Browsing by Subject "fMRI"
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Item Alcohol-induced fragmentary blackouts : associated memory processes and neural correlates(2010-08) Wetherill, Reagan Rochelle, 1979-; Fromme, Kim; Schnyer, David M.; Tucker, David M.; Beevers, Christopher; Springer, David W.Alcohol-induced blackouts, or periods of anterograde amnesia without loss of consciousness, were a diagnostic indicator in Jellinek’s (1952) theory of alcoholism and have been correlated with alcohol use problems (Campbell & Hodgins, 1993; Goodwin, Crane, & Guze, 1969; Ryback, 1970; Tarter & Schneider, 1976). Other findings suggest that blackouts are a warning sign of problem drinking, but not a predictor of alcohol use disorders (Anthenelli, Klein, Tsuang, Smith, & Schuckit, 1994). Most published research on blackouts focuses on cognitive deficits among older alcohol-dependent adults, yet recent research indicates prevalence rates for blackouts as high as 50% among college students (White, Jamieson-Drake, & Swartzwelder, 2002). In addition, young adults who reported experiencing a blackout were later told that they had vandalized property, driven a car, or engaged in other risky behaviors without remembering (Buelow & Koeppel, 1995). Despite their high prevalence and associated negative consequences, relatively little is known about alcohol-induced blackouts or their neural, social, and behavioral correlates among non-dependent populations. The current research explored individual variation in memory functioning under sober and intoxicated conditions and alcohol’s effects on neural activation during memory processes.Item Bridging the gap between psychological and neural models of judgment : applying a dual-process framework to neural systems of social and emotional judgment(2012-05) Bhanji, Jamil Palacios; Beer, Jennifer S., 1974-; Maddox, W T.; Henderson, Marlone D.; Gershoff, Andrew D.; Schnyer, David M.Psychological models of judgment and decision-making that focus on dual processes distinguish between two modes of judgment. One mode of judgment uses incomplete, probabilistic associations that lead to good-enough judgments for most situations. A second mode of judgment uses more complete information and applies deterministic decision rules to reason through a decision. The two modes operate in parallel but they can also interact and may be viewed as ends of a continuum. Although some psychology researchers have hypothesized that the two modes of information processing are carried out by distinct neural systems, neural research has not fully tested the distinctions that psychological research has drawn between the two modes. Three studies aim to address the gap between psychological and neural models of judgment and decision-making. Study 1 addresses the lack of neural research comparing judgments based on probabilistic information (characteristic of the first mode of judgment in dual-process models) with judgments based on deterministic rules (characteristic of the second mode of judgment in dual-process models). Specifically, Study 1 compares basic probabilistic judgments and deterministic rule-based judgments to identify neural regions that are preferentially associated with one mode of judgment. Study 2 moves toward a more ecologically valid investigation of neural systems associated with judgments based on probabilistic associations. That is, Study 2 examines a probabilistic cue that is used in real-world judgments: affect. Study 3 examines neural regions associated with the interaction of the two modes of judgment in the underexplored domain of social evaluation. Modes of judgment may interact when the second mode of judgment uses new information to adjust a judgment previously driven by the first mode of judgment, as when a hiring manager uses information about a job candidate to adjust a first impression initially based on appearance. Study 3 examines the neural systems involved when people use newly available information to adjust a previously made affectively-driven judgment. Findings in the three studies contribute to scientific understanding of how neural regions support judgment, but do not definitively identify separable neural systems for dual-process modes of judgment.Item Cerebrovascular reactivity and the fMRI-BOLD response in cardiorespiratory fitness(2015-08) Gonzales, Mitzi Michelle; Haley, Andreana P.; Tanaka, Hirofumi; Mumford, Jeanette A; Schnyer, David M; Maddox, W. ToddAccumulating evidence indicates that poorer vascular health accelerates cognitive decline and increases the likelihood of dementia in old age. Aerobic fitness, as a protective factor against vascular dysfunction, may thus serve to attenuate age-related cognitive pathology. The overarching aim of the current investigations was to determine the impact of cardiorespiratory fitness on cognition and its underlying neural substrates. Sedentary and endurance-trained middle-aged adults underwent general health assessment, neuropsychological testing, and functional magnetic resonance imaging (fMRI) during a working memory task and a hypercapnic (breath-hold) challenge. As compared with sedentary age-matched controls, the endurance-trained adults displayed a trend towards better executive function performance and faster reaction time on the working memory task, indicating enhanced speed of information processing. The neural substrates underlying fitness-related cognitive enhancement were explored by examining the blood oxygen level dependent (BOLD) response to a 2-Back working memory task. Additionally, breath-hold calibration of the working memory task was performed in order reduce vascular variance and provide a closer approximation of the neural contributions to the BOLD signal. After breath-hold