The Relationship Between Brain Activation for Taking Others' Perspective and Interoceptive Abilities in Autism Spectrum Disorder: An fMRI Study.

Objectives: In this functional magnetic resonance imaging study, we aimed to investigate the differences in brain activation between individuals with autism spectrum disorder (ASD) and typically developing (TD) individuals during perspective taking. We also examined the association between brain activation and empathic and interoceptive abilities. Methods: During scanning, participants from the ASD (n=17) and TD (n=22) groups were shown pain stimuli and asked to rate the level of the observed pain from both self- and other-perspectives. Empathic abilities, including perspective taking, were measured using an empathic questionnaire, and three dimensions of interoception were assessed: interoceptive accuracy, interoceptive sensibility, and interoceptive trait prediction errors. Results: During self-perspective taking, the ASD group exhibited greater activation in the left precuneus than the TD group. During other-perspective taking, relative hyperactivation extended to areas including the right precuneus, right superior frontal gyrus, left caudate nucleus, and left amygdala. Brain activation levels in the right superior frontal gyrus while taking other-perspective were negatively correlated with interoceptive accuracy, and those in the left caudate were negatively correlated with perspective taking ability in the ASD group. Conclusion: Individuals with ASD show atypical brain activation during perspective taking. Notably, their brain regions associated with stress reactions and escape responses are overactivated when taking other-perspective. This overactivity is related to poor interoceptive accuracy, suggesting that individuals with ASD may experience difficulties with the self-other distinction or atypical embodiment when considering another person's perspective.

Graph Theoretical Analysis of Brain Structural Connectivity in Patients with Alcohol Dependence.

This study aimed to compare brain structural connectivity using graph theory between patients with alcohol dependence and social drinkers. The participants were divided into two groups; the alcohol group (N=23) consisting of patients who had been hospitalized and had abstained from alcohol for at least three months and the control group (N=22) recruited through advertisements and were social drinkers. All participants were evaluated using 3T magnetic resonance imaging. A total of 1000 repeated whole-brain tractographies with random parameters were performed using DSI Studio. Four hundred functionally defined cortical regions of interest (ROIs) were parcellated using FreeSurfer based on the Schaefer Atlas. The ROIs were overlaid on the tractography results to generate 1000 structural connectivity matrices per person, and 1000 matrices were averaged into a single matrix per subject. Graph analysis was performed through igraph R package. Graph measures were compared between the two groups using analysis of covariance, considering the effects of age and smoking pack years. The alcohol group showed lower local efficiency than the control group in the whole-brain (F=5.824, p=0.020), somato-motor (F=5.963, p=0.019), and default mode networks (F=4.422, p=0.042). The alcohol group showed a lower global efficiency (F=5.736, p=0.021) in the control network. The transitivity of the alcohol group in the dorsal attention network was higher than that of the control (F=4.257, p=0.046). Our results imply that structural stability of the whole-brain network is affected in patients with alcohol dependence, which can lead to ineffective information processing in cases of local node failure.

Hippocampal Subfields and White Matter Connectivity in Patients with Subclinical Geriatric Depression.

Despite an abundance of research related to the functional and structural changes of the brain in patients with geriatric depression, knowledge related to early alterations such as decreased white matter connectivity and their association with cognitive decline remains lacking. We aimed to investigate early alterations in hippocampal microstructure and identify their associations with memory function in geriatric patients with subclinical depression. Nineteen participants with subclinical geriatric depression and 19 healthy controls aged ≥65 years exhibiting general cognitive function within the normal range were included in the study and underwent assessments of verbal memory. Hippocampal subfield volumes were determined based on T1-weighted magnetization-prepared rapid gradient echo (T1-MPRAGE) images, while group tractography and connectometry analyses were conducted using diffusion tensor images. Our findings indicated that the volumes of whole bilateral hippocampus, cornus ammonis (CA) 1, molecular layer, left subiculum, CA3, hippocampal tail, right CA4, and granule cell/molecular layers of the dentate gyrus (GC-ML-DG) were significantly smaller in the subclinical depression group than in the control group. In the subclinical depression group, verbal learning was positively correlated with the volumes of the CA1, GC-ML-DG, molecular layer, and whole hippocampus in the right hemisphere. The fractional anisotropy of the bilateral fornix was also significantly lower in the subclinical depression group and exhibited a positive correlation with verbal learning and recall in both groups. Our results suggest that hippocampal microstructure is disrupted and associated with memory in patients with subclinical depression.

