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This thesis considers the importance of the inferior parietal lobe for calculation and Arabic number comparison. The first experiment demonstrates that repetitive Transcranial Magnetic Stimulation (rTMS) can be used on normal subjects to replicate findings from studies of patients whose ability to calculate after brain injury was impaired. While subjects were solving addition tasks, rTMS was applied over anterior and posterior areas of the inferior parietal lobule and the adjoining intraparietal sulcus (aIPL+S, pIPL+S). In line with results from patient studies, magnetic stimulation showed a disruptive effect only over left IPL+S. It had no disruptive effect when delivered over right inferior parietal lobule and the adjoining intraparietal sulcus. To investigate the representation of number magnitude in the human brain rTMS was subsequently applied to the same inferior parietal regions while subjects performed a number comparison task. With numbers between 31 and 99, repetitive TMS over the pIPL+S disrupted organisation of the putative "number line". rTMS had no disruptive effect when delivered over aIPL+S, in either the left or right hemisphere. With numbers between 1 and 9, however, TMS over the pIPL+S did not impair task performance. Here, TMS had a disruptive effect when delivered over aIPL+S, in either the left or right hemisphere, thus suggesting that areas in the inferior parietal lobes might be specialised for certain number sizes. The idea of a spatial mental number line was further investigated in a detailed single-case description of a person with an automatic mental number line. In the last experiment, functional Magnetic Resonance Imaging (fMRI) was used to investigate number comparison. The fMRI study gave some indication that small numbers might be represented in the aIPL+S region. In general, the fMRI results suggest that parietal cortical contribution to number magnitude representation is intimately related to its role in basic sensorimotor processes.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 131-154).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 145-158).

Lateral intraparietal area (LIP) neurons are thought to compute the decision of where to look. Specifically, their firing rate is thought to represent accumulated evidence for a decision by ramping up to a high level, the putative decision bound, before an eye movement to a given location. However, LIP neurons are also highly responsive to visual stimuli. Because all previous research put a visual stimulus (a saccadic target) in the response field (RF) location of a neuron during decision formation, it is unknown if LIP neurons can still show decision computation without this visual drive. We therefore recorded the spiking activity of LIP neurons in a conventional decision task where a monkey decides the direction of a noisy motion stimulus and indicates his decision with a saccade. On half the trials, the Choice Targets remained on for the whole trial, as is conventionally done. On the remaining trials, targets were flashed at the beginning of the trial and absent during motion-viewing. Furthermore, we recorded the activity of any neuron with an RF, instead of only neurons exhibiting persistent memory activity before an instructed saccade. This enabled us to also test the long-held assumption that only cells with persistent memory activity show decision signals. Our results show that 1) cells without persistent activity indeed show decision signals, 2) population response drops without RF stimulation (although individual neurons were affected in diverse ways), 3) distinct, repeating response “motifs” exist among cells, 4) a signal exists where neural response is lower for stronger motion strength stimuli, regardless of direction. These results prove that contrary to dogma, a neuron’s ability to show a long “memory” response is not related to an ability to accumulate evidence over time for a decision. Also, LIP firing rate cannot be interpreted as a pure decision variable because it simultaneously represents decision-irrelevant, visual stimuli. Finally, diverse, but repeating responses among cells suggest the existence of cell types in LIP. These results demonstrate that LIP acts as a bank of potentially useful signals, and raises the question of how they might be used for a decision. / text

In many everyday activities, we must visually process multiple objects embedded in complex real world scenes. Our visual system can flexibly extract behaviorally relevant visual information from such scenes, even though it has a severely limited processing capacity. This dissertation proposes that human superior intra-parietal sulcus (IPS) plays a central role in this flexible visual information processing. In Chapter 1, using functional magnetic resonance imaging (fMRI) with univariate analysis, I found that distractor processing in superior IPS was attenuated when target locations were known in advance. In Chapter 2, using multi-voxel pattern analysis (MVPA), I showed that superior IPS encoded object shapes, but only when such information was required by task. In Chapter 3, I showed that, given a set of perceptually distinct, but semantically grouped visual inputs, superior IPS could represent abstract object identity. The neural similarity of identities in superior IPS significantly correlated with perceived similarity between identities, confirming the representation in this region indeed reflected identity. Taken together, these results suggest that human superior IPS encodes a wide range of visual information, from simple features to abstract identities, in a task-dependent manner, enabling flexible goal-directed visual information processing in the human brain. / Psychology

Thesis (M.Sc. (Anatomy)) -- Mahidol University, 1976.

