Neuropsychological Intra-individual Variability in Traumatic Brain Injury: Clinical Utility, Classification, and Associations with Outcomes

Traumatic brain injury (TBI) survivors experience a range of sequelae including neurobiological brain changes, cognitive impairment, psychological difficulties, and functional changes. Neuropsychological assessment after injury is used to characterize current strengths and weaknesses to inform prognosis and interventions. There is currently no reliable and consistent method of assessing and classifying injuries in the post-acute and chronic phases of moderate to severe TBI (msTBI) that is associated with long term psychosocial outcomes. This study aimed to combine the use of within-person variability on neuropsychological test batteries and in cognitive response latency, known as intra-individual variability (IIV), with a novel cognitive phenotyping method to investigate the clinical and classification utility of neuropsychological IIV in msTBI survivors. Adult msTBI survivors (n = 31) and healthy control participants (n = 30) completed a comprehensive neuropsychological testing battery, a computerized dual working memory flanker task, and assessments of mood, behaviors, and functional impairment. When compared to healthy controls, msTBI survivors demonstrated higher IIV on the overall test battery, learning and memory, executive functioning, and attention/working memory domains. Overall test battery IIV was not associated with any of the outcome domains measured. TBI survivors had significantly higher reaction time IIV compared to healthy controls especially at a high working memory demand level, however; there were no significant differences between working memory demand levels for either group. Cluster analysis results identified four distinct IIV based cognitive phenotypes which differed on quality-of-life ratings, impairment in ability functioning, and participation in social roles and activities. Finally, results of goodness of fit tests were mixed and a within domain IIV model was the best fit for only quality of life ratings and impairment in adjusting to limitations after brain injury. Despite noted limitations, the current findings have implications for advancing the precision and utility of clinical neuropsychological assessment with msTBI. Further research is needed to better understand connections between IIV and clinical outcomes, use of IIV as a discrete construct in clinical assessment, and neurocognitive mechanisms driving IIV changes following TBI. Advisor: Kathy Chio

The Impact of Mild Traumatic Brain Injury, Schizophrenia Spectrum Disorders, and Neurocognitive Deficits on Violent Crime

Mild traumatic brain injury (mTBI) and schizophrenia spectrum disorders (SSD) are conditions characterized by frontal lobe deficits. Past research has shown increased violent and aggressive behavior in both conditions; however, few studies have examined the mechanisms driving this relationship, particularly in non-athlete or non-veteran populations. The current study examined the neurodegenerative effects of repeated mTBI over time on cognitive flexibility and stability deficits in a homeless population. Additionally, we investigated the mediating effects of these deficits on the impact of both repeated lifetime mTBI and presence of an SSD on violent crime. Consistent with expectations, the number of lifetime mTBIs positively predicted violence levels across multiple measures of violent crime, however cognitive flexibility and stability deficits did not mediate this relationship. Furthermore, comorbidity of mTBI and SSD increased the frequency of violent crimes greater than either condition alone. Implications for risk assessment, intervention strategies and violence reduction are discussed

The Effect of Cyclic Loading Frequency on Corrosion-Fatigue Crack Growth in High-Strength Riser Materials

Corrosion-fatigue is a significant design consideration in deepwater floating production systems. Mechanical loading is accentuated due to the compliant nature of these structures, and sour service conditions can also occur either due to the nature of the crude production or due to seawater flooding of the reservoir to enhance production yield. New high-strength riser steels have recently been developed to meet the demands of deepwater development. The objective of this study was to characterize the corrosion-fatigue resistance of these materials in terms of crack growth rates as a function of applied stress intensity factor range (ΔK), as well as cyclic loading frequency. Experiments were performed on five different steels with yield strengths ranging from 848 to 1080 MPa. Two environments were considered: seawater with cathodic protection to simulate the environment outside of the riser, and a sour brine environment with low oxygen (&amp;lt; 10 ppb) to simulate the environment inside the riser. Not all steels were tested in the sour brine environment since not all were designed to operate in sour service. For both environments, higher strength steels were found to exhibit higher growth rates and lower saturation frequencies. Fatigue crack growth rates as a function of ΔK were also measured, and exhibited two different frequency responses. At high ΔK, the classical frequency response occurred: decreased frequency gave increased crack growth rates. At low ΔK, an inverse frequency effect was observed: deceased frequency gave decreased crack growth rates, as well as increased corrosion-fatigue crack growth thresholds. These differences are believed to be caused by different underlying processes controlling crack growth — specifically, material-environment reaction kinetics at high ΔK, and crack closure due to corrosion-product wedging at low ΔK. The practical significance of these results is discussed, including selection of frequencies for corrosion-fatigue crack growth testing, and applicability of results to structural integrity assessments.</jats:p

Quantitative super-resolution imaging with qPAINT

Counting molecules in complexes is challenging, even with super-resolution microscopy. Here, we use the programmable and specific binding of dye-labeled DNA probes to count integer numbers of targets. This method, called quantitative points accumulation in nanoscale topography (qPAINT), works independently of dye photophysics for robust counting with high precision and accuracy over a wide dynamic range. qPAINT was benchmarked on DNA nanostructures and demonstrated for cellular applications by quantifying proteins in situ and the number of single-molecule FISH probes bound to an mRNA target