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Photomechanical materials interact with light to elicit a mechanical response. They are the basis of a new class of smart materials which can serve as the active element in actuators, thus creating light-powered devices. The origin of the mechanical response is a volume change induced by a solidsolid or solidliquid phase transition in the material. This light-induced volume change can be performed two different ways: through a photochemical reaction or through the photothermal effect. In this thesis, both pathways are discussed, and photomechanical actuation is demonstrated in piston-type actuators and polymer films. In Chapter 3, the photoisomerization kinetics of a third-generation donor acceptor Stenhouse adduct (DASA) are examined over a range of concentrations. DASAs are a novel photoswitch which absorb in the visible and near-infrared spectral regions. It switches efficiently at micromolar concentrations in both liquid solution and in polymers, but as the photochrome concentration is increased there is a dramatic inhibition of the photoisomerization. The physical origin of the inhibition of photoswitching at high photochrome concentrations must be understood if the DASA class of molecules is to be used for applications like photomechanical actuation. In Chapter 4, a photothermal solidliquid transition is studied because of its large volume expansion. Photoactive composites made of small molecules doped in a phase change material (PCM) are used in a commercial wax actuator to generate useful mechanical work. It is demonstrated that small molecules can act as absorbers to enable a photothermal solidliquid melting transition in eicosane, a low molecular weight PCM. The stability, work density, and efficiency of the actuator containing these PCMs are investigated, and it is found that the actuators are competitive with electrically powered devices. In Chapter 5, further investigation of the small molecule-PCM composite is conducted using a custom-built actuator to gain insight on how the actuator should be optimized to maximize its work output. This new actuator consists of a simpler geometry which allows for the comparison with theoretical work density models. In Chapter 6, an azobenzene derivative (AZO) that can undergo photochemical melting at room temperature, is investigated as a potential candidate for photomechanical actuation. AZO is incorporated in a variety of polymer hosts to create thin films capable of bending when irradiated with light. We find that doping polymers with AZO can provide a general strategy to make photomechanical polymers using a reversible photochemical reaction that induces a solidliquid phase transition.

The ability to empathize with another person's inner experience is believed to be a central element of our social interactions. Previous research has focused on cognitive (e.g., theory of mind) and emotional (e.g., emotional contagion) empathy, and less on behavioral factors (i.e., the ability to respond empathically). Recent studies suggest that the Default Mode Network (DMN) mediates individual variability in distinct empathy-related behaviors. However, little is known about DMN activity during actual empathic responses, understood in this study as the ability to communicate our understanding of the others' experience back to them. This study used an empathy response paradigm with 28 participants (22-37 years old) to analyze the relationship between the quality of empathic responses to 14 empathy-eliciting vignettes and patterns of attenuation in the DMN. Overall, the results suggest that high levels of empathic response, are associated with sustained activation of the DMN when compared with lower levels of empathy. Our results demonstrate that the DMN becomes increasingly involved in empathy-related behavior, as our level of commitment to the other's experience increases. This study represents a first attempt to understand the relation between the capacity for responding in a supportive way to others' needs and the intra-individual variability of the pattern of the DMN attenuation. Here we underline the critical role that the DMN plays in high-level social cognitive processes and corroborate the DMN role in different psychiatric disorders associated with a lack of empathy.

Decline in cognitive functioning among rescue and recovery workers who responded in the aftermath of the September 11, 2001, World Trade Center (WTC) attacks is of emerging interest. Responders are vulnerable to cognitive decline from exposure to airborne toxins present at the WTC site, as well as from WTC-related mental and physical health conditions. To better understand the relationship between occupational WTC exposure, mental health, physical health and subjective cognitive functioning, we examined the mediating role of health status in the association between exposure and subjective cognitive concerns in a multi-site, longitudinal investigation of the WTC General Responder cohort (n = 16,380 responders; n = 58,575 visits) for the period 2002–2015. Through latent class analyses, we identified a four-level marker of cognitive concerns based on information from a Self-Administered Mental Health Questionnaire. Using generalized linear mixed models with random intercepts, we observed that a higher intensity WTC exposure composite was associated with greater cognitive concerns, and that this association was operating almost entirely through mental health comorbidities, not physical health comorbidities. In fully adjusted models, the inclusion of probable depression, anxiety, PTSD and use of psychotropic medications attenuated the association between highest WTC exposure and greatest cognitive concerns. Physical health did not appear to be on the pathway between WTC exposure and cognitive concerns. Understanding the underlying sources of cognitive concerns may help identify vulnerable members of the General Responder cohort and potentially aid clinical decision-making, such as treatment choice and enhanced screening options. Earlier diagnosis and symptom treatment may help preserve functional independence.

