Differential impact of stress on risk-taking behaviour in individuals using hippocampus versus caudate nucleus-dependent virtual navigation strategies

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Previous results from our laboratory have shown that stress has a different impact on people using the hippocampus when navigating (spatial learners) compared to those using the caudate nucleus (response learners). The hippocampus is important for spatial and episodic memory while the caudate nucleus is involved in forming habits and reward-seeking behaviour. We have previously shown that when children are exposed to a psychological stressor (i.e., being told a nurse was arriving in 30 minutes to draw blood with a needle), response learners display an increase in cortisol, a hormone released by the adrenal cortex, while spatial learners do not. Cortisol and stress have an impact on brain structures, including the hippocampus, and behaviours such as risk-taking. Further, we have shown that risk-taking behaviour as measured during a gambling task is also higher in people who are response learners. In the current grant, we will therefore investigate the neural and hormonal mechanisms by which stress has an impact on decision making, including risk-taking behavior, on these two populations and assess if spatial memory training targeting the hippocampus can mitigate risk-taking. We will first test if a psychological stressor (i.e., asking people to speak and perform a difficult math problem in front of a panel of evaluators) will cause an increase in cortisol amoungst adult response learners compared to spatial learners. We will then assess if this psychological stressor will increase risk-taking behaviour in a gambling task in response learners in comparison to spatial learners. We will also correlate the magnitude of the cortisol stress response with levels of risk-taking behaviour, to better understand the relationship between these two factors. A longitudinal spatial memory training study that uniquely targets and increases volume in the hippocampus will then be conducted. We will assess if spatial memory training over 16-weeks will have the ability to reduce risk-taking behaviour and cortisol stress response in both spatial and response learners, and test is one population preferentially benefits from such training. We will also collect structural magnetic resonance imaging scans before and after training to evaluate increases in hippocampal grey matter, and correlate this measure with changes in risk-taking behaviour. This grant will be fundamental to understand the basic neural and hormonal mechanisms involved in the interplay between competing multiple memory systems that have a direct impact on decision making. We will also be able to further evaluate if experience-dependent training can positively impact these neural mechanisms. This basic research can eventually lead to specific cognitive interventions that could benefit the cognitive health of Canadians at all stages of life, through further bridging the rodent and human literatures on the role of stress on learning and memory.