3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Are there order specific patterns of cortical gyrification and if so why?(2008-12-10T11:53:58Z) Pillay, PraneshriAbstract (for Chapter 2) Objective: The aim was to test the hypothesis that the order is a significant phylogenetic grouping in terms of quantifiable gyrification indices. Method: The gyrification index (GI) was measured from serial sections of the brain of twenty five different mammalian species, representing the different orders i.e. primates, carnivores, artiodactyls and rodents. Image J analysis was used to measure the contours of the cerebral cortex and the GI was calculated using three different methods of analysis i.e. complete vs outer; gyral vs sulcal and outer vs inner surface contours. The measurements were then computed against the brain weights of each species within the order. Results: An increasing GI correlates with an increasing brain weight in all the mammalian orders. Each order has its own specific allometric patterns that are significantly different from the other orders examined. The artiodactyls were the mammals with the most gyrencephalic brains, these species being significantly more gyrencephalic than all other mammals when species of similar brain weights are compared. The North American beaver has an atypically lissencephalic brain for its size, differing from the trend for increased gyrencephaly found in the other rodent species examined. Conclusions: Our results show definite trends and patterns specific to each order. So it would seem that the order is a significant phylogenetic grouping in terms of this neural parameter, from which we can predict with a reasonable degree of certainty, the GI of any species of a particular order, if we know the brain weight. Abstract (for Chapter 3) The mammalian order has proven to be a significant phylogenetic grouping in terms of gyrification from which we can predict with a reasonable degree of certainty, the GI of any species of a particular order, if we know the brain weight. We have attempted in the present study to identify potential causes for gyrification at the class level by investigating relationships at the level of the order. It appears that clues to the extent and pattern of gyrification in the different mammalian orders might be related to the bones that constitute the braincase. The external surface areas of the bones of the cranial vault of seventeen different mammalian species were measured using a microscribe digitiser. These values were plotted against brain weight from which we could then calculate residual values, determining if there was more or less external cranial vault area than expected for the size of the brain. These residuals were then plotted against the gyrification indices determined in a previous study for the species examined. Results indicated that for the primates and artiodactyls the skull may potentially be considered as a limiting factor on the expansion of the cerebral cortex; however, the carnivore and rodent orders show conflicting results which suggest that the relative surface area of the skull appears to have no effect on the quantitative extent of gyrencephaly. These inconclusive findings suggest that causes contributing to the quantitative extent of gyrification across mammals may be multifactorial, and more parameters may need to be included in the analysis to arrive at an answer.Item Fissures of the frontal operculum in as a South African sample(2006-11-16T07:36:51Z) Kamanzi-wa, SylviaThis study primarily seeks to confirm two systems of classifying the sulci of the frontal operculum1 (F3): the radiologically derived system of Ebeling et al (1989) involving four Types of Sulcal Connections, and the anatomical classification of the anterior rami of the lateral fissure, involving three patterns. Sulcal- and intersulcal- lengths are also considered. The sample consisted of 220 cadaveric hemispheres; 65 of which were whole brains (control category); and 90 consisting of equal numbers of separate right- and lefthemispheres (case category). Specimens were orientated by examining relevant features of: the lateral fissure; the postcentral sulcus; and the central fissure. Features of the remaining boundary sulci (precentral sulcus / sulci, and inferior frontal sulcus) of F3 were also considered. The focus was on examining the: frequency of occurrence, shape, and connections of the sulci of the F3. The sulci of F3 were designated as: major sulci [anterior ascending (AAR)- and anterior horizontal (AHR)- rami, and stem of the anterior rami when present); and accessory sulci (sulci of the –pars opercularis and –pars triangularis). Sulcal lengths were measured using thread, with needles as anchors. Intersulcal lengths were recorded as straight-line distances between parallel pins inserted into the sulci of the frontoparietal operculum. Specimens fixed outside the cranial cavity were excluded from measurement. The reliability of the data was monitored, by repeating the observations. The two systems of classification were broadly confirmed. The criteria for the Types of Sulcal Connections were modified in view of the findings on double precentral sulci and the connections of the opercular sulcus (which occurred as either one or as two sulci). A sulcus of the pars triangularis (which occurred as either one, two, or as three sulci) was found to be a useful landmark. The Chi-square test was applied to the data in the two systems of classification. There were no significant interhemispheric differences with respect to the incidences of: Types 1-4 of Sulcal Connections, or Patterns of the Anterior Rami (I, Y, and VU). Sulcal lengths were similar to that reported by Ono et al (1990). The Student t-test was applied to sample sizes 18 and above. No significant interhemispheric differences, in the lengths of the sulci that were considered, were found. A significant 1 The definition of the frontal operculum as the inferior frontal gyrus only, is used for the purposes of this study. The frontal operculum may also be abbreviated as F3. v difference was found in two instances when comparing the case- and control- categories. Intersulcal distances are reported on in the frontal- and frontoparietal- operculum.