Recent functional neuroimaging research has highlighted the role of the posterior parietal cortex (PPC) during episodic memory retrieval (Vilberg & Rugg, 2007; Vincent et al., 2006; Wagner et al., 2005; Wheeler & Buckner, 2003; Yonelinas et al., 2005). It has been shown that the PPC is active during the retrieval of old information, when subjects incorrectly believe that new information has been encountered before (false alarms), and when retrieval is accompanied by recollection (Wagner et al., 2005). A preliminary positron emission tomography (PET) study suggests that the PPC is also active when retrieval occurs unintentionally or incidentally, prompted by the presence of an old stimulus item. Collectively these studies suggest that activity in the PPC may be driven by familiarity, irrespective of task demands and independent of its veracity. The main goal of this thesis was to explore, with functional magnetic resonance imaging (fMRI), the conditions under which activity in the PPC may be modulated by the familiarity of veridical and perceived memories. Subjects were presented with scene/word pairs that were repeated 1, 3, or 7 times on Day 1. On Day 2, while MRI scans were recorded, subjects studied either, new items, old pairs (same-form) one additional time (2nd,, 4th, or 8th presentation), or pairs in which the word associated with each picture was changed (different-form) one additional time (2nd,, 4th, or 8th presentation). Same form pairs activated bilateral inferior parietal lobule compared to novel pairs replicating the findings from the PET study on incidental retrieval. Same and different form pairs did not differ on amount of parietal activity. Additionally, same form pairs that were repeated 8 times displayed more PPC activity than same form pairs repeated two and four times while there was no difference across different form repetitions. Together these results indicate that items that are old and that those that are new but are perceived as old activate the inferior parietal lobule.

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Made available in DSpace on 2014-06-11T19:32:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-04-28Bitstream added on 2014-06-13T21:04:27Z : No. of bitstreams: 1 coradazzi_lf_dr_araca.pdf: 554297 bytes, checksum: c5cfb463f29a39c5571e8140faed3c14 (MD5) / Devido a sua micro-arquitetura de composição cortical, baixo padrão de reabsorção e a possibilidade de obtenção de grande quantidade de tecido ósseo, o osso da calota craniana se destaca como uma das principais áreas doadoras para grandes reconstruções de maxilas atróficas para posterior reabilitação com próteses implanto-suportadas. O objetivo desse estudo foi de observar e mensurar, através de avaliação histológica e histométrica, os eventos celulares que ocorrem na interface de união do enxerto onlay de osso parietal na maxila de 10 pacientes, após um período de 6 meses de incorporação. As biópsias foram realizadas no momento da instalação dos implantes osseointegráveis. A área de contato ósseo representou 78,75% e a de contato conjuntivo em fase de remodelação 21,25%. A região de união conjuntiva entre o enxerto ósseo com o leito receptor apresentou osso neoformado (41,26%), medula (36,06%), tecido osteóide (15,86%) e tecido conjuntivo (6,80%). Em todas as amostras houve uma boa incorporação do enxerto ao leito receptor, com atividade osteogênica ativa e ausência de células inflamatórias. / Because of its micro-architecture of cortical composition, low standard of absorption and the possibility to obtain large amount of bone tissue, the calvarial bone is highlighted as a good donor area for large reconstructions of atrophic jaw for subsequent rehabilitation with implant-supported prosthesis. The aim of this study was to observe and measure through histological and histometric evaluation, the cellular events that occur at the interface of union from onlay parietal bone graft on the maxilla of 10 patients, after a period of 6 months of incorporation. The biopsies were performed at the time of installation of osseointegrated implants. The bone contact area represented 78.75% and connective contact 21.25%. The region of connective union between the bone graft to the maxillae presented new bone formation (41.26%), marrow bone (36.06%), osteoid tissue (15.86%) and connective tissue (6.80%). All samples had good graft incorporation to the receptor bed with osteogenic activity and absence of inflammatory cells.