. Combining across regional volumes or cognitive measures resulted in fair-to-good discrimination of group membership, but including neurocognitive and non-collinear regional volume measures together resulted in a receiver-operating-characteristic (ROC) curve with improved diagnostic discrimination. Larger BA10 volume in dorsolateral prefrontal cortex (DLPFC) significantly predicted less symptom severity in SPD.

CONCLUSIONS

These findings suggest that temporal lobe volume and spatial-working memory performance are promising biological/phenotype markers for likelihood of SPD classification, while greater DLPFC volume may serve as a protective factor.

Sex differences in the weighting of metric and categorical information in spatial location memory

According to the Category Adjustment model, remembering a spatial location involves the Bayesian combination of fine-grained and categorical information about that location, with each cue weighted by its relative certainty. However, individuals may differ in terms of their certainty about each cue, resulting in estimates that rely more or less on metric or categorical representations. To date, though, very little research has examined individual differences in the relative weighting of these cues in spatial location memory. Here, we address this gap in the literature. Participants were asked to recall point locations in uniform geometric shapes and in photographs of complex, natural scenes. Error patterns were analyzed for evidence of a sex difference in the relative use of metric and categorical information. As predicted, women placed relatively more emphasis on categorical cues, while men relied more heavily on metric information. Location reproduction tasks showed a similar effect, implying that the sex difference arises early in spatial processing, possibly during encoding.

Mapping gray matter reductions in obstructive sleep apnea: an activation likelihood estimation meta-analysis

STUDY OBJECTIVES

The authors reviewed the literature on the use of voxel-based morphometry (VBM) in obstructive sleep apnea (OSA) magnetic resonance imaging (MRI) studies via the use of a meta-analysis of neuroimaging to identify consistent and specific structural deficits in patients with sleep apnea compared with healthy subjects.

DESIGN

Neuroimaging meta-analysis.

DATA SOURCES

We used PubMed to retrieve articles published between January 2000 and February 2012.

STUDY SELECTION

The authors included all VBM research on patients with OSA and healthy controls. They compared the findings of the studies by using gray matter volume (GMV) or gray matter concentration (GMC) to index differences in gray matter.

DATA EXTRACTION

Stereotactic data were extracted from eight VBM studies of 213 patients with OSA and 195 control subjects.

RESULTS

Regional gray matter reduction in the bilateral parahippocampus and less-convincing right superior frontal and left middle temporal gyri was demonstrated in patients with sleep apnea using an activation likelihood estimation (ALE) procedure to analyze significant differences.

CONCLUSIONS

Significant reductions in gray matter in patients with sleep apnea occurred in the bilateral parahippocampus and less-convincing frontotemporal regions, which may be related to the neurocognitive processing abnormalities that are common among populations of patients with sleep apnea.

Focusing narrowly or broadly attention when judging categorical and coordinate spatial relations: a MEG study

We measured activity in the dorsal system of the human cortex with magnetoencephalography (MEG) during a matching-to-sample plus cueing paradigm, where participants judged the occurrence of changes in either categorical or coordinate spatial relations (e.g., exchanges of left versus right positions or changes in the relative distances) between images of pairs of animals. The attention window was primed in each trial to be either small or large by using cues that immediately preceded the matching image. In this manner, we could assess the modulatory effects of the scope of attention on the activity of the dorsal system of the human cortex during spatial relations processing. The MEG measurements revealed that large spatial cues yielded greater activations and longer peak latencies in the right inferior parietal lobe for coordinate trials, whereas small cues yielded greater activations and longer peak latencies in the left inferior parietal lobe for categorical trials. The activity in the superior parietal lobe, middle frontal gyrus, and visual cortex, was also modulated by the size of the spatial cues and by the type of spatial relation change. The present results support the theory that the lateralization of each kind of spatial processing hinges on differences in the sizes of regions of space attended to by the two hemispheres. In addition, the present findings are inconsistent with the idea of a right-hemispheric dominance for all kinds of challenging spatial tasks, since response times and accuracy rates showed that the categorical spatial relation task was more difficult than the coordinate task and the cortical activations were overall greater in the left hemisphere than in the right hemisphere.

