the cerebellum is also implicated in motor learning process , associative learning ( 1 - 4 ) , and various cognitive or sensory discrimination tasks ( 5 - 9 ) . studies on the cerebellum have contributed to our understanding of brain development , maturation , and plasticity .
acrobatically trained rats showed greater numbers of synapses on a purkinje cell compared to exercise or inactive animals .
the volume of molecular layer was also larger in the acrobat - trained group than in the exercise or inactive group ( 10 ) .
mice allowed to exercise during postnatal period had purkinje cells with larger dendritic trees and greater numbers of dendritic spines than sedentary littermates ( 11 ) .
thanks to recent developments in medical imaging technique such as computerized tomography ( ct ) or magnetic resonance imaging ( mri ) , in vivo morphometric analyses of human brain became possible .
cerebellar size with respect to physiological variables such as age , gender , intelligence , and motor skill was studied by several investigators ( 12 - 16 ) .
the recent mri - based cerebellar volumetric study of musicians suggested a possibility of macroscopic plasticity in the human cerebellum ( 17 , 18 ) . since basketball players practice motor skills everyday for a long time , it is possible to conceive that basketball - related motor learning could affect the morphological plasticity of cerebellum .
therefore , we hypothesize that the absolute ( acv ) or the relative cerebellar volumes ( rcv ) of basketball players are greater than that of controls . in order to investigate macroscopic cerebellar plasticity associated with motor skill learning in humans ,
we compared the size of total brain volume , absolute cerebellar volume , and relative cerebellum volume of basketball players with those of control group .
19 male basketball players were recruited from several university teams in korea through direct visiting interviews as an athletic group ( ag ) .
the athletes , whose heights over 190 cm , were ruled out in this study to minimize the variation as maximal as possible .
20 healthy control group ( cg ) subjects were recruited through advertisements at korea university web pages . among the volunteers , subjects
whose age and height matched the basketball players and who would not do any regular exercise were selected for this study .
all procedures were fully explained to the subjects and the duration of exercise training was checked . through the history of alcohol consumption and a neurological examination by a neurologist of korea university medical center , any individual with a possible neurological abnormality were excluded in this study .
the members of ag have played basketball for 8 yr in average and they have spent plenty of day time for highly skilled basketball training .
magnetic resonance imaging was performed on 1.5-telsa magnetom vision ( siemens , erlangen , germany ) .
the following parameters were used for the volumetric acquisition : tr=9.7 msec , te=4 msec , flip angle=12 degree , slice thickness = continuous 2.0 mm , matrix 192256 . after the acquisition of mr images , the dicom ( digital imaging and communications in medicine ) files were transferred to an ibm compatible pc from sun workstation with v - work software version 3.5 ( cybermed , korea ) . using 3-d medical software package ( cybermed , korea ) used in a previous study ( 19 ) , brain tissue on the mr images were separated from non - brain tissue ( skull and meninges ) for whole brain and cerebellar volumetric measurement .
threshold and region - growing technique were applied to generate a new image , representing brain without any scalp and skull ( 20 , 21 ) .
the cut - off between the brainstem and spinal cord was the last horizontal slice including cerebellum .
although this is somewhat arbitrary , there are no obvious and accepted gross anatomical landmarks to distinguish brainstem from spinal cord on mr images . using the last horizontal slice including cerebellum , in brains that were anterior commissure ( ac)-posterior commissure ( pc ) aligned , ensured that the cut - off was reliable ( 18 ) .
the cerebellum was segmented manually from the brainstem and cerebellar peduncles according to neuroanatomical landmarks ( 18 , 22 , 23 ) and criteria similar to those adopted in the previous volumetric studies of the cerebellum ( 24 , 25 ) . on sagittal slices , the cerebellar peduncles were removed from the cerebellar white matter according to the following procedure ( fig .
1 ) : on the mid - sagittal slice a vertical line was drawn ( at the angle of 90 degree to a line connecting the anterior and posterior commissure ) which touched the posterior border of the inferior colliculus .
this perpendicular line was overlaid on all sagittal slices and was used as a guide to divide the cerebellar peduncles from the brainstem .
cerebellar cortex anterior to this line was not expelled and was manually traced as part of the cerebellum ( note in fig .
