Memory formation and recall depend on a complex circuit that includes the hippocampus and associated cortical regions. The goal of this thesis was to understand how two of the cortical connections, the medial entorhinal cortex (MEC) and medial prefrontal cortex (mPFC), influence spatial and nonspatial activity in the hippocampus. Cells in the MEC exhibit prominent spatially selective activity and have been hypothesized to drive place representation in the hippocampus. In Experiment 1 the MEC was transiently inactivated using the inhibitory opsin ArchaerhodopsinT (ArchT), and simultaneous recordings from CA1 were made as rats ran on an elliptical track. In response to MEC disruption some cells in the hippocampus shifted the preferred location of activity, some changed firing rate and others were unaffected. The new representation that developed following MEC disruption remained stable despite the fact that inhibition was transient. If the MEC is the source of spatial activity in the hippocampus the activity would be either time-locked to periods of inhibition or unstable throughout the period of inconsistent input. These results show that the MEC guides spatial representation in the hippocampus but does not directly drive spatial firing. The mPFC is generally thought to guide behavior in response to contextual elements. Experiment 2 examined the interaction between the mPFC and the hippocampus as rats performed a contextual discrimination task. Recordings were made in CA1, and the mPFC was disrupted using ArchT during the odor sampling phase of the discrimination. As animals perform this task neurons in the hippocampus respond to a conjunction of odor and location which indicates an association of what and where information in the hippocampus. Optogenetic disruption of the mPFC led to a decrease in nonspatial representation. Individual cells showed lower levels of odor selectivity, but there was no change in the level of spatial representation. This indicates that the mPFC is important for determining how the hippocampus represents nonspatial information but does not alter the spatial representation. The results are discussed within a model of memory formation that includes binding spatial and nonspatial information in the hippocampus.

Human pluripotent stem cell (hPSC)-derived neuronal and glial material presents a relatively new opportunity to model human neurophysiology in both health, and disease. Validation of regionally-defined hPSC-derived neurones and glia cultures thus represents the founding blocks of technology that aims to complement existing models. Principally, the relevance of in vitro hPSC-derived material is determined by how representative it is of native material, yet at present the physiology of these cells remains underexplored. Here, electrophysiology and pharmacology are used to functionally assess hPSC-derived excitatory cortical neurones (hECNs), motorneurones (MNs) and oligodendrocyte-lineage cells in the context of regional-specific properties and maturation. These properties are then examined in material derived from hPSCs generated from patients with neurological disorders. This thesis examines of the properties of GABAARs and strychnine-sensitive glycine receptors (GlyRs) in hECNs by assessing their subunit composition, and compares these with studies which have made comparable investigations of rodent tissue where maturation is associated with a shift in GABAA and GlyR compositions. Using pharmacology and RNAseq analysis, GABAAR and GlyRs in hECNs were found to possess receptor populations typical of those reported in the immature cortex. hECNs generated from patients harbouring a mutation to the Disrupted-in-schizophrenia-gene 1 (DISC1), a candidate schizophrenia gene, were then examined. Imbalances in the excitation/inhibition balance are suspected in schizophrenia and, in this regard, the intrinsic excitability properties alongside expression and composition of major neurotransmitter receptors and intracellular chloride concentration were assessed. No obvious differences in excitability or functional expression of AMPARs, GABAARs or NMDARs were observed between case and control derived neurones. Receptor composition and intracellular chloride concentrations were found to be predominantly immature-like, however, AMPAR composition and intracellular chloride concentration were found to be like that of adult cortical neurones. These data are discussed in the context of modelling DISC1-associated pathologies. Thirdly, MNs from hPSCs generated from ALS patients harbouring mutations on the C9ORF72 gene were examined. The hypothesis that increased glutamate-mediated excitoxicity could, in part, be explained by increased expression of Ca2+- permeable AMPARs was examined. The estimated mean single-channel conductance of AMPARs was found to be high in MNs derived from ALS patients, reminiscent of Ca2+-permeable AMPARs and was reversed by gene-editing of the C9ORF72 mutation. Finally, oligodendrocytes generated from ALS patients harbouring TARDBP mutations were examined. Distinctive electrophysiological shifts in oligodendrocytes-lineage cell development are reported. A similar AMPAR phenotype of elevated Ca2+-permeable AMPAR expression was observed in oligodendrocytes derived from two patient hPSC lines and was rescued in an isogenic, gene-edited line, raising the intriguing possibility of convergence in pathophysiologies in the nature of the overlap between cell-type, AMPAR pathology and excitotoxicity in ALS disease progression mechanisms.