calibration, the endurance-trained adults displayed greater working memory-related activation in the right middle frontal gyrus, indicating that fitness likely benefits the neural processes underlying cognition over and above global fitness-related changes in cerebrovascular reactivity. Finally, endothelial function was examined as a potential mechanism underlying fitness-related differences in cerebrovascular reactivity. Peripheral endothelial function failed to predict the BOLD signal to hypercapnia, suggesting that the response may be governed by nonendothelial-dependent vasoregulators. In summary, higher cardiorespiratory fitness at midlife may increase executive function abilities by enabling greater recruitment of neural resources during challenging cognitive tasks. Longitudinal studies will be instrumental in determining if these fitness-related changes are capable of modulating the trajectory of cognitive decline across the lifespan.Item Characterizing the age-related decline of memory monitoring : neuroimaging and genetic approaches(2011-05) Pacheco, Jennifer Lynn; Schnyer, David M.; Maddox, W T.; Beevers, Christopher G.; Haley, Andreana; Holahan, CaroleMemory monitoring, or the ability to accurately assess one’s memory retrieval success, is known to be declined for older adults. The behavioral decline has been well explored, and is specific to tasks of source monitoring; tasks involving item memory monitoring do not show age-related deficits. This study attempts to further characterize the decline by exploring neuroanatomical contributions to the decline, and genetic influences that may explain performance variability in older adults. Older adults were genotyped for the serotonin transporter (5-HTTLPR) gene, and those that are carriers of the low-expressing allele demonstrate the expected age-related decline of source monitoring performance when compared to younger adults. Interestingly, older adults who lack this allele did not display any decline in performance when compared to younger adults. Neuroanatomical correlates of task performance indicate that prefrontal regions in the inferior and lateral cortices support accurate source memory monitoring, likely through their role in the proper selection of memory cues and inhibition of irrelevant information. This relationship suggests that age-related atrophy occurring in these structures could be responsible for the performance deficits on source memory monitoring tasks. There was no direct relationship seen between genotype for the 5-HTTLPR gene and cortical volumes, however diffusion tensor imaging shows that older adults who carry this allele have altered connections between the medial temporal lobe, responsible for memory retrieval, and prefrontal cortex, which monitors the retrieval process. Through stronger connections of critical networks, older adults who lack the 5-HTTLPR short allele may be able to compensate for the age-related atrophy seen in the prefrontal cortex. Functional results further indicate that the older adult non-carriers recruit inferior and lateral frontal regions to a greater extent than the older adult carriers during accurate memory monitoring. These results begin to suggest a neuroprotective mechanism for the 5-HTTLPR genotype, wherein some older adults may be able to postpone the expected decline of memory monitoring by retaining the ability to recruit essential inferior frontal structures through more organized white matter pathways.Item Hemodynamic measurements and modeling for functional magnetic resonance imaging(2014-05) Khan, Reswanul Kabir; Hoffmann, Gerald W.In imaging, short wavelength (high-frequency) particles scattered from targets typically yield greater spatial resolutions than longer wavelengths. X-Rays, for example are typically within 2 orders of magnitude of a nanometer wavelength to achieve desired resolutions for medical imaging. Although better for imaging, this poses a health risk for subjects as ionizing radiation and this limits its use. Functional Magnetic Resonance Imaging (fMRI) avoids this issue by using radiation of much larger wavelengths, 4.8 m (62.5 MHz), that are relatively harmless. Instead of scattering, these photons are used to excite protons between spin-states in an external magnetic field. Magnetization relaxation rates and dephasing as a function of space and time are then measured to reconstruct images. This dissertation develops experimental methods to understand and interpret the biophysical underpinnings of fMRI in terms of blood flow and oxygen concentration changes. In neuroscience, fMRI may be used to deduce brain activity. Brain activity is a general term related to neuronal firing rate, which metabolizes oxygen. Deoxygenated blood increases proton spin dephasing. This is the physical mechanism that ultimately yields contrast in the fMRI signal. This is known as Blood-Oxygen Level Dependent (BOLD) contrast. A critical piece of information in this process, hemodynamics, is the dynamics of cerebral (brain) oxygen concentrations in relation to blood flow. The hemodynamics of BOLD contrast fMRI and its relation to brain activity is vital. In this dissertation, I have classified hemodynamic data as a function of space and time in cerebral cortex as well as testing a rudimentary hemodynamic model. I have taken fMRI measurements in three human subjects to identify spatial and temporal hemodynamic trends in brain. Furthermore, I've analyzed laser-speckle imaging in three subjects to identify spatiotemporal trends in blood speed. The final portion of this dissertation relates developments of a hemodynamic model of BOLD.Item Measuring visual stimulation and attention signals in human superior colliculus using high-resolution fMRI(2013-05) Katyal, Sucharit; Ress, David