Retinotopic and lateralized processing of spatial frequencies in human visual cortex during scene categorization

Using large natural scenes filtered in spatial frequencies, we aimed to demonstrate that spatial frequency processing could not only be retinotopically mapped but could also be lateralized in both hemispheres. For this purpose, participants performed a categorization task using large black and white photographs of natural scenes (indoors vs. outdoors, with a visual angle of 24° × 18°) filtered in low spatial frequencies (LSF), high spatial frequencies (HSF), and nonfiltered scenes, in block-designed fMRI recording sessions. At the group level, the comparison between the spatial frequency content of scenes revealed first that, compared with HSF, LSF scene categorization elicited activation in the anterior half of the calcarine fissures linked to the peripheral visual field, whereas, compared with LSF, HSF scene categorization elicited activation in the posterior part of the occipital lobes, which are linked to the fovea, according to the retinotopic property of visual areas. At the individual level, functional activations projected on retinotopic maps revealed that LSF processing was mapped in the anterior part of V1, whereas HSF processing was mapped in the posterior and ventral part of V2, V3, and V4. Moreover, at the group level, direct interhemispheric comparisons performed on the same fMRI data highlighted a right-sided occipito-temporal predominance for LSF processing and a left-sided temporal cortex predominance for HSF processing, in accordance with hemispheric specialization theories. By using suitable method of analysis on the same data, our results enabled us to demonstrate for the first time that spatial frequencies processing is mapped retinotopically and lateralized in human occipital cortex.

Visual perceptual strengths and weaknesses in adults with intellectual disabilities compared with a birth year-matched norm

BACKGROUND

The ventral and dorsal streams are considered to be the brain substrates of vision for perception and action, respectively. Using the Developmental Test of Visual Perception (DTVP), the current study examined whether visual perceptual strengths and weaknesses in adults with intellectual disabilities (ID) were attributable to the dichotomy of the visual streams.

METHOD

In study 1, DTVP performance was compared among mild, moderate and severe adult ID groups; study 2 contrasted adult ID groups with and without Down syndrome (DS). To prevent possible contamination by the Flynn effect, participants were matched by birth year with the norm of the DTVP original edition.

RESULTS

Independent of the extent of ID among the three groups in study 1 and the aetiological group difference in study 2, relative strength was found for two DTVP tasks: eye-hand coordination and distinguishing target figures from interference background. Relative weakness was obtained in identifying a figural category. Participants with DS demonstrated exceptional weakness in discerning a target from either mirror-imaged or rotated alternatives, in addition to figural-category detection.

CONCLUSIONS

Visual perceptual strengths and weaknesses in persons with ID were difficult to explain on the basis of two visual streams. An interpretation originating in a different research context (e.g. frontal-lobe dysfunction) appears to be required for explaining visual perceptual weaknesses in persons with ID. For persons with DS, strong frontal-lobe dysfunction with atypical lateralisation might be the pathological determinant of visual perceptual weaknesses.

Age-related changes in right middle frontal gyrus volume correlate with altered episodic retrieval activity

Age-related deficits in episodic retrieval have been associated with volume reductions in the middle frontal gyrus (MFG). However, it remains unclear how this age-related reduction in MFG volume correlates with neural activity during retrieval. To address this, we conducted in vivo volumetry of the frontal cortex in young and older human adults and found more volume loss on the right than on the left MFG with age. We then examined how left and right MFG volume correlated with fMRI activity during successful retrieval of item, spatial context, and temporal context information in both age groups. In young adults, larger right MFG volume was positively correlated with greater activity in a commonly found episodic retrieval network that included bilateral dorsolateral prefrontal cortex (DLPFC) and bilateral inferior parietal cortex. Within this network, left DLPFC and right inferior parietal cortex activity predicted memory performance. In older adults, a positive structure-function association in DLPFC for either left or right MFG/DLPFC was not observed. Instead, right MFG volume was negatively correlated with activity in several regions in older adults, including the parahippocampal cortex (PHC) and anterior cingulate. Less activity in the PHC region predicted better item memory, and less activity in the anterior cingulate predicted better spatial context accuracy in older adults. We conclude that age-related change in the structure-function association in MFG/DLPFC impacts retrieval activity and performance, and those older adults with larger right MFG volume attempt to compensate for this change by modifying activity in other brain regions to help retrieval performance.

Cognitive impairment and EEG background activity in adults with Down's syndrome: a topographic study

OBJECTIVE

Studies correlating electroencephalographic (EEG) data and cognitive performance in Down's syndrome (DS) showed conflicting results. The aims of this study were to investigate the sources of EEG rhythms in adults with DS at three dimensional representation of current source density (CSD) using exact/standard Low Resolution Electromagnetic Tomography (e/sLORETA), and their correlation with cognitive performance.