White matter integrity in alcohol-dependent patients with long-term abstinence.

ABSTRACT: Based on association studies on amounts of alcohol consumed and cortical and subcortical structural shrinkage, we investigated the effect of chronic alcohol consumption on white matter pathways using probabilistic tractography.Twenty-three alcohol-dependent men (with an average sobriety of 13.1 months) from a mental health hospital and 22 age-matched male healthy social drinkers underwent 3T magnetic resonance imaging. Eighteen major white matter pathways were reconstructed using the TRActs Constrained by UnderLying Anatomy tool (provided by the FreeSurfer). The hippocampal volumes were estimated using an automated procedure. The lifetime drinking history interview, Alcohol Use Disorder Identification Test, Brief Michigan Alcoholism Screening Test, and pack-years of smoking were also evaluated.Analysis of covariance controlling for age, cigarette smoking, total motion index indicated that there was no definite difference of diffusion parameters between the 2 groups after multiple comparison correction. As hippocampal volume decreased, the fractional anisotropy of the right cingulum-angular bundle decreased. Additionally, the axial diffusivity of right cingulum-angular bundle was positively correlated with the alcohol abstinence period.The results imply resilience of white matter in patients with alcohol dependence. Additional longitudinal studies with multimodal methods and neuropsychological tests may improve our findings of the changes in white matter pathways in patients with alcohol dependence.

Disrupted Association Between Empathy and Brain Structure in Attention-Deficit/Hyperactivity Disorder.

OBJECTIVES: To investigate the relationship between brain structure and empathy in early adolescents with attention-deficit/hyperactivity disorder (ADHD). METHODS: Nineteen early adolescents with ADHD and 20 healthy controls underwent 3T MRI. All the participants were assessed for different aspects of empathy using measures including the Interpersonal Reactivity Index and Empathy Quotient. Cortical thickness and subcortical structural volume based on T1-weighted scans were analyzed using FreeSurfer. RESULTS: Cognitive empathy (t=-2.52, p=0.016) and perspective taking (t=-2.10, p=0.043) were impaired in the ADHD group compared with the control group. The cluster encompassing the left posterior insular, supramarginal, and transverse temporal cortices [cluster-wise p-value (CWP)=0.001], which are associated with emotional empathy, was significantly smaller in the ADHD group, and the volume of the left nucleus accumbens was greater than that of the control group (F=10.12, p=0.003, effect size=0.22). In the control group, the left superior temporal (CWP=0.002) and lingual cortical (CWP=0.035) thicknesses were positively associated with cognitive empathy, while the right amygdala volume was positively associated with empathic concern (Coef=14.26, t=3.92, p=0.001). However, there was no significant correlation between empathy and brain structure in the ADHD group. CONCLUSION: The ADHD group had a smaller volume of the cortical area associated with emotional empathy than the control group, and there was no brain region showing significant correlation with empathy, unlike in the control group.

Cognitive and Emotional Empathy in Young Adolescents: an fMRI Study.

OBJECTIVES: We investigated the differences in cognitive and emotional empathic ability between adolescents and adults, and the differences of the brain activation during cognitive and emotional empathy tasks. METHODS: Adolescents (aged 13-15 years, n=14) and adults (aged 19-29 years, n=17) completed a range of empathic ability questionnaires and were scanned functional magnetic resonance imaging (fMRI) during both cognitive and emotional empathy task. Differences in empathic ability and brain activation between the groups were analyzed. RESULTS: Both cognitive and emotional empathic ability were significantly lower in the adolescent compared to the adult group. Comparing the adolescent to the adult group showed that brain activation was significantly greater in the right transverse temporal gyrus (BA 41), right insula (BA 13), right superior parietal lobule (BA 7), right precentral gyrus (BA 4), and right thalamus whilst performing emotional empathy tasks. No brain regions showed significantly greater activation in the adolescent compared to the adult group while performing cognitive empathy task. In the adolescent group, scores of the Fantasy Subscale in the Interpersonal Reactivity Index, which reflects cognitive empathic ability, negatively correlated with activity of right superior parietal lobule during emotional empathic situations (r=-0.739, p=0.006). CONCLUSION: These results strongly suggest that adolescents possess lower cognitive and emotional empathic abilities than adults do and require compensatory hyperactivation of the brain regions associated with emotional empathy or embodiment in emotional empathic situation. Compensatory hyperactivation in the emotional empathy-related brain areas among adolescents are likely associated with their lower cognitive empathic ability.

