You Can't Have It Both Ways: An Examination of Congruency Effects in Task Switching.

Environmental contexts help us set relevant goals and guide appropriate behaviors. In situations in which a single stimulus affords multiple responses, cognitive control processes allow us to establish the appropriate goal based on the present context and activate rules associated with the current goal. This enables execution of correct responses, even when those responses are inconsistent with alternative responses afforded by the same stimulus. The experiments in this dissertation use task-switching paradigms to examine how individuals respond to situations in which a single stimulus can afford two responses. These behavioral studies examine congruency effects, the performance differences between congruent trials, for which the same response is always appropriate, and incongruent trials, for which the appropriate response differs depending on the currently-relevant task. Experiments 1 and 2 examine the possibility that congruency effects observed in task switching are fundamentally similar to congruency effects in Stroop paradigms by comparing task-switching congruency effects in conditions with and without Stroop-like interference. In both experiments, congruency effects in task switching interact with Stroop-like congruency effects, suggesting a common mechanism. Based on the results in Experiments 1 and 2, I suggest that automatic activation of a category by attributes of the stimulus that have previously been relevant underlies congruency effects in Stroop and task-switching situations. This hypothesis is supported by findings in Experiments 3 and 4 that task-switching congruency effects are absent for conditions in which a stimulus is never assigned to different categories on different trials. Congruency effects across these paradigms can be accounted for by a generalized model of competition driven by repeated assignment of stimuli to competing categories.Ph.D.PsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78914/1/askren_1.pd

Hippocampal Contribution to Context Encoding across Development Is Disrupted following Early-Life Adversity

Context can drastically influence responses to environmental stimuli. For example, a gunshot should provoke a different response at a public park than a shooting range. Little is known about how contextual processing and neural correlates change across human development or about individual differences related to early environmental experiences. Children (N = 60; 8–19 years, 24 exposed to interpersonal violence) completed a context encoding task during fMRI scanning using a delayed match-to-sample design with neutral, happy, and angry facial cues embedded in realistic background scenes. Outside the scanner, participants completed a memory test for context-face pairings. Context memory and neural correlates of context encoding did not vary with age. Larger hippocampal volume was associated with better context memory. Posterior hippocampus was recruited during context encoding, and greater activation in this region predicted better memory for contexts paired with angry faces. Children exposed to violence had poor memory of contexts paired with angry faces, reduced hippocampal volume, and atypical neural recruitment on encoding trials with angry faces, including reduced hippocampal activation and greater functional connectivity between hippocampus and ventrolateral prefrontal cortex (vlPFC). Greater hippocampus-vlPFC connectivity was associated with worse memory for contexts paired with angry faces. Posterior hippocampus appears to support context encoding, a process that does not exhibit age-related variation from middle childhood to late adolescence. Exposure to dangerous environments in childhood is associated with poor context encoding in the presence of threat, likely due to greater vlPFC-dependent attentional narrowing on threat cues at the expense of hippocampus-dependent processing of the broader context

The Functional Connectivity Landscape of the Human Brain

Functional brain networks emerge and dissipate over a primarily static anatomical foundation. The dynamic basis of these networks is inter-regional communication involving local and distal regions. It is assumed that inter-regional distances play a pivotal role in modulating network dynamics. Using three different neuroimaging modalities, 6 datasets were evaluated to determine whether experimental manipulations asymmetrically affect functional relationships based on the distance between brain regions in human participants. Contrary to previous assumptions, here we show that short- and long-range connections are equally likely to strengthen or weaken in response to task demands. Additionally, connections between homotopic areas are the most stable and less likely to change compared to any other type of connection. Our results point to a functional connectivity landscape characterized by fluid transitions between local specialization and global integration. This ability to mediate functional properties irrespective of spatial distance may engender a diverse repertoire of cognitive processes when faced with a dynamic environment.</p

Executive attention networks show altered relationship with default mode network in PD

Attention dysfunction is a common but often undiagnosed cognitive impairment in Parkinson's disease that significantly reduces quality of life. We sought to increase understanding of the mechanisms underlying attention dysfunction using functional neuroimaging. Functional MRI was acquired at two repeated sessions in the resting state and during the Attention Network Test, for 25 non-demented subjects with Parkinson's disease and 21 healthy controls. Behavioral and MRI contrasts were calculated for alerting, orienting, and executive control components of attention. Brain regions showing group differences in attention processing were used as seeds in a functional connectivity analysis of a separate resting state run. Parkinson's disease subjects showed more activation during increased executive challenge in four regions of the dorsal attention and frontoparietal networks, namely right frontal eye field, left and right intraparietal sulcus, and precuneus. In three regions we saw reduced resting state connectivity to the default mode network. Further, whereas higher task activation in the right intraparietal sulcus correlated with reduced resting state connectivity between right intraparietal sulcus and the precuneus in healthy controls, this relationship was absent in Parkinson's disease subjects. Our results suggest that a weakened interaction between the default mode and task positive networks might alter the way in which the executive response is processed in PD