The daily variation in background light intensity (irradiance) can entrain the endogenous clock in the suprachiasmatic nucleus (SCN) to the external environment. The only source of this photic information in mammals is the eye, which is primarily a visual organ. It is therefore highly specialised to detect high frequency spatiotemporal modulations. This together with the adaptation which occurs within the retina could be present difficulties when encoding global irradiance. This raises the question of whether spatial patterns, which are present in our everyday viewing, might affect the ability of the SCN to receive 'true irradiance' signals and entrain to the external environment. My first approach was to determine whether individual SCN cells might receive a 'true irradiance' signal. To this end I mapped and characterised the receptive field properties of SCN neurons using in vivo electrophysiology. Indeed a handful of neurons (full field cells) responded to light anywhere in the visual scene and thus may act as 'irradiance detectors'. However, the vast majority of cells only sampled local radiance from a limited area of the visual scene. Having mapped the receptive field properties it became clear that cells which sampled from a limited area of the visual scene would be sensitive to spatial contrast (patterns). To examine the effect of spatiotemporal contrast on the SCN I examined two SCN outputs: locomotor activity and neuronal firing rates. Although spatiotemporal modulation in light intensity could induce large amplitude oscillations in neuronal activity; the time averaged firing rate and locomotor activity, which are believed to be determined by irradiance, were largely unaffected by spatial patterns. This led to the conclusion that the SCN can multiplex photic information into information regarding irradiance, and spatial information by encoding them under different timescales. Melanopsin has been heralded as the key photopigment for encoding irradiance and entraining the SCN. However such experiments have been only performed using diffuse light stimuli. Here I investigated the role of melanopsin under natural viewing conditions which incorporated spatial patterns. Under such stimuli the SCN response can be almost entirely accounted for by the melanopic irradiance of the stimuli.

xiv, 152 p. Adviser: Terry Takahashi (Biology Dept.). Chapter 2 of this dissertation has been previously published in the Journal of Neurophysiology. Citation: Whitchurch EA and Takahashi TT. Combined auditory and visual stimuli facilitate head saccades in the barn owl (Tyto alba). J Neurophysiol 96: 730-745, 2006. / A print copy of this title is available through the UO Libraries under the call number: SCIENCE QL696.S85 W54 2006 / Survival depends on our ability to detect and integrate sensory information from multiple modalities, allowing for the most efficient behavioral response. For example, barn owls must combine sights and sounds from the environment to localize potential prey. A vole scurrying through a drift of dried leaves is more likely to meet its doom if a nearby owl can both faintly see and hear it. How does the brain take two physically discreet inputs and combine them into a unified representation of the surrounding multisensory world? Moreover, how is this internal representation transformed into the most efficient behavioral response? This dissertation comprises original research addressing these questions in the barn owl with two distinct approaches: First, Chapters II and III describe orientation behavior in response to auditory, visual, and audiovisual stimuli. Chapter II probes the effect of stimulus strength on saccadic behavior and the nature of audiovisual integration, and was taken from a co-authored publication. Chapter III explores the behavioral consequence of an induced stimulus asynchrony in audiovisual integration and was taken from a co-authored manuscript being prepared for publication. The second experimental approach is described in Chapters IV and V. These chapters probe the physiological basis of saccadic behavior by measuring single-neuron responses to auditory, visual, and audiovisual stimuli. Chapter IV describes how auditory responses of neurons from the external nucleus of the inferior colliculus depend on sound pressure level. Chapter V describes activity of optic tectum neurons in response to auditory, visual, and audiovisual stimuli. The behavioral findings described herein suggest that barn owls often incorporate both the speed of the auditory system and the accuracy of the visual system when localizing a multisensory stimulus, even when the two modalities are presented asynchronously. The physiological studies outlined in this dissertation show that sensory representations in the midbrain can be used to predict general trends in saccadic behavior: Neuronal thresholds were within the range of observed behavioral thresholds. Responses to multisensory stimuli were enhanced relative to unisensory stimuli, possibly corresponding to enhanced multisensory behavior. These data support fundamental rules in multisensory integration that may apply across species.

