Experimental and computational investigations addressing how various neural functions are achieved in the brain converged in recent years to a unified idea that the neural activity underlying most of the cognitive functions is distributed over large scale networks comprising various cortical and subcortical areas. Modeling approaches represent these areas and their connections using diverse models of neurocomputational units engaged in graph-like or neural field-like structures. Regardless of the manner of network implementation, simulations of large scale networks have encountered significant difficulties mainly due to the time delay introduced by the long range connections. To decrease the computational effort, it is common to assume severe approximations to simplify the descriptions of the neural dynamics associated with the system's units. In this dissertation we propose an alternative framework allowing the prevention of such strong assumptions while efficiently representing th e dynamics of a complex neural network. First, we consider the dynamics of small scale networks of globally coupled non-identical excitatory and inhibitory neurons, which could realistically instantiate a neurocomputational unit. We identify the most significant dynamical features the neural population exhibits in different parametric configuration, including multi-cluster dynamics, multi-scale synchronization and oscillator death. Then, using mode decomposition techniques, we construct analytically low dimensional representations of the network dynamics and show that these reduced systems capture the dynamical features of the entire neural population. The cases of linear and synaptic coupling are discussed in detail. In chapter 5, we extend this approach for spatially extended neural networks. / We consider the dynamical behavior of a neural field-like network, which incorporates many biologically realistic characteristics such as heterogeneous local and global connectivity as well as dispersion in the neural membrane excitability. We show that in this case as well, we can construct a reduced representation, which may capture well the dynamical features of the full system. The method outlined in this dissertation provides a consistent way to represent complex dynamical features of various neural networks in a computationally efficient manner. / by Roxana A. Stefanescu. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

Autism is a neurodevelopmental disorder that is characterized by deficits involving social interaction, communication, and perception. Although there is much research that has examined functional neural connectivity in individuals with autism, few have conducted these studies in very young children while awake across EEG power and coherence measures. Anomalies in EEG coherence and power have been associated with deficits in executive function and mental activity. The present study examined neural activation and functional connectivity with an EEG, in children ages 3 -5, during an eyesclosed baseline period. Discrete Fourier Transform was performed on artifact-free segments of EEG data to produce power density values. In addition, coherence measurements were examined to assess functional connectivity in the alpha bandwidth during the baseline recording. Children with autism spectrum disorder (ASD) demonstrated reduced alpha coherence in fronto-temporal regions and between right temporal sites when compared to typically developing (TD) children. In addition, the reduction in coherence was based on ASD severity, such that high-functioning children with ASD showed greater coherence than low-functioning children with ASD. Children with ASD also displayed reduced power in the alpha, beta, and theta frequency bandwidths in frontal, temporal, central, and occipital regions compared to TD children. Interestingly, delta power differentiated children based on developmental status such that high-functioning children with ASD demonstrated the greatest delta power, followed by TD children, and then low-functioning children with ASD. Finally, TD children demonstrated left anterior temporal EEG asymmetry in the alpha bandwidth, whereas children with high-functioning ASD exhibited left posterior temporal EEG asymmetry and right frontal EEG asymmetry. Thus, the results suggest that children with ASD exhibit atypical patterns of brain activity and functional connectivity compared to their typically developing counterparts. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.

