alcohol dependence is the most prevalent substance use disorder   that can lead individuals with the disorder to serious health - related   and social problems . according to a report by nutt and colleagues ( 2007 ) , the level of potential harm and risk of alcohol use and misuse was among the top five with heroin and cocaine .
the 12-month prevalence of alcohol dependence is reported to be approximately 2% to 6% in the general populations . in part reflecting the high potential harm and high prevalence of alcohol dependence , there have been a number of studies on how chronic alcohol use or alcohol dependence interacts with the structure of the brain of animals   and humans .
overall brain atrophy , including the lesser volumes of gray matter and white matter with increased cerebrospinal fluid , in patients with alcohol use disorders , has consistently been reported .
deficits in the prefrontal cortex , temporal cortex , cerebellum , striatum , hippocampus and amygdala   have also been reported in patients with alcohol dependence .
neuropathological studies have shown that the alcohol - related neuronal and glial loss would preferentially involve the prefrontal cortex   among cortical regions .
functional neuroimaging studies demonstrated altered metabolism or activation of the frontal cortex in association with the deteriorated neuropsychological functioning .
cortical thickness analysis , a reliable and valid method , can capture important information on cortical structures .
durazzo and colleagues exhibited that alcohol - dependent adults had thinner cortical regions in the left anterior cingulate cortex , bilateral frontal cortex , and bilateral insula than healthy controls .
other researchers found that alcohol - dependent adults had reduced cortical thickness in the widespread brain regions of the superior frontal , precentral , postcentral , middle frontal , middle and superior temporal , middle temporal , and the lateral occipital cortex than healthy comparison participants . in the report by momenan and colleagues , participants with alcohol dependence exhibited thinner cortical regions that encompass the medial superior frontal cortex , insula , precentral and the precuneus of the right hemisphere as well as the superior frontal gyrus of the left hemisphere , in comparison with the healthy controls .
previous studies have reported widespread cortical deficits without covarying out the effects associated with the global atrophy of the brain . among these widespread regions that show
alcohol - related atrophy , we wanted to localize the cortical regions that may be particularly vulnerable to alcohol consumption .
we therefore undertook the cortical thickness analysis adjusting for the hemispheric average cortical thickness , in 21 detoxified alcohol - dependent patients and matched 22 healthy comparison subjects .
the objective of this study was to identify brain regions with cortical thickness alterations that exceed the level of global alterations in alcohol dependence .
we used the whole brain - wise cortical thickness analysis , which is validated histologically   and with manual outlining method .
we also investigated whether the magnitude of deficits are correlated with the alcohol use - related variable .
given the studies that suggest the preferential involvement of prefrontal cortex among brain structural and functional alterations in alcohol dependence , we hypothesized that patients with alcohol dependence would have thinner prefrontal cortex in comparison with healthy comparison subjects , after correcting for the global cortical thinning associated with alcohol dependence .
patients with alcohol dependence were enrolled from the inpatient unit of the department of neuropsychiatry in a university - affiliated hospital , seoul , south korea .
age - matched healthy comparison subjects were recruited from the community via the local advertisement during the same study period .
inclusion criteria for alcohol dependence group were ( 1 ) age between 20 and 70 , and ( 2 ) diagnosis of alcohol dependence according to the diagnostic and statistical manual of mental disorders - iv by 2 board - certified psychiatrists .
exclusion criteria for both alcohol dependence and control groups were ( 1 ) any symptoms or signs of confusion , major medical disorders including kidney disease and chronic liver disease , and/or malnutrition , ( 2 ) presence or history of neurological disorders , ( 3 ) presence or history of any mental disorders other than alcohol dependence or comorbid depressive disorders , including alcohol - induced persistent dementia , alcohol - induced amnestic disorder , or alcohol withdrawal delirium ( 3 ) history of head injury , and ( 4 ) any contraindications to magnetic resonance imaging ( mri ) such as pace makers , claustrophobia , or metal implants .
additional exclusion criteria for control group were ( 1 ) presence or history of mental disorders including alcohol abuse and ( 2 ) current alcohol consumption greater than 14 equivalent standard drinks for men , 7 for women , per time . after being detoxified for 2 weeks , all patients underwent physical examination by a physician and the routine laboratory tests to screen out any major medical disorders .
t1 and t2 weighted mr images were obtained using 1.5 tesla siemens whole body scanner .
repetition time [ tr]=2,050 ms , echo time [ te]=4.39 ms , inversion time [ ti]=1,100 ms , number of excitation [ nex]=2 , flip angle [ fa]=15 , slice thickness=1.3 mm , field of view [ fov]=180180 mm , acquisition matrix=256180 .
