Visual evoked electrical and magnetic response to half-field stimulation using pattern reversal stimulation

The visual evoked magnetic response to half-field stimulation using pattern reversal was studied using a dc-SQUID coupled to a second-order gradiometer. The main component of the magnetic response consisted of a positive wave at around 100ms (P100M). At the same time this component was present the reponse to half-field stimulation consisted of an outgoing field contralateral and extending to the midline. When the left half-field was stimulates the outgoing field was over the posterior right visual cortex and when the right half field was stimulated it was over the left anterior visual cortex. These findings would correltly identify a source located in the contralateral visual cortex. The orientation of the dipoles was not that previously assumed to explain the paradoxical lateralization of the visual evoked potential. The results are discussed in terms of both electrical and magnetic models of the calcarine fissure.

The development of calibration and adaptive filtering procedures for neuromagnetic studies of human visual function

This thesis first considers the calibration and signal processing requirements of a neuromagnetometer for the measurement of human visual function. Gradiometer calibration using straight wire grids is examined and optimal grid configurations determined, given realistic constructional tolerances. Simulations show that for gradiometer balance of 1:104 and wire spacing error of 0.25mm the achievable calibration accuracy of gain is 0.3%, of position is 0.3mm and of orientation is 0.6°. Practical results with a 19-channel 2nd-order gradiometer based system exceed this performance. The real-time application of adaptive reference noise cancellation filtering to running-average evoked response data is examined. In the steady state, the filter can be assumed to be driven by a non-stationary step input arising at epoch boundaries. Based on empirical measures of this driving step an optimal progression for the filter time constant is proposed which improves upon fixed time constant filter performance. The incorporation of the time-derivatives of the reference channels was found to improve the performance of the adaptive filtering algorithm by 15-20% for unaveraged data, falling to 5% with averaging. The thesis concludes with a neuromagnetic investigation of evoked cortical responses to chromatic and luminance grating stimuli. The global magnetic field power of evoked responses to the onset of sinusoidal gratings was shown to have distinct chromatic and luminance sensitive components. Analysis of the results, using a single equivalent current dipole model, shows that these components arise from activity within two distinct cortical locations. Co-registration of the resulting current source localisations with MRI shows a chromatically responsive area lying along the midline within the calcarine fissure, possibly extending onto the lingual and cuneal gyri. It is postulated that this area is the human homologue of the primate cortical area V4.

The visually evoked magnetic response (VEMR) to a pattern onset/offset stimulus

This study characterizes the visually evoked magnetic response (VEMR) to pattern onset/offset stimuli, using a single channel BTi magnetometer. The influence of stimulus parameters and recording protocols on the VEMR is studied with inferences drawn about the nature of cortical processing, its origins and optimal recording strategies. Fundamental characteristics are examined, such as the behaviour of successive averaged and unaveraged responses; the effects of environmental shielding; averaging; inter- and intrasubject variability and equipment specificity. The effects of varying check size, field size, contrast and refractive error on latency, amplitude and topographic distribution are also presented. Latency and amplitude trends are consistent with previous VEP findings and known anatomical properties of the visual system. Topographic results are consistent with the activity of sources organised according to the cruciform model of striate cortex. A striate origin for the VEMR is also suggested by the results to quarter, octant and annulus field stimuli. Similarities in the behaviour and origins of the sources contributing to the CIIm and CIIIm onset peaks are presented for a number of stimulus conditions. This would be consistent with differing processing event in the same, or similar neuronal populations. Focal field stimuli produce less predictable responses than full or half fields, attributable to a reduced signal to noise ratio and an increased sensitivity to variations in cortical morphology. Problems with waveform peak identification are encountered for full field stimuli that can only be resolved by the careful choice of stimulus parameters, comparisons with half field responses or with reference to the topographic distribution of each waveform peak. An anatomical study of occipital lobe morphology revealed large inter- and intrasubject variation in calcarine fissure shape and striate cortex distribution. An appreciation of such variability is important for VEMR interpretation, due to the technique's sensitivity to source depth and orientation, and it is used to explain the experimental results obtained.