xiii, 143 p. : ill. (some col.) / The cognitive ability to group information into chunks is a well known phenomenon, however, the effects of chunking on visual representations is not well understood. Here we investigate the effects of visual chunking using Gestalt grouping principles in two tasks: visual working memory change detection and multiple object tracking. Though both these tasks have been used to study cognitive functions in the past, including object-based attention, attentional control and working memory capacity, the effect of grouping on mental representations in these tasks has not been well characterized. That is, while researches have measured effects of grouping on behavioral output in similar tasks, there are few studies of the effects of grouping on neurophysiological indices of object representations. Indeed, these current studies are the first to use event-related potentials (ERPs) to elucidate the effect of grouping on active mental representations of visual stimuli. In the visual working memory task, observers remembered either the color or orientation of pacman stimuli across a delay. We manipulated the collinearity of these objects, whether or not they formed a Kanizsa triangle figure, and measured the behavioral and electrophysiological effects. In the multiple object tracking task, a subset of identical stimuli were briefly cued as targets and then their motion was tracked by participants. We manipulated whether and which Gestalt heuristics were used to bind targets together during their motion and measured the effects on behavior and electrophysiology. In both tasks we compared the grouped to ungrouped conditions. We found that across experiments and tasks behavioral performance was enhanced in grouping conditions compared to ungrouped conditions. Furthermore, the waveforms evoked by grouped stimuli were reduced compared to waveforms produced in response to locally identical but ungrouped stimuli. These data suggest that the mental representation of visual objects may be reshaped moment-by-moment by grouping cues or task demand, giving rise to a flexible, active and dynamic yet parsimonious representation of the visual world. / Committee in charge: Edward K. Vogel, Chair; Edward Awh, Member; Ulrich Mayr, Member; Paul van Donkelaar, Outside Member

Objetivo: Caracterizar as respostas do Mismatch Negativity (MMN) em crianças com limiares auditivos dentro dos padrões de normalidades e sem queixas auditivas. Métodos: Estudo do tipo transversal. Participaram desta pesquisa crianças de cinco a onze anos, sem queixas auditivas. Todos os participantes realizaram avaliação audiológica periférica com medidas de imitância acústica, audiometria tonal e audiometria vocal previamente à realização do MMN. Para a execução do procedimento eletrofisiológico, MMN, foi utilizado o equipamento Masbe ATC Plus da marca Contronic. Os eletrodos foram fixados nas posições Fpz (eletrodo ativo), M1 e M2 (eletrodos referência) e na fronte (eletrodo terra). A intensidade utilizada para evocar o potencial foi de 80 dBNA, o estímulo frequente utilizado foi de 1.000 Hz e o estímulo raro de 2.000 Hz. Os estímulos foram apresentados em ambas as orelhas de modo monoaural. As crianças realizaram a avaliação sentadas e foram condicionadas a assistirem a um vídeo sem som, no tablet, enquanto o procedimento era realizado. Resultados: Para o grupo feminino, a média das latências e amplitudes foi de 177,3 ms e 5,01 μV na orelha direita e de 182,4 ms e 5,39 μV na orelha esquerda. Quanto ao grupo masculino, a média das latências foi de 194,4 ms na orelha direita e 183,6 ms na orelha esquerda, com amplitude de 5,11 μV na orelha direita e 5,83 μV na orelha esquerda. Não houve diferença estatisticamente significante nos valores de latência e amplitude entre orelhas (p=0,867 e p=0,178), idade (p>0,20) e sexo dos participantes (p>0,05). Conclusão: Os valores encontrados nas latências e amplitudes do potencial MMN são semelhantes aos