t1 weighted images of 7 subjects were obtained with slightly different image acquisition protocol ( tr=1,960 ms , te=4.38 ms , ti=1,100 ms , nex=2 , flip angle [ fa]=15 , slice thickness=1.5 mm , fov=250 x 250 , acquisition matrix=256 x 180 ) .
t2 weighted images were acquired in order to screen for gross brain abnormality ( tr=9,710 ms , te=120 ms , nex=2 , flip angle [ fa]=170 , slice thickness=3 mm ) .
smoothing processes were conducted using an iterative nearest - neighbor averaging procedure with the full - width half maximum ( fwhm ) 15 mm 2-d gaussian kernel . for calculating statistical difference maps of cortical thickness between alcohol dependence and healthy comparison groups , general linear model ( glm ) with cortical thickness at each vertex as the dependent variable has been used .
non - cortical areas of medial wall and corpus callosum were excluded from the model building .
hemispheric average cortical thickness was included in the model as a covariate since there was a significant difference in hemispheric average cortical thickness between groups and our aim was to identify the particularly vulnerable cortical regions beyond the global brain atrophy associated with alcohol dependence .
5,000 permutation simulations have been performed with random group - label shuffling , with a threshold for a significant vertex of p<0.05 .
clusters with the size that would pass the family - wise error rate correction were considered significant .
thickness values of the surface point with highest z values ( local maxima ) within the cluster , where significant group differences of cortical thickness were found , were extracted for post hoc analyses .
pair - wise correlations were used to test whether there were associations between the magnitude of cortical thickness deficits in patients with alcohol dependence and the duration of alcohol use . considering the relatively modest sample size , sensitivity analyses to rule out the possibility that the current results may be modulated by other confounding factors such as comorbid depression , anxiety symptoms and scan parameter difference were performed .
local maxima thickness values within the cluster extracted as described above were subjected to linear regression models that included the scan parameter difference , the presence of comorbid depression as defined by 19 or more scores on the 17-item hamilton depression rating scale ( hdrs ) , or the presence of anxiety as defined by 40 or more scores on the state - trait anxiety inventory ( stai - t )   as additional covariates .
computations were performed using stata version 11 ( stata corp . , college station , tx , usa ) .
patients with alcohol dependence were enrolled from the inpatient unit of the department of neuropsychiatry in a university - affiliated hospital , seoul , south korea .
age - matched healthy comparison subjects were recruited from the community via the local advertisement during the same study period .
inclusion criteria for alcohol dependence group were ( 1 ) age between 20 and 70 , and ( 2 ) diagnosis of alcohol dependence according to the diagnostic and statistical manual of mental disorders - iv by 2 board - certified psychiatrists .
exclusion criteria for both alcohol dependence and control groups were ( 1 ) any symptoms or signs of confusion , major medical disorders including kidney disease and chronic liver disease , and/or malnutrition , ( 2 ) presence or history of neurological disorders , ( 3 ) presence or history of any mental disorders other than alcohol dependence or comorbid depressive disorders , including alcohol - induced persistent dementia , alcohol - induced amnestic disorder , or alcohol withdrawal delirium ( 3 ) history of head injury , and ( 4 ) any contraindications to magnetic resonance imaging ( mri ) such as pace makers , claustrophobia , or metal implants .
additional exclusion criteria for control group were ( 1 ) presence or history of mental disorders including alcohol abuse and ( 2 ) current alcohol consumption greater than 14 equivalent standard drinks for men , 7 for women , per time . after being detoxified for 2 weeks , all patients underwent physical examination by a physician and the routine laboratory tests to screen out any major medical disorders .
t1 and t2 weighted mr images were obtained using 1.5 tesla siemens whole body scanner .
repetition time [ tr]=2,050 ms , echo time [ te]=4.39 ms , inversion time [ ti]=1,100 ms , number of excitation [ nex]=2 , flip angle [ fa]=15 , slice thickness=1.3 mm , field of view [ fov]=180180 mm , acquisition matrix=256180 . t1 weighted images of 7 subjects were obtained with slightly different image acquisition protocol ( tr=1,960 ms , te=4.38 ms , ti=1,100 ms , nex=2 , flip angle [ fa]=15 , slice thickness=1.5 mm , fov=250 x 250 , acquisition matrix=256 x 180 ) .
t2 weighted images were acquired in order to screen for gross brain abnormality ( tr=9,710 ms , te=120 ms , nex=2 , flip angle [ fa]=170 , slice thickness=3 mm ) .
smoothing processes were conducted using an iterative nearest - neighbor averaging procedure with the full - width half maximum ( fwhm ) 15 mm 2-d gaussian kernel .
for calculating statistical difference maps of cortical thickness between alcohol dependence and healthy comparison groups , general linear model ( glm ) with cortical thickness at each vertex as the dependent variable has been used .
non - cortical areas of medial wall and corpus callosum were excluded from the model building .
hemispheric average cortical thickness was included in the model as a covariate since there was a significant difference in hemispheric average cortical thickness between groups and our aim was to identify the particularly vulnerable cortical regions beyond the global brain atrophy associated with alcohol dependence .
