Bottom-up Visual Integration in the Medial Parietal Lobe

A tripartite view of the posterior cingulate cortex

The posterior cingulate cortex (PCC) is one of the least understood regions of the cerebral cortex. By contrast, the anterior cingulate cortex has been the subject of intensive investigation in humans and model animal systems, leading to detailed behavioural and computational theoretical accounts of its function. The time is right for similar progress to be made in the PCC given its unique anatomical and physiological properties and demonstrably important contributions to higher cognitive functions and brain diseases. Here, we describe recent progress in understanding the PCC, with a focus on convergent findings across species and techniques that lay a foundation for establishing a formal theoretical account of its functions. Based on this converging evidence, we propose that the broader PCC region contains three major subregions - the dorsal PCC, ventral PCC and retrosplenial cortex - that respectively support the integration of executive, mnemonic and spatial processing systems. This tripartite subregional view reconciles inconsistencies in prior unitary theories of PCC function and offers promising new avenues for progress.

Right hemi-alexia

While pure alexia was long considered a disconnection syndrome, it may also be a selective visual word agnosia due to damage to the visual word form area. Disconnection is still the likely explanation of hemi-alexias, though, particularly when splenial lesions damage inter-hemispheric projections and cause left hemi-alexia. An intra-hemispheric disconnection causing right hemi-alexia is theoretically possible but seems very rare, with only a single report that has been challenged on the grounds of inadequate perimetry. We describe the case of PH, who had a severe reading deficit in her right hemifield. Detailed perimetry showed only a small relative hemi-scotoma along the horizontal meridian, while word reading was impaired over a much larger expanse of her right hemifield, in which object recognition was spared. Reading, lexical decisions, and perceptual discrimination of words were impaired in the right hemifield, and this extended to letters and numbers, with a trend to an effect on the perception of an unfamiliar script, namely Korean. On magnetic resonance imaging she had a large left lateral occipital meningioma with vasogenic edema of occipital white matter tracts. Functional magnetic resonance imaging showed that the visual word form area was located just anterior to the mass. Her perceptual abnormalities resolved after resection of the tumor. We conclude that right hemi-alexia exists and is most likely due to intra-hemispheric disconnection of occipital input to the visual word form area.

Feasibility of a Home-Based Tablet App for Dexterity Training in Multiple Sclerosis: Usability Study

BACKGROUND

Persons with multiple sclerosis (MS) often experience dexterous difficulties during the performance of activities of daily living, such as fastening buttons, handling coins, or writing, therefore impacting their health-related quality of life. Mobile health (mHealth) solutions, such as tablet apps, may be used to train impaired dexterous skills. The feasibility of a tablet app-based dexterity home-based intervention in MS (TAD-MS) has not been explored yet in persons with MS.

OBJECTIVE

The aim of this pilot study was to evaluate the feasibility and usability of home-based dexterity training with a tablet app in both persons with MS and healthy subjects.

METHODS

A total of 9 persons with MS, aged 35-71 years, with an Expanded Disability Status Scale score between 2 and 7.5, performed the TAD-MS for 4 weeks, five times a week, with each training session lasting approximately 30 minutes. Participants' impaired dexterity was measured by the Nine-Hole Peg Test. A total of 10 age-matched healthy subjects also tested and rated the usability of the app. Outcome measures were the adherence rate as well as usability measured by the System Usability Scale and a Custom User Engagement Questionnaire (CUEQ).

RESULTS

High feasibility of the tablet app-based dexterity training program was shown by a 97% adherence rate to the training protocol (ie, mean 19.4/20 sessions completed, SD 0.8). High system usability scores (ie, mean 85.39%, SD 11.67) and overall high scores given in the CUEQ (ie, mean 8.2/10, SD 1.4) further point to high usability of the app. Neither demographic variables nor dexterity levels affected the use of the app.

CONCLUSIONS

This pilot study is the first to demonstrate high feasibility and usability of a new tablet app-based dexterity home-based training program among both persons with MS and healthy individuals. Whether this kind of training improves dexterity will need to be evaluated in a randomized controlled trial.

Building Memory Representations for Exemplar-Based Judgment: A Role for Ventral Precuneus

The brain networks underlying human multiple-cue judgment, the judgment of a continuous criterion based on multiple cues, have been examined in a few recent studies, and the ventral precuneus has been found to be a key region. Specifically, activation differences in ventral precuneus (as measured with functional magnetic resonance imaging, fMRI) has been linked to an exemplar-based judgment process, where judgments are based on memory for previous similar cases. Ventral precuneus is implicated in various episodic memory processes, notably such that increased activity during learning in this region as well as in the ventromedial prefrontal cortex (vmPFC) and the medial temporal lobes (MTL) have been linked to retrieval success. The present study used fMRI during a multiple-cue judgment task to gain novel neurocognitive evidence informative for the link between learning-related activity changes in ventral precuneus and exemplar-based judgment. Participants (N = 27) spontaneously learned to make judgments during fMRI, in a multiple-cue judgment task specifically designed to induce exemplar-based processing. Contrasting brain activity during late learning to early learning revealed higher activity in ventral precuneus, the bilateral MTL, and the vmPFC. Activity in the ventral precuneus and the vmPFC was found to parametrically increase between each judgment event, and activity levels in the ventral precuneus predicted performance after learning. These results are interpreted such that the ventral precuneus supports the aspects of exemplar-based processes that are related to episodic memory, tentatively by building, storing, and being implicated in retrieving memory representations for judgment.