A Low-Cost, Computer-Interfaced Drawing Pad for fMRI Studies of Dysgraphia and Dyslexia

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Salience network connectivity is reduced by a meal and influenced by genetic background and hypothalamic gliosis.

Background/objectivesThe salience network (SN) comprises brain regions that evaluate cues in the external environment in light of internal signals. We examined the SN response to meal intake and potential genetic and acquired influences on SN function.Subjects/methodsMonozygotic (MZ; 40 pairs) and dizygotic (15 pairs) twins had body composition and plasma metabolic profile evaluated (glucose, insulin, leptin, ghrelin, and GLP-1). Twins underwent resting-state functional magnetic resonance imaging (fMRI) scans before and after a standardized meal. The strength of SN connectivity was analyzed pre- and post-meal and the percentage change elicited by a meal was calculated. A multi-echo T2 MRI scan measured T2 relaxation time, a radiologic index of gliosis, in the mediobasal hypothalamus (MBH) and control regions. Statistical approaches included intraclass correlations (ICC) to investigate genetic influences and within-pair analyses to exclude genetic confounders.ResultsSN connectivity was reduced by a meal ingestion (β = -0.20; P &lt; 0.001). Inherited influences on both pre- and post-meal connectivity were present (ICC MZ twins 26%, P &lt; 0.05 and 47%, P &lt; 0.001, respectively), but not percentage change in response to the meal. SN connectivity in response to a meal did not differ between participants with obesity and of normal weight (χ2(1) = 0.93; P = 0.33). However, when participants were classified as having high or low signs of MBH gliosis, the high MBH gliosis group failed to reduce the connectivity in response to a meal (z = -1.32; P = 0.19). Excluding genetic confounders, the percentage change in SN connectivity by a meal correlated to body fat percentage (r = 0.24; P &lt; 0.01).ConclusionsSN connectivity was reduced by a meal, indicating potential participation of the SN in control of feeding. The strength of SN connectivity is inherited, but the degree to which SN connectivity is reduced by eating appears to be influenced by adiposity and the presence of hypothalamic gliosis

Hippocampal Contribution to Context Encoding across Development Is Disrupted following Early-Life Adversity

Context can drastically influence responses to environmental stimuli. For example, a gunshot should provoke a different response at a public park than a shooting range. Little is known about how contextual processing and neural correlates change across human development or about individual differences related to early environmental experiences. Children (N = 60; 8–19 years, 24 exposed to interpersonal violence) completed a context encoding task during fMRI scanning using a delayed match-to-sample design with neutral, happy, and angry facial cues embedded in realistic background scenes. Outside the scanner, participants completed a memory test for context-face pairings. Context memory and neural correlates of context encoding did not vary with age. Larger hippocampal volume was associated with better context memory. Posterior hippocampus was recruited during context encoding, and greater activation in this region predicted better memory for contexts paired with angry faces. Children exposed to violence had poor memory of contexts paired with angry faces, reduced hippocampal volume, and atypical neural recruitment on encoding trials with angry faces, including reduced hippocampal activation and greater functional connectivity between hippocampus and ventrolateral prefrontal cortex (vlPFC). Greater hippocampus-vlPFC connectivity was associated with worse memory for contexts paired with angry faces. Posterior hippocampus appears to support context encoding, a process that does not exhibit age-related variation from middle childhood to late adolescence. Exposure to dangerous environments in childhood is associated with poor context encoding in the presence of threat, likely due to greater vlPFC-dependent attentional narrowing on threat cues at the expense of hippocampus-dependent processing of the broader context. SIGNIFICANCE STATEMENT The ability to use context to guide reactions to environmental stimuli promotes flexible behavior. Remarkably little research has examined how contextual processing changes across development or about influences of the early environment. We provide evidence for posterior hippocampus involvement in context encoding in youth and lack of age-related variation from middle childhood to late adolescence. Children exposed to interpersonal violence exhibited poor memory of contexts paired with angry faces and atypical neural recruitment during context encoding in the presence of threatening facial cues. Heightened attention to threat following violence exposure may come at the expense of encoding contextual information, which may ultimately contribute to pathological fear expressed in safe contexts

Salience network connectivity is reduced by a meal and influenced by genetic background and hypothalamic gliosis.