A case of bilateral perisylvian syndrome with reading disability

Bilateral Perisylvian Syndrome (BPS) often presents with epilepsy and significant behavioral impairments that can include mental retardation, dysarthria, delayed speech development, and delayed fine motor development (Graff-Radford et al., 1986 and Kuzniecky et al., 1993). While a small subset of BPS cases have been described as having relatively isolated language delays (Leventer et al., 2010), BPS is not expected in children with dyslexia. As part of a Medical University of South Carolina, IRB approved multi-site study involving retrospective and de-identified dyslexia data, we unexpectedly identified a 14.05 year old male with evidence of BPS whose father had been diagnosed with dyslexia and dysgraphia. This child had been recruited for a neuroimaging study on dyslexia from a school specializing in educating children with dyslexia. The T1-weighted MRI scan from this child demonstrated a highly unusual perisylvian sulcal/gyral patterning that is a defining feature of BPS (Fig. 1). BPS cases exhibit bilateral dysgenesis of the Sylvian fissure and surrounding gyri, which appears to occur because of a limited or absent arcuate fasciculus (Kilinc, Ekinci, Demirkol, & Agan, 2015). This BPS case also had a relatively enlarged atrium of the lateral ventricle that is consistent with the BPS anatomical presentation and reduction of parietal white matter (Graff-Radford et al., 1986, Kilinc et al., 2015 and Toldo et al., 2011).

The Relationship Between Cadwaladerite Al(OH)2Cl∙4H2O and Lesukite Al2(OH)5Cl∙2H2O as Investigated by SEM, PXRD, FTIR and Raman Spectroscopy

Cadwaladerite (Al(OH)2Cl∙4H2O) collected from Cerro Pintados, Chile described by Gordon in 1941 is designated as “doubtful” by the IMA. Material collected from the same locality in 2015 resembling the description of cadwaladerite gave a powder XRD pattern similar to lesukite (Al2(OH)5Cl∙2H2O). However, Gordon provided no X-ray data for his material from Cerro Pintados. In order to determine whether cadwaladerite and lesukite are the same mineral species, measurements were made on a suite of samples from various localities. A portion of the material collected by Gordon in 1941 was also obtained from the Mineralogical Museum of Harvard University. Type material of lesukite from a fumarolic environment at the Tolbachik Fissure in Kamchatka, Russia was obtained as well as lesukite from the Maria Mine, Chile (Arica Province) and a previously undescribed locality for lesukite (Barranaca del Sulfato, Mejillones Peninsula, Antofagasta Province). All samples are yellow to yellow-orange in colour and all exhibit small cubic crystals (up to 50µm), even Gordon’s cadwaladerite which was thought to be amorphous. The Chilean samples are all associated with halite and sometimes with anhydrite. These five samples were studied by SEM, FTIR, powder XRD, and Raman spectroscopy. A ratio of Al:Cl less than or equal to 1.3:1 was observed for all the samples, including measurements made on lesukite from the Russian locality Vergasova et al. studied in 1997, and determined to have a 2:1 ratio. SEM-EDS analyses also show all samples to have minor iron substitution, as well as copper substitution in two samples. FTIR spectra are very similar for all samples. Raman spectroscopy done on both samples collected in Cerro Pintados and the Russian lesukite gave similar spectra. Powder XRD analyses on all samples showed spectra identified to be lesukite, including Gordon’s cadwaladerite. Crystal cell parameters calculated from powder XRD ranged from 19.778Å to 19.878Å. Results using modern instrumental techniques confirm Gordon’s cadwaladerite, collected in 1939 and described in 1941, and lesukite are the same mineral species.

