Bilingualism is becoming more common in world and, despite being much discussed their impact on the language, there s not much knowledge about the effect of different linguistic backgrounds in auditory processing skills. We know that, when a person is exposed to two languages, it increases speed and efficiency of information processing and, therefore, bilingual subject is benefited in development and recognition of patterns of important sounds for speech understanding. Investigate and compare performance of auditory skills in normal hearing adults with different levels of late bilingualism between them, and normal hearing monolingual people using behavioral and electrophysiological tests.This study is descriptive, quantitative and transversal. The sample was consisted of 65 subjects (Monolingual Group (MG) with 13 speakers of Portuguese; Teachers group (GT): 13 bilingual language - schools teachers - (Portuguese - English) and language school students at different levels of proficiency (Portuguese-English): 13 at advanced level (AG); 13 at intermediate level (IG); 13 at basic level (BG)) with normal hearing and no complaints about auditory processing abilities, aged 18-35 years. They were subjected to behavioral tests: Staggered Spondaic Word test (SSW), which evaluates attention skills, memory and figure-ground for verbal sounds; Random Gap Detection Test (RGDT) that assesses ability of temporal resolution; and electrophysiological test Long Latency Auditory Evoked Potential (LLAEP) with verbal stimuli (syllables / ba / - frequent stimulus and / di / - rare stimulus) evaluating memory, attention and auditory discrimination. In a general way, in analysis between groups, there were significant differences with higher values to age, SSW and lower values to RGDT for teachers, compared with monolinguals. Comparing students at different levels of English learning, there were higher values for RGDT and latency of component N1 for basic level of proficiency. Late bilinguals people have further development of attention ability and auditory memory, when compared to monolingual ones. In addition to that, there is an improvement in temporal resolution ability as English learning level increases. / O bilinguismo está cada vez mais comum no mundo e, apesar de ser bastante discutido o seu impacto sobre a linguagem, pouco se sabe sobre o efeito de diferentes origens linguísticas nas habilidades de processamento auditivo. Sabe-se que, quando uma pessoa é exposta a duas línguas, aumenta-se a velocidade e a eficácia do processamento da informação. Portanto, o sujeito bilíngue é beneficiado no desenvolvimento e reconhecimento dos padrões de sons importantes para a compreensão de fala. Esta dissertação visa investigar e comparar o desempenho de habilidades auditivas em indivíduos adultos normo-ouvintes com diferentes níveis de bilinguismo tardio entre si e em relação a normo-ouvintes monolíngues por meio de testes comportamentais e de teste eletrofisiológico. Esse estudo tem caráter descritivo, quantitativo e transversal. A amostra foi composta por 65 sujeitos: Grupo Monolíngue (GM): tre13ze indivíduos falantes da língua portuguesa; Grupo Professores (GP): 13 bilíngues professores de escolas de idiomas (português/inglês); alunos de escolas de idiomas em diferentes níveis de aprendizado (português/inglês): 13 no nível avançado (GA); 13 no nível intermediário (GI); 13 no nível básico (GB), com limiares auditivos tonais dentro dos limites da normalidade e sem queixas de habilidades de processamento auditivo, com idade entre 18 e 35 anos. Os sujeitos foram submetidos aos seguintes testes comportamentais: teste dicótico de dissílabos alternados (SSW), o qual avalia as habilidades de atenção, memória e figura-fundo para sons verbais; teste de detecção de gap (RGDT), que avalia a habilidade de resolução temporal; e teste eletrofisiológico potencial evocado auditivo de longa latência (PEALL) com estímulos verbais (sílabas /ba/ estímulo frequente e /di/ estímulo raro), a fim de avaliar memória, atenção e discriminação auditiva. De maneira geral, na análise entre grupos, houve diferenças significativas, com maiores valores de idade, SSW e menores valores de RGDT para os professores, quando comparados com os monolíngues. Comparando os alunos em diferentes níveis de aprendizado da língua inglesa, verificou-se maiores valores de RGDT e latência do componente N1 para o nível básico de proficiência. Concluiu-se que bilíngues tardios possuem aperfeiçoamento da habilidade de atenção e memória auditiva quando comparados aos monolíngues. Há, também, um aprimoramento da habilidade de resolução temporal conforme aumenta o nível de aprendizado da língua inglesa.