Gestalt Perception in Children With Visual Impairments: Item-Specific Performance and Looking Behavior

Visual closure is the ability to visualize a complete whole when an incomplete picture is presented. The aim of the present study was to investigate the Kaufman Gestalt closure task in children with cerebral and ocular visual impairments. Looking behavior was assessed by an eye tracker system to quantify the number and duration of fixations. We found that children with visual impairments due to cerebral damage show weaker Gestalt perception and had different looking patterns than children with ocular or without visual impairments. Children with brain damage performed significantly worse on the animate items than the group without brain damage.

The posterior cingulate cortex: Insights from structure and function

The posterior cingulate cortex (PCC) (Brodmann areas 23/31) is one of the least well-understood regions of the cortex. The PCC has very high levels of metabolic consumption, and network analyses of functional and structural data suggest it is a core hub in the human connectome; however, contemporary neuroscience lacks a clear account of its functional significance. Consequently, many studies over the last decade have focused on understanding the role this region plays in cognition, particularly given its apparent tendency to deactivate during demanding external tasks. Consistent with the cytoarchitecture, recent work, leveraging complex analytical approaches, highlight that the connections the PCC forms with other regions are heterogeneous, going beyond a single network, while recent studies of its function highlight a role in a wide range of complex forms of cognition including memory, navigation, and narrative comprehension. This constellation of observations highlights a role for PCC in a set of cognitive processes that are supported by internal representations but may lack a common type of representational content. Together, these structural and functional studies contribute to an emerging view of the PCC as contributing to how cognition unfolds rather than what it is focused on.

Lacrimal Caruncle Nevus with Papilloma

Purpose

The aim of this article is to report a case of lacrimal caruncle nevus with papilloma.

Methods

This is a case report of a 39-year-old female with a progressively enlarging pigmented lesion on the left lacrimal caruncle. She had been aware of a raised whitish wart on the top of this pigmented lesion for several months before her initial visit. Slit lamp examination revealed a papillomatous lesion over a well-circumscribed, pigmented lesion on the left lacrimal caruncle.

Results

The histopathological examination of the excised tumor disclosed 2 characteristic findings, which include nests of nevus cells within the dermis and papillomatous structures which had fibrovascular cores overlying squamous cell epithelia with variable levels of acanthosis. The findings were consistent with an intradermal nevus and a papilloma arising from the conjunctival epithelium of the nevus.

Conclusion

This is the first case report of a lacrimal caruncle nevus with papilloma. The clinical history and pathological findings of this case underscore the fact that an intradermal nevus primarily occurred on the lacrimal caruncle, after which a papilloma arose from the epithelium of the nevus as a consequence of human papillomavirus autoinoculation.

Neural Correlates of Drug-Related Attentional Bias in Heroin Dependence

The attention of drug-dependent persons tends to be captured by stimuli associated with drug consumption. This involuntary cognitive process is considered as attentional bias (AB). AB has been hypothesized to have causal effects on drug abuse and drug relapse, but its underlying neural mechanisms are still unclear. This study investigated the neural basis of AB in abstinent heroin addicts (AHAs), combining event-related potential (ERP) analysis and source localization techniques. Electroencephalography data were collected in 21 abstinent heroin addicts and 24 age- and gender-matched healthy controls (HCs) during a dot-probe task. In the task, a pair of drug-related image and neutral image was presented randomly in left and right side of the cross fixation, followed by a dot probe replacing one of the images. Behaviorally, AHAs had shorter reaction times (RTs) for the congruent condition compared to the incongruent condition, whereas this was not the case in the HCs. This finding demonstrated the presence of AB towards drug cues in AHAs. Furthermore, the image-evoked ERPs in AHAs had significant shorter P1 latency compared to HCs, as well as larger N1, N2, and P2 amplitude, suggesting that drug-related stimuli might capture attention early and overall require more attentional resources in AHAs. The target-related P3 had significantly shorter latency and lower amplitude in the congruent than incongruent condition in AHAs compared to HCs. Moreover, source localization of ERP components revealed increased activity for AHAs as compared to HCs in the dorsal posterior cingulate cortex (dPCC), superior parietal lobule and inferior frontal gyrus (IFG) for image-elicited responses, and decreased activity in the occipital and the medial parietal lobes for target-elicited responses. Overall, the results of our study confirmed that AHAs may exhibit AB in drug-related contexts, and suggested that the bias might be related to an abnormal neural activity, both in early and late attention processing stages.

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.

Direct cortical stimulation of human posteromedial cortex

BACKGROUND

The posteromedial cortex (PMC) is a collective term for an anatomically heterogeneous area of the brain constituting a core node of the human default mode network (DMN), which is engaged during internally focused subjective cognition such as autobiographical memory.

METHODS

We explored the effects of causal perturbations of PMC with direct electric brain stimulation (EBS) during presurgical epilepsy monitoring with intracranial EEG electrodes.

RESULTS

Data were collected from 885 stimulations in 25 patients implanted with intracranial electrodes across the PMC. While EBS of regions immediately dorsal or ventral to the PMC reliably produced somatomotor or visual effects, respectively, we found no observable behavioral or subjectively reported effects when sites within the boundaries of PMC were electrically perturbed. In each patient, null effects of PMC stimulation were observed for sites in which intracranial recordings had clearly demonstrated electrophysiologic responses during autobiographical recall.

CONCLUSIONS

Direct electric modulation of the human PMC produced null effects when standard functional mapping methods were used. More sophisticated stimulation paradigms (e.g., EBS during experimental cognitive tests) will be required for testing the causal contribution of PMC to human cognition and subjective experience. Nonetheless, our findings suggest that some extant theories of PMC and DMN contribution to human awareness and subjective conscious states require cautious re-examination.