Rev. Neurosci. 2016; aop *Corresponding author: Zahra Jafari, Department of Neuroscience, Canadian Centre for Behavioural Neuroscience (CCBN), University of Lethbridge, Lethbridge, AB, Canada, T1K-3M4; and Department of Basic Sciences in Rehabilitation, School of Rehabilitation Sciences, Iran University of Medical Science (IUMS), Tehran, Iran, 15875-4391, e-mail: zahra.jafari@uleth.ca; jafari.z@iums.ac.ir Bryan E. Kolb and Majid H. Mohajerani: Department of Neuroscience, Canadian Centre for Behavioural Neuroscience (CCBN), University of Lethbridge, Lethbridge, AB, Canada, T1K-3M4 Zahra Jafari*, Bryan E. Kolb and Majid H. Mohajerani Effect of acute stress on auditory processing: a systematic review of human studies DOI 10.1515/revneuro-2016-0043 Received July 17, 2016; accepted August 21, 2016 Abstract: Stress is an integral part of modern life. Although there is a large body of literature regarding the harmful effects of chronic stress on different aspects of human life, acute stress is the most common form of stress, resulting from the demands and pressures of the recent past and the anticipated demands and pressures of the near future. In spite of its pervasive nature, less attention has been paid to the impact of acute stress on sensory processing than to the consequences of chronic stress, particularly concerning auditory processing. In this systematic review, the impact of experimental acute stress on the auditory processing of healthy adults was investigated. The results revealed the adverse effects of acute physical and psycho- logical stresses on auditory processing. According to the open field of research on stress and the auditory system and the high possibility of experiencing different types of acute stresses in various life environments, including test- ing places, it seems that more investigations are needed to identify and manage different types of acute stresses in both clinical and research situations. Keywords: acute stress; auditory; cognition; human; physical stress; psychological stress. Introduction Behavior is formed by neuroplastic changes that occur in the brain after various experiences over the life span of an organism. ‘Stress’ plays a substantial role in shaping behavior and brain function (Kolb et al., 2013; Hunter et al., 2015; Kolb and Gibb, 2015; Oken et al., 2015). Stress is widely used in everyday language to refer to a variety of distressing situations (Horner, 2003; Bali and Jaggi, 2015) and represents a deviation from some norm or steady state (Lazarus, 1993). Stressors may be physical (environmental and physiological), psychological/mental (cognitive and emotional), or mixed. Physical stresses have a direct effect on the body and cause direct metabolic or physiological changes (Bali and Jaggi, 2015). However, what is harmful to actual tissues in physical stress may not be the same as what is adverse psychologically. Psychological stress is a reaction to diverse threats that arise out of the person’s relationship with the environment (Lazarus, 1993). These threats may be cognitive (affecting thought processes) or emotional (affecting feeling responses, such as anger or fear; Bali and Jaggi, 2015). Stresses may be ‘acute’ or ‘chronic’ depending on the duration of the stressor. Acute stress that lasts a few minutes activates particular cells to release hormones and other chemicals into the blood- stream that prepare the body for injury or infection during ‘fight-or-flight’. It increases proinflammatory cytokines of blood levels. Chronic stress that lasts from a period of days to years is associated with even higher levels of proinflam- matory cytokines but potentially results in different health outcomes, including dysregulation of the immune system and increased risk for chronic diseases, such as athero- sclerosis (Morey et al., 2015). During exposure to stresses, the brain initiates the release of multiple transmitters, peptides, and hormones throughout the body (Joels and Baram, 2009), with the aim of coping with the stressful situation and restoring the organism’s balance (i.e. home- ostasis). In particular, two systems are involved during acute stress: (1) the fast-acting sympathetic nervous system and (2) the slow hypothalamus-pituitary-adrenal (HPA) axis. The activation of the sympathetic nervous system leads to the release of the catecholamines adrenaline and noradrenaline from the adrenal medulla, which results in autonomic responses such as an increase in heart rate or enhanced blood flow to the skeletal muscles to prepare the organism for an eventual ‘fight-or-flight’ response. The activation of the HPA axis leads to some intermediate steps and results in the release of glucocorticoids (mainly cortisol in humans and corticosterone in rodents) from the adrenal cortex. The glucocorticoids then enter the brain and bind to high-affinity mineralocorticoid receptors and low-affinity glucocorticoid receptors (Reul and de Kloet, 1985; Schwabe et al., 2012; Xiong and Zhang, 2013). Brought to you by | University of Florida Authenticated Download Date | 10/10/16 10:23 AM