Autism and Beauty: Neural Correlates of Aesthetic Experiences in Autism Spectrum Disorder.

OBJECTIVES: The purpose of this study was to investigate whether the neural activity of autism spectrum disorder (ASD) patients is different from that of normal individuals when performing aesthetic judgments. METHODS: We recruited typical ASD patients without savant skills (ASD group, n=17) and healthy controls (HC group, n=19) for an functional magnetic resonance imaging study. All subjects were scanned while performing aesthetic judgment tasks on two kinds of artwork (magnificent landscape images and fractal images). Differences in brain activation between the two groups were assessed by contrasting neural activity during the tasks. RESULTS: The aesthetic judgment score for all images was significantly lower in the ASD group than in the HC group. During the aesthetic judgment tasks, the ASD group showed less activation than the HC group in the anterior region of the superior frontal gyrus, and more activation in the temporoparietal area and insula, regardless of the type of images being judged. In addition, during the aesthetic judgment task for the fractal images, the ASD group exhibited greater neural activity in the amygdala and the posterior region of the middle/inferior temporal gyrus (Brodmann area 37) than the HC group. CONCLUSION: The results of this study suggest that the brain activation patterns associated with aesthetic experiences in ASD patients may differ from those of normal individuals.

Asymmetrical Electroencephalographic Change of Human Brain During Sleep Onset Period.

OBJECTIVE: Human cerebral hemisphere is known to function asymmetrically with daytime left hemisphere superiority in most right-handed persons. It may have relevance to the localization of specific function of the brain. This study attempted to reveal whether the functional cerebral asymmetry in the wakeful state is still maintained throughout the sleep onset period. METHODS: Thirty-channel EEG was recorded in 61 healthy subjects. The EEG power spectra of each of the seven frequencies were compared between the two kinds of 30-second states; the wakeful stage and the late-sleep stage 1. RESULTS: The asymmetrical indices of sleep stage 1 at several fronto-central leads were decreased in the delta, theta, alpha-2, and all beta bands. Conversely, at parts of parieto-occipital leads showed an increase in the indices of the theta, alphas, beta-1, and beta-2 bands. Any fronto-central leads did not show an increase in the index, and no parieto-occipital leads showed a decrease. CONCLUSION: During the sleep onset period, power spectral asymmetry of the brain showed a different pattern from the wakeful stage. This asymmetrical pattern of EEG powers may suggest a reversal of the left hemispheric dominance during sleep.

Deblurring visual evoked potentials using commercially available software.

Visual evoked potentials are useful clinical tools to study visual pathways of the brain. Although the temporal resolution is unsurpassed by other brain imaging technologies, the spatial resolution is diminished or blurred by the low conductance of the electrical signals through the skull. Methods have been proposed to improve the spatial resolution by downwardly projecting the electrical signals measured on the scalp to the surface of the cerebral cortex through the inverse solution of the equations governing static current flow. We describe the adaptation and combination of commercially available engineering software programs to solve this inverse problem and report the results of a sample run of the system. Before deblurring, the visual evoked potentials appeared to be diffusely localized over the posterior scalp. After deblurring, the visual evoked potentials were only found at the electrodes closest to the visual cortex, as would be predicted by our current knowledge of neuroanatomy.

Surface-Based Parameters of Brain Imaging in Male Patients with Alcohol Use Disorder.

