Event Timing in Associative Learning

Associative learning relies on event timing. Fruit flies for example, once trained with an odour that precedes electric shock, subsequently avoid this odour (punishment learning); if, on the other hand the odour follows the shock during training, it is approached later on (relief learning). During training, an odour-induced Ca++ signal and a shock-induced dopaminergic signal converge in the Kenyon cells, synergistically activating a Ca++-calmodulin-sensitive adenylate cyclase, which likely leads to the synaptic plasticity underlying the conditioned avoidance of the odour. In Aplysia, the effect of serotonin on the corresponding adenylate cyclase is bi-directionally modulated by Ca++, depending on the relative timing of the two inputs. Using a computational approach, we quantitatively explore this biochemical property of the adenylate cyclase and show that it can generate the effect of event timing on associative learning. We overcome the shortage of behavioural data in Aplysia and biochemical data in Drosophila by combining findings from both systems

The role of pericytes in microcirculatory dysfunction after subarachnoid hemorrhage

Subarachnoid hemorrhage is a subtype of stroke that is caused by a bleeding into the subarachnoid space. Cerebral ischemia develops early after the bleeding and has a negative influence on outcome in patients. The underlying pathophysiology triggering early ischemia has not been characterized in detail. Suggested pathomechnisms are pial microvasospasm, endothelial dysfunction and microthrombosis. The aim of the current thesis was to characterize and reveal the pathophysiology of microcirculatory perfusion deficits early after subarachnoid hemorrhage. The main hypothesis was that pericytes constrict upon subarachnoid hemorrhage and thereby induce capillary spasm and hamper parenchymal blood flow dynamics. We found that pial arterioles constrict in three different characteristic patterns and that spastic vessel segments were continuously covered with vascular smooth muscle cells. Superficial microvasospasm was associated with reduced blood flow velocity and significant reduction of endothelial intracellular Ca2+ concentration which may be a trigger for endothelial dysfunction. Reduced blood flow velocity in combination with reduced vessel diameter diminished total blood volume that reached the parenchymal microcirculation via penetrating arterioles. This led to a severe reduction of perfused capillary volume in the cortex. Leukocyte numbers that were sticking in capillaries and venules were increased after subarachnoid hemorrhage but their numbers were too low to explain severe perfusion deficits. Capillaries revealed a significantly reduced vessel diameter after subarachnoid hemorrhage, however vessel narrowings were not co-localizing with sites where pericytes were associated to capillaries. Furthermore pericytes neither underwent cell death nor migrated away from capillaries within 24 hours after the bleeding. In conclusion we showed that microvasospasm on the brain surface lead to severe perfusion deficits in the parenchyma. Microvasospasm are probably induced by vascular smooth muscle cells and are accompanied by reduced intracellular Ca2+ concentration in endothelial cells. Pericytes do not play a major role in the pathophysiology of early ischemia after subarachnoid hemorrhage: they neither migrate, nor die or induce capillary spasm

Olfactory learning in Drosophila

Animals are able to form associative memories and benefit from past experience. In classical conditioning an animal is trained to associate an initially neutral stimulus by pairing it with a stimulus that triggers an innate response. The neutral stimulus is commonly referred to as conditioned stimulus (CS) and the reinforcing stimulus as unconditioned stimulus (US). The underlying neuronal mechanisms and structures are an intensely investigated topic. The fruit fly Drosophila melanogaster is a prime model animal to investigate the mechanisms of learning. In this thesis we propose fundamental circuit motifs that explain aspects of aversive olfactory learning as it is observed in the fruit fly. Changing parameters of the learning paradigm affects the behavioral outcome in different ways. The relative timing between CS and US affects the hedonic value of the CS. Reversing the order changes the behavioral response from conditioned avoidance to conditioned approach. We propose a timing-dependent biochemical reaction cascade, which can account for this phenomenon. In addition to form odor-specific memories, flies are able to associate a specific odor intensity. In aversive olfactory conditioning they show less avoidance to lower and higher intensities of the same odor. However the layout of the first two olfactory processing layers does not support this kind of learning due to a nested representation of odor intensity. We propose a basic circuit motif that transforms the nested monotonic intensity representation to a non-monotonic representation that supports intensity specific learning. Flies are able to bridge a stimulus free interval between CS and US to form an association. It is unclear so far where the stimulus trace of the CS is represented in the fly's nervous system. We analyze recordings from the first three layers of olfactory processing with an advanced machine learning approach. We argue that third order neurons are likely to harbor the stimulus trace