Influence of dental materials used for sealing caries lesions on laser fluorescence measurements

The aim of this study was to determine the influence of thickness and aging on the intrinsic fluorescence of sealing materials and their ability to block fluorescence from the underlying surface as assessed using a laser fluorescence device. Cavities of 0.5 mm and 1 mm depth were drilled into acrylic boards which were placed over two surfaces with different fluorescence properties: a low-fluorescence surface, to assess the intrinsic fluorescence of the sealing materials, and a high-fluorescence surface, to assess the fluorescence-blocking ability of the sealing materials. Ten cavities of each depth were filled with different sealing materials: Adper Scotchbond Multi-Purpose, Adper Single Bond 2, FluroShield, Conseal f and UltraSeal XT Plus. Fluorescence was measured with a DIAGNOdent pen at five different time points: empty cavity, after polymerization, and 1 day, 1 week and 1 month after filling. The individual values after polymerization, as well as the area under the curve for the different periods were submitted to ANOVA and the Tukey test (p < 0.05). At 0.5 mm, Scotchbond, FluroShield and UltraSeal showed insignificant changes in intrinsic fluorescence with aging and lower fluorescence after polymerization than Single Bond and Conseal. At 1 mm, Scotchbond and FluroShield showed the lowest intrinsic fluorescence, but only Scotchbond showed no chagnes in fluorescence with aging. At both depths, Scotchbond blocked significantly less fluorescence. All sealing materials blocked more fluorescence when applied to a depth of 1 mm. At 0.5 mm, fissure sealants blocked more fluorescence than adhesives, and did not show significant changes with aging. Scotchbond had the least affect on the fluorescence from the underlying surface and would probably have the least affect on the monitoring of sealed dental caries by laser fluorescence.

Age an origin of the "Mexican Onyx" at San Antonio Texcala (Puebla, Mexico)

A great variety of color banded CaC03 is known as „Mexican Onyx“, and is extensively used for ornamental purposes. Within the San Antonio Texcala mining district an area of about 24.000 m2 is covered by a thick travertine crust with a calculated volume of at least 2,8 x 1061. It originates from warm waters that emerge on young fissures and faults. It seems to be likely that the travertine formation is related to the hydrothermal activity of the Transmexican Volcanic Belt and to the seismicity of this zone. The deposit is built up by different travertine varieties. The main lithotypes are: (1) dense crystalline laminated travertine; (2) ray crystal travertine; (3) shrub layer travertine; (4) irregular porous travertine; (5) travertine breccia. Textural variation seems to be related to water temperature/distance from the emergence point, rapid or slow degassing of CO, and bacterial influence. At the moment, a light green banded variety (native sulfur impurities) is mined. It is the facture fill of a morphological prominent fissure-ridge travertine. U/Th data indicate, that the travertine has been deposited since at least 52 + 5 ka.

História eruptiva do sistema vulcânico fissural dos picos e avaliação da susceptibilidade a escoadas lávicas (ilha de S. Miguel - Açores)

Tese de Doutoramento, Geologia (Vulcanologia), 18 de Julho 2013, Universidade dos Açores.

Fissura placentária de gatas SRD, Felis catus - Linnaeus, 1758: aspectos macro e microscópicos

Nossa pesquisa consiste no estudo esquemático macroscópico na placenta de gatos e a sua caracterização como tipo, placenta zonária, que 62,5% dos casos apresenta uma fissura na área distal do funículo umbilical. Esse é formado por uma área justa fetal, área justa placentária e área média, encontrando achados histológicos de 2 artérias, uma veia, 2 pedículos vitelínicos e 2 pedículos alantoidianos. Na fissura, encontramos um epitélio alantoidiano cobrindo esta área em 10% dos casos e, em 90% dos achados foram encontrados um trofoblasto diminuído comparado com outras áreas placentárias fora da fissura. Portanto, a placenta felina, com sua relação materno fetal mostra uma placenta zonária incompleta, diferente do ocorrido nos outros carnívoros.