Made available in DSpace on 2016-03-15T19:41:23Z (GMT). No. of bitstreams: 1 Darlene Godoy de Oliveira.pdf: 3172504 bytes, checksum: 95d543d037f25f72c573d89ce7ccd732 (MD5) Previous issue date: 2014-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Developmental Dyslexia has a main deficit the effective word recognition, which is a complex cognitive processing due perceptual skills, language and later stages of syntactic and semantic integration. Among the wide range neurobiological evidence related this disorder in childhood and across life-span, event-related potential measures indicates differentiated pattern in amplitudes, latencies and hemispheric processing in different stages of sensory/perceptual, orthographic, phonologic and semantic processing. These electrophysiological evidences are related to behavioral deficits and to reading compensatory mechanisms in Dyslexia. The present thesis aimed to verify and compare the behavioral and electrophysiological pattern of adults (Study 1) and children and adolescents (Study 2) with and without Dyslexia during a Lexical Decision task. The sample of Study 1 comprised by 20 dyslexics and 23 normal readers with college degree. In Study 2, twenty dyslexic children and adolescents and twenty normal readers were included. All participants were matched for gender, age and educational level and performed a battery of intelligence, reading, writing and phonological awareness tasks. The lexical decision task was composed by regular high frequency words in Brazilian Portuguese, quasi-words derived from real words and pseudowords not derived from real words. Behavioral results in both studies revealed that dyslexics had worse accuracy and increased reaction times in all lexical categories. ERPs analysis of Study 1 indicated greater amplitudes in right P100 for both groups. The N170, N400 and LPC were reduces on the left hemisphere for dyslexics. N400 and LPC were higher for words and quasi-words, stimuli that are represented on orthographic and phonological lexicon. Correlations data in all sample verified reduced N170 and LPC left amplitudes associated with good performance in behavioral reading, writing and phonological awareness tests. GD with slow behavioral performance exhibited higher N170 and N400 on left hemisphere. Study 2 results indicated greater P100 on right hemisphere for all lexical categories in all sample, and reduced for DG. N170 were higher at left side and for quasi-words. N400 were higher for words and quasi-words, as well reduced in left hemisphere for DG. LPC were higher in left hemisphere for pseudowords and reduced in dyslexics. Correlational results revealed reduced left N170, N400 and LPC in dyslexics with slow behavioral performance. Controls with slow performance exibithed higher P100 amplitudes, as well higher left N400 if they had higher reading skills. Generally, ERP analysis indicated lacks of hemispheric specialization in dyslexics. The absence of ERP group differences on Study 2 can be related to developmental reading fluency processes, although we verified positive correlations between higher linguistic ERP amplitudes and better behavioral performances for both children and adults. We conclude that dyslexic children and adults present differenciated ERP amplitudes and hemispheric distribution during reading in Brazilian Portuguese. / A Dislexia do Desenvolvimento tem como déficit principal o reconhecimento eficaz de palavras, sendo este um processamento cognitivo complexo. Dentre as evidências neurobiológicas do transtorno, disléxicos apresentam alterações nos potenciais relacionados a eventos durante o reconhecimento de palavras, com padrão diferenciado de latência, amplitude e processamento hemisférico nos estágios sensório/perceptual, ortográfico, fonológico e semântico. Estes indicam déficits no processamento eletrofisiológico e uso de mecanismos compensatórios de leitura. Esta tese objetivou mensurar e comparar o padrão comportamental e eletrofisiológico de adultos (Estudo 1) e crianças e adolescentes (Estudo 2) com e sem Dislexia do Desenvolvimento durante uma tarefa de decisão lexical. Participaram do Estudo 1 vinte universitários disléxicos e vinte e três adultos bons leitores. Participaram do Estudo 2 vinte crianças e adolescentes disléxicos e vinte controles bom leitores. Os participantes foram pareados por sexo, idade e nível de escolaridade e realizaram uma bateria de testes de inteligência, leitura, escrita e consciência fonológica. A tarefa de decisão lexical foi composta por palavras regulares de alta frequência no português brasileiro, quase-palavras derivadas de palavras reais e pseudopalavras não derivadas. Os resultados comportamentais da tarefa de decisão lexical nos estudos indicaram pior acurácia, maior omissão e lentidão no julgamento dos itens de todas as classes lexicais pelos disléxicos. Análises dos ERPs no Estudo 1 indicaram maior amplitude do P100 no hemisfério direito em ambos os grupos. Os potenciais N170, N400 e LPC foram reduzidos no hemisfério esquerdo dos disléxicos. O N400 e o LPC foram mais pronunciados nas palavras e quase-palavras, estímulos com representação no léxico fonológico e ortográfico. Correlações com os dados da amostra total; indicaram menores amplitudes N170 e LPC no hemisfério esquerdo associadas à alta acurácia nos testes comportamentais de leitura, escrita e consciência fonológica, enquanto