5,000 permutation simulations have been performed with random group - label shuffling , with a threshold for a significant vertex of p<0.05 .
clusters with the size that would pass the family - wise error rate correction were considered significant .
thickness values of the surface point with highest z values ( local maxima ) within the cluster , where significant group differences of cortical thickness were found , were extracted for post hoc analyses .
pair - wise correlations were used to test whether there were associations between the magnitude of cortical thickness deficits in patients with alcohol dependence and the duration of alcohol use . considering the relatively modest sample size , sensitivity analyses to rule out the possibility that the current results may be modulated by other confounding factors such as comorbid depression , anxiety symptoms and scan parameter difference were performed .
local maxima thickness values within the cluster extracted as described above were subjected to linear regression models that included the scan parameter difference , the presence of comorbid depression as defined by 19 or more scores on the 17-item hamilton depression rating scale ( hdrs ) , or the presence of anxiety as defined by 40 or more scores on the state - trait anxiety inventory ( stai - t )   as additional covariates .
computations were performed using stata version 11 ( stata corp . , college station , tx , usa ) .
there were no significant differences in age and sex between diagnostic groups ( table 1 ) .
patients with alcohol dependence drank alcohol more frequently and more heavily than healthy comparison subjects ( table 1 ) .
patients with alcohol dependence had general cortical thinning ( left hemispheric average cortical thickness ( mm ) : 2.440.07 [ healthy comparison subjects ] vs 2.240.27 [ patients with alcohol dependence ] , t=3.35 , p=0.002 ) ( right hemispheric average cortical thickness ( mm ) : 2.450.07 [ healthy comparison subjects ] vs 2.250.23 [ patients with alcohol dependence ] , t=3.77 , p<0.001 ) . in order to identify regionally specific cortical deficits in patients with alcohol dependence compared to healthy comparison subjects , hemispheric average cortical thickness was added as a covariate in the whole brain vertex - wise analysis . in the glm model that includes age and average cortical thickness as covariates , significant cortical thickness deficits in patients with alcohol dependence , compared to healthy comparison subjects , were noted in the left superior frontal cortex , after correcting for multiple comparisons with the permutation method ( fig .
1 ) ( cluster size=1489.5 mm ; number of vertices in the cluster=2,035 ; talairach coordinates = x [ -15.3 ] , y [ 61.8 ] , z [ 5.0 ] ; cluster p value=0.024 ) . given that different scanning parameter may influence on the cortical thickness variations , analysis was re - run with scan parameter as a covariate .
when analysis was repeated covarying for comorbid depression that may be associated with thinner prefronto - temporal cortex , the diagnostic group effect remained significant ( p=0.001 ) . when analysis was repeated covarying for comorbid anxiety that may also be associated with thinner prefronto - temporal cortex , the diagnostic group effect remained significant in the left superior frontal cluster ( p=0.017 ) .
post hoc correlation analysis between cortical thicknesses in the left superior frontal cluster of significant group difference and duration of alcohol use in alcohol dependence group demonstrated the significant association ( r=-0.55 ; p=0.02 ) ( fig .
cortical thicknesses in the left superior frontal cluster was also correlated with the clinical institute withdrawal assessment for alcohol scores ( r=-0.548 , p=0.028 ) .
otherwise we found no significant results between cortical thicknesses in the left superior frontal cluster and audit scores ( r=0.048 , p=0.859 ) ; and calculated alcohol use ( alcohol dose x frequency x duration ) ( r=-0.193 , p=0.509 ) .
in the current study , we have identified the brain region with altered cortical thickness in patients with alcohol dependence .
the region of cortical thickness deficits in patients with alcohol dependence encompassed primarily the superior frontal cortex , after adjusting for the effects on the global cortical atrophy induced by alcohol dependence ( fig .
this is consistent with prior reports indicating that chronic alcohol use may have the most detrimental effects on prefrontal cortical regions .
the level of n - acetyl aspartate , the viability marker of neurons , was decreased in prefrontal brain regions in chronic alcohol abusers .
neuronal and glial loss has consistently been noted in the prefrontal cortical regions , particularly in the superior frontal cortex .