observados na literatura científica compulsada, em crianças com desenvolvimento típico e sem queixas auditivas. / Aim: To characterize the answers of Mismatch Negativity (MMN) in children with hearing thresholds within the normality patterns and without auditory complaints. Methods: Transversal type study. Children between 5 and 11 years old without auditory complaints have participated in this research. All the participants have done peripheral audiological evaluation with acoustic immittance measures, tonal audiometry and vocal audiometry previously to MMN execution. To perform the electrophysiological procedure, MMN, it was used Masbe ATC Plus equipment from Contronic brand. The electrodes were fixed in Fpz (active electrode), M1 and M2 (reference electrodes) and front (earth electrode) positions. The intensity used to evoke the potential was 80 dBNA, the frequent stimulus used was 1.000 Hz and the rare stimulus was 2.000 Hz. The stimuli were presented in both ears monoaurally. Children performed the assessment sat and they were conditioned to watch a video without sound, on a tablet computer, while the procedure was performed. Results: For the female group, the average of the latencies and amplitudes was 177,3 ms and 5,01 μV for the right ear and 182,4 ms and 5,39 μV for the left ear. Regarding the male group, the average of latencies was 194,4 ms for the right ear and 183,6 ms for the left ear, with an amplitude of 5,11 μV for the right ear and 5,83 μV for the left ear. There was no significant statistically difference for the values of latency and amplitude among ears (p=0,867 and p=0,178), age (p>0,20) and gender of the participants (p>0,05). Conclusion: The values found in the latencies and amplitudes of MMN potential are similar to those observed in the scientific literature examined, in children with typical development and without auditory complaints.

Delayed-rectifier potassium channels comprised of the Kv1.2 subunit are critical in maintaining appropriate neuronal excitability and determining the threshold for action potential firing. This is attributed in part to the interaction of the Kv1.2 subunit with an unidentified molecule that confers bimodal channel activation gating, allowing neurons to adapt to repetitive trains of stimulation and protecting against hyperexcitability. It is well established that the Sigma-1 receptor (Sig-1R) regulates members of the Shaker K+ channel family at baseline and upon Sig-1R ligand-activation. While an interaction between Kv1.2 and Sig-1R has been previously demonstrated, the biophysical nature of this interaction has not been elucidated. We hypothesized that Sig-1R may regulate the Kv1.2 biophysical properties and may further act as the unidentified modulator of Kv1.2 activation gating. To explore the interaction between Kv1.2 and Sig-1R, whole-cell voltage-clamp electrophysiology and apFRET imaging experiments were performed in recombinant HEK293 cells transiently transfected with Kv1.2 and Sig-1R. It was found that ligand-activation of Sig-1R decreases Kv1.2 current amplitude, likely due to a ligand-dependent change in Sig-1R activity rather than increased association of Sig-1R with Kv1.2. Further, we show that Sig-1R interacts with Kv1.2 in baseline conditions to modulate bimodal activation gating. We show that Sig-1R modulation of Kv1.2 is abolished both in the presence of Kvβ2, a known auxiliary subunit of Kv1.2, and following expression of the Sig-1R mutation underlying ALS16 (Sig-1R-E102Q). These data respectively suggest that Kvβ2 physically occludes the interaction of the Sig-1R with Kv1.2, and that E102 may be a residue critical for efficient Sig-1R modulation of Kv1.2. Taken together, this data provides novel insights regarding the modulation of neuronal delayed-rectifier potassium channels by Sig-1R. This work provides a new role for Sig-1R in the regulation of neuronal excitability and introduces a mechanism of pathophysiology in Sig-1R dysfunction.