que no GD, o N170 e o N400 foram mais pronunciados no hemisfério esquerdo dos sujeitos mais lentos nas tarefas. Análises do Estudo 2 indicaram P100 maior no hemisfério direito em todas as categorias lexicais nos dois grupos, e reduzido no GD. O N170 tendeu a ser mais pronunciado no hemisfério esquerdo e nas quase-palavras. O N400 foi maior nas palavras e quase-palavras, sendo reduzido no hemisfério esquerdo do GD. O LPC foi maior no hemisfério esquerdo para as pseudopalavras e foi reduzido no GD. Foram encontradas correlações negativas entre amplitudes do N170, N400 e LPC esquerdo nos disléxicos com o tempo de execução nas tarefas comportamentais. No GC, o P100 foi maior nos sujeitos mais lentos e houve associação positiva dasamplitudes do N400 esquerdo e acurácia na leitura. No geral, as análises dos ERPs nos experimentos indicam déficits de especialização hemisférica em disléxicos. Ausências de diferenças entre os grupos do Estudo 2 nos ERPs analisados podem estar relacionadas a fatores desenvolvimentais da leitura, embora tanto em crianças como em adultos disléxicos já haja associação positiva entre bom desempenho comportamental e maiores amplitudes nos ERPs linguísticos. Conclui-se que crianças e adultos disléxicos apresentam padrão diferenciado de amplitudes e distribuição hemisférica em distintos ERPs durante a leitura no Português Brasileiro.

La navigation spatiale désigne la capacité de s'orienter et se repérer dans un environnement, et est particulièrement altérée chez les personnes âgées. Dans ce travail de thèse, nous proposons d'identifier les mécanismes sous-tendant le déclin de cette fonction chez les seniors. Nous avons comparé les performances de participants âgés à celles de sujets jeunes lors de tâches spatiales, et employé la technique des potentiels évoqués (PE) afin d’analyser les mécanismes neuronaux sous-jacents. Nous avons montré une atteinte de la localisation allocentrique chez les seniors, tandis que la localisation égocentrique semble préservée. Nous avons étudié l'efficience de processus visuo-perceptifs et attentionnels chez les sujets âgés. L'analyse des PE montre une préservation des processus perceptifs avec l'âge, tandis que les processus d'attention spatiale semblent particulièrement décliner. Enfin, les processus d'encodage spatial semblent également affectés chez les sujets âgés. / Spatial navigation refers to the ability to find one's way in complex environments, and is particularly affected in elderly individuals. We aimed to better understand the mechanisms underlying age-related deficits in spatial navigation, focusing on early cognitive processes. For this purpose, we compared performances obtained by elderly individuals above 60 years and by younger adults during spatial tasks, and used the event-related potentials (ERP) technique to investigate underlying neural processes. First, we found that allocentric localization is impaired in aging, whereas egocentric localization seems to be preserved. Then, we investigated the role of visuo-perceptive or attentional processes in spatial cognition, and their preservation in aging. ERP showed that perceptive processes seem to be preserved in elderly individuals, whereas spatial attention processes were impaired in these subjects. Finally, we showed that encoding processes are also particularly affected by aging.

L’objectif de ce travail de thèse a été d’avancer dans la compréhension des mécanismes par lesquels les émotions positives modulent cognition et comportement. En nous basant sur des mesures comportementales et électrophysiologiques, nous avons abordé ce questionnement chez des volontaires sains, et des personnes souffrant de schizophrénie, pathologie dans laquelle les affects n’influencent pas le comportement de manière appropriée. Nos résultats montrent que les émotions positives diminuent de manière globale la préparation attentionnelle, un des mécanismes de contrôle cognitif. Néanmoins, lorsqu’elles sont associées à un fort niveau de motivation, elles permettent au contraire une mobilisation plus importante du contrôle cognitif. Cette modulation du contrôle cognitif par les émotions positives est plus susceptible d’apparaitre chez les personnes présentant une tendance marquée à ressentir des émotions négatives. Chez les personnes souffrant de schizophrénie, cette modulation ne s’effectue pas de manière appropriée, y compris lorsque l’expérience affective positive est induite de manière non consciente. / The aim of this project was to deepen our understanding of the mechanisms by which positive emotions modulate cognition and behavior. By using behavioral and electrophysiological measures, we addressed this question in a population of healthy controls, and in patients suffering from schizophrenia, because in this disease affect does not appropriately modulate behavior. Our results show that positive emotions globally decrease attentional preparation, a cognitive control mechanism. Nevertheless, when associated with a high level of motivation, they allow for improved recruitment of cognitive control. This modulation of cognitive control by positive emotions is more likely to appear in individuals who have a marked tendency towards experiencing negative emotions. In patients suffering from schizophrenia, this modulation is not appropriate, not even for non-consciously induced positive affective experiences.

