Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting

To investigate the nature of plasticity in the adult visual system, perceptual learning was measured in a peripheral orientation discrimination task with systematically varying amounts of external (environmental) noise. The signal contrasts required to achieve threshold were reduced by a factor or two or more after training at all levels of external noise. The strong quantitative regularities revealed by this novel paradigm ruled out changes in multiplicative internal noise, changes in transducer nonlinearites, and simple attentional tradeoffs. Instead, the regularities specify the mechanisms of perceptual learning at the behavioral level as a combination of external noise exclusion and stimulus enhancement via additive internal noise reduction. The findings also constrain the neural architecture of perceptual learning. Plasticity in the weights between basic visual channels and decision is sufficient to account for perceptual learning without requiring the retuning of visual mechanisms.     

Evaluation of the aortic root by MRI: insights from patients with homozygous familial hypercholesterolemia

Hepatitis C chronically infects approximately 1.5% of Americans and is the most common clinical problem facing hepatologists. Since the virus was initially described in 1989, development of an effective therapy has been challenging. Although several different therapeutic agents have been used, no therapy has been shown to reliably eradicate the virus. Interferon-alpha, a cytokine with immunostimulatory and anti-viral properties, has become the therapy of choice for patients with chronic hepatitis C infection. Trials assessing the efficacy of interferon-alpha have characterized host and viral factors predictive of responses to treatment. A thorough understanding of these predictive factors is requisite to providing cost-effective therapeutic decisions for the patient with chronic hepatitis C infection.     

Antibody- and cell-mediated immune responses of Actinobacillus pleuropneumoniae-infected and bacterin-vaccinated pigs

The number involved in and the rate of migration of donor leucocytes into the following recipient organs (spleen, thymus, bone marrow, lung and mesenteric lymph nodes) were measured in two rat models of orthotopic liver transplantation (OLT) using donor-specific MHC class I antibodies. The first OLT model is one that does not require immunosuppression in order to achieve tolerance and involved the transplantation of DA (MHC haplotype, RT1a) livers into PVG (RT1c) recipients. The second model was one that required a 7-day (10 mg/kg) treatment with cyclosporin A (CsA) to achieve tolerance and used DA donors into Lewis (RT1(1)) recipients. Recipient organs were biopsied on days 3, 20 and 87 following OLT and donor leucocyte migration was quantified by immunohistochemistry and computer densitometry of immunoblots of detergent-solublized tissues in order to resolve both membrane-bound and soluble donor MHC class I antigen. In a separate experiment, spleen biopsies were taken following OLT on days 3 and 15 from the naturally tolerizing OLT model (DA into PVG), treated with and without CsA for 7 days and compared with the (DA into Lewis) model. The initial rate of leucocyte migration between days 3 and 21 following OLT was found to be the most rapid into the spleen, followed by the bone marrow and mesenteric lymph nodes in the naturally tolerant (DA into PVG) model when compared with the (DA into Lewis) model. The number of donor leucocytes in the spleen and mesenteric lymph nodes in both models was, however, approximately the same by 87 days. No real difference in the rate of leucocyte migration was seen in the thymus or the lung for both transplant models over the time course assayed. CsA was found to lower the rate of donor leucocyte migration only over the period it was administered. The rate of donor leucocyte migration into the spleen was still much lower 15 days after OLT in the (DA into Lewis) model compared with the (DA into PVG) model treated with and without CsA. Thus the differences in the rate of donor leucocyte migration into the spleen, bone marrow and mesenteric lymph nodes immediately following OLT may offer an explanation as to why the (DA into PVG) combination is able to accept a transplanted liver without immunosuppressive therapy.     

The cement mantle in the Exeter impaction allografting technique. A cause for concern

The postoperative radiographs of 35 patients who underwent impaction allografting of the proximal femur were reviewed. Of Gruen zones that could be clearly visualized, 39.9% contained areas where cement was absent. Even when an adequate mantle was present, cement voids were commonly seen. These cement mantle deficiencies were confirmed in a series of cadaveric impaction allografting procedures. They appear to be a consequence, at least in part, of an inadequate differential between trial and actual component sizes. Additionally, 4 patients were identified with significant component migration secondary to radiographically visible cement mantle fractures within the first 6 months of surgery. It is concluded that the surgical technique requires modification to ensure a more consistent cement mantle and clinical result.     

Intermodality, retrospective image registration in the thorax

The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.     

Filtration of diaspirin crosslinked hemoglobin into lung and soft tissue lymph

Diaspirin crosslinked hemoglobin (DCHb) is a new blood substitute manufactured from human blood. To evaluate its microvascular filtration properties, we infused DCLHb into unanesthetized sheep (10%, 20 ml/kg) and measured the flow and composition of lung and soft tissue lymph. For comparison, we also infused human serum albumin (HSA; 10%, 20 ml/kg). DCLHb raised systemic and pulmonary arterial pressures from baseline values of 83 +/- 7 and 13 +/- 2 mm Hg, respectively, to peak values of 113 +/- 9 and 26 +/- 3 mm Hg (p < 0.05 versus baseline). These increases were significantly greater than those associated with HSA, which raised systemic and pulmonary arterial pressures from baseline values of 86 +/- 4 and 13 +/- 2 mm Hg, respectively, to peak values of 97 +/- 3 and 21 +/- 7 mm Hg (p <= 0.05 versus baseline and versus DCLHb). These differences reflect the known pressor properties of DCLHb. Accordingly, DCLHb raised lung and soft tissue lymph flows to peak values of 12.2 +/- 3.8 and 1.6 +/- 0.7 ml/30 min, respectively, while HSA raised lung and soft tissue lymph flows to peak values of 7.5 +/- 4.8 and 4.6 +/- 1.9 ml/30 min, respectively (p <= 0.05 versus DCLHb). The half-times of DCLHb equilibration from plasma into lung and soft tissue lymph of 1. 0 +/- 0.3 and 2.1 +/- 1.1 h, respectively, were significantly faster than HSA equilibration half-times of 3.1 +/- 0.2 and 3.8 +/- 0.9 h. Filtration differences between DCLHb and HSA appear to be due to the pressor properties DCLHb.