Measuring the effects of stress on cognitive function in real-world and laboratory contexts: the potential protective effects of phospholipid supplementation

There is a well-defined relationship between stress and cognition. The intake of phospholipids has the potential to attenuate responses to stress and thus protect cognitive performance. The aims of this thesis were (a) develop suitable methodologies, both in the real-world and laboratory, to examine the effects of stress on cognition; (b) identify characteristics of individuals who may be particularly stress vulnerable; and (c) assess the potential for a phospholipid intervention to attenuate the response to stress and the impact of this stress exposure on cognitive function. These aims were addressed in four studies. Studies 1 – 3 aimed to identify a number of design and methodological conditions suitable for a phospholipid intervention assessing cognitive performance under stress (Study 4). The identification of a naturalistic or laboratory stress context capable of eliciting cortisol responses over repeated exposures, selection of cognitive tests sensitive to stress impairment, and characterising individuals with an increased tendency towards high cortisol responsivity to stress were the key preparatory methodological factors examined in Studies 1 – 3. Studies 1 (N = 16) and 2 (N = 17) explored the feasibility of employing a real-world audition stress context for a dietary intervention. Whilst this context was sufficient to elicit significant cortisol responses (Study 1), this was not consistently shown (Study 2), and suggestive of poor test-retest reliability. Study 3 (N = 24) demonstrated that a combined physical/psychosocial laboratory stressor was sufficient to elicit significant, and comparable, cortisol responses over repeated exposures. Three tests of prefrontal cortex-mediated cognitive function (n-back, ospan, and task-switch test) were demonstrated to be sensitive to stress impairment (Studies 2 – 3) and the Perfectionism: Organisation dimension of perfectionism emerged as a positive predictor of cortisol responsivity (Studies 1 – 3). The laboratory stressor, identified cognitive tests, and a sample selected on the basis of high perfectionist tendency, were identified as appropriate methodologies for the dietary intervention. These methodologies were employed in a randomised placebo-controlled six week phospholipid intervention (N = 54) assessing cognitive performance after an acute physical/psychosocial stressor (pre- and post-intervention). Phospholipid intake was associated with increased cortisol response, and significant elevations in sympathetic and subjective arousal. Cognitive performance was unaffected by phospholipid intake. A trend for attenuated anticipatory subjective stress suggested a modest stress-buffering effect of phospholipids. Further examination of the relationship between perfectionism and cortisol, and determinants of reduced habituation to the laboratory stressor employed, are warranted. The methodological advances developed herein offer a suitable framework for future research further assessing the potential stress-buffering effect of phospholipids in samples characterised by cognitive vulnerabilities (e.g., the elderly).