Stress, cognition and functional connectivity in the healthy human
Stress is known to negatively impact physiological and psychological processes in humans. While chronic exposure to stress has been implicated in the pathology of numerous physiological and neuropsychological disorders, acute stress exposure has also been shown to impair cognitive task performance. Since the brain is the primary organ involved in detecting and responding to stressors, neuroimaging techniques have been used to explore the structural and functional neural correlates of stress. The studies presented here attempted to examine how acute stress might affect the temporally correlated activation of multiple brain regions, also known as functional connectivity, while performing cognitive tasks. Of additional interest was the role of gender and presence of the short allele polymorphism on the promoter region of the serotonin transporter gene, both factors known to influence stress susceptibility, in determining effects of stress on functional connectivity during cognitive task performance. Forty-five participants with no history of neurological or psychiatric disorders were recruited to participate in the study and underwent two sessions of functional magnetic resonance imaging -- one session involved exposure to the Montreal Imaging Stress Test (MIST) to induce stress and the other session had control tasks that did not induce stress. The participants were blinded to the stress induction. Following exposure to the stress or no stress control task, the participants performed verbal fluency tasks, verbal problem-solving tasks and the emotional faces task. A priori regions of interest were defined for each of the tasks and functional connectivity differences between the a priori regions of interest under stress and no stress were examined. Additionally, the influence of gender and genotype were also examined. Results reveal specific gender and genotype-based differences in regional functional connectivity under stress and no stress during the cognitive tasks even in the absence of differences in overall task performance. The results begin to elucidate the specific neural underpinnings of stress susceptibility in healthy individuals. The implications of these results in better understanding the neural correlates of stress related cognitive impairments, and may ultimately be helpful for neuropsychiatric disorders such as anxiety, depression and posttraumatic stress disorders and may help us move towards developing targeted neuropharmacological therapeutic interventions are discussed.
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