Staying adiabatic with unknown energy gap

We introduce an algorithm to perform an optimal adiabatic evolution that operates without an apriori knowledge of the system spectrum. By probing the system gap locally, the algorithm maximizes the evolution speed, thus minimizing the total evolution time. We test the algorithm on the Landau-Zener transition and then apply it on the quantum adiabatic computation of 3-SAT: The result is compatible with an exponential speed-up for up to twenty qubits with respect to classical algorithms. We finally study a possible algorithm improvement by combining it with the quantum Zeno effect.Comment: 4 pages, 4 figure

Inelastic neutron scattering study and Hubbard model description of the antiferromagnetic tetrahedral molecule Ni4Mo12

The tetrameric Ni(II) spin cluster Ni4Mo12 has been studied by INS. The data were analyzed extensively in terms of a very general spin Hamiltonian, which includes antiferromagnetic Heisenberg interactions, biquadratic 2-spin and 3-spin interactions, a single-ion magnetic anisotropy, and Dzyaloshinsky-Moriya interactions. Some of the experimentally observed features in the INS spectra could be reproduced, however, one feature at 1.65 meV resisted all efforts. This supports the conclusion that the spin Hamiltonian approach is not adequate to describe the magnetism in Ni4Mo12. The isotropic terms in the spin Hamiltonian can be obtained in a strong-coupling expansion of the Hubbard model at half-filling. Therefore detailed theoretical studies of the Hubbard model were undertaken, using analytical as well as numerical techniques. We carefully analyzed its abilities and restrictions in applications to molecular spin clusters. As a main result it was found that the Hubbard model is also unable to appropriately explain the magnetism in Ni4Mo12. Extensions of the model are also discussed.Comment: 12 pages, 12 figure

Associations among Task Self-Efficacy, Physical Activity and Subjective Wellbeing

The physical and psychological health benefits resulting from physical activity engagement have been documented in previous literature, including the connection between physical activity and subjective wellbeing (SWB). Associations have also been found between task-related self-efficacy and physical activity, connecting these concepts to Bandura\u27s Social Cognitive Theory (SCT; Bandura, 1982, 1997), such that retaining a higher belief in one\u27s physical activity abilities has been associated with successful physical activity engagement. Previous literature has documented these separate associations, but not as much focus has been placed on examining task self-efficacy, physical activity, and SWB in one model, especially during the time of physical activity adoption. Utilizing data from 58 adults, we conducted a path analysis to examine autoregressive and cross-lagged paths that encompassed 4 waves of data and 3 weeks of time. Significant autoregressive trends were observed for task self-efficacy, physical activity, and SWB, such that these variables increased over time, but the included cross-lagged paths were not found to be significant, indicating a lack of a relationship between task self-efficacy and physical activity, between physical activity and SWB, and between task self-efficacy and SWB. Significant age effects did not emerge, indicating similar scores in task self-efficacy, physical activity, and SWB across younger, middle-aged, and older adults. Similarities and differences between our study and the previous literature are discussed, along with proposing crucial aspects to consider in future studies and interventions on this topic

Noise-Cancelling Headphones as an Intervention to Maintain Classroom Time Spent On-Task for Students With Autism Spectrum Disorder