Orientador: Alexandre Luiz Souto Borges / Coorientadora: Cristiane Campos Costa Quishida / Banca: Cesar Rogério Pucci / Banca: Bruno Vinícius Manzolli Rodrigues / Resumo: O objetivo desse estudo foi sintetizar mantas não tecidas de nanofibras (NFs) de Polietilmetacrilato (PEMA) com adição de nistatina (NYS) e avaliar a atividade antimicrobiana nas resinas reembasadoras rígidas e macias. Realizou- se o teste microbiológico da CIM de NYS para a inativação da C. albicans. NFs foram sintetizadas pela técnica da eletrofiação, utilizando-se solução de PEMA puro e NYS e PEMA. Para a síntese das NFs de PEMA, foi produzida uma solução de PEMA dissolvido em Dimetilformamida (DMF) e 1,1,2,2 Tetracloroetano (TCE), logo após foram adicionadas duas concentrações de NYS (10 e 20 mg/ml) obtidas do teste CIM. As amostras foram analisadas em Microscopia Eletrônica de Varredura (MEV), Análise de molhabilidade, Análise de Difratometria de Raios-X (DRX) e Espectroscopia de Infravermelho por Transformada de Fourier (FTIR). Após a análise em MEV foi realizada a média dos diâmetros das fibras com Software ImageJ. As atividades antimicrobianas foram avaliadas por meio do teste de difusão em ágar. As NFs de PEMA apresentaram diâmetro menor, o padrão NF/PEMA apresentou 0,42µm enquanto que a NF/20 1,14 µm e a NF/10 foi de 0,87 µm. As fibras foram consideradas hidrofóbicas por meio da análise de molhabilidade. O DRX e o FTIR comprovaram a presença de PEMA e sugeriram a presença de NYS. O teste de difusão em ágar demonstrou que as fibras não conseguiram inibir a proliferação de C. albicans / Abstract: The objective of the study was to synthesize nanofibers (NFs) of Polyethylmethacrylate (PEMA) with addition of Nystatin (NYS) and to evaluate an antimicrobial activity in rigid and soft resins. Microbiological testing of NYS MIC for inactivation of C. albicans was performed. NFs were synthesized using the electrochemical technique using pure PEMA and NYS and PEMA solutions. For a synthesis of PEMA NFs, a solution of PEMA dissolved in Dimethylformamide (DMF) and 1,1,2,2 Tetrachloroethane (TCE) was produced, following doses of NYS concentrations (10 and 20 mg / ml) obtained from the CIM. As samples were analyzed in Scanning Electron Microscopy (SEM), Goniometer, X-ray Diffraction Analysis (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). After an SEM analysis, a mean of the fiber diameters was performed with ImageJ Software. The antimicrobial activities were evaluated by means of the agar diffusion test. As the PEMA NFs presented smaller diameter, the NF / PEMA standard showed 0.42 μm whereas NF / 20 1.14 μm and the NF / 10 was 0.87μm. The fibers were considered hydrophobic by means of the wettability analysis. The DRX and the FTIR proved a presence of PEMA and suggested a presence of NYS. The diffusion test on agar demonstrated that as fibers failed to inhibit a proliferation of C. albicans / Mestre

Objetivo: Caracterizar as respostas do Mismatch Negativity (MMN) em crianças com limiares auditivos dentro dos padrões de normalidades e sem queixas auditivas. Métodos: Estudo do tipo transversal. Participaram desta pesquisa crianças de cinco a onze anos, sem queixas auditivas. Todos os participantes realizaram avaliação audiológica periférica com medidas de imitância acústica, audiometria tonal e audiometria vocal previamente à realização do MMN. Para a execução do procedimento eletrofisiológico, MMN, foi utilizado o equipamento Masbe ATC Plus da marca Contronic. Os eletrodos foram fixados nas posições Fpz (eletrodo ativo), M1 e M2 (eletrodos referência) e na fronte (eletrodo terra). A intensidade utilizada para evocar o potencial foi de 80 dBNA, o estímulo frequente utilizado foi de 1.000 Hz e o estímulo raro de 2.000 Hz. Os estímulos foram apresentados em ambas as orelhas de modo monoaural. As crianças realizaram a avaliação sentadas e foram condicionadas a assistirem a um vídeo sem som, no tablet, enquanto o procedimento era realizado. Resultados: Para o grupo feminino, a média das latências e amplitudes foi de 177,3 ms e 5,01 μV na orelha direita e de 182,4 ms e 5,39 μV na orelha esquerda. Quanto ao grupo masculino, a média das latências foi de 194,4 ms na orelha direita e 183,6 ms na orelha esquerda, com amplitude de 5,11 μV na orelha direita e 5,83 μV na orelha esquerda. Não houve diferença estatisticamente significante nos valores de latência e amplitude entre orelhas (p=0,867 e p=0,178), idade (p>0,20) e sexo dos participantes (p>0,05). Conclusão: Os valores encontrados nas