Dissociating activity in the lateral intraparietal area from value using a visual foraging task

We make decisions about where to look approximately three times per second in normal viewing. It has been suggested that eye movements may be guided by activity in the lateral intraparietal area (LIP), which is thought to represent the relative value of objects in space. However, it is not clear how values for saccade goal selection are prioritized while free-viewing in a cluttered visual environment. To address this question, we compared the neural responses of LIP neurons in two subjects with their saccadic behavior and three estimates of stimulus value. These measures were extracted from the subjects' performance in a visual foraging task, in which we parametrically controlled the number of objects on the screen. We found that the firing rates of LIP neurons did not correlate well with the animals' behavior or any of our estimated measures of value. However, if the LIP activity was further normalized, it became highly correlated with the animals' decisions. These data suggest that LIP activity does not represent value in complex environments, but that the value can easily be extracted with one further step of processing. We propose that activity in LIP represents attentional priority and that the downstream normalization of this activity is an essential process in guiding action.     

A Mirror in the Mind: A Case of Visual Allaesthesia in Homonymous Hemianopia

We report the case of a 61-year-old female patient with intracranial bleeding in left parietal and parieto-temporal regions and a history of epilepsy and migraine. MR images showed lesions of the optic radiation, but primary visual cortical areas were intact. Perimetric testing revealed an incomplete right hemianopia. The patient claimed that visual percepts from her intact field were projected as “mirror images” into the hemianopic field. The illusory images were weak and sometimes difficult to detect, but focusing spatial attention on the “mirror” image increased its saliency. Drawings the patient made of her pseudo-hallucinations revealed that the illusions were lateral transpositions instead of mirror images of real objects. The illusions were tilted in clockwise direction and were never colored, although color discrimination was unimpaired in the patient's left hemifield. We quantified the characteristics of the pseudohallucinations in several experiments: The patient was asked to adjust the position, rotation angle, and size of a white test card in her blind field so that it corresponded with the illusory projection of a card of standard size and position that was presented in the intact field. The test card was compressed in horizontal size by 20% and positioned 17° visual angle to the right of the standard, shifted 1.5° upward or downward, and rotated in clockwise direction by 22.6° on average. Large objects in the intact field were projected incompletely into the blind area. Our patient's symptoms are similar to those reported in earlier case studies of visual allaesthesia. We hypothesize that the “mirror image” is induced by sparse input from contralesional V1 via the corpus callosum upstream of the lesion site and a lack of inhibition or hyperexcitability of ipsilesional early visual areas after deafferentation. The rotation of the illusions may be induced by the parietal lesions causing faulty co-ordinate computations, e.g., an inability to integrate visual and otholitic input.     

Site-Dependent Effects of tDCS Uncover Dissociations in the Communication Network Underlying the Processing of Visual Search

BackgroundThe right posterior parietal cortex (rPPC) and the right frontal eye field (rFEF) form part of a network of brain areas involved in orienting spatial attention. Previous studies using transcranial magnetic stimulation (TMS) have demonstrated that both areas are critically involved in the processing of conjunction visual search tasks, since stimulation of these sites disrupts performance.ObjectiveThis study investigated the effects of long term neuronal modulation to rPPC and rFEF using transcranial direct current stimulation (tDCS) with the aim of uncovering sharing of these resources in the processing of conjunction visual search tasks.MethodsParticipants completed four blocks of conjunction search trials over the course of 45 min. Following the first block they received 15 min of either cathodal or anodal stimulation to rPPC or rFEF, or sham stimulation.ResultsA significant interaction between block and stimulation condition was found, indicating that tDCS caused different effects according to the site (rPPC or rFEF) and type of stimulation (cathodal, anodal, or sham). Practice resulted in a significant reduction in reaction time across the four blocks in all conditions except when cathodal tDCS was applied to rPPC.ConclusionsThe effects of cathodal tDCS over rPPC are subtler than those seen with TMS, and no effect of tDCS was evident at rFEF. This suggests that rFEF has a more transient role than rPPC in the processing of conjunction visual search and is robust to longer-term methods of neuro-disruption. Our results may be explained within the framework of functional connectivity between these, and other, areas.     

The Associations between Visual Attention and Facial Expression Identification in Patients with Schizophrenia

Objective

Visual search is an important attention process that precedes the information processing. Visual search also mediates the relationship between cognition function (attention) and social cognition (such as facial expression identification). However, the association between visual attention and social cognition in patients with schizophrenia remains unknown. The purposes of this study were to examine the differences in visual search performance and facial expression identification between patients with schizophrenia and normal controls, and to explore the relationship between visual search performance and facial expression identification in patients with schizophrenia.

Methods

Fourteen patients with schizophrenia (mean age=46.36±6.74) and 15 normal controls (mean age=40.87±9.33) participated this study. The visual search task, including feature search and conjunction search, and Japanese and Caucasian Facial Expression of Emotion were administered.

Results

Patients with schizophrenia had worse visual search performance both in feature search and conjunction search than normal controls, as well as had worse facial expression identification, especially in surprised and sadness. In addition, there were negative associations between visual search performance and facial expression identification in patients with schizophrenia, especially in surprised and sadness. However, this phenomenon was not showed in normal controls.

Conclusion

Patients with schizophrenia who had visual search deficits had the impairment on facial expression identification. Increasing ability of visual search and facial expression identification may improve their social function and interpersonal relationship.     

Assessment of spatial neglect using computerised feature and conjunction visual search tasks

The purpose of this study was to assess the diagnostic sensitivity of tasks employing feature and conjunction visual searches in stroke patients with unilateral spatial neglect (USN).

Seventy-two stroke patients (right/left hemispheric damage with/without USN) and 39 healthy controls participated in the study. Hit rate and reaction time measures of feature and conjunction searches were tested using a newly developed computerised programme for the assessment of visual spatial attention (VISSTA). In addition, subjects received a set of diagnostic paper-and-pencil tests, and were also assessed for the impact of neglect on activities of daily living. Results indicated that the computerised test clearly differentiated between stroke patients and healthy controls, and between the different patient groups. USN patients showed significant contralesional disadvantage in both feature and conjunction visual search tasks. It is proposed that computerised assessment of visual search capacity is a useful and sensitive adjunct to standard paper-and-pencil tests of USN, with the advantage of testing responses based on attention shifts under a time constraint. The learning effects that limit the usefulness of paper-and-pencil tests in longitudinal studies are less likely to affect a computerised test, making it more suitable for monitoring treatment-induced or natural recovery by way of repeated testing.     

Representational demands modulate involvement of perirhinal cortex in face processing

The classic view holds that the medial temporal lobes (MTL) are dedicated to declarative memory functioning. Recent evidence, however, suggests that perirhinal cortex (PrC), a structure within the anterior MTL, may also play a role in perceptual discriminations when representations of complex conjunctions of features, or of gestalt‐characteristics of objects must be generated. Interestingly, neuroimaging and electrophysiological recordings in nonhuman primates have also revealed a face patch in the anterior collateral sulcus with preferential responses to face stimuli in various task contexts. In the present fMRI study, we investigated the representational demands that influence PrC involvement in different types of judgments on human faces. Holding stimulus complexity constant, we independently manipulated the nature of the task and the orientation of the stimuli presented (through face inversion). Aspects of right PrC showed increased responses in a forced‐choice recognition‐memory and a perceptual‐oddity task, as compared to a feature‐search task that was included to probe visual detection of an isolated face feature. Effects of stimulus orientation in right PrC were observed when the recognition‐memory condition for upright faces was compared with all other experimental conditions, including recognition‐memory for inverted faces‐a result that can be related to past work on the role of PrC in object unitization. Notably, both effects in right PrC paralleled activity patterns in broader networks of regions that also included the right fusiform gyrus and the amygdala, regions frequently implicated in face processing in prior research. As such, the current findings do not support the view that reference to a prior study episode clearly distinguishes the role of PrC from that of more posterior ventral visual pathway regions. They add to a growing body of evidence suggesting that the functional role of specific MTL structures may be best understood in terms of the representations that are required by the task and the stimuli at hand. © 2013 Wiley Periodicals, Inc.     