OBJECTIVE: The structural alteration of brain shown in patients with alcohol use disorder (AUD) can originate from both alcohol effects and genetic or developmental processes. We compared surface-based parameters of patients with AUD with healthy controls to prove the applicability of surface-based morphometry with head size correction and to determine the areas that were sensitive to brain alteration related to AUD. METHODS: Twenty-six abstinent male patients with AUD (alcohol group, mean abstinence=13.2 months) and twenty-eight age-matched healthy participants (control group) were recruited from an inpatient mental hospital and community. All participants underwent a 3T MRI scan. Surface-based parameters were determined by using FreeSurfer. RESULTS: Every surface-based parameter of the alcohol group was lower than the corresponding control group parameter. There were large group differences in the whole brain, grey and white matter volume, and the differences were more prominent after head size correction. Significant group differences were shown in cortical thicknesses in entire brain regions, especially in parietal, temporal and frontal areas. There were no significant group differences in surface areas, but group difference trends in surface areas of the frontal and parietal cortices were shown after head size correction. CONCLUSION: Most of the surface-based parameters in alcohol group were altered because of incomplete recovery from chronic alcohol exposure and possibly genetic or developmental factors underlying the risk of AUD. Surface-based morphometry with controlling for head size is useful in comparing the volumetric parameters and the surface area to a lesser extent in alcohol-related brain alteration.

Volume of hippocampal subfields in patients with alcohol dependence.

Alcohol-induced hippocampal atrophy has been well documented in many studies and is known to affect various subfields. Given the functional heterogeneity of these subfields, we investigated the precise effects of alcohol-induced damage in these areas. Twenty-six male patients with alcohol dependence (alcohol group) and twenty-six age-matched male healthy social drinkers were recruited from a mental health hospital and the community respectively, with the aim of comparing the hippocampal subfields between groups. Each participant underwent a 3T MRI scan. Hippocampal subfield volumes were estimated using an automated procedure and drinking history recorded using Lifetime Drinking History, Alcohol Use Disorder Identification Test, and the Brief Michigan Alcoholism Screening Test. The alcohol group showed a lower total hippocampus volume, specifically in the left presubiculum, fimbria, and bilateral subiculum. Regression analysis assessing the influence of age and group showed that group was a more significant factor than age in most subfields. Our findings suggest that alcohol dependence alters hippocampal subfield volumes. Further longitudinal studies on the interaction of structural and neurocognitive changes would improve our understanding of brain structural changes resulting from long-term alcohol consumption.

Three-Dimensional Electroencephalographic Changes on Low-Resolution Brain Electromagnetic Tomography (LORETA) During the Sleep Onset Period.

Electroencephalographic (EEG) patterns during sleep are markedly different from those measured during the waking state, but the process of falling asleep is not fully understood in terms of biochemical and neurophysiological aspects. We sought to investigate EEG changes that occur during the transitional period from wakefulness to sleep in a 3-dimensional manner to gain a better understanding of the physiological meaning of sleep for the brain. We examined EEG 3-dimensionally using LORETA (low-resolution electromagnetic tomography), to localize the brain region associated with changes that occur during the sleep onset period (SOP). Thirty-channel EEG was recorded in 61 healthy subjects. EEG power spectra and intracortical standardized LORETA were compared between 4 types of 30-second states, including the wakeful stage, transition stage, early sleep stage 1, and late sleep stage 1. Sleep onset began with increased delta and theta power and decreased alpha-1 power in the occipital lobe, and increased theta power in the parietal lobe. Thereafter, global reductions of alpha-1 and alpha-2 powers and greater increases of theta power in the occipito-parietal lobe occurred. As sleep became deeper in sleep stage 1, beta-2 and beta-3, powers decreased mainly in the frontal lobe and some regions of the parieto-temporo-limbic area. These findings suggest that sleep onset includes at least 3 steps in a sequential manner, which include an increase in theta waves in the posterior region of the brain, a global decrease in alpha waves, and a decrease in beta waves in the fronto-central area.

[Effects of Silver-Care-Robot Program on Cognitive Function, Depression, and Activities of Daily Living for Institutionalized Elderly People].

PURPOSE: The purpose of this study was to identify the effects on cognitive function, depression, and activities of daily living of Silver-Care-Robot Program for institutionalized elders. METHODS: This study was a nonequivalent control group pretest-posttest design. The participants were 42 institutionalized elders (17 in the experimental group and 25 in the control group). The Silver-Care-Robot Program was provided as an intervention which was conducted twice a week for 5 weeks. The Silver-Care-Robot Program is an integrated entertainment program to help the mental, emotional, and physical health of elderly people. Pre-test was conducted on the two groups, and, in order to examine the effects of intervention, a post-test was conducted after 5 weeks. RESULTS: There were significant differences in cognitive function and ADL (activities of daily living) between two groups after the program. But the difference in depression in the institutionalized elders was not statistically significant between the two groups. CONCLUSION: The Silver-Care-Robot Program should be considered as a regular program for cognitive function and activities of daily living for institutionalized elders.