latências e amplitudes do potencial MMN são semelhantes aos observados na literatura científica compulsada, em crianças com desenvolvimento típico e sem queixas auditivas. / Aim: To characterize the answers of Mismatch Negativity (MMN) in children with hearing thresholds within the normality patterns and without auditory complaints. Methods: Transversal type study. Children between 5 and 11 years old without auditory complaints have participated in this research. All the participants have done peripheral audiological evaluation with acoustic immittance measures, tonal audiometry and vocal audiometry previously to MMN execution. To perform the electrophysiological procedure, MMN, it was used Masbe ATC Plus equipment from Contronic brand. The electrodes were fixed in Fpz (active electrode), M1 and M2 (reference electrodes) and front (earth electrode) positions. The intensity used to evoke the potential was 80 dBNA, the frequent stimulus used was 1.000 Hz and the rare stimulus was 2.000 Hz. The stimuli were presented in both ears monoaurally. Children performed the assessment sat and they were conditioned to watch a video without sound, on a tablet computer, while the procedure was performed. Results: For the female group, the average of the latencies and amplitudes was 177,3 ms and 5,01 μV for the right ear and 182,4 ms and 5,39 μV for the left ear. Regarding the male group, the average of latencies was 194,4 ms for the right ear and 183,6 ms for the left ear, with an amplitude of 5,11 μV for the right ear and 5,83 μV for the left ear. There was no significant statistically difference for the values of latency and amplitude among ears (p=0,867 and p=0,178), age (p>0,20) and gender of the participants (p>0,05). Conclusion: The values found in the latencies and amplitudes of MMN potential are similar to those observed in the scientific literature examined, in children with typical development and without auditory complaints.

Hearing in noise is facilitated by the auditory system’s ability to separate sound into small auditory segments. Separation of sound is achieved using an auditory mechanism called temporal resolution that codes for small silent gaps in an acoustic stimulus. This thesis proposes a new method for measuring temporal resolution and applied it to a small pilot group of individuals with tinnitus. Previous studies have postulated that tinnitus can “fill” in silent gaps thereby making gap detection more difficult. This was shown in studies using the gap prepulse inhibition acoustic startle where the amplitude of a startle response indicates the subject’s ability to detect a small silent gap. However studies using behavioural gap detection do not show significant differences in people with reported tinnitus. Thus the behavioural evidence does not appear to support the hypothesis that tinnitus can “fill” in silent gaps. In this thesis a new method was proposed for measuring neural gap detection: the mismatch negativity response (MMN). The mismatch negativity responses were compared to behavioural measures of gap detection in thirty-five normal hearing adults: five with reported tinnitus and thirty without tinnitus. They underwent recordings to gapped stimuli ranging from 2- to 40-ms gap durations. The stimuli were either a broadband or narrowband noise presented in the absence or presence of a filler noise. Results of these experiments found the broadband and narrowband noises elicited MMNs to silent gaps. The amplitude of the MMN increased with larger gap durations. When filled, the amplitude of the entire waveform was proportionally reduced for all gap durations. However, for the tinnitus group the filler reduced the largest gap durations elicited MMNs amplitudes disproportionately more than for the smaller gap durations. The high and low filler noise reduced the amplitude of the 40-ms gap MMNs. This was not reflective in the behavioural performance of gap detection as there were no significant group differences. These studies show that neural gap detection can be measured using mismatch negativities. Reduced behavioural gap detection performance is reflected by a smaller amplitude of the MMN for suprathrehold gaps. This was shown in both normal hearing participants with elevated behavioural gap detection thresholds and participants with tinnitus. Therefore, electrophysiological recordings to gaps may provide further information on the underlying mechanisms involved in impaired gap detection that may not be captured by behavioural measures alone.