1 that this included parts of the anterior lobe , biventer and flocculus on more lateral slices and of the tonsils and anterior lobe of the vermis on more medial slices ) .
the final segmented cerebellum consisted of the cerebellar hemispheres , deep nuclei and vermis ( 18 ) .
two raters measured the total brain volume ( tbv ) , the absolute ( acv ) and the relative cerebellar volumes ( rcv ) .
the inter - rater reliability ( two tailed , pearson correlation coefficient ) in tbv , acv and rcv was 0.94 ( p=0.00 ) , 0.93 ( p=0.00 ) and 0.96 ( p=0.00 ) , respectively .
tbv , acv and rcv were calculated by summing data obtained by multiplying each area by slice thickness ( 2 mm ) using 3-d model of the total brain and the absolute cerebellum ( fig .
2 ) . we chose to normalize acv to tbv in order to exclude the inter - subject variability in tbv as a source of variance in acv measurements , by calculating rcv in each subject as a percent ratio of their tbv , where rcv ( % ) = acv / tbv100 .
there is precedence in selecting brain volume or brain weight rather than body height to normalize brain morphometric data ( 18 , 26 , 27 ) .
statistical analyses were performed using spss for window , version 12.0 ( spss inc . ,
student 's t - tests were performed to assess the effect of motor learnig on tbv , acv , and rcv .
all analyses were two - tailed , and a p - value < 0.05 was considered as statistically significant .
19 male basketball players were recruited from several university teams in korea through direct visiting interviews as an athletic group ( ag ) .
the athletes , whose heights over 190 cm , were ruled out in this study to minimize the variation as maximal as possible .
20 healthy control group ( cg ) subjects were recruited through advertisements at korea university web pages . among the volunteers , subjects
whose age and height matched the basketball players and who would not do any regular exercise were selected for this study .
all procedures were fully explained to the subjects and the duration of exercise training was checked . through the history of alcohol consumption and a neurological examination by a neurologist of korea university medical center , any individual with a possible neurological abnormality were excluded in this study .
the members of ag have played basketball for 8 yr in average and they have spent plenty of day time for highly skilled basketball training .
magnetic resonance imaging was performed on 1.5-telsa magnetom vision ( siemens , erlangen , germany ) .
the following parameters were used for the volumetric acquisition : tr=9.7 msec , te=4 msec , flip angle=12 degree , slice thickness = continuous 2.0 mm , matrix 192256 . after the acquisition of mr images , the dicom ( digital imaging and communications in medicine ) files were transferred to an ibm compatible pc from sun workstation with v - work software version 3.5 ( cybermed , korea ) .
using 3-d medical software package ( cybermed , korea ) used in a previous study ( 19 ) , brain tissue on the mr images were separated from non - brain tissue ( skull and meninges ) for whole brain and cerebellar volumetric measurement . threshold and region - growing technique were applied to generate a new image , representing brain without any scalp and skull ( 20 , 21 ) .
the cut - off between the brainstem and spinal cord was the last horizontal slice including cerebellum .
although this is somewhat arbitrary , there are no obvious and accepted gross anatomical landmarks to distinguish brainstem from spinal cord on mr images . using the last horizontal slice including cerebellum , in brains that were anterior commissure ( ac)-posterior commissure ( pc ) aligned , ensured that the cut - off was reliable ( 18 ) .
the cerebellum was segmented manually from the brainstem and cerebellar peduncles according to neuroanatomical landmarks ( 18 , 22 , 23 ) and criteria similar to those adopted in the previous volumetric studies of the cerebellum ( 24 , 25 ) . on sagittal slices , the cerebellar peduncles were removed from the cerebellar white matter according to the following procedure ( fig .
1 ) : on the mid - sagittal slice a vertical line was drawn ( at the angle of 90 degree to a line connecting the anterior and posterior commissure ) which touched the posterior border of the inferior colliculus .
this perpendicular line was overlaid on all sagittal slices and was used as a guide to divide the cerebellar peduncles from the brainstem .
cerebellar cortex anterior to this line was not expelled and was manually traced as part of the cerebellum ( note in fig .
1 that this included parts of the anterior lobe , biventer and flocculus on more lateral slices and of the tonsils and anterior lobe of the vermis on more medial slices ) .
the final segmented cerebellum consisted of the cerebellar hemispheres , deep nuclei and vermis ( 18 ) .
two raters measured the total brain volume ( tbv ) , the absolute ( acv ) and the relative cerebellar volumes ( rcv ) .
the inter - rater reliability ( two tailed , pearson correlation coefficient ) in tbv , acv and rcv was 0.94 ( p=0.00 ) , 0.93 ( p=0.00 ) and 0.96 ( p=0.00 ) , respectively .
tbv , acv and rcv were calculated by summing data obtained by multiplying each area by slice thickness ( 2 mm ) using 3-d model of the total brain and the absolute cerebellum ( fig .
