The role of human motion processing complex, MT+, during sustained perception and attention

Thesis advisor: Scott D. SlotnickThe overarching aim of this dissertation is to examine the role of human motion processing complex, MT+ during sustained perception and attention. MT+ is comprised of sub-region MT, which processes motion in the contralateral visual field (i.e., left hemisphere MT processes motion in the right visual field and vice versa), and sub-region MST, which processes motion in both the contralateral and ipsilateral visual fields. Whereas previous transcranial magnetic stimulation (TMS) research has provided compelling evidence that region MT+ is necessary for low-level motion processing, Chapter 1 describes an experiment testing whether the sub-region MT is necessary for contralateral low-level motion processing. Chapter 2 describes an experiment that dissociates low-level sensory attentional modulation in MT+ from high-level attentional control processing in the parietal cortex (i.e., during sustained attention). Chapter 3 describes an experiment investigating the role of MT+ during aesthetic processing when viewing visual art. Importantly, this experiment tests whether the aesthetic is tied to not only low-level motion processing in MT+ but also high-level processing in frontal regions. Taken together, the results across the three experiments provide novel evidence for the role of MT+ during low-level motion processing during sustained perception and attention. Moreover, these low-level motion processing effects together with the observed high-level processes in frontal-parietal regions provide neural mechanisms for the cognitive processes of sustained perception and attention.Thesis (PhD) — Boston College, 2012.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Psychology

Conscious Processing During Retrieval Can Occur in Early and Late Visual Regions

Previous evidence has suggested a functional-anatomic dissociation between conscious and nonconscious processing during retrieval where early visual regions BA17/18 are associated with nonconscious processing and late visual regions BA19/37 are associated with conscious processing. However, evidence for this dissociation has only been observed using a limited number of experimental paradigms. In the present functional magnetic resonance imaging (fMRI) study, we tested the hypothesis that conscious processing during retrieval can occur in BA17/18 using memorial paradigms that recruited processing in these early visual regions. During the encoding phase of Experiment 1, abstract shapes with colored and oriented internal lines were presented to the left and right of fixation. During the retrieval phase, old shapes and new shapes were presented at fixation and participants classified each item as “old-left”, “old-right”, or “new”. The contrast of spatial memory-hits>spatial memory-misses (with accurate item memory) produced activity in BA17/18. During the encoding phase of Experiment 2, abstract shapes with colored and oriented internal lines were presented at fixation. During the retrieval phase, old shapes, changed shapes (with the same outline but different colored and oriented internal lines), and new shapes were presented at fixation and participants made an old-new classification during runs with a specific retrieval orientation or a non-specific retrieval orientation. Critically, the contrast of old-hits>old-misses during specific retrieval orientation produced activity in BA17/18. The results of the present experiments support the hypothesis that conscious processing during retrieval can occur in BA17/18.Psycholog

Decoding the emotional valence of future thoughts

Affective future thinking allows us to prepare for future outcomes, but we know little about neural representation of emotional future simulations. We used a multi-voxel pattern analysis to determine whether patterns of neural activity can reliably distinguish between positive and negative future simulations. Neural patterning in the anterior cingulate and ventromedial prefrontal cortices distinguished positive from negative future simulations, indicating that these regions code for the emotional valence of future events. These results support prior findings that anterior medial regions contain representations of emotions across various stimuli, and contribute to identifying potential rewarding outcomes of future events. More broadly, these results demonstrate that the phenomenological features of future thinking can be decoded using neural activity

Influence of management practices on the incidence of Systole albipennis Walker in fennel (Foeniculum vulgare Mill.) seeds

The chalcid wasp Systole albipennis Walker (Hymenoptera : Eurytomidae) was observed as the most important pest of fennel (Foeniculum vulgareMill.) seeds under field conditions in Haryana State, India. Studies on influence of management practices on pest infestation indicated that sowing the crop in December-January resulted in maximum seed infestation (up to 17 per cent) and minimum yields (1.1 q/ha) as against October sown crop which resulted in minimum (4 per cent) seed infestation and higher yields (32 q/ha). Plant population per unit area did not affect wasp infestation, though total yield was significantly affected. The loss of seed weight due to wasp infestation was higher in October sown crop, as seeds from this sowing are well developed and infestation of even a single seed amounts to increased loss of seed weight. &nbsp