La particularité du temps est de n’être l’objet d’aucun système sensoriel, contrairement aux stimulations lumineuses ou sonores. Quelles sont les opérations cognitives, en dehors de l’horloge interne, qui sont impliquées dans le fait que nous soyons capables de dire qu’une durée est plus courte qu’une autre ? Quelle est la dynamique de ces processus ? Pour le déterminer, nous nous sommes basés sur l’étude du comportement et des potentiels évoqués dans des tâches de discrimination temporelle. Plusieurs objectifs ont été poursuivis. Premièrement, il s’agissait de déterminer les processus, ainsi que leur dynamique, pouvant être mis en évidence dans la manipulation de l’information temporelle. Un deuxième objectif consistait à préciser l’impact du contexte sur le recrutement et la dynamique de ces processus. Un dernier objectif était d’explorer l’effet de la durée présentée et celui de la consigne sur les processus impliqués dans le traitement temporel et sur leur dynamique. Les résultats principaux sont les suivants. Premièrement, des composantes évoquées frontopariétales indexaient la comparaison, la prise de décision, l’attention et la mémoire de travail. Deuxièmement, ces activités étaient modulées par la saillance perceptive. En outre, une durée particulièrement saillante permet de terminer la comparaison avant la fin du stimulus. Troisièmement, le contexte de présentation modulait les activités évoquées associées au moment où la décision est prise. En conclusion, cette thèse met en évidence que les processus à l’œuvre dans la perception temporelle ne sont pas spécifiques au traitement des durées, comme l’attention et la mémoire de travail. / The peculiarity of time is that it is not the object of any sensory system, contrary to the stimuli consisting of light or sound. What cognitive operations, apart from the internal clock, are involved in the fact that we are able to say that one duration is shorter than another? What is the dynamic of these processes? To determine it, we have based ourselves on the study of the behavior and the event-related potentials in several tasks of temporal discrimination. Several objectives were adressed. The first objective was to determining the processes and associated ERPs, as well as their dynamics that can be demonstrated in the manipulation of the temporal information. A second aim was to specify the impact of the context on recruitment and the dynamics of these processes. A final objective was to investigate the effect of the duration presented and that of the instruction on the processes involved in the temporal treatment as well as on their dynamics. The main results are as follows. First, frontoparietal event-related components indexed comparison, decision making, orientation of attention and working memory. Secondly, these activities were modulated by the perceptual salience of a duration. Moreover, a particularly salient duration allow the end of the comparison before the end of the stimulus. Third, the impact of the presentation context modulated the evoked activities associated at the time the decision is made. In conclusion, this thesis shows that the processes at work in time perception are not specific to the treatment of durations, such as attention and working memory.