METHODS

Twenty-five adults with DS underwent a neuropsychological battery and 5 min of resting, eye-closed 29-channel EEG were recorded. After e/sLORETA analysis, data were compared with those from age and gender-matching control subjects as following: absolute and relative power in delta (1-3 Hz), theta (4-7 Hz), alpha1 (8-9 Hz), alpha2 (10-12 Hz), beta1 (13-18 Hz), beta2 (19-21 Hz), beta3 (22-30 Hz); alpha and theta bands adjusted to individual alpha peak frequency (IAF). Current source activities in DS group in regions showing significant differences compared with controls underwent correlation analysis with psychometric scores.

RESULTS

In DS, IAF was shifted to lower frequencies and correlated positively with Wechsler Adult Intelligence Scale and Mini-Mental State examination. Compared with controls, DS showed increased CSD in: theta, alpha-1, and beta1 classical bands and in IAF-adjusted bands, while relative alpha2 was decreased. A negative correlation between cognitive performance and theta/alpha CSD in the right frontal lobe and right posterior cingulate cortex was found. The relative alpha2 correlated positively with cognitive tests.

CONCLUSIONS

Increased CSD in DS, correlating with cognitive performance, for both slow and fast rhythms suggests involving of cortical and subcortical mechanisms. LORETA might be useful for objective measure of cognitive decline in DS.

The what and why of perceptual asymmetries in the visual domain

Perceptual asymmetry is one of the most important characteristics of our visual functioning. We carefully reviewed the scientific literature in order to examine such asymmetries, separating them into two major categories: within-visual field asymmetries and between-visual field asymmetries. We explain these asymmetries in terms of perceptual aspects or tasks, the what of the asymmetries; and in terms of underlying mechanisms, the why of the asymmetries. Tthe within-visual field asymmetries are fundamental to orientation, motion direction, and spatial frequency processing. between-visual field asymmetries have been reported for a wide range of perceptual phenomena. foveal dominance over the periphery, in particular, has been prominent for visual acuity, contrast sensitivity, and colour discrimination. Tthis also holds true for object or face recognition and reading performance. upper-lower visual field asymmetries in favour of the lower have been demonstrated for temporal and contrast sensitivities, visual acuity, spatial resolution, orientation, hue and motion processing. Iin contrast, the upper field advantages have been seen in visual search, apparent size, and object recognition tasks. left-right visual field asymmetries include the left field dominance in spatial (e.g., orientation) processing and the right field dominance in non-spatial (e.g., temporal) processing. left field is also better at low spatial frequency or global and coordinate spatial processing, whereas the right field is better at high spatial frequency or local and categorical spatial processing. All these asymmetries have inborn neural/physiological origins, the primary why, but can be also susceptible to visual experience, the critical why (promotes or blocks the asymmetries by altering neural functions).

Similarities in the patterns of prefrontal cortex activity during spatial and temporal context memory retrieval after equating for task structure and performance

Event-related functional magnetic resonance imaging was used to assess healthy adults while they performed spatial and temporal context memory tasks matched in task structure. After equating task structure between spatial versus temporal context tasks, subjects reported using similar strategies across tasks and we observed no significant differences in accuracy and reaction time performance between tasks. We used three methods of statistical analysis to interrogate similarities and differences in whole-brain activity across retrieval tasks, while focussing on prefrontal cortex (PFC) activations: multivariate partial least squares analysis (PLS), univariate statistical parametric mapping (SPM) and conjunction analysis. The PLS and conjunction analyses indicated that the overall pattern of PFC activity was similar across both temporal and spatial context retrieval tasks; but the SPM results indicated that some of these PFC regions exhibited differences in the degree to which they were engaged between tasks. However, none of these methods identified unique PFC activations specific to mediating spatial and/or temporal context retrieval. These results indicate that, overall, similar patterns of PFC activity were observed during temporal and spatial context memory retrieval once task structure and performance were equated.

