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Biomedical subjects

H Volz

Publications and source records attributed to H Volz.

7 recordsLinked to original sources
PubMed2000

Supporting evidence for the model of cognitive dysmetria in schizophrenia--a structural magnetic resonance imaging study using deformation-based morphometry.

The aim of the study was to investigate whether there is any structural evidence for the model of 'cognitive dysmetria' in schizophrenia if an automatic whole-brain analysis method is used. High-resolution magnetic resonance scans were obtained for 75 schizophrenic patients and 75 controls. These data were analysed using the recently developed deformation-based morphometry allowing the assessment of volumetric differences without a priori definition of regions of interest. When compared with controls, we found reduced volumes in patients with schizophrenia in the frontal lobe (gyrus frontalis superior, medius and medialis), the temporal lobe (gyrus temporalis superior and inferior), the thalamus, the left cerebellar hemisphere and the right cerebellar vermis. There was an increase in volume in the right putamen. To date, this is the first structural magnetic resonance imaging study to demonstrate that the three key-elements of the model of cognitive dysmetria--frontal lobe, thalamus, and cerebellum--are reduced in volume in schizophrenic patients. This highlights the importance of this concept for future investigations.

Adult↗
PubMed1999

Decreased frontal activation in schizophrenics during stimulation with the continuous performance test--a functional magnetic resonance imaging study.

The Continuous Performance Test (CPT) has become an essential constituent of the neuropsychological investigation of schizophrenia. Also, a vast number of brain imaging studies, mostly PET investigations, have employed the CPT as a cognitive challenge and established a relative hypofrontality in schizophrenics compared to controls. The aim of the present investigation was to clarify whether this predescribed hypofrontality could also be verified using functional magnetic resonance imaging (fMRI). 20 healthy volunteers and 14 schizophrenics on stable neuroleptic medication were included. Imaging was performed using the CPT-double-T-version and a clinical 1.5 T MRI-scanner with a single slice technique and a T(2)*-weighted gradient-echo-sequence. The schizophrenics exhibited a decreased activation in the right mesial prefrontal cortex, the right cingulate and the left thalamus compared to controls. These results obtained by fMRI are discussed in relation to published findings using PET.

Adult↗
PubMed1997

Three-dimensional caricatures of human heads: distinctiveness and the perception of facial age.

A standard facial-caricaturing algorithm was applied to a three-dimensional representation of human heads. This algorithm sometimes produced heads that appeared 'caricatured'. More commonly, however, exaggerating the distinctive three-dimensional information in a face seemed to produce an increase in the apparent age of the face--both at a local level, by exaggerating small facial creases into wrinkles, and at a more global level via changes that seemed to make the underlying structure of the skull more evident. Concomitantly, de-emphasis of the distinctive three-dimensional information in a face made it appear relatively younger than the veridical and caricatured faces. More formally, face-age judgments made by human observers were ordered according to the level of caricature, with anticaricatures judged younger than veridical faces, and veridical faces judged younger than caricatured faces. These results are discussed in terms of the importance of the nature of the features made more distinct by a caricaturing algorithm and the nature of human representation(s) of faces.

Age Factors↗
PubMed1996

Hyperacuity for spatial localization of contrast-modulated patterns.

The acuity for localizing the position of a grating and other first order patterns which are defined directly by the luminance distribution, is much higher than the resolution for such gratings. This well-described phenomenon usually is referred to as hyperacuity, and is regarded as a cortical function which is not limited by the optics and the sampling properties of the eye. Second order patterns which can be defined by the distribution of local contrast gained some interest because they require more complex processing mechanisms than first order patterns. We investigated how well gratings and bars which are exclusively defined by the variation of the local contrast of static random dot patterns can be localized in space. In this case localization acuity does not reach the precision which is known for first order patterns. However, the localization of contrast-modulated patterns can be almost one order of magnitude better than second order grating resolution, and therefore reaches into the hyperacuity range. In combination with findings for motion-defined or stereo-defined patterns it is concluded that the brain mechanisms responsible for the localization of features in the visual scene have not only access to first order information which is available immediately from the retinal image, but in addition, to second order information which has to be extracted from the retinal intensity distribution by some sort of nonlinear processing.

Adult↗
PubMed1992

Quantitation of soluble HLA class I antigen in human albumin and immunoglobulin preparations for intravenous use by solid-phase immunoassay.

Soluble HLA class I antigens in human plasma preparations possibly play a role in HLA sensitization and modulation of the immune response. We therefore have determined their concentration in albumin and immunoglobulin preparations from several commercial sources and compared these values to the concentration in normal human sera. For this purpose we used a newly developed solid-phase enzyme immunoassay employing rabbit anti-mouse antibody, monomorphic HLA class I monoclonal antibody and a polyclonal enzyme-linked beta 2-microglobulin-specific antiserum. Soluble HLA antigen concentration in 14 albumin batches from 6 manufacturers and in 16 immunoglobulin batches from 11 manufacturers ranged from 0 to 9.6 and from 0 to 20.9 ng/ml. The concentration in normal human sera 1,328 +/- 954 ng/ml (n = 54). We conclude that the concentration of soluble HLA concentration in albumin and immunoglobulin preparations is more than 50 times lower than in normal human serum, but considerable differences exist between products of various manufacturers.

Antibodies, Monoclonal↗