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Psychological Stress and Cellular Aging  

Idan Shalev and Waylon J. Hastings

Stress is a multistage process during which an organism perceives, interprets, and responds to threatening environmental stimuli. Physiological activity in the nervous, endocrine, and immune systems mediates the biological stress response. Although the stress response is adaptive in the short term, exposure to severe or chronic stressors dysregulates these biological systems, promoting maladaptive physiology and an accelerated aging phenotype, including aging on the cellular level. Two structures implicated in this process of stress and cellular aging are telomeres, whose length progressively decreases with age, and mitochondria, whose respiratory activity becomes increasingly inefficient with advanced age. Stress in its various forms is suggested to influence the maintenance and stability of these structures throughout life. Elucidating the interrelated connection between telomeres and mitochondria and how different types of stressors are influencing these structures to drive the aging process is of great interest. A better understanding of this subject can inform clinical treatments and intervention efforts to reduce (or even reverse) the damaging effects of stress on the aging process.


Spatial Vision for Action  

Eli Brenner and Jeroen B. J. Smeets

The way we see the world seems perfect, but it is not. What we see at any moment is based on a very limited part of the information that is available to us, and even details of that part are not always judged correctly. Moreover, perception is often inconsistent. There are persistent idiosyncratic discrepancies between visual and haptic spatial judgments. Even within the visual modality, related attributes such as size and position can be judged in a manner that is inconsistent with the physical relationship between them. People deal with all these differences and inconsistencies by selecting the best attributes to rely on for the task at hand and updating the information whenever possible. Doing so is presumably responsible for people’s proficiency in interacting with their environment, even when faced with the constantly changing spatial relationships with objects in the environment that result from using tools or that arise from the observer or the object moving. The best information to use depends not only on the goal of the action but also on how quickly and how reliably information can be acquired. This makes it complicated to make general claims about spatial vision for action, but it also provides unique opportunities to determine which attributes are used to guide our actions and evaluate why. Such opportunities can be used to identify the attributes that are used to perform a task, for instance revealing that judgments of position rather than size are used to determine how far to open one’s grip when grasping an object. They can also be used to determine how information guides ongoing movements, showing that judgments of position are continuously updated rather than inferred from judged motion. It is evident that we still have a lot to learn about how spatial vision guides action.


The Medicalization of Stress  

Vanessa L. Burrows

Stress has not always been accepted as a legitimate medical condition. The biomedical concept stress grew from tangled roots of varied psychosomatic theories of health that examined (a) the relationship between the mind and the body, (b) the relationship between an individual and his or her environment, (c) the capacity for human adaptation, and (d) biochemical mechanisms of self-preservation, and how these functions are altered during acute shock or chronic exposure to harmful agents. From disparate 19th-century origins in the fields of neurology, psychiatry, and evolutionary biology, a biological disease model of stress was originally conceived in the mid-1930s by Canadian endocrinologist Hans Selye, who correlated adrenocortical functions with the regulation of chronic disease. At the same time, the mid-20th-century epidemiological transition signaled the emergence of a pluricausal perspective of degenerative, chronic diseases such as cancer, heart disease, and arthritis that were not produced not by a specific etiological agent, but by a complex combination of multiple factors which contributed to a process of maladaptation that occurred over time due to the conditioning influence of multiple risk factors. The mass awareness of the therapeutic impact of adrenocortical hormones in the treatment of these prevalent diseases offered greater cultural currency to the biological disease model of stress. By the end of the Second World War, military neuropsychiatric research on combat fatigue promoted cultural acceptance of a dynamic and universal concept of mental illness that normalized the phenomenon of mental stress. This cultural shift encouraged the medicalization of anxiety which stimulated the emergence of a market for anxiolytic drugs in the 1950s and helped to link psychological and physiological health. By the 1960s, a growing psychosomatic paradigm of stress focused on behavioral interventions and encouraged the belief that individuals could control their own health through responsible decision-making. The implication that mental power can affect one’s physical health reinforced the psycho-socio-biological ambiguity that has been an enduring legacy of stress ever since. This article examines the medicalization of stress—that is, the historical process by which stress became medically defined. It spans from the mid-19th century to the mid-20th century, focusing on these nine distinct phases: 1. 19th-century psychosomatic antecedent disease concepts 2. The emergence of shell-shock as a medical diagnosis during World War I 3. Hans Selye’s theorization of the General Adapation Syndrome in the 1930s 4. neuropsychiatric research on combat stress during World War II 5. contemporaneous military research on stress hormones during World War II 6. the emergence of a risk factor model of disease in the post-World War II era 7. the development of a professional cadre of stress researchers in the 1940s and 50s 8. the medicalization of anxiety in the early post–World War II era 9. The popularization of stress in the 1950s and pharmaceutical treatments for stress, marked by the cultural assimilation of paradigmatic stress behaviors and deterrence strategies, as well pharmaceutical treatments for stress.


The Perception of Self-Orientation  

Laurence R. Harris

Self-orientation perception refers to our perceived self-orientation relative to gravity. An internal representation of self-orientation is derived from sensory cues indicating either directly or indirectly the direction of gravity relative to the body. The internal representation can be measured in the laboratory or clinic using visual or haptic measures, or even the body itself. However, each measure is affected differently by the availability of cues and the observer’s actual orientation relative to gravity, suggesting multiple, simultaneous representations of gravity. Visual, vestibular, somatosensory and proprioceptive cues are combined by multisensory integration to provide the most reliable estimates. Multisensory integration provides a robust perception of self-orientation for adults but means that children have a much lower precision in judging vertical before multisensory integration mechanisms are mature. The neurophysiological basis of the perception of self-orientation is a network of brain areas reflecting the multisensory processes that underlie it. This network provides some redundancy that can be exploited for potential patient recovery. Future work will perfect models for predicting perceived self-orientation in ever more challenging situations and how we can improve performance of pilots, divers and astronauts as they explore new situations and new gravity fields, and improve how we, and especially older people, can continue to enjoy our lifelong dance with gravity.



Neil E. Rowland

Thirst is a specific and compelling sensation, often arising from internal signals of dehydration but modulated by many environmental variables. There are several historical landmarks in the study of thirst and drinking behavior. The basic physiology of body fluid balance is important, in particular the mechanisms that conserve fluid loss. The transduction of fluid deficits can be discussed in relation to osmotic pressure (osmoreceptors) and volume (baroreceptors). Other relevant issues include the neurobiological mechanisms by which these signals are transformed to intracellular and extracellular dehydration thirsts, respectively, including the prominent role of structures along the lamina terminalis. Other considerations are the integration of signals from natural dehydration conditions, including water deprivation, thermoregulatory fluid loss, and thirst associated with eating dry food. These mechanisms should also be considered within a broader theoretical framework of organization of motivated behavior based on incentive salience.