Hypohydration alters pre-frontal cortex haemodynamics, but does not impair motor learning

<p>It is unknown how hypohydration influences fine motor performance training and motor learning. Here, 30 participants (aged 19-46 years) were randomly assigned to a hypohydration (HYPO) or control (CON) group (both <i>n</i> = 15). Moderate hypohydration (~ 2.4% loss in body mass) was produced in HYPO via active dehydration before a 46 min fluid restricted rest period was undertaken. The conclusion of rest coincided with when CON attended the facilities. Both groups undertook a discrete sequence production task consisting of 6 training blocks, and returned ~ 300 min later to complete a delayed retention and transfer test while euhydrated. Bilateral pre-frontal cortex (PFC) haemodynamics were assessed using functional near-infrared spectroscopy throughout training and delayed learning assessments. Response time improved across training (<i>P</i> < 0.01) and was similar between the groups (both <i>P</i> = 0.22). Analysis of training PFC haemodynamics revealed a significant group by block interaction for oxygenated (O₂Hb; <i>P</i> < 0.01), but not deoxygenated haemoglobin (<i>P</i> = 0.77). In training block 1, bilateral O2Hb was higher in HYPO (<i>P</i> = 0.02), while bilateral O2Hb increased in CON between blocks 2-3 and 5-6 (both P ≤ 0.03). During the delayed retention and transfer test, no group differences or interactions were found in response time, response error, or PFC haemodynamics (all <i>P</i> ≥ 0.27). Moderate hypohydration does increase PFC activation during motor skill learning, however, this appears to be transient and of little consequence to training or delayed retention or transfer performance.</p>