Number perception, its neural basis and its relationship to how numerical stimuli are presented have been challenging research topics in cognitive neuroscience for many years. A primary question that has been addressed is whether the perception of the quantity of a visually presented number stimulus is dissociable from its early visual perception. The present study examined the possible influence of visual quality judgment on quantity judgments of numbers. To address this issue, volunteer adult subjects performed a mental number comparison task in which two-digit stimulus numbers (Arabic number format), among the numbers between 31 and 99 were mentally compared to a memorized reference number, 65. Reaction times (RTs) and neurophysiological (i.e. electroencephalographic (EEG) data) responses were acquired simultaneously during performance of the two-digit number comparison task. In this particular quantity comparison task, the number stimuli were classified into three distance factors. That is, numbers were a close, medium or far distance from the reference number (i.e., 65). In order to evaluate the relationship between numerical stimulus quantity and quality, the number stimuli were embedded in varying degrees of a typical visual noise form, known as "salt and pepper noise" (e.g., the visual noise one perceives when viewing a photograph taken with a dusty camera lens). In this manner, the visual noise permitted visual quality to be manipulated across three levels: no noise, medium noise (approximately 60% degraded visual quality from nonoise), and dense noise (75% degraded visual quality from no-noise). / The RTs provided the information about the overt responses; however, the temporal relationship of visual quality (starts earlier than quantity perception) and quantity were examined using eventrelated potentials (ERPs) extracted from continuous EEG recordings. The analysis of the RTs revealed that the judgment of number quantity is dependent upon visual number quality. In addition, the same effect was observed over the ERP components occurring between 100 ms and 300 ms after stimulus onset time over the posterior electrodes. Principal components analysis (PCA) and independent component analysis (ICA) methods were used to further analyze the ERP data. The consistent results of the PCA and ICA were used to represent the spatial brain dynamics, as well as to obtain temporal dynamics. The overall conclusion of the present study is that ERPs, ICs and PCs along with RTs suggested a strategy of quantitative perception (i.e., number comparison) based on the qualitative attributes of the stimuli highlighting the importance of the design of the task and the methodology / by Meltem Ballan. / Thesis (Ph.D.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Male C7BL/6J mice were implanted with bilateral dorsal CA1 guide cannulae. After confirming that intrahippocampal microinfusion of muscimol impaired hippocampal function, demonstrated by impaired performance in the Morris water maze, the influence of intrahippocampal muscimol was tested in the Novel Object Recognition paradigm. During a test session 24 h after the last habituation/sample session, mice were presented with one familiar object and one novel object. Successful retention of object memory was inferred if mice spent more time exploring the novel object than the familiar object. Results demonstrate that muscimol infused into dorsal CA1 region prior to the test session eliminates novel object preference, indicating that the hippocampus is necessary for the retrieval of this non-spatial memory - a topic that has garnered much debate. Understanding the similarities between rodent and human hippocampal function could enable future animal studies to effectively answer questions about diseases and disorders affecting human learning and memory. / by Lisa Rios. / Thesis (M.A.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

The human prefrontal cortex (PFC) is associated with complex cognitive behaviors such as planning for the future, memory for serial order, social information processing and language. Understanding how the PFC has changed through time is central to the study of human neural evolution. Here we investigate the expansion of the PFC by measuring relative surface area of the PFC in Pan troglodytes and Homo sapiens. Magnetic resonance images (MRI's) from 8 preserved chimpanzee brains (3 male and 5 female adults) were segmented and measured. The results of this study indicate that there are gross anatomical differences between the chimpanzee and human prefrontal cortex beyond absolute size. The lower surface area to volume ratio in PFC of the chimpanzee when compared to a human indicates less gyral white matter in this region and thus, less associative connectivity. This anatomical evidence of a difference corresponds with the lesser cognitive complexity observed in chimpanzees. / by Ian D. George. / Thesis (M.A.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

The endogenous, or voluntary, control of visuospatial attention relies upon interactions within a frontoparietal dorsal attention network (DAN) and this network’s top-down influence on visual occipital cortex (VOC). While these interactions have been shown to occur during attention tasks, they are also known to occur to some extent at rest, but the degree to which task-related interactions reflect either modulation or reorganization of such ongoing intrinsic interactions is poorly understood. In addition, it is known that in spatial neglect—a syndrome following unilateral brain lesions in which patients fail to attend to the contralesional side of space—symptom severity covaries with disruptions to intrinsic interhemispheric interactions between left and right homologous regions of the DAN; however, similar covariance with disruptions to intrahemispheric interactions within the DAN, and between the DAN and VOC, has not been demonstrated. These issues are addressed herein via the measurement of both undirected and directed functional connectivity (UFC, DFC) within the DAN and between the DAN and VOC. UFC and DFC were derived from correlations of, and multivariate vector autoregressive modeling of, fMRI BOLD time-series, respectively. Time-series were recorded from individuals performing an anticipatory visuospatial attention task and individuals at rest, as well as from stroke patients either with or without neglect and age-matched healthy controls. With regard to the first issue, the results show that relative to rest, top-down DAN-to-VOC influence and within-DAN coupling are elevated during task performance, but also that intrinsic connectivity patterns are largely preserved during the task. With regard to the second issue, results show that interhemispheric imbalances of intrahemispheric UFC and DFC both within the DAN and between the DAN and VOC strongly correlate with neglect severity, and may co-occur with functional decoupling of the hemispheres. This work thus demonstrates that the intrinsic functional integrity of the DAN and its relationship to VOC is crucial for the endogenous control of visuospatial attention during tasks, and that the compromise of this integrity due to stroke likely plays a role in producing spatial neglect. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

