18 for example reported faster responses to negative stimuli in the left visual half field. While changes in cortisol levels are linked with neurodevelopmental and mental disorders, effects of acute stress and the accompanying stress hormones on FHAs are not well understood as only a few selective studies investigated this association. Cortisol affects cortical networks by binding to glucocorticoid (GR) and mineralocorticoid (MR) receptors 17. This in turn stimulates the release of adrenocorticotropic hormone from the anterior pituitary, which leads to release of cortisol from the cortex of the adrenal medulla 16. The slower-acting Hypothalamus–Pituitary–Adrenal (HPA) axis triggers secretion of corticotrophin-releasing hormone from the hypothalamus. As an indirect measure of sympathetic nervous system activity, alpha amylase in saliva can be used 15. There are two systems that respond to acute stress: The sympathetic nervous system constitutes the faster one, triggering release of adrenaline and noradrenaline from the adrenal medulla 14. Cortisol constitutes one of the major stress hormones in the human body 13. Importantly, stress has been suggested to be a major influence factor in the pathogenesis of almost all of these disorders and most of them have been related to changes in basal or stress induced cortisol concentrations 12. Several psychiatric and neurodevelopmental disorders have been associated with changes in structural and functional hemispheric asymmetries 9, 10, 11. This inhibition can be modulated via hormonal influences 8. Thus, activation of the dominant hemisphere can lead to inhibition of the non-dominant hemisphere during task processing. While networks in both hemispheres contribute to task processing, each hemisphere is specialized for different aspects of the task 4.Ī possible mechanism underlying the emergence of functional hemispheric asymmetries (FHAs) is inhibition through the corpus callosum 5, 6: glutamatergic fibers in the corpus callosum synapse on GABAergic interneurons 7. On the functional level, asymmetries emerge through dominance of one hemisphere for processing in a given task many cortical processes like language perception or hand motor control are lateralized to one hemisphere 2, 3. Hemispheric asymmetries constitute a basic organizational principle of the vertebrate brain 1. As other studies reported an effect of stress hormones on functional hemispheric asymmetries on a neuro-functional level, future research using neuronal imaging methods would be helpful in the characterization of the relation of hemispheric asymmetries and stress hormones. This suggests that an increase in cortisol does not influence dichotic listening performance on a behavioral level. This partially corroborates the results of a previous study we performed using social stress to induce cortisol increases. While we could replicate previously reported findings for these tasks in the placebo session, we could not detect any differences in asymmetry between hydrocortisone and placebo treatment. In the Banich–Belger task, across-field advantages were determined to quantify interhemispheric integration. Lateralization quotients were determined for both reaction times and correctly identified syllables in both dichotic listening tasks. Both times, a verbal and an emotional dichotic listening task to assess language and emotional lateralization, as well as a Banich–Belger task to assess interhemispheric integration were applied. Overall, 60 participants were tested after administration of 20 mg hydrocortisone or a placebo tablet in a cross-over design. Therefore, it was the aim of the present study to investigate the acute effects of cortisol on functional hemispheric asymmetries. On the molecular level, this modulation may be caused by a stress-related increase in cortisol, a major stress hormone. It has been suggested that acute stress can affect functional hemispheric asymmetries by modulating inhibitory function of the corpus callosum, the white matter pathway that connects the two hemispheres. The short-term effects of acute stress exposure on functional hemispheric asymmetries are less well investigated. Chronic stress has been shown to have long-term effects on functional hemispheric asymmetries in both humans and non-human species.
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