Influence of management practices on the incidence of Systole albipennis Walker in fennel (Foeniculum vulgare Mill.) seeds

The chalcid wasp Systole albipennis Walker (Hymenoptera : Eurytomidae) was observed as the most important pest of fennel (Foeniculum vulgareMill.) seeds under field conditions in Haryana State, India. Studies on influence of management practices on pest infestation indicated that sowing the crop in December-January resulted in maximum seed infestation (up to 17 per cent) and minimum yields (1.1 q/ha) as against October sown crop which resulted in minimum (4 per cent) seed infestation and higher yields (32 q/ha). Plant population per unit area did not affect wasp infestation, though total yield was significantly affected. The loss of seed weight due to wasp infestation was higher in October sown crop, as seeds from this sowing are well developed and infestation of even a single seed amounts to increased loss of seed weight. &nbsp

Controlled release from zein matrices: Interplay of drug hydrophobicity and pH

Purpose: In earlier studies, the corn protein zein is found to be suitable as a sustained release agent, yet the range of drugs for which zein has been studied remains small. Here, zein is used as a sole excipient for drugs differing in hydrophobicity and isoelectric point: indomethacin, paracetamol and ranitidine. Methods: Caplets were prepared by hot-melt extrusion (HME) and injection moulding (IM). Each of the three model drugs were tested on two drug loadings in various dissolution media. The physical state of the drug, microstructure and hydration behaviour were investigated to build up understanding for the release behaviour from zein based matrix for drug delivery. Results: Drug crystallinity of the caplets increases with drug hydrophobicity. For ranitidine and indomethacin, swelling rates, swelling capacity and release rates were pH dependent as a consequence of the presence of charged groups on the drug molecules. Both hydration rates and release rates could be approached by existing models. Conclusion: Both the drug state as pH dependant electrostatic interactions are hypothesised to influence release kinetics. Both factors can potentially be used factors influencing release kinetics release, thereby broadening the horizon for zein as a tuneable release agent

The Evaluation of a Rapid In Situ HIV Confirmation Test in a Programme with a High Failure Rate of the WHO HIV Two-Test Diagnostic Algorithm

BACKGROUND: Concerns about false-positive HIV results led to a review of testing procedures used in a Médecins Sans Frontières (MSF) HIV programme in Bukavu, eastern Democratic Republic of Congo. In addition to the WHO HIV rapid diagnostic test algorithm (RDT) (two positive RDTs alone for HIV diagnosis) used in voluntary counselling and testing (VCT) sites we evaluated in situ a practical field-based confirmation test against western blot WB. In addition, we aimed to determine the false-positive rate of the WHO two-test algorithm compared with our adapted protocol including confirmation testing, and whether weakly reactive compared with strongly reactive rapid test results were more likely to be false positives. METHODOLOGY/PRINCIPAL FINDINGS: 2864 clients presenting to MSF VCT centres in Bukavu during January to May 2006 were tested using Determine HIV-1/2 and UniGold HIV rapid tests in parallel by nurse counsellors. Plasma samples on 229 clients confirmed as double RDT positive by laboratory retesting were further tested using both WB and the Orgenics Immunocomb Combfirm HIV confirmation test (OIC-HIV). Of these, 24 samples were negative or indeterminate by WB representing a false-positive rate of the WHO two-test algorithm of 10.5% (95%CI 6.6-15.2). 17 of the 229 samples were weakly positive on rapid testing and all were negative or indeterminate by WB. The false-positive rate fell to 3.3% (95%CI 1.3-6.7) when only strong-positive rapid test results were considered. Agreement between OIC-HIV and WB was 99.1% (95%CI 96.9-99.9%) with no false OIC-HIV positives if stringent criteria for positive OIC-HIV diagnoses were used. CONCLUSIONS: The WHO HIV two-test diagnostic algorithm produced an unacceptably high level of false-positive diagnoses in our setting, especially if results were weakly positive. The most probable causes of the false-positive results were serological cross-reactivity or non-specific immune reactivity. Our findings show that the OIC-HIV confirmation test is practical and effective in field contexts. We propose that all double-positive HIV RDT samples should undergo further testing to confirm HIV seropositivity until the accuracy of the RDT testing algorithm has been established at programme level