alcohol use has been associated with the decreased performances in executive and attention tasks that are important function of the prefrontal cortex .
pre - existing vulnerability in these regions may predispose individuals to alcohol dependence , since the function of these regions are to executively control over drug craving and seeking .
these regions may be associated with the compulsive substance - related behaviors , which is also in line with our finding that shows the association between duration of alcohol use with the magnitude of the cortical deficits in this region .
the current findings do not provide information regarding whether the pre - existing prefrontal cortical deficits have rendered individuals vulnerable to alcohol dependence , whether neurotoxicity of chronic alcohol use , including the oxidative stress , have damaged the cortex , or whether both processes have contributed to the observed findings . supporting evidence for
the neurotoxicity as the cause of prefrontal deficits may come from the reports that show patients with longer abstinence have lesser deficits .
it has also been suggested that subjects with alcohol dependence may have prefrontal cortex that are less recuperative from toxic effects and may undergo vicious cycle after initial exposure to substances .
considering that alcohol dependence can be divided into two subtypes , type 1 more environmentally influenced , and type 2 more genetically induced , a comparison between type 1 and type 2 alcohol dependent patients in a study with larger sample with balanced composition of type 1 and type 2 alcohol dependence may provide an opportunity to approach this question .
longitudinal brain imaging study that follows up patients with alcohol dependence would also provide important insights .
this study alone does not provide direct information as to cellular level mechanisms that may underlie the observed deficits of the cortical thickness .
however , there is a vast literature describing the impact of chronic alcohol on the brain .
miguel - hidalgo and colleagues ( 2002 ) reported , in their study with the postmortem brain of alcohol - dependent patients without wernicke or korsakoff syndromes , that the glial pathology of reduced size and density was the most characteristic finding .
kril and colleagues ( 1997 ) have shown selective loss of non - gabaergic pyramidal neurons .
selective dendritic retraction , rather than cellular death , has been suggested as main pathology related to the volume loss of the gray matter .
there is a study that examined the cortical thickness differences in subjects with fetal alcohol syndrome or prenatal alcohol exposure , compared to control subjects , which demonstrated deficits in prefronto - temporo - parietal regions .
however , few studies have examined cortical thickness in alcohol - dependent adults . the cortical thickness analysis has been reported to provide information on an important aspect of the gray matter structure , complementary to the conventional volumetry or the vbm .
for example , highly folded regions could have high gray matter density in vbm analysis since there would be more voxels of gray matter within a fixed radius , but thinner cortical thickness .
this is the first study that used cortical thickness analysis in patients with alcohol dependence excluding comorbid substance use , which showed regionally specific cortical thickness deficits in alcohol dependence .
large age range , though covaried in the statistical model , can be another weakness of the study . with the current study of a cross - sectional design , information on whether the observed cortical deficits would be progressive and
nicotine dependence , which is highly comorbid with alcohol dependence , has also been reported to be associated with cortical atrophy , particularly that in frontal cortex .
now that we neither were able to exclude participants with co - morbid nicotine dependence nor delineate the effects of alcohol dependence from those of nicotine dependence , the current results may have been confounded by the effects of chronic nicotine use . intellectual ability has also been reported to be associated with the prefrontal cortical development .
the fact that the intelligence quotient was not included in the statistical model for comparisons of cortical thickness measures , is also an important limitation of the current study .
future studies in larger samples with narrow age range and with neuropsychological assessments for the frontal lobe function , would provide valuable information . although there could be challenges in following up patients with alcohol dependence , long - term prospective longitudinal study is also warranted .
 alcohol dependence is a serious disorder that can be related with a number of potential health - related and social consequences . 
 cortical thickness measurements would provide important information on the cortical structural alterations in patients with alcohol dependence . 
 twenty - one patients with alcohol dependence and 22 healthy comparison subjects have been recruited and underwent high - resolution brain magnetic resonance ( mr ) imaging and clinical assessments . t1-weighted mr images were analyzed using the cortical thickness analysis program . 
 significantly thinner cortical thickness in patients with alcohol dependence than healthy comparison subjects was noted in the left superior frontal cortical region , correcting for multiple comparisons and adjusting with age and hemispheric average cortical thickness . 
 there was a significant association between thickness in the cluster of the left superior frontal cortex and the duration of alcohol use . 
 the prefrontal cortical region may particularly be vulnerable to chronic alcohol exposure . 
 it is also possible that the pre - existing deficit in this region may have rendered individuals more susceptible to alcohol dependence . 
INTRODUCTION
MATERIALS AND METHODS
Subjects
Brain magnetic resonance (MR) image acquisition and cortical thickness analysis
Statistical analysis
RESULTS
DISCUSSION