This study investigated electroencephalographic differences related to cue (central left- or right-directed arrows) in a covert endogenous visual spatial attention task patterned after that of Hopf and Mangun (2000). This was done with the intent of defining the timing of components in relation to cognitive processes within the cue-target interval. Multiple techniques were employed to do this. Event-related potentials (ERPs) were examined using Independent Component Analysis. This revealed a significant N1, between 100:200 ms post-cue, greater contralateral to the cue. Difference wave ERPs, left minus right cue-locked data, divulged significant early directing attention negativity (EDAN) at 200:400 ms post-cue in the right posterior which reversed polarity in the left posterior. Temporal spectral evolution (TSE) analysis of the alpha band revealed three stages, (1) high bilateral alpha precue to 120 ms post-cue, (2) an event related desynchronization (ERD) from approximately 120 ms: 500 ms post-cue, and (3) an event related synchronization (ERS) rebound, 500: 900 ms post-cue, where alpha amplitude, a measure of activity, was highest contralateral to the ignored hemifield and lower contralateral to the attended hemifield. Using a combination of all of these components and scientific literature in this field, it is possible to plot out the time course of the cognitive events and their neural correlates. / by Edward Justin Modestino. / Vita. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

This study investigates affect coding within the therapeutic relationship, by exploring the client's and therapist's perception of the relationship and the facial and vocal affect expressed by both parties. A sample of 14 therapy sessions each having 1800 data points was collected. The Working Alliance Inventory Short Form (WAI-S) and Real Relationship Inventory (RRI) were completed after each recorded session. The participants were therapists and clients at a university counseling center in South Florida. Data were analyzed using one-tailed t tests, descriptive statistics, scores from RRI and the WAI-S and percentages of negative, neutral and positive affect. Statistically significant relationships were found between seconds of therapist negative affect (t(13)= -2.065, p. <.05) and seconds of therapist neutral affect (t(13)= -1.959, p. <.05) for clients who dropped out of therapy. The seconds of negative affect coded for clients (t(13) = -1.396, p. >.05) was approaching statistical significance for clients who drop out of therapy. This study provides theoretical and empirical support for linking the presence of facial affect in the first session and its effects on the therapeutic relationship and thus client retention or drop out. The clinical implications of these findings are also discussed. / by Ashley J. Luedke. / Thesis (Ph.D.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

SK channels are small conductance Ca2+-activated K+ channels expressed throughout the CNS. SK channels modulate the excitability of hippocampal CA1 neurons by affecting afterhyperpolarization and shaping excitatory postsynaptic responses. Such SK-mediated effects on activity-dependent neuronal excitability and synaptic strength are thought to underlie the modulatory influence of SK channels on memory encoding. Here,the effect of a new SK1 selective activator, GW542573X, on hippocampal-dependent object memory, contextual and cued conditioning, and trace fear conditioning was examined. The results demonstrated that pre- but not post-training systemic administration of GW542573X impaired object memory and trace fear memory in mice 24 h after training. Contextual and cued fear memory were not disrupted. These current data suggest that activation of SK1 subtype-containing SK channels impairs long-term memory. These results are consistent with converging evidence that SK channel activation suppressed behaviorally triggered synaptic plasticity necessary for encoding hippocampal-dependent memory. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

We sought to better understand human motor control by investigating functional interactions between the Supplementary Motor Area (SMA), dorsal Anterior Cingulate Cortex (dACC), and primary motor cortex (M1) in healthy adolescent participants performing visually coordinated unimanual finger-movement and n-back working memory tasks. We discovered modulation of the SMA by the dACC by analysis of fMRI BOLD time series recorded from the three ROIs (SMA, dACC, and M1) in each participant. Two measures of functional interaction were used: undirected functional connectivity was measured using the Pearson product-moment correlation coefficient (PMCC), and directed functional connectivity was measured from linear autoregressive (AR) models. In the first project, task-specific modulation of the SMA by the dACC was discovered while subjects performed a coordinated unimanual finger-movement task, in which the finger movement was synchronized with an exogenous visual stimulus. In the second project, modulation of the SMA by the dACC was found to be significantly greater in the finger coordination task than in an n-back working memory, in which the same finger movement signified a motor response indicating a 0-back or 2-back working memory match. We thus demonstrated in the first study that the dACC sends task-specific directed signals to the supplementary motor area, suggesting a role for the dACC in top-down motor control. Finally, the second study revealed that these signals were significantly greater in the coordinated motor task than in the n-back working memory task, suggesting that the modulation of the SMA by the dACC was associated with sustained, continuous motor production and/or motor expectation, rather than with the motor movement itself. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection