Flexible, capacity-limited activity of posterior parietal cortex in perceptual as well as visual short-term memory tasks

It has recently been shown, using functional magnetic resonance imaging with a change detection paradigm, that activity in posterior parietal cortex (PPC) correlates with the limited number of objects held in visual short-term memory (VSTM). We replicate this finding and extend it to tasks that use similar stimuli, but without explicit memory requirements. As well as a perceptual task used previously (detecting an item at fixation), 2 additional tasks were designed to increase attentional demands across space (searching for a red item anywhere in the array) and across both space and time (detecting a staggered offset after prolonged viewing of the array). During the VSTM task, a capacity-limited set-size effect was seen in PPC as well as occipital and frontal regions. However, the PPC showed similar activity during 2 of the tasks not requiring VSTM. These findings cannot easily be explained by behavioral performance measures or memory demands alone, suggesting a role of the PPC in processing a limited number of discrete object representations, whether in the current perceptual scene or working memory. The differential influence of item load across perceptual tasks is consistent with task requirements affecting the form of these representations.     

How does an fMRI voxel sample the neuronal activity pattern: Compact-kernel or complex spatiotemporal filter?

Recent studies suggested that fMRI voxel patterns can convey information represented in columnar-scale neuronal population codes, even when spatial resolution is insufficient to directly image the patterns of columnar selectivity (Kamitani and Tong, 2005; Haynes and Rees, 2005). Sensitivity to subvoxel-scale pattern information, or “fMRI hyperacuity,” would greatly enhance the power of fMRI when combined with pattern information analysis techniques (Kriegeskorte and Bandettini, 2007). An individual voxel might weakly reflect columnar-level information if the columns within its boundaries constituted a slightly unbalanced sample of columnar selectivities (Kamitani and Tong, 2005), providing a possible mechanism for fMRI hyperacuity. However, Op de Beeck (2009) suggests that a coarse-scale neuronal organization rather than fMRI hyperacuity may explain the presence of the information in the fMRI patterns. Here we argue (a) that the present evidence does not rule out fMRI hyperacuity, (b) that the mechanism originally suggested for fMRI hyperacuity (biased sampling by averaging within each voxel's boundaries; Kamitani and Tong, 2005) will only produce very weak sensitivity to fine-grained pattern information, and (c) that an alternative mechanism (voxel as complex spatiotemporal filter) is physiologically more accurate and promises stronger sensitivity to fine-grained pattern information: We know that each voxel samples the neuronal activity pattern through a unique fine-grained structure of venous vessels that supply its blood oxygen level-dependent signal. At the simplest level, the drainage domain of a venous vessel may sample the neuronal pattern with a selectivity bias (Gardner, 2009; Shmuel et al., 2009). Beyond biased drainage domains, we illustrate with a simple simulation how temporal properties of the hemodynamics (e.g., the speed of the blood in the capillary bed) can shape spatial properties of a voxel's filter (e.g., how finely structured it is). This suggests that a voxel, together with its signal-supplying vasculature, may best be thought of as a complex spatiotemporal filter. Such a filter may well have greater sensitivity to high spatial frequencies than the Gaussian or averaging-box kernels typically invoked to characterize voxel sampling (compact kernels, both of which would act like anti-aliasing filters that minimize such sensitivity). Importantly, the complex-spatiotemporal-filter hypothesis of fMRI hyperacuity can account for the observed robustness to slight shifts of the voxel grid caused by head motion: Because the fine-grained components of the filter are vascular, they will remain in a constant relationship to the neuronal patterns sampled as the voxel grid is slightly shifted.     

Spontaneous mandibular regeneration: another option for mandibular reconstruction in children?

Treatment for conditions of the mandible may require resection of the affected segment, and this may need reconstruction. There are case reports of spontaneous regeneration of segments of excised mandibles that resulted in reduced or no need for reconstruction, and we present four such cases. The age at presentation ranged from 6 to 12 years. In all cases the periosteum was preserved during resection. All patients showed evidence of spontaneous regeneration, both clinically and radiographically, between 3 and 5 months after resection. The planned delayed reconstruction meant that these patients either did not need any bony reconstruction, or needed less than had originally been anticipated. Such regeneration is mostly reported in children, and is thought to be the result of an intact periosteal layer. In patients having planned mandibular resections, where the periosteum is preserved, some spontaneous regeneration should be anticipated and final reconstruction delayed until this is complete.     

Reliability evaluation of inter-eminence line,Akagi and Dalury lines for intraoperative tibial rotation: An osteology-based study

Background

This large osteology study examined the reliability, reproducibility and correlation between previously described tibial tray rotation alignment lines (including Akagi and Dalury lines). In addition, it described a novel inter-eminence line utilising the tibial plateau inter-condylar eminences as a landmark.

