No description available.

It has been argued that patients with frontal lobe lesions are impaired in temporal context memory and, more generally, in retrieving the source of one's knowledge or ideas. Furthermore, it has been speculated that a failure to retrieve source information may result in an increased susceptibility to distortions of episodic memories in patients with frontal lobe lesions. The precise role of the frontal cortex, however, in source or episodic retrieval is not clear. Does this region of cortex play a primary role or a secondary, executive role in the processing of such memories? Studies of patients with temporal lobe lesions have also shown impairments in episodic memory, including difficulties in the retrieval of source information. An important issue, therefore, is whether these two brain regions make different contributions to the processing of source information and to the retrieval of episodic memories. / In the present experiments, patients with unilateral excisions restricted to frontal cortex or to the anterior temporal lobe were compared on various tasks examining source memory performance and the accurate retrieval of episodic information. The results of these studies failed to support the general contention that patients with frontal cortex excisions have source (or temporal context) memory impairments. Instead, differences between these patients and normal control subjects appeared to be contingent on whether strategic organizational or control processes were necessary for efficient processing of episodic information. The memory of patients with left temporal lobe excisions, on the other hand, was significantly impaired for both content and source information in most tasks. Furthermore, these subjects showed high rates of inaccuracies and distortions of memory. The false memories of this patient group were attributed to a combination of their poor memory for the specific items of the task and their over-reliance on semantic "gist" or on inferential knowledge about the events. Patients with right temporal lobe excisions were generally less severely impaired on the verbal memory tasks compared with those with left-sided lesions, but were impaired in their memory for the contextual aspects of an event.

Mémoire (M.A.)-- Université du Québec à Chicoutimi, 2002. / En tête du titre : Université du Québec, mémoire présenté comme exigence partielle de la maîtrise en psychologie offerte à l'Université du Québec à Chicoutimi en vertu d'un protocole d'entente avec l'Université du Québec à Trois-Rivières. CaQTU Comprend des réf. bibliogr. : p. 106-116.

Mémoire (M.Ps)-- Université du Québec à Chicoutimi. 2002. / Document électronique également accessible en format PDF. CaQCU

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.

No description available.

Psychiatric disorders and cognitive impairment are increasingly being described in patients with vestibular pathology. Yet frameworks that describe the link between emotion, memory and the vestibular system have yet to reach maturity, partly because studies have not yet provided detailed accounts of behavioral changes in experimental animals, or in man. One of the goals of this thesis was to use experimental psychology to define changes in memory and emotional behaviour in rats given bilateral vestibular deafferentation (BVD, n=18) or sham surgery (Sham, n=17). In an elevated-plus maze task, BVD rats made up to 166% greater open arm entries and spent up to 42% more time in the open arms compared to Sham rats. In an elevated-T maze task, BVD rats failed to develop a normal learned inhibition response to open space. In an open field maze BVD rats consistently showed 50-60% greater movement velocity, spent on average 35% more time in the inner most aversive part of the arena, and failed to show the normal boundary-seeking behaviour (thigmotaxis) typical of untreated or Sham rats. In a social interaction test BVD rats spent up to 34% less time engaged in social contact compared to Sham rats. In a hyponeophagia test, BVD rats� latency to eat was 70% greater than Sham rats at 3-weeks post-op., however this difference disappeared at 3- and 5-months. These findings suggest that BVD treatment may in some cases disrupt normal behavioral inhibition. Memory performance was also affected. In a T-maze task BVD rats achieved 40-60% correct arm entries, compared to 90-100% for Sham controls. In a foraging task carried out in darkness, BVD rats� initial homing angle was random, homing paths were ~70% longer, and reference memory errors were ~56% greater compared to Sham rats. To elucidate possible neurochemical substrates for these behavioral changes, western blot assays on monoamine proteins were carried out on tissue from a naïve set of rats (BVD n=6; Sham n=6). In BVD rats, serotonin transporter protein expression was 39% lower in CA1 hippocampus and 27% lower in the forebrain region, despite forebrain tryptophan hydroxylase expression being 34% upregulated. Tyrosine hydroxylase expression in the forebrain region was 27% lower in BVD rats. Proteins related to synaptogenesis were also investigated. In the dentate gyrus SNAP-25 was 37% upregulated in BVD rats, while in area CA2/3 of the hippocampus neurofilament-L was 13% upregulated. Forebrain and entorhinal cortex drebrin expression was 28% and 38% downregulated in BVD rats. Neurofilament-L was also 31% downregulated in the forebrain region of BVD rats. To test whether any of these behavioral or biochemical changes may have been attributable to chronic physiological stress, a corticosterone assay was carried out at the conclusion of behavioral testing; however, the no significant between treatment differences were found. In conclusion, vestibular information appears to be needed for the acquisition of spatial and reference memory as well as the normal expression of emotional behaviour. The neurochemical changes described herein point toward possible substrates for these behaviors, however their full significance has yet to be determined.

This thesis investigated melodic memory and perception in patients with unilateral left (LT) or right (RT) temporal-lobe lesions and in normal control (NC) subjects. Experiment I examined learning and 24-hour retention of unfamiliar tunes and nonsense words. Both temporal-lobe groups were impaired in learning the tunes and the words. Long-term retention of these stimuli showed that subjects with a RT lobectomy were more impaired in recognizing the tunes than the words, while subjects with a LT lobectomy were more impaired in recognizing the words than the tunes. This study demonstrated the differenting roles of the right and the left temporal lobes in long-term retention of musical and verbal information, respectively. Experiment IIa and IIb investigated memory for songs (words sung to a tune). Recognition of the melodic component resulted in a deficit for both RT and LT groups, but the nature of the impairment seems to be related to the side of the lesion. Patients with LT lobectomy showed deficits in tune recognition mediated by words, but not for tunes sung without words. Patients with RT lobectomy were impaired in tune recognition, whether or not words were sung to the tunes. On the other hand, the well-known verbal memory deficit was shown after a LT lobectomy when the words actually form part of the stimulus as well as when the words are spoken. In experiment III two melodic discrimination tasks were created to test the hypothesis that the RT and the LT lobes are specialized for global and local information processing, respectively. The results showed that impairments under both experimental conditions regardless of the side of the temporal lobectomy suggest that the two temporal lobes are involved in the processing of contour and interval information.

Selective attention involves focusing on one event among many, and is largely responsible for an organism's ability to respond efficiently to the environment. The location at which attention is focused is a function of an ongoing tension between external cues and internal goals. Control over selective attention is often described as an executive process, attributable to the function of the frontal lobes of the brain. The present experiments investigated the role of the frontal cortex in attentional control, through the study of patients with focal cortical lesions and through functional neuroimaging in neurologically normal subjects. It was found that patients with unilateral surgical resections from the frontal cortex were as efficient as patients with temporal-lobe resections and normal controls at attending selectively to a visual stimulus at one location in the presence of irrelevant distracting stimuli. In fact, those patients whose lesions invaded the anterior cingulate gyrus tended to be less reactive to changes in irrelevant stimuli. However, patients with frontal cortex lesions were mildly impaired in a different task in which they used visual cues to direct attention voluntarily to a different location from one trial to the next. In addition, patients with excisions from the right frontal cortex performed less efficiently with increasing time spent on a task, suggesting an important role for this region in sustained attention. These observations prompted a further study of attention using positron emission tomography in normal subjects. This experiment was designed to identify the brain regions that were more active during trials in which cues could be used to direct attention voluntarily, relative to trials in which uninformative cues were presented. The striatum and extrastriate cortex were the only regions in which blood flow correlated positively with the proportion of trials containing informative cues. The present studies indicate that the frontal

No description available.