Substantial research has been done on the electroencephalogram (EEG) neural signals generated by feedback within a simple choice task, and there is much evidence for the existence of a reward prediction error signal generated in the anterior cingulate cortex of the brain when the outcome of this type of choice does not match expectations. However, less research has been done to date on the neural responses to intermediate outcomes in a multi-step choice task. Here, I investigated the neural signals generated by a complex, non-deterministic task that involved multiple choices before final win/loss feedback in order to see if the observed signals correspond to predictions made by reinforcement learning theory. In Experiment One, I conducted an EEG experiment to record neural signals while participants performed a computerized task designed to elicit the reward positivity, an event-related brain potential (ERP) component thought to be a biological reward prediction error signal. EEG results revealed a difference in amplitude of the reward positivity ERP component between experimental conditions comparing unexpected to expected feedback, as well as an interaction between valence and expectancy of the feedback. Additionally, results of an ERP analysis of the amplitude of the P300 component also showed an interaction between valence and expectancy. In Experiment Two, I used machine learning to classify epoched EEG data from Experiment One into experimental conditions to determine if individual states within the task could be differentiated based solely on the EEG data. My results showed that individual states could be differentiated with above-chance accuracy. I conclude by discussing how these results fit with the predictions made by reinforcement learning theory about the type of task investigated herein, and implications of those findings on our understanding of learning and decision-making in humans. / Graduate

Researchers are often interested in comparing brain activity between experimental contexts. Event-related potentials (ERPs) are a common electrophysiological measure of brain activity that is time-locked to an event (e.g., a stimulus presented to the participant). A variety of decomposition methods has been used for ERP data among them temporal exploratory factor analysis (EFA). Essentially, temporal EFA decomposes the ERP waveform into a set of latent factors where the factor loadings reflect the time courses of the latent factors, and the amplitudes are represented by the factor scores. An important methodological concern is to ensure the estimates of the condition effects are unbiased and the term variance misallocation has been introduced in reference to the case of biased estimates. The aim of the present thesis was to explore how exploratory factor analytic methods can be made less prone to variance misallocation. These efforts resulted in a series of three publications in which variance misallocation in EFA was described as a consequence of the properties of ERP data, ESEM was proposed as an extension of EFA that acknowledges the structure of ERP data sets, and regularized estimation was suggested as an alternative to simple structure rotation with desirable properties. The presence of multiple sources of (co-)variance, the factor scoring step, and high temporal overlap of the factors were identified as major causes of variance misallocation in EFA for ERP data. It was shown that ESEM is capable of separating the (co-)variance sources and that it avoids biases due to factor scoring. Further, regularized estimation was shown to be a suitable alternative for factor rotation that is able to recover factor loading patterns in which only a subset of the variables follow a simple structure. Based on these results, regSEMs and ESEMs with ERP-specific rotation have been proposed as promising extensions of the EFA approach that might be less prone to variance misallocation. Future research should provide a direct comparison of regSEM and ESEM, and conduct simulation studies with more physiologically motivated data generation algorithms.

<p>Touch plays a key role in facilitating social communication and is often presented in conjunction with auditory stimuli such as speech. Individuals with autism spectrum disorder (ASD) frequently show atypical behavioral responsivity to both tactile and auditory stimuli, which is associated with increased ASD symptomatology. However, as discussed throughout Chapter 1, the neural mechanisms associated with responsivity to tactile and auditory stimuli in ASD are not fully understood. For example, some have argued that differences in responding to tactile and auditory stimuli may be attributed to sensory and perceptual factors, whereas others suggest that these differences could be related to atypicalities in allocation of attention to incoming stimuli. In Chapter 2, I address these competing hypotheses by examining early and late ERP components (indicative of perceptual and attentional processing respectively) in response to tactile and auditory stimuli. Next, despite the evidence suggesting that touch plays a role in modulating attention in typical development (TD), it is unclear whether touch cues affect the response of the phasic alerting network – a subcomponent of attention – in ASD and TD, and whether the alerting response may be atypical in children with ASD. In Chapter 3, I address this gap in the literature by examining whether tactile cues presented at different intervals before auditory targets facilitate reaction times differently in children with ASD and TD. Lastly, because prior research has shown associations between sensory and attentional processes and ASD symptomatology, in Chapters 2 and 3, I examine the associations of neural and behavioral indices of tactile and auditory processing with ASD symptomatology and language skills in children with ASD and TD. </p><p>In Chapter 2, I show that children in both the ASD and TD groups do not exhibit differences in both early and later neurological responses to tactile and auditory stimuli, suggesting that under certain experimentally-controlled conditions, behavioral differences to tactile and auditory stimuli may not be attributable to atypicalities in perceiving or attending to the incoming sensory input. However, neural responsivity to tactile and auditory stimuli is linked with sensory responsivity and social skills in all children. Specifically, reduced early contralateral activation to tactile stimuli is related to increased tactile symptoms, and reduced early amplitudes to auditory oddball stimuli are associated with impairments in reciprocal social communication in children with ASD as well as when examined across all children, and greater tendency of overall sensory hyper-reactivity. Additionally, in the TD group, greater later amplitudes to touch and auditory oddball stimuli are related to differences in reciprocal social communication and sensory reactivity respectively, indicating that patterns of allocation of attention may be related to ASD-like traits in typical development. Lastly, there is an association between greater sensitivity to changes to a stream of auditory stimuli and expressive language skills in all children. These results suggest that, although there are no group differences between neurological responses to tactile and auditory stimuli in ASD and TD, individual neural differences may be related to sensory and socio-communicative skills in all children. </p><p>In Chapter 3, I show that although children with ASD responded more slowly than children with TD, both groups displayed faster reaction times as a result of tactile cues before auditory targets, suggesting equivalent phasic alerting in response to tactile stimuli. Longer intervals between cues and targets benefitted children in both groups resulting in faster reaction times. Contrary to my hypotheses, touch-related behavioral facilitation was not associated with ASD symptomatology and language skills. </p>Taken together, the results of these studies suggest that, at least in certain contexts and with certain cues, children with ASD may show typical neurological processing in response to tactile and auditory stimuli, and that touch may facilitate the response of the alerting network similarly in ASD and TD. Therefore, everyday behavioral differences in response to tactile and auditory stimuli may be related to the specific nature of the stimuli as well as social contexts in which such stimuli are more likely to be encountered. Differences between processing rich and dynamic sensory stimuli experienced in the outside world vs experimentally-controlled sensory stimuli presented in the laboratory settings are discussed in Chapter 4. Additionally, I argue that individual responses expected in social vs non-social experimental settings may affect neural and behavioral responses in individuals with ASD. Finally, future research directions are discussed.

