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published_or_final_version / abstract / toc / Clinical Psychology / Master / Master of Social Sciences

This thesis includes several studies investigating the right medial temporal-lobe contribution to memory for the location of objects in an array. Three arrays of toy objects were constructed and shown to be comparable in difficulty on the basis of tests with undergraduate students. These arrays were then employed as the test material for examining memory with tasks of immediate or delayed recall within a single trial, in addition to learning-to-criterion across multiple trials. Normal control subjects and patients with unilateral resection from the anterior temporal lobe were tested. The patients had undergone either selective amygdalo-hippocampectomy or anterior temporal lobectomy that either spared or largely invaded the hippocampal formation. The only groups showing impairment were those with large resections from the right hippocampal region; this deficit was noted on immediate recall, delayed recall, and incremental learning of the spatial arrays. In 75 of the patients tested, postoperative magnetic resonance scans were used to measure the extent of tissue remaining in the medial temporal-lobe structures; from multiple regression analyses, the extent of right hippocampus remaining was found to be the best predictor of array-learning performance. The notion that the hippocampus encodes spatial information in a map-like or allocentric manner (O'Keefe and Nadel, 1978) was explored by requiring normal control subjects and patients with unilateral temporal-lobe lesions to reconstruct the spatial arrays from a vantage-point other than that from which they had previously viewed the arrays. Contrary to prediction, the allocentric manipulation failed, in general, to elicit any additional impairment. Taken together, the results indicate that damage limited to the medial-temporal region in the right hemisphere is sufficient to disrupt memory for the location of objects. Within this region, the hippocampus appears to be the most critical structure for building, over suc

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.

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.

No description available.

No description available.

No description available.