A single-subject research design was utilized to study the effects of noise-cancelling headphones on students with autism spectrum disorder (ASD) in the classroom. Academic success has long been linked to students’ time spent on-task in the classroom. Interventions to maintain time spent on-task have been studied and researched but many, currently employed, are not considered to be evidence-based practices (EBP). This is due to the rigorous criteria an EBP requires. Aversion and avoidance to sensory stimuli has long been studied as a common symptom for children with ASD; auditory sensory overload is one of these hypersensitivities affecting children of this population. The inability to habituate to novel classroom noises, for students with ASD, may facilitate inattention and lack of academic success. Compulsory education and the federal mandate to educate children in his/her least restrictive environment often places students, of all abilities, in a general education classroom, for partial or a full school day. Educators, therefore, are responsible for implementing all accommodations and modifications, inclusive of students with ASD. The specific accommodations and modifications are delineated by the students’ individualized education plan, including accommodations to maintain time spent on-task. This study explored the effectiveness of classroom use of noise-cancelling headphones utilizing a nonconcurrent multiple baseline design across participants and curricula to visually analyze the functional relationship between noise- cancelling headphones and time spent on-task. This was implemented to answer the following research questions: (1) does the use of noise-cancelling headphones increase time spent on-task for students with ASD, measured by time spent in active listening, active engagement during independent reading tasks; (2) does the use of noise-cancelling headphones increase time spent on-task for students with ASD, measured by time spent in active listening, active engagement during independent math tasks; (3) do the participants view the usage of the noise-cancelling headphones as socially valid and effective; finally (4) do the participants’ teachers view the usage of the noise-cancelling headphones as socially valid and effective? Behaviorism theory was the foundation for this study; simply stated, a behavior will increase (on-task behavior) with removal, or prevention, of an aversive stimulus (auditory input). This is completely dependent on behavioral function, specifically, escape or avoidance of certain auditory input. Increased behavior as a result of removal of an aversive stimulus is also known as negative reinforcement. Therefore, it was hypothesized that with use of noise-cancelling headphones, ambient noise would be removed from the students’ environments and time spent on-task in math and reading would increase. It was also hypothesized that all the participants and the participants’ teachers would find the intervention socially valid and effective. If the teachers view the intervention as easily implemented and effective, the practitioner becomes the researcher. If the participants view the intervention as beneficial, increasing classroom time spent on-task may result in increased academic success. Visual analyses of level, trend, and variability were used to interpret data through graphing momentary time sampling data in baseline and intervention phases. Reliability would have been established through inter-observer agreement (IOA), however, due to COVID-19, IOA was not collected and the data presented are hypothetical. Results from the visual analyses demonstrate a positive functional relationship between increased time spent on-task and noise-cancelling headphone use.Additionally, this study would have employed a social validity survey to answer research questions three and four

Comparing Measures of Physical Activity Intensity, Duration, and Frequency Using Receiver Operator Characteristic Curve Analyses

The United States Department of Health and Human Services (HHS) recommends adults to engage in weekly moderate- or vigorous-intensity physical activity based on its association with various physical and psychological health benefits (HHS, 2008; Schoenborn, Adams, & Peregoy, 2013). These physical activity recommendations contain important information for three physical activity components: intensity, frequency, and duration. The current physical activity literature contains gaps, with a lack of specificity for which components are being studied. Although some of the literature does describe the physical activity components, there are many discrepancies in the level of agreement across subjective and objective measures, along with the same basic analyses being utilized across studies. With data from 56 adults (Mage = 43.2, SD= 16.5), receiver operator characteristic (ROC) curve analyses were conducted for two weeks’ data to assess the agreement between a one-week recall questionnaire, daily diary accounts, and accelerometer data for the three physical activity components (intensity, frequency, and duration). For intensity and duration of physical activity, the worst agreement existed between the accelerometer and questionnaire, with the area under the curve (AUC) indicating chance agreement at best (AUC = 0.447-0.598); the accelerometer and daily diary measures generally exhibited chance-to-poor agreement (AUC = 0.331-0.671); and the daily diary and questionnaire showed the largest range from chance-to-good agreement (AUC = 0.482-0.794). The strongest agreement was shown for frequency of physical activity, especially for mild-intensity physical activity (AUC = 0.836) at Week 2. Across moderate-to-vigorous-, mild-, and sedentary-intensity behaviors, participants experienced the worst agreement for sedentary behaviors (AUC = 0.331-0.686), with most of the sedentary-specific intensity, frequency, and duration AUC scores showing chance agreement. The current study significantly expands and adds to the literature by focusing on all three physical activity components across moderate-to-vigorous-, mild-, and sedentary-intensity activities, as well as utilizing advanced analyses to assess the agreement between two subjective measures and one objective measure. The findings highlight the importance of educating adults about the physical activity components, different intensities, and methods of tracking and reporting activity

Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18

The low-temperature elementary spin excitations in the AFM molecular wheel Fe18 were studied experimentally by inelastic neutron scattering and theoretically by modern numerical methods, such as dynamical density matrix renormalization group or quantum Monte Carlo techniques, and analytical spin-wave theory calculations. Fe18 involves eighteen spin-5/2 Fe(III) ions with a Hilbert space dimension of 10^14, constituting a physical system that is situated in a region between microscopic and macroscopic. The combined experimental and theoretical approach allowed us to characterize and discuss the magnetic properties of Fe18 in great detail. It is demonstrated that physical concepts such as the rotational-band or L&E-band concepts developed for smaller rings are still applicable. In particular, the higher-lying low-temperature elementary spin excitations in Fe18 or AFM wheels in general are of discrete antiferromagnetic spin-wave character.Comment: 16 pages, 10 figure