An FMRI study investigating adolescent brain activation by rewards and feedback.

OBJECTIVE: This study aimed to investigate the adolescent brain activation patterns in response to performance feedback (PF), social reward (SR) and monetary reward (MR) and their association with psychological factors. METHODS: Functional magnetic resonance imaging (fMRI) was performed while middle school boys (n=15) performed tests pertained to PF, SR and MR. The brain activation pattern in each condition was investigated, and the extent of brain activation in each of the three conditions was compared at once. RESULTS: The caudate and the dorsal prefrontal area were activated in all three conditions. Furthermore, the cuneus showed significantly greater activation in the PF condition than the SR or MR condition. And the self - related areas, such as the right precentral gyrus and paracenral lobule, were more activated in the SR condition than the PF or MR condition. The left middle frontal gyrus was more activated in the MR condition than the PF or SR condition. CONCLUSION: Not only various reward stimuli but also feedback stimulus might commonly activate dorsal prefrontal and subcortical area in adolescents. Moreover, several different brain activation patterns were also observed in each condition. The results of this study could be applied to planning of learning and teaching strategy for adolescents in various ways.

Abnormal brain activation of adolescent internet addict in a ball-throwing animation task: possible neural correlates of disembodiment revealed by fMRI.

While adolescent internet addicts are immersed in cyberspace, they are easily able to experience 'disembodied state'. The purposes of this study were to investigate the difference of brain activity between adolescent internet addicts and normal adolescents in a state of disembodiment, and to find the correlation between the activities of disembodiment-related areas and the behavioral characteristics related to internet addiction. The fMRI images were taken while the addiction group (N=17) and the control group (N=17) were asked to perform the task composed with ball-throwing animations. The task reflected on either self-agency about ball-throwing or location of a ball. And each block was shown with either different (Changing View) or same animations (Fixed View). The disembodiment-related condition was the interaction between Agency Task and Changing View. Within-group analyses revealed that the addiction group exhibited higher activation in the thalamus, bilateral precentral area, bilateral middle frontal area, and the area around the right temporo-parietal junction. And between-group analyses showed that the addiction group exhibited higher activation in the area near the left temporo-parieto-occipital junction, right parahippocampal area, and other areas than the control group. Finally, the duration of internet use was significantly correlated with the activity of posterior area of left middle temporal gyrus in the addiction group. These results show that the disembodiment-related activation of the brain is easily manifested in adolescent internet addicts. Internet addiction of adolescents could be significantly unfavorable for their brain development related with identity formation.

Correlation of microperimetry with fundus autofluorescence and spectral-domain optical coherence tomography in repaired macular holes.

PURPOSE: To investigate the correlation of microperimetry with fundus autofluorescence (FAF), spectral-domain optical coherence tomography (SD-OCT), and visual acuity (VA) in order to better characterize visual outcomes after successful macular hole (MH) surgery. DESIGN: Cross-sectional case series. METHODS: Postoperative VA, microperimetry, FAF, and SD-OCT images from 23 eyes of 23 patients who underwent successful MH surgery were obtained. FAF images were examined using the Heidelberg retina angiograph 2, and foveal structure and macular sensitivity were evaluated with SD-OCT and microperimetry. The mean retinal sensitivities within the central 9 degrees (microperimetry, mean), the retinal sensitivity of the foveal center (microperimetry, center), and the difference between the values obtained for the foveal center or mean of study and fellow eyes (microperimetry, centerdiff and microperimetry, meandiff, respectively) were measured with microperimetry. RESULTS: Microperimetry (mean) was well correlated with microperimetry (center) in both study and fellow eyes. Poor postoperative VA was correlated with large microperimetry (meandiff). Following successful MH surgery, FAF of all eyes decreased markedly. There was a positive correlation between microperimetry (centerdiff) and degree of FAF of study eyes. However, a decrease in FAF after MH surgery was not correlated well with either degree of defect in the junction between photoreceptor inner and outer segment (IS/OS) or central retinal thickness on SD-OCT. CONCLUSIONS: The amount of remaining FAF is related to macular sensitivity as measured by microperimetry after successful MH surgery. Function of photoreceptors and retinal pigment epithelium as well as integrity can be estimated by measuring the decrease in FAF after successful MH surgery. Moreover, functional correlation with microperimetry provides both morphologic and functional information on repaired MHs.