Hemispheric asymmetries in categorical perception of orientation in infants and adults

Orientation CP is the faster or more accurate discrimination of two orientations from different categories (e.g., oblique1 and vertical1) compared to two orientations from the same category (e.g., oblique1 and oblique2), even when the degree of difference is equated across conditions. Here, we assess whether there are hemispheric asymmetries in this effect for adults and 5-month-old infants. Experiment 1 identified the location of the vertical-oblique category boundary. Experiment 2, using a visual search task with oriented lines found that adult search was more accurate when the target and distractors were from different orientation categories, compared to targets and distractors of an equivalent physical difference taken from the same category. This effect was stronger for targets lateralized to the left visual field (LVF) than the right visual field (RVF), indicating a right hemisphere (RH) bias in adult orientation CP. Experiment 3, replicated the RH bias using different stimuli and also investigated the impact of visual and verbal interference on the category effect. Experiment 4, using the same visual search task, found that infant search was also faster when the target and distractors were from different orientation categories than the same, yet this category effect was stronger for RVF than LVF lateralized targets, indicating a LH bias in orientation CP at 5 months. These findings are contrasted to equivalent studies on the lateralization of color CP (e.g., Gilbert, Regier, Kay, & Ivry, 2005). The implications for theories on the contribution of the left and right hemispheres of the infant and adult brain to categorical computations are discussed.

Synchronous retinotopic frontal-temporal activity during long-term memory for spatial location

Early visual areas in occipital cortex are known to be retinotopic. Recently, retinotopic maps have been reported in frontal and parietal cortex during spatial attention and working memory. The present event-related potential (ERP) and functional magnetic resonance imaging (fMRI) study determined whether spatial long-term memory was associated with retinotopic activity in frontal and parietal regions, and assessed whether retinotopic activity in these higher level control regions was synchronous with retinotopic activity in lower level visual sensory regions. During encoding, abstract shapes were presented to the left or right of fixation. During retrieval, old and new shapes were presented at fixation and participants classified each shape as old and previously on the "left", old and previously on the "right", or "new". Retinotopic effects were manifested by accurate memory for items previously presented on the left producing activity in the right hemisphere and accurate memory for items previously presented on the right producing activity in the left hemisphere. Retinotopic ERP activity was observed in frontal regions and visual sensory (occipital and temporal) regions. In frontal cortex, retinotopic fMRI activity was localized to the frontal eye fields. There were no significant ERP or fMRI retinotopic memory effects in parietal regions. The present long-term memory retinotopic effects complement previous spatial attention and working memory findings (and suggest retinotopic activity in parietal cortex may require an external peripheral stimulus). Furthermore, ERP cross-correlogram analysis revealed that retinotopic activations in frontal and temporal regions were synchronous, indicating that these regions interact during retrieval of spatial information.

Conscious and nonconscious memory effects are temporally dissociable

Intentional (explicit) retrieval can reactivate sensory cortex, which is widely assumed to reflect conscious processing. In the present study, we used an explicit visual memory event-related potential paradigm to investigate whether such retrieval related sensory activity could be separated into conscious and nonconscious components. During study, abstract shapes were presented in the left or right visual field. During test, old and new shapes were presented centrally and participants classified each shape as "old-left", "old-right", or "new". Conscious activity was isolated by comparing accurate memory for shape and location (old-hits) with forgotten shapes (old-misses), and nonconscious activity was isolated by comparing old-left-misses with old-right-misses and vice versa. Conscious visual sensory activity had a late temporal onset (after 800 ms) while nonconscious visual sensory activity had an early temporal onset (before 800 ms). These results suggest explicit memory related sensory activity reflects both conscious and nonconscious processes that are temporally dissociable.

Relationships among plasma dehydroepiandrosterone and dehydroepiandrosterone sulfate, cortisol, symptoms of dissociation, and objective performance in humans exposed to underwater navigation stress

BACKGROUND

A growing body of research has provided evidence that dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are involved in an organism's response to stress and that it may provide beneficial behavioral and neurotrophic effects.

METHODS

This study investigated plasma DHEA and DHEAS, cortisol, psychological symptoms of dissociation, and military performance in 41 healthy active duty subjects enrolled in the military Combat Diver Qualification Course (CDQC).

RESULTS

Baseline values of DHEA and DHEAS were significantly and positively predictive of superior performance in the underwater navigation exam; in addition, DHEA and DHEAS were significantly and negatively related to stress-induced symptoms of dissociation during performance of the task. Similarly, participants who reported fewer symptoms of dissociation exhibited superior military performance and increased levels of DHEA after the test.

CONCLUSIONS

These data provide prospective, empiric evidence that DHEA and DHEAS are associated with superior stress tolerance, fewer symptoms of dissociation, and superior, objectively assessed, military performance.