2 ) . we chose to normalize acv to tbv in order to exclude the inter - subject variability in tbv as a source of variance in acv measurements , by calculating rcv in each subject as a percent ratio of their tbv , where rcv ( % ) = acv / tbv100 .
there is precedence in selecting brain volume or brain weight rather than body height to normalize brain morphometric data ( 18 , 26 , 27 ) .
statistical analyses were performed using spss for window , version 12.0 ( spss inc . ,
student 's t - tests were performed to assess the effect of motor learnig on tbv , acv , and rcv .
all analyses were two - tailed , and a p - value < 0.05 was considered as statistically significant .
the comparison of tbv between ag and cg revealed no significant effect of persistent motor learning ( table 2 ; student t - test p=0.21 ) .
the average tbv of ag was 1355.6473.20 cm , whereas that of cg was 1390.1494.96 cm ( table 2 ) .
the volumetry of acv showed no significant difference between two groups ( table 2 ; student t - test p=0.07 ) .
the average acv of ag was 138.929.06 cm and that of cg was 145.5613.06 cm .
the acv of both groups in this study was slightly smaller than the result of filipek et al .
( 15210.5 cm ) ( 24 ) , and was larger than that of average korean ( 12610.38 cm ) which was previously reported by rhyu et al .
the effect of motor learning on rcv showed no statistical differences between ag and cg group ( table 2 ; student t - test p=0.38 ) .
the average rcv of ag was 10.260.65 cm , whereas that of cg was 10.490.97 cm . through the morphometric analyses of cerebellum in basketball players
, we could not detect any statistical differences in tbv , acv , and rcv .
recent morphometric analysis of albert einstein 's brain implied that his exceptional intelligence might be associated with larger inferior parietal lobe than that of age - matched control group ( 28 ) .
the relatively larger cerebellum of musicians suggested that acquisition and continual practice of complex motor skill may contribute to the macroscopic plasticity ( 17 , 18 ) as in other animal training models , in which the data suggested strong correlation between motor skill learning and cerebellar plasticity ( 1 ) .
although we tried to match the age and height as possible , there were significant difference between ag and cg .
the previous study clearly demonstrated that cerebellar volume was comparatively stable during young adults , but considerable reductions and increasing variability became obvious around the age of 50 yr ( 25 , 29 ) and there was little correlation between height and cerebellar volume ( 16 ) .
so , it was thought that height and age variable did not affect the result of this study .
this failure might come from different natures of the motor skills used by musicians and basketball players . playing musical instruments
consists of relatively fine movements , whereas playing basketball consists of coarser movements using big muscles .
the cerebellar plasticity according to the properties of motor skills needs to be explored further .
differential responses of neurogenesis in adult mice according to exercise modules may support this hypothesis .
mice that had access to a running wheel have the greater number of newly formed brain cells compared with the mice of the control or swimming group ( 30 ) .
another example can be found in acrobatically trained rats , whose volume of cerebellar molecular layer is bigger than those of rats received forced or voluntary exercises , or raised in inactive condition ( 1 ) . unlike the animal subjects , human subjects do various kinds of daily physical activities even though they do not do regular exercises .
the restriction of motor activity in the animal experiments is much more easily done compared to that in the human experiments .
we might observe microscopic plasticity in the cerebellum of ag as acrobat trained rats , if we could ran ultra - structural analysis . in conclusion , this study finds no significant differences in tbv , acv , and rcv between basketball players and non - basketball players . although macroscopic plasticity was not observed in this study , present results might be valuable data in that this is the first comparative study of cerebellar volume between basketball players and non - basketball players .
longitudinal , functional levels study and lobular volumetry may be required to demonstrate this hypothesis .
 cerebellum is a key structure involved in motor learning and coordination . in animal models , 
 motor skill learning increased the volume of molecular layer and the number of synapses on purkinje cells in the cerebellar cortex . 
 the aim of this study is to investigate whether the analogous change of cerebellar volume occurs in human population who learn specialized motor skills and practice them intensively for a long time . 
 magnetic resonance image ( mri)-based cerebellar volumetry was performed in basketball players and matched controls with v - works image software . 
 total brain volume , absolute and relative cerebellar volumes were compared between two groups . 
 there was no significant group difference in the total brain volume , the absolute and the relative cerebellar volume . 
 thus we could not detect structural change in the cerebellum of this athlete group in the macroscopic level . 
INTRODUCTION
MATERIALS AND METHODS
Subjects
MRI acquisition
Volumetry
Statistics
RESULTS
DISCUSSION