***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: In adults the cranium is a rigid bony vault of fixed size and therefore the intra-cranial volume is a constant which equals the sum of the volume of the brain , the intra-cranial volume of CSF and the intra-cranial volume of blood . There can be marked changes in the volumes of these three intra-cranial compartments which may influence susceptibility to brain damage after head injury . This is the first study to investigate the relationship between dehydration and changes in the volume of the brain and the cerebral ventricles .  Six healthy control subjects underwent magnetic resonance imaging of the brain before and after a period of exercise in an environmental chamber . The subjects lost between 2.1 % and 2.6 % of their body mass due to water loss through sweating . We found a correlation between the degree of dehydration and the change in ventricular volume ( r=0.932 , p=0.007 ) . The changes in ventricular volume caused by dehydration were much larger than those seen in day-to-day fluctuations in a normally hydrated healthy control subject BACKGROUND Total body water ( TBW ) volume is reported to decrease with age , but much of the published data are 20 to almost 50 years old and are cross-sectional . Proper interpretation of clinical levels of TBW and trends with age necessitates the availability of current longitudinal data from healthy individuals . METHODS Mixed longitudinal data for TBW of 274 white men and 292 white women ( 18 to 64 years of age ) in the Fels Longitudinal Study were collected on a regular schedule over a recent eight-year period . The concentration of deuterium was measured by deuterium nuclear magnetic resonance spectroscopy . Body composition estimates were made with dual-energy x-ray absorptiometry , and r and om effect models were used to determine the patterns of change over time with and without covariates . RESULTS The mean TBW data for the Fels men are either similar to or approximately 2 to as much as 6 liters greater than that reported by most other investigators 20 to 50 years ago . For Fels women , the mean TBW ranges from approximately 2 to as much as 5 liters less than that reported previously . These comparisons with much earlier studies reflect cohort effects and the secular changes in overall body size that have occurred during the past 60 to 70 years . These findings are reinforced by the fact that some early data sets included individuals born almost 140 years ago . After adjusting for the covariate effects of total body fat ( TBF ) and fat-free mass ( FFM ) with age , there were no significant age or age-squared effects on TBW in the men . In the women , after adjusting for the covariate associations of TBF and FFM with age , there was a small , but significant , negative linear association of TBW with age . In the men and women , the mean ratio of TBW to weight declined with age as a function of an increase in body fatness and more so for the men than the women . CONCLUSION The findings from these mixed longitudinal data indicate that TBW volume , on average , maintains a reasonable degree of stability in men and women through a large portion of adulthood . These TBW data are recommended as current reference data for healthy adults 
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These very interesting findings could suggest a common cause for altered brain function in these patients .
Now , if this were the case , then hypovolemia result ing from systemic dehydration could also reduce brain volume ( Dickson et al. , 2005 ; Duning et al. , 2005 ) .
This “ hypothesis ” of dehydration is supported further by work showing that total body water decreases with age ( Chumlea et al. , 1999 ) as well as with increasing BMI ( Ritz et al. , 2008 ) , thus suggesting that aged and /or obese and /or diabetic patients could be chronically dehydrated .
It has been suggested that increased drinking would go some way to alleviating some of the signs of the dehydration and the decreased metabolism .
It would be very interesting to investigate just what influence these changes in brain volume , and thus neuronal volume and metabolism with dehydration and rehydration , would have on cognitive impairment associated with aging and associated with T2DM , obesity , as well as cardiovascular , and Alzheimer 's disease .
In contrast to what has been found in the pathophysiology mentioned above , dehydration in healthy humans does not appear to have a great influence on brain volume changes ( Kempton et al. , 2009 ) .
Whereas in healthy adolescences , again with no obvious changes in brain volume , dehydration appeared to negatively impact “ executive functions such as planning and visuo-spatial processing ” where individuals needed to exert a higher level of neuronal activity in order to achieve the same performance level ( Kempton et al. , 2011 ) .
It should be noted that these effects were noticed with short-term dehydration , whereas the overall effects of long-term , or chronic , dehydration appear to be more global affecting various parts of the body ( obesity , insulin resistance , blood pressure ) as well as the brain ( cognitive dysfunction ) .