Background/objectivesThe salience network (SN) comprises brain regions that evaluate cues in the external environment in light of internal signals. We examined the SN response to meal intake and potential genetic and acquired influences on SN function.Subjects/methodsMonozygotic (MZ; 40 pairs) and dizygotic (15 pairs) twins had body composition and plasma metabolic profile evaluated (glucose, insulin, leptin, ghrelin, and GLP-1). Twins underwent resting-state functional magnetic resonance imaging (fMRI) scans before and after a standardized meal. The strength of SN connectivity was analyzed pre- and post-meal and the percentage change elicited by a meal was calculated. A multi-echo T2 MRI scan measured T2 relaxation time, a radiologic index of gliosis, in the mediobasal hypothalamus (MBH) and control regions. Statistical approaches included intraclass correlations (ICC) to investigate genetic influences and within-pair analyses to exclude genetic confounders.ResultsSN connectivity was reduced by a meal ingestion (β = -0.20; P &lt; 0.001). Inherited influences on both pre- and post-meal connectivity were present (ICC MZ twins 26%, P &lt; 0.05 and 47%, P &lt; 0.001, respectively), but not percentage change in response to the meal. SN connectivity in response to a meal did not differ between participants with obesity and of normal weight (χ2(1) = 0.93; P = 0.33). However, when participants were classified as having high or low signs of MBH gliosis, the high MBH gliosis group failed to reduce the connectivity in response to a meal (z = -1.32; P = 0.19). Excluding genetic confounders, the percentage change in SN connectivity by a meal correlated to body fat percentage (r = 0.24; P &lt; 0.01).ConclusionsSN connectivity was reduced by a meal, indicating potential participation of the SN in control of feeding. The strength of SN connectivity is inherited, but the degree to which SN connectivity is reduced by eating appears to be influenced by adiposity and the presence of hypothalamic gliosis

Profiles of White Matter Microstructure in a Population-Based Cohort of Elderly Patients

<div>Neurodegenerative diseases are among the most costly to society. While much has been learned about the underlying mechanism of neurodegeneration in recent decades, improvements in the standard of care remain elusive. One barrier in translating research to the clinic is that studies are often conducted with a carefully chosen set of inclusion and exclusion criteria in order to reduce uncontrolled variation in the sample, while in the clinic patients often present with mixed pathology and complex comorbidities.</div><div><br></div><div>In this study, we present an exploratory cross-sectional analysis of white matter microstructure in a population sample of elderly patients thawere recruited as a sample of the general population, some of whom later went on to develop neurodegenerative diseases</div><div><br></div><div>This poster was presented at the 2017 meeting of the Organization for Human Brain Mapping in Vancouver, BC</div

Brain connectivity tracks effects of chemotherapy separately from behavioral measures

Several studies in cancer research have suggested that cognitive dysfunction following chemotherapy, referred to in lay terms as “chemobrain”, is a serious problem. At present, the changes in integrative brain function that underlie such dysfunction remain poorly understood. Recent developments in neuroimaging suggest that patterns of functional connectivity can provide a broadly applicable neuromarker of cognitive performance and other psychometric measures. The current study used multivariate analysis methods to identify patterns of disruption in resting state functional connectivity of the brain due to chemotherapy and the degree to which the disruptions can be linked to behavioral measures of distress and cognitive performance. Sixty two women (22 healthy control, 18 patients treated with adjuvant chemotherapy, and 22 treated without chemotherapy) were evaluated with neurocognitive measures followed by self-report questionnaires and open eyes resting-state fMRI scanning at three time points: diagnosis (M0, pre-adjuvant treatment), 1 month (M1), and 7 months (M7) after treatment. The results indicated deficits in cognitive health of breast cancer patients immediately after chemotherapy that improved over time. This psychological trajectory was paralleled by a disruption and later recovery of resting-state functional connectivity, mostly in the parietal and frontal brain regions. Mediation analysis showed that the functional connectivity alteration pattern is a separable treatment symptom from the decreased cognitive health. Current study indicates that more targeted support for patients should be developed to ameliorate these multi-faceted side effects of chemotherapy treatment on neural functioning and cognitive health. Keywords: Breast cancer, Chemobrain, Functional connectivity, Resting-state BOL