BruceThe superior colliculus (SC) is a laminated oculomotor structure in the midbrain. In non-human primates SC has long been known to contain a retinotopically-organized map of visual stimulation in its superficial layers, which is aligned to a map of saccadic eye movements in the deeper layers. Microstimulation and electrophysiology experiments have shown that SC also plays a key role in covert visuospatial attention and suggest that attentional modulation also occurs in a retinotopic manner. Retinotopic organization of the visual field can be non-invasively mapped in humans using functional MRI with a technique called phase-encoded retinotopy. In this technique, rotating wedges and expanding rings of visual stimuli are used to map the polar angle and eccentricity dimensions of a polar coordinates system, respectively. A similar technique can also be used to map spatial attention by keeping the visual stimulus constant and cueing subjects to attend to apertures of rotating wedges and expanding rings within the stimulus. A previous study using fMRI has shown the polar angle representation of visual stimulation in human SC but was unable to find a representation of eccentricity. This work uses high-resolution fMRI along with special surface analysis techniques developed in our lab to demonstrate maps of both polar angle and eccentricity for visual stimulation. Moreover, visual attention is also shown to be topographically organized within SC and in registration with visual stimulation. Finally, in human visual cortex, fMRI is known to show activity for sustained spatial attention even in the absence of a significant visual stimulus, an attentional "base response". In this work, SC is shown to exhibit a similar sustained attention base response using a threshold-contrast detection paradigm. This base response was compared with a response for attention with visual stimulation. The peak amplitude of the base response occurred more deeply within SC tissue than the peak for attention with stimulation. It is proposed that this reflects the specific attentional enhancement of the deeper visuomotor neurons, which are hypothesized to be a direct neuronal correlate of the oculomotor theory of attention.Item Resting state functional connectivity of the limbic cerebellum: vermis lobules IV, VII, and IX(2015-12) Kostic, Anne Cadence; Allen, Greg, doctor of clinical psychology; Stark, KevinThe cerebellum is classically known for its role in motor functioning; however, research has shown cerebellar involvement in other domains, including memory, attention, and emotional functioning. Animal studies, lesion studies, and imagining studies have contributed to our understanding of the wide array of cerebellar functions. Research specifically examining connections between the cerebellum and other systems of the brain has greatly expanded our understanding of the complexities of the cerebellum’s dynamic involvement with functional brain systems in addition to the motor system. Additionally, research has found the cerebellum to be involved in multiple disorders and is one of the most consistent sites of abnormality in autism. Connections between the cerebellum and the limbic system are thought to support cerebellar involvement in emotional functioning, affect, social cognition, and possibly in disorders indicative of impaired limbic-related functions, including autism. However, the functional connectivity of the limbic system and the cerebellum has not been comprehensively studied using functional connectivity magnetic resonance imaging (fcMRI) procedures. Therefore, the purpose of this present study is to determine the functional connectivity of specific cerebellar vermis with structures of the limbic system to contribute to the understanding of the organization of the limbic cerebellum. This study uses fcMRI and functional connectivity analysis to determine to functional coherence of three vermis ROIs with limbic structures. It is hypothesized that posterior vermis lobule ROIs will show significant functional coherence with limbic brain regions, suggesting posterior vermis involvement in the circuitry of the limbic cerebellum.Item Reward modulation of medial temporal lobe function during associative encoding and cued recall(2010-05) Wolosin, Sasha Monica; Preston, Alison R.; Beer, Jennifer S.Emerging evidence suggests that hippocampal memory processing is modulated by midbrain regions under conditions of reward, resulting in enhanced encoding of episodic information—long-term memory for events. Current theories further suggest that hippocampal subregions may have distinct roles in episodic memory formation, and may be differentially influenced by dopaminergic midbrain inputs. Using high-resolution functional magnetic resonance imaging (fMRI), the present study investigated hippocampal subregional function as well as activation in surrounding medial temporal lobe (MTL) cortex, midbrain, and nucleus accumbens during associative encoding and cued recall under varying conditions of reward. A high-value or low-value monetary cue preceded a pair of objects indicating potential reward for successful retrieval of the association. At test, participants performed cued recall followed by match (correct association) or mismatch (incorrect association) probe decisions and received feedback on their performance. Behaviorally, cued recall performance was superior for pairs preceded by high reward cues at encoding relative to pairs preceded by low reward cues. FMRI analysis revealed regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showing subsequent memory effects (greater encoding activation for remembered, compared to forgotten associations) and reward effects (greater activation for