Evaluating Affordable Cranial Ultrasonography in East African Neonatal Intensive Care Units

Neuroimaging is a valuable diagnostic tool for the early detection of neonatal brain injury, but equipment and radiologic staff are expensive and unavailable to most hospitals in developing countries. We evaluated an affordable, portable ultrasound machine as a quantitative and qualitative diagnostic tool and to establish whether a novice sonographer could effectively operate the equipment and obtain clinically important information. Cranial ultrasonography was performed on term healthy, pre-term and term asphyxiated neonates in Rwandan and Kenyan hospitals. To evaluate the detection of ventriculomegaly and compression injuries, we measured the size of the lateral ventricles and corpus callosum. The images were also assessed for the presence of other cerebral abnormalities. Measurements were reliable across images, and cases of clinically relevant ventriculomegaly were detected. A novice sonographer had good-to-excellent agreement with an expert. This study demonstrates that affordable equipment and cranial ultrasound protocols can be used in low-resource settings to assess the newborn brain.     

Pro‐B cells propagated in stromal cell‐free cultures reconstitute functional B‐cell compartments in immunodeficient mice

Up to now long‐term in vitro growth of pro‐B cells was thought to require stromal cells. However, here we show that fetal liver (FL) and bone marrow (BM) derived pro‐B cells can be propagated long‐term in stromal cell‐free cultures supplemented with IL‐7, stem cell factor and FLT3 ligand. Within a week, most cells expressed surface CD19, CD79A, λ5, and VpreB antigens and had rearranged immunoglobulin D‐J heavy chain genes. Both FL and BM pro‐B cells reconstituted the B‐cell compartments of immuno‐incompetent Rag2‐deficient mice, with FL pro‐B cells generating follicular, marginal zone (MZB) and B1a B cells, and BM pro‐B cells giving rise mainly to MZB cells. Reconstituted Rag2‐deficient mice generated significant levels of IgM and IgG antibodies to a type II T‐independent antigen; mice reconstituted with FL pro‐B cells generated surprisingly high IgG₁ titers. Finally, we show for the first time that mice reconstituted with mixtures of pro‐B and pro‐T cells propagated in stromal cell‐free in vitro cultures mounted a T‐cell‐dependent antibody response. This novel stromal cell‐free culture system facilitates our understanding of B‐cell development and might be applied clinically.     

Decision making and set shifting impairments are associated with distinct symptom dimensions in obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is clinically heterogeneous. The authors examined how specific OCD symptom dimensions were related to neuropsychological functions using multiple regression analyses. A total of 39 OCD patients and 40 controls completed the Iowa Gambling Task (IGT; A. Bechara, A. R. Damasio, H. Damasio, & S. W. Anderson, 1994), which is a test of decision making, and the Wisconsin Card Sorting Test (R. K. Heaton, 1981), which is a test of set shifting. OCD patients and controls showed comparable decision making. However, patients with prominent hoarding symptoms showed impaired decision making on the IGT as well as reduced skin conductance responses. OCD patients had poorer set shifting abilities than controls, and symmetry/ordering symptoms were negatively associated with set shifting. These results help explain previous inconsistent findings in neuropsychological research in OCD and support recent neuroimaging data showing dissociable neural mechanisms involved in mediating the different OCD symptom dimensions.     

Lifetime Substance Use and HIV Sexual Risk Behaviors Predict Treatment Response to Contingency Management Among Homeless,Substance-Dependent MSM

Abstract

Homeless, substance-dependent men who have sex with men (MSM) continue to suffer health disparities, including high rates of HIV. One-hundred and thirty one homeless, substance- dependent MSM were randomized into a contingency management (CM) intervention to increase substance abstinence and health-promoting behaviors. Participants were recruited from a community-based, health education/risk reduction HIV prevention program and the research activities were also conducted at the community site. Secondary analyses were conducted to identify and characterize treatment responders (defined as participants in a contingency management intervention who scored at or above the median on three primary outcomes). Treatment responders were more likely to be Caucasian/White (p < .05), report fewer years of lifetime methamphetamine, cocaine, and polysubstance use (p ≤ .05), and report more recent sexual partners and high-risk sexual behaviors than nonresponders (p < .05). The application of evidence-based interventions continues to be a public health priority, especially in the effort to implement effective interventions for use in community settings. The identification of both treatment responders and nonresponders is important for intervention development tailored to specific populations, both in service programs and research studies, to optimize outcomes among highly impacted populations.