The genetic factors affecting drinking behaviors of korean young adults with variant aldehyde dehydrogenase 2 genotype.

OBJECTIVE: We determined whether aldehyde dehydrogenase 2 (ALDH2) activity alters the way in which drinking behaviors are affected by gene polymorphisms of other alcohol-metabolizing enzymes and serotonin-related proteins. METHODS: Through a follow-up survey with a cohort comprising 551 university freshmen over a period of 6 years, we examined the genetic factors affecting drinking behaviors. In 2000, drinking behaviors were assessed and tryptophan hydroxylase (TPH) and ALDH2 gene polymorphisms were determined. Drinking behaviors were repeated in 2006 (n=150), and the gene polymorphisms of ADH1B, ADH1C, CYP2E1, 5-HTR2A 1438A/G, and 5-HTR2A IVS2 were also determined. RESULTS: In 2000, the variant and wild-type ALDH2 groups exhibited little difference in terms of drinking frequency and problem drinking. Furthermore, some genotypes influenced only the variant group: ADH1B*2/*2 was associated with a lower drinking frequency, and CYP2E1 c2 allele was associated with an increased risk of problem drinking. In 2006, drinking frequency and risk of problem drinking were significantly lower in the variant group than in the wild-type group. However, the TPH AA genotype disturbed that difference, meaning that the subjects in the variant group had developed a similar level of risk of problem drinking to that in the wild-type group. CONCLUSION: Korean university freshmen who were identified as a variant group drank as frequently as those in the wild-type group. For the subsequent 6 years they drank less frequently, thus decreasing the risk of problem drinking. However, that frequency drop was interrupted in those with gene polymorphisms such as ADH1B*1, CYP2E1 c2, and TPH A.

Comparison of retinal nerve fibre layer thickness measurements calculated by the optic nerve head map (NHM4) and RNFL3.45 modes of spectral-domain optical coherence tomography (RTVue-100).

AIM: To evaluate and compare retinal nerve fibre layer (RNFL) thickness measured by direct scanning (RNFL3.45 mode) and re-sampling from datasets (NHM4 mode) of RTVue-100 optical coherence tomography (OCT). METHODS: Thirty-six healthy subjects and 76 subjects with glaucoma were imaged with Stratus OCT (fast RNFL mode, RNFL3) and RTVue-100 OCT (NHM4 (RNFL1) and RNFL3.45 (RNFL2) modes). Measurement reproducibility was assessed in NHM4 and RNFL3.45 modes of RTVue-100 OCT (intraclass correlation coefficient (ICC)). Agreement between different RNFL measurements was analysed by Bland-Altman plot. The areas under the receiver operating characteristic (ROC) curves (AUCs) for discrimination between healthy and glaucoma were compared between the different RNFL measurements. RESULTS: Both NHM4 and RNFL3.45 modes showed excellent measurement reproducibilities (ICC 0.831-0.978). RNFL thicknesses by two different modes of the RTVue-100 OCT, and by the Stratus OCT, were correlated in all sectors, including average. There was no significant difference between RNFL1 and RNFL2 data. However, RNFL thickness in glaucomatous eyes by the RTVue-100 OCT was significantly greater than that measured by Stratus OCT. RNFL thicknesses determined by the two different modes of RTVue-100 OCT were in excellent agreement (95% limits of agreement -6.53 to 6.95 mum). All three RNFL measurements showed good glaucoma discrimination ability (AUC = RNFL1 0.970, RNFL2 0.962, RNFL3 0.971). CONCLUSIONS: RNFL thickness determined by direct scanning and re-sampling from datasets of RTVue-100 OCT were in good agreement. However, both measurements in glaucomatous subjects were significantly different from those with the Stratus OCT. Those findings should be considered when a patient is followed-up using different types of OCT.

Correlation between the severity of obstructive sleep apnea and heart rate variability indices.

The