high-value, compared to low-value associations) during stimulus encoding. Within several of these regions, individual differences in reward-related encoding activation were correlated with the degree of the behavioral reward effect (better memory for high-value compared to low-value object pairs). At retrieval, regions in midbrain and subiculum predicted successful associative recall, and regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showed reward effects in the absence of explicit reward cues. Within several MTL regions, activation was greater for match than mismatch probes. These findings are consistent with theories suggesting that reward-based motivation influences memory formation through interactions between dopaminergic midbrain and hippocampus.Item The development of bias in perceptual and financial decision-making(2014-08) Chen, Mei-Yen, Ph. D.; Poldrack, Russell A.; Maddox, W. Todd; Huk, Alexander C.; Pillow, Jonathan; Dhillon, Inderjit S.Decisions are prone to bias. This can be seen in daily choices. For instance, when the markets are plunging, investors tend to sell stocks instead of purchasing them with lower prices because people in general are more sensitive to the potential losses than the potential gains, or loss averse, in making financial choices. This also can be seen in laboratory tests. When participants receive higher payoffs for successfully discriminating a visual stimulus as one choice against the other, they begin choosing this higher-rewarded option more often even though the objective evidence indicates the alternative. In my dissertation, I used mathematical models and functional magnetic resonance imaging (fMRI) to track the development of bias in perceptual and financial decision-making and presented evidence characterizing the experience-sensitive and domain-general decision-making process in the human brains. The first chapter showed that bias could be developed through associating decision contexts and reward feedback from trial to trial in perceptual decision-making. Although the surface task differed, this learning process involved the same prediction error driven mechanisms implemented in the dopaminergic system as in financial decision-making. Furthermore, the frontal cortex increased its strength of connection between visual and value systems that accounted for the growth of perceptual bias. The second chapter extended this feedback-driven acquisition process to examine the influences of experience on loss aversion in financial decision-making. The results showed that people learned to make riskier or more conservative decisions according to the feedback that they had received in different decision contexts. This alternation in loss aversion was achieved through modulation of the value system’s sensitivity toward the potential gains in evaluation. The frontal cortex mediated this change. The third chapter used a mathematical model to identify the changes in financial decision-making that occurred faster than the temporal resolution of fMRI. The results suggested that people might simplify financial information into some rules of thumb for making a choice. These findings not only integrated the knowledge in different domains of decision neuroscience but also shed lights onto how one may refine the decision-making process against experiences.Item The effect of reward-based motivation on associative memory processing in the medial temporal lobes(2013-05) Wolosin, Sasha Monica; Preston, Alison R.; Beer, Jennifer S; Huk, Alexander C; Poldrack, Russell A; Schnyer, David MWhat determines whether an experience is encoded to memory? One factor is reward-based motivation: we are more likely to remember information if we believe it will lead to future rewards. Memory critically depends on the integrity of the medial temporal lobes (MTL). Notably, the MTL is comprised of subregions that are hypothesized to serve different functions in memory and may be differentially influenced by reward. The present research examines how reward-based motivation influences associative memory processing within MTL subregions of the human brain. In two high-resolution functional magnetic resonance imaging (fMRI) studies, a high-value or low-value monetary cue preceded a pair of objects indicating potential reward for successful retrieval of the association on a later memory test. Memory was enhanced for pairs preceded by high-value compared to low-value reward cues, however participants differed in the degree to which reward value influenced memory. In fMRI Study 1, the behavioral effect of reward on memory was associated with reward-related activation changes in hippocampal subregions dentate gyrus/CA₂,₃ and enhanced connectivity between dentate gyrus/CA₂,₃ and reward-related midbrain regions during encoding and retrieval. In fMRI Study 2, patterns of MTL activations represented reward context, showing greater consistency among events of the same reward value than among events of different reward values. Successful memory formation was associated with enhanced hippocampal reward representations during the anticipatory cue phase prior to object pair encoding. During object pair encoding, the degree of reward representation in hippocampus and more specifically dentate gyrus/CA₂,₃ was associated with individual differences in the behavioral effect of reward on memory. Finally, a series of behavioral studies demonstrate that during motivated learning, associative memory accuracy increases monotonically with increasing reward value, and may be enhanced when participants must maintain information about reward cues in short-term memory prior to encoding. These findings indicate that reward-based motivation enhances associative memory processing specifically within dentate