Browsing by Author "Rojas, Donald C., committee member"
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Item Open Access Evaluating the effectiveness of varying doses of supplemental tryptophan as a calmative in horses(Colorado State University. Libraries, 2016) Davis, Brittany P., author; Grandin, Temple, advisor; Engle, Terry E., committee member; Ransom, Jason I., committee member; Rojas, Donald C., committee memberTryptophan (Trp), the amino acid precursor to serotonin, is a common ingredient in many commercial equine calming supplements. However, there is little scientific research to support the efficacy of tryptophan at modifying horse behavior. The objective of this study was to examine how various doses of tryptophan supplementation impacted reactive behavior and physiological stress measurements in the horse. Eleven horses (9 geldings, 2 mares) were given four treatments—0 mg Trp/kg bodyweight (CON), 20 mg Trp/kg bodyweight (LOW), 40 mg Trp/kg bodyweight (MED), and 60 mg Trp/kg bodyweight (HIGH)—in a randomized crossover design. Each treatment lasted three days. On Days 1 and 3 of each treatment, horses underwent a behavior test to measure startle response. Heart rate measurements and the speed at which the horses fled from startling stimuli were recorded. In addition, serum glucose, lactate, and cortisol levels were analyzed both immediately before the startle test and again 15 minutes after the test. Significant sedative effects were seen at LOW Day 1 on heart rate increase during the startle test (P = 0.05) and on change in serum lactate levels (P = 0.03). At MED Day 1, sedative effects were seen on change in serum cortisol levels (P = 0.01). Some excitatory effects were seen at MED Day 3 on the time for heart rate to return to baseline after the startle test (P = 0.03). No significant effects were seen at HIGH Day 1 or Day 3. A subset of blood samples was analyzed for serum free Trp and the ratio of Trp to other large neutral amino acids, which verified treatment effect.Item Open Access Optical imaging of emotional responding to sensational stimuli in high and low risk-seeking individuals(Colorado State University. Libraries, 2017) Kentopp, Shane, author; Conner, Bradley T., advisor; Rojas, Donald C., committee member; Riggs, Nathaniel R., committee memberSensation seeking is a reward-based personality construct linked to engagement in risky behavior. A neural and conceptual overlap between emotion and reward suggests there is an emotional component to sensation seeking. The current study sought to assess the theorized emotional component of sensation seeking by measuring a distinct pattern of visual cortex activation that accompanies the induction of emotion via visual stimuli. Undergraduate participants were recruited based on a prescreening personality assessment. Thirty-five participants were sorted into groups with either high or low scores on risk seeking (a facet of sensation seeking) and exposed to emotional, sensational, and neutral video stimuli. Participants rated their emotional response and reward valuation following each video. Activation in the primary visual cortex was measured using functional near-infrared spectroscopy (fNIRS). Activation during the sensational conditions was assessed for similarity to the emotional conditions and compared between risk seeking groups. Imaging results revealed no significant differences between conditions or groups. Participant responses to stimuli indicated that individuals high in risk seeking experienced a more positive emotional response to sensational videos than individuals low in risk seeking. Participant responses to stimuli also indicated that individuals high in risk seeking endorsed a stronger approach response to sensational stimuli. The study encountered methodological challenges, which limited its statistical power and ability to measure the hypothesized effects. Stimulus response data, however, provided preliminary support for the role of emotional processes in risky behavior amongst individuals high in sensation seeking. These findings suggest that targeting emotion regulation processes in individuals who are high in sensation seeking may be an effective approach to reducing engagement in risky behavior.Item Open Access Studying age-related changes in white matter microstructure in healthy aging using noninvasive MRI techniques(Colorado State University. Libraries, 2020) Mendez Colmenares, Andrea, author; Thomas, Michael L., advisor; Burzynska, Agnieszka Z., advisor; Rojas, Donald C., committee memberAge-related deterioration of the white matter (WM), such as demyelination, is an important mechanism of cognitive decline in healthy aging. Lifestyle factors can influence the course of WM aging. Most evidence have used diffusion tensor imaging (DTI) metrics, but these are not specific to myelin or axons. Therefore, in this study we compared DTI metrics to a proposed proxy of myelin content, the T1-weighted image (T1-WI) to T2-weighted image (T2-WI) ratio with respect to their ability to: detect time-by-intervention interactions, predict processing speed ability, and their correlations with each other and age. We used longitudinal data from 169 cognitively healthy older adults (60-79yrs). MRI imaging (3T Siemens Trio) included 0.9mm3 MPRAGE, 1.7×1.7x3mm3 T2w and DTI (30 diff. dir., bval= 0 and 1000s/mm2, 1.7×1.7x3mm3). T1w/T2w was calculated using internal intensity calibration. We used FSL-FDT to extract DTI metrics, focused on major WM tracts using tract-based spatial statistics in FSL. From the WM skeleton, we calculated mean values for 12 regions-of-interest. Processing speed was assessed using the Virginia Cognitive Aging Battery. Results showed that the T1w/T2w produced greater time-by-intervention interactions than DTI-FA, especially in the posterior (β=0.27, p=0.01) and anterior (β=0.33, p=0.01) limb of the internal capsule. The T1w/T2w (in the whole WM) correlated with processing speed (β=-0.13, p=0.02). T1w/T2w correlated with DTI in regions with high fiber coherence/high myelin content; and with age in regions with high myelin content. Results suggest that the T1w/T2w offers greater ability than DTI to detect short-term longitudinal changes in WM, but they seem to reflect different microstructural properties in the WM. Further research is needed to gain a better understanding of its biological underpinnings and significance.