Autonomic adaptations mediate the effect of hydration on brain functioning and mood: Evidence from two randomized controlled trials

Figures

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  Figure 1. The experimental procedure.

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  Figure 2. The effect of drinking water on the average length of the RR interval, SDNN and RMSSD. Data are the changes (end of the morning minus baseline) for each index compared across the two conditions. Top panel: Study 1. When participants were hypo-hydrated they had a lower R-R (i.e a higher HR) (p < 0.03), lower SDRR (i.e a lower HRV) (p < 0.01) and reduced parasympathetic activity (i.e. lower RMSSD) (p < 0.03). Bottom panel: Study 2. If water was consumed participants had an increase in their average R-R interval (p < 0.001), a larger standard SDNN (p < 0.027), and a larger RMSSD (p < 0.031). RR, interbeat interval, SDNN, standard deviation of normal to normal R-R interval, RMSSD, root mean square of the standard deviation.

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  Figure 3. Peak activity in PoCG (top) and mOFC (bottom) water >hypo-hydration.

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  Figure 4. (A) Peak activity in vCG water >hypo-hydration. Correlation between neuronal activity in the vCG and (B). RR interval (C). anxiety and (D). difficulty ratings. Data are Pearson’s r coefficient for difference scores (no water – water).

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  Figure 5. Schematic illustration of the mediation analysis used in study 2. The total effect of water on rating of anxiety was significant (B = 16.321, LLCI 3.729, ULCI 28.913). The direct effect (when the influence of SDNN was considered) was not significant (B = 12.763, LLCI -0.257, ULCI 25.784). When water was not consumed participants were more anxious (F(1,54) = 4.706, p < 0.034). A decrease in HRV (SDRR) was associated with an increase in anxiety levels (r = 0.335, p < 0.012). The indirect effect Water → SDNN → Anxiety was significant (B = 3.557, LLCI 0.212, ULCI 8.321).

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  Figure 6. Map showing the brain areas associated with autonomic modulation. Left data from present study. Right areas controlling HRV reproduced from Thayer et al. (2012) with permission.

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  Figure 7. Arithmetic task and Visual analogue scale example stimuli. The crosses are fixation points when otherwise the screen is blank. At the third image the participant indicated whether the right or left number was correct by pushing a button.