gyrus/CA₂,₃ through interactions with reward-related midbrain regions. Furthermore, these results suggest that associative memory may be facilitated when information about reward context is incorporated into stored memory representations. Collectively, these findings shed light on fundamental mechanisms through which reward impacts associative memory.Item Using the neural level of analysis to understand the computational underpinnings of positivity biases in self-evaluation(2012-05) Hughes, Brent Laurence, 1981-; Beer, Jennifer S., 1974-; Gosling, Samuel D.; Neff, Lisa A.; Preston, Alison A.; Swann, Jr., William B.Decades of research have demonstrated that people sometimes provide self-evaluations that emphasize their most flattering qualities. Different theoretical accounts have been offered to explain the mechanisms underlying positively-biased self-evaluation. Some researchers theorize that positively-biased self-evaluations arise from a self-protection motivation because positivity biases increase in situations of heightened self-esteem threat. Alternative views question whether self-protection motivation is a necessary or even dominant source of positivity bias by demonstrating that positively-biased self-evaluations occur even when threat is not heightened, and that a general judgment approach leads to positivity biases in some domains but also to negativity biases in other domains. One reason for this gap in knowledge is that behavioral measures are limited in their ability to resolve whether the processes underlying positively-biased self-evaluation are the same or different depending on contextual motivators. Neuroimaging methods are well suited to examine whether different mechanisms underlie similar behaviors, specifically similar positively-biased responses in different contexts. The four studies presented here explore the neural mechanisms of positively-biased self-evaluation by first identifying a core set of neural regions associated with positivity bias (Study 1A and 1sB), examining whether a heightened self-protection motivation changes the engagement of those neural systems (Study 2), and specifying the precise mechanisms supported by those regions (Study 3). Studies 1A and 1B revealed evidence for a neural system comprised of medial and lateral orbitofrontal cortex (OFC) and, to a lesser extent dorsal anterior cingulate (dACC) that was modulated by positivity bias. Study 2 found that a heightened self-protection motivation changes the engagement of medial OFC in positively-biased self-evaluation. Finally, Study 3 found evidence that medial OFC may support a common mechanism in positively-biased judgment that is implemented differently as a function of the motivational context. Taken together, these studies represent a first step toward developing a neural model of positively-biased self-evaluation. The findings provide some preliminary evidence that positivity biases may represent distinct processes in different motivational contexts. This dissertation sets the stage for future work to examine how specific positively-biased cognitive mechanisms may be supported by specific neural systems and computations as a function of motivational contexts.Item What the neuropsychologist said to the neuroradiologist : two methods of lateralization of landuage in pre-surgical assessment of children with intractable epilepsy(2013-08) Potvin, Deborah Claire; Keith, Timothy, 1952-; Nussbaum, NancyFor children with intractable epilepsy, surgery provides significant reduction in seizure frequency, with no significant declines in intellectual or behavioral functioning (Datta, et al., 2011). Prior to surgery, children must undergo a thorough assessment to determine the location of the seizure-focus and to evaluate risks of post-operative impairment (Lee, 2010). Currently, fMRI offers one of the most reliable and least invasive means of localizing language prior to surgery (McDonald, Saykin, William & Assaf, 2006). Dichotic listening, a behavioral task in which subjects are asked to listen to two competing stimuli simultaneously, offers a possible alternative for children who cannot complete fMRI studies. Previous studies have relied on research-based listening tasks and the type of quantitative analysis of the fMRI rarely available in the clinical setting. Instead, this study examined how well dichotic listening results predict language lateralization from fMRI within a clinical setting. Data were gathered through a records review of 13 children with intractable epilepsy referred to Austin Neuropsychology through the epilepsy treatment team at Dell Children’s Medical Center. Overall, children classified as atypical language dominance on the fMRI studies showed lower levels of right ear advantage on the dichotic listening measure. Despite this trend, a discriminant analysis using the dichotic listening results to predict fMRI classification showed no significant improvement over chance classification. A secondary analysis examined factors related to a child’s ability to complete an fMRI language study, comparing 12 children from the original sample with 6 children referred through the same process and over the same time period who could not obtain a successful fMRI determination of language lateralization. Overall, children who successfully completed the fMRI language studies showed a trend of lower levels of difficulty with behavioral regulation and higher levels of intelligence. Although the non-significant results highlight the limitations of dichotic listening as a clinical tool, the failure rate within the total sample, along with the information about the roles of intelligence and behavioral regulation, may help spur the development of alternative methods of language lateralization.