Background: A companion paper (Crowley et al., 2020) reports on the neuroimaging and neuropsychological profiles of statistically determined idiopathic non-dementia Parkinson’s disease (PD). Objective: The current investigation sought to further examine subtle behavioral clock drawing differences within the same PD cohort by comparing 1) PD to non-PD peers on digitally acquired clock drawing latency and graphomotor metrics, and 2) PD memory, executive, and cognitively well phenotypes on the same variables. Methods: 230 matched participants (115 PD, 115 non-PD) completed neuropsychological tests and dCDT. Statistically-derived PD cognitive phenotypes characterized PD participants as PD low executive (PDExe; n = 25), PD low memory (PDMem; n = 34), PD cognitively well (PDWell; n = 56). Using a Bayesian framework and based on apriori hypotheses, we compared groups on: total completion time (TCT), pre-first hand latency (PFHL), post-clock face latency (PCFL), total clock face area (TCFA), and total number of pen strokes. Results: Fewer strokes and slower performance to command were associated with higher odds of PD diagnosis, while a larger clock face in the copy condition was associated with lower odds of PD diagnosis. Within PD cognitive phenotypes, slower performance (TCT, PCFL) and smaller clock face to command were associated with higher odds of being PDExe than PDWell, whereas larger clock faces associated with higher odds of being PDMem than PDWell. Longer disease duration, more pen strokes (command) and smaller clocks (command) associated with higher odds of being PDExe than PDWell. Conclusion: Digitally-acquired clock drawing profiles differ between PD and non-PD peers, and distinguish PD cognitive phenotypes.

When navigating unfamiliar social environments, it is important to identify who is powerful. Knowing who has power can be challenging because there may be limited social information available to an observer, and because people achieve influence for many reasons. In experiments with 3- to 5-year-old children (n = 192) and adults (n = 32), we investigated the developmental origins and conceptual structure of power judgments based on physical appearance. First, we examined participants’ judgments of strength and authority from facial structure and expansive body posture; next, we used a matching task to assess whether children thought that powerful faces and bodies “go together”. With age, children became increasingly sensitive to these two appearance cues and viewed both as evidence for both strength and authority. Unlike children, however, adults did not attribute strength to expansive body postures. Moreover, by 4 years, children brought facial and postural information together, indicating that they have formed a single, coherent representation of how they think powerful people appear. Overall, children’s sensitivity to postures preceded faces and their attributions of strength preceded authority, suggesting that an early capacity for assessing formidability may support later-emerging notions of power that are determined in a more normative manner.

The aim of the present study is to explore obsessive-compulsive disorder (OCD)-related abnormalities in white matter connectivity in OCD for a core region associated with inhibitory control [i.e. inferior frontal gyrus (IFG)]. Fifteen patients with OCD (11 men) and 15 healthy controls (nine men) underwent diffusion tensor imaging scanning to study four diffusivity indexes of white matter integrity [fractional anisotropy, mean diffusivity (MD), axial diffusivity and radial diffusivity (RD)]. The results showed that persons with OCD manifested significantly lower fractional anisotropy levels in the bilateral IFG as well as its parcellations in the pars opercularis, pars triangularis, and pars orbitalis. Significantly higher levels of MD, RD were evident for the OCD group in the IFG as a whole as well as in the bilateral subregions of the pars triangularis and pars opercularis (for MD and RD), the right side of the pars orbitalis (for RD), and the left side of the pars triangularis and right side pars opercularis (for axial diffusivity). Overall, the results suggest significant alterations in structural connectivity, probably associated with myelination and axonal abnormalities in the IFG of OCD patients., This work was partially supported by a research award to the first author (O.F.G.) from the Brain Imaging Network Grid/FCT (Portugal). Jorge Leite (SFRH/BPD/86027/2012) and Sandra Carvalho (SFRH/BPD/86041/2012) are supported by grants from the Portuguese Foundation for Science and Technology (FCT) and European Union (FSE-POPH).

Several studies have shown that basic emotions are responsible for a significant enhancement of early visual processes and increased activation in visual processing brain regions. It may be possible that the cognitive uncertainty and repeated behavioral checking evident in Obsessive Compulsive Disorder (OCD) is due to the existence of abnormalities in basic survival circuits, particularly those associated with the visual processing of the physical characteristics of emotional-laden stimuli. The objective of the present study was to test if patients with OCD show evidence of altered basic survival circuits, particularly those associated with the visual processing of the physical characteristics of emotional stimuli. Fifteen patients with OCD and 12 healthy controls underwent functional magnetic resonance imaging acquisition while being exposed to emotional pictures, with different levels of arousal, intended to trigger the defensive and appetitive basic survival circuits. Overall, the present results seem to indicate dissociation in the activity of the defense and appetitive survival systems in OCD. Results suggest that the clinical group reacts to basic threat with a strong activation of the defensive system mobilizing widespread brain networks (i.e., frontal, temporal, occipital-parietal, and subcortical nucleus) and blocking the activation of the appetitive system when facing positive emotional triggers from the initial stages of visual processing (i.e., superior occipital gyrus).