Children learn their first language simply by listening to the linguistic utterances provided by their caregivers and other speakers around them. In order to extract meaning and grammatical rules from these utterances, children must track regularities in the input, which are omnipresent in language. The ability to discover and adapt to these statistical regularities in the input is termed statistical learning and has been suggested to be one of the key mechanisms underlying language acquisition. In this thesis, I investigated a special case of statistical learning, non-adjacent dependency (NAD) learning. NADs are grammatical dependencies between distant elements in an utterance, such as is and -ing in the sentence Mary is walking. I examined which factors play a role in the development of NAD learning by illuminating this process from different stand points: the first study compares NAD learning in the linguistic and the non-linguistic domain during the earliest stages of development, at 4 months of age. This study suggests that at this age, NAD learning seems to be domain-specific to language. The second study puts a spotlight on the development of NAD learning in the linguistic domain and proposes that there may be a sensitive period for linguistic NAD learning during early childhood. Finally, the third study shows that children can not only recall newly learned NADs in a test immediately following familiarization, but also recall them after a retention period, which is critical to show more long-term learning. Overall, the findings in this thesis further illuminate how NADs, as a spotlight into language acquisition, are learned, stored in memory, and recalled.

Schizophrenia is a troubling and severe mental illness that is only incompletely treated by currently available drugs. New drug development is hindered by a scarcity of functionally relevant pharmacodynamic biomarkers that are translatable across preclinical and human subjects. Although psychosis is a major feature of schizophrenia, cognitive and negative symptoms determine the long-term functional outcomes for patients. Stimulus-evoked neural synchrony at gamma (~ 40 Hz) frequency plays an important role in the processing and integration of sensory information. Not surprisingly, schizophrenia patients show deficits in gamma oscillations. NMDA receptor (NMDAR) activation on fast-spiking parvalbumin-positive interneurons is deemed important for the generation of gamma oscillations. NMDA hypofunction has been proposed as an alternative hypothesis to the well-known dopamine dysregulation to explain the neurochemical abnormalities associated with schizophrenia. For this dissertation, we validated a preclinical model to pharmacologically probe NMDA-mediated gamma oscillations by further characterizing the auditory-steady state response (ASSR) in female Sprague Dawley rats. The ASSR is a measure of cortical neural synchrony evoked in response to periodic auditory stimuli. ASSR at 40 Hz is consistently disrupted in patients. First, we established the reliability of click train-evoked 40 Hz ASSR and tone-evoked gamma oscillations in 6 separate sessions, spread over a 3-week period. Then we established the sensitivity of these neural synchrony measures to acute NMDAR blockade using the high affinity NMDA channel blocker MK-801, using a repeated measures design. Next, we compared the reliability and sensitivity of the 40 Hz ASSR from two distinct recording sites. Results from this study showed that as compared to vertex, temporal recording showed a greater gamma synchrony. However, the temporal recording had poor test-retest reliability and lower sensitivity to MK-801-induced disruption. Lastly, we characterized the dose-response profiles of an NMDA co-agonist D-serine, an atypical (clozapine) and a typical (haloperidol) antipsychotic, on the 40 Hz ASSR. Results from these studies showed that only clozapine was effective in robustly augmenting 40 Hz ASSR. Furthermore, only clozapine pretreatment had partial protective effect against MK-801 induced ASSR disruption. Overall, this work establishes that vertex recorded 40 Hz ASSR is a reliable neural synchrony biomarker in female SD rats that is amenable for bidirectional pharmacodynamic modulation.