Online information for parents caring for their premature baby at home: A focus group study and systematic web search

Background

Online resources are a source of information for parents of premature babies when their baby is discharged from hospital.

Objectives

To explore what topics parents deemed important after returning home from hospital with their premature baby and to evaluate the quality of existing websites that provide information for parents post‐discharge.

Methods

In stage 1, 23 parents living in Northern Ireland participated in three focus groups and shared their information and support needs following the discharge of their infant(s). In stage 2, a World Wide Web (WWW) search was conducted using Google, Yahoo and Bing search engines. Websites meeting pre‐specified inclusion criteria were reviewed using two website assessment tools and by calculating a readability score. Website content was compared to the topics identified by parents in the focus groups.

Results

Five overarching topics were identified across the three focus groups: life at home after neonatal care, taking care of our family, taking care of our premature baby, baby's growth and development and help with getting support and advice. Twenty‐nine sites were identified that met the systematic web search inclusion criteria. Fifteen (52%) covered all five topics identified by parents to some extent and 9 (31%) provided current, accurate and relevant information based on the assessment criteria.

Conclusion

Parents reported the need for information and support post‐discharge from hospital. This was not always available to them, and relevant online resources were of varying quality. Listening to parents needs and preferences can facilitate the development of high‐quality, evidence‐based, parent‐centred resources.     

元数据研究在医学数据资源共享中的作用

目的在医学数据资源共享中,通过对元数据的研究对异构医学数据资源进行检索与发现.方法研究元数据的定义与特征,制定元数据标准、然后建立目录服务系统进行数据检索服务.结果建立了基于元数据的目录服务体系,实现了数据发现服务.结论元数据方法的研究是对异构数据进行检索与发现的有效方法,也是实现医学数据资源共享的重要途径.     

Isolation,synthesis and characterization of ω-TRTX-Cc1a,a novel tarantula venom peptide that selectively targets L-type CaV channels

Spider venoms are replete with peptidic ion channel modulators, often with novel subtype selectivity, making them a rich source of pharmacological tools and drug leads. In a search for subtype-selective blockers of voltage-gated calcium (Ca_V) channels, we isolated and characterized a novel 39-residue peptide, ω-TRTX-Cc1a (Cc1a), from the venom of the tarantula Citharischius crawshayi (now Pelinobius muticus). Cc1a is 67% identical to the spider toxin ω-TRTX-Hg1a, an inhibitor of Ca_V2.3 channels. We assembled Cc1a using a combination of Boc solid-phase peptide synthesis and native chemical ligation. Oxidative folding yielded two stable, slowly interconverting isomers. Cc1a preferentially inhibited Ba²⁺ currents (I_Ba) mediated by L-type (Ca_V1.2 and Ca_V1.3) Ca_V channels heterologously expressed in Xenopus oocytes, with half-maximal inhibitory concentration (IC₅₀) values of 825 nM and 2.24 μM, respectively. In rat dorsal root ganglion neurons, Cc1a inhibited I_Ba mediated by high voltage-activated Ca_V channels but did not affect low voltage-activated T-type Ca_V channels. Cc1a exhibited weak activity at Na_V1.5 and Na_V1.7 voltage-gated sodium (Na_V) channels stably expressed in mammalian HEK or CHO cells, respectively. Experiments with modified Cc1a peptides, truncated at the N-terminus (ΔG1–E5) or C-terminus (ΔW35–V39), demonstrated that the N- and C-termini are important for voltage-gated ion channel modulation. We conclude that Cc1a represents a novel pharmacological tool for probing the structure and function of L-type Ca_V channels.