*********************************
There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
*********************************
Doctoral Thesis Proposal
School of Biological Sciences, Georgia Institute of Technology
September 29, 2016, 11:00, Room 1253 555 14th St.
Title: Do body water deficits and exercise-heat stress affect brain structure, function, and neuromotor performance?
Student: Matthew T. Wittbrodt, M.S.
Committee Members: Mindy L. Millard-Stafford Ph.D. (advisor), Audrey L. Duarte Ph.D., J. Chris Mizelle Ph.D., Michael N. Sawka Ph.D., and Lewis A. Wheaton Ph.D.
Abstract
There is reason to believe body water deficits (hypohydration) adversely impact the central nervous system
despite protective physiological mechanisms to maintain brain homeostasis. Early animal models suggested
brain volume is preserved during severe hypohydration (10% body mass loss), likely from osmolyte
production to maintain the osmotic equilibrium between intra- and extracellular compartments. Current
neuroimaging techniques (e.g., magnetic resonance imaging) allow real-time in vivo measurement of human
brain morphology and localized hemodynamic responses during a cognitive task. Of the few studies utilizing
MRI to investigate hypohydration-mediated effects on brain morphology, most suggest brain volume does
not change, but specific structures (e.g., lateral ventricles) are altered at moderate levels (2-4% body mass
loss). However, the relationship between changes in other brain structures and decrements in cognitive
function is not well-established. Most computerized tests of cognition require a motor response involving
a terminal movement (e.g., button press) via activation of the neuromotor system. Neuromotor system
processing can be divided into two major phases: motor planning (i.e., from visual perception through
the determination of a movement goal) and movement execution (i.e., pressing a button after movement
goal determination). Disruption to motor planning and/or movement execution can have potentially severe
consequences such as degraded driving performance, increased navigation errors, and elevated rate of occupational
accidents. Whether neuromotor performance is adversely impacted (e.g., slowed reaction time,
reduced accuracy) or requires additional neural resources (e.g. elevated primary motor cortex activation)
to perform a given task following hypohydration is unclear. The goal of this thesis is to investigate
whether moderate hypohydration elicited by sweat losses during exercise-heat stress alters
brain structures and if the observed changes are associated with impaired task performance
and neuromotor function. My overall hypothesis is moderate hypohydration will alter brain morphology
due to water shifts out of intracellular compartments (grey and white matter crenation) into extracellular
spaces (expanding brain ventricles, cerebrospinal fluid) eliciting elevated brain activations and degraded
neuromotor performance during repetitive upper extremity movements requiring variable levels of decision
making. Aim 1 will quantify changes in brain structures due to moderate hypohydration induced by sweat
loss during exercise-heat stress. Aim 2 will correlate these structural changes to neural resource requirements
and performance errors during rhythmically paced movements. Aim 3 will evaluate which phases
of neuromotor processing (e.g., motor planning, movement execution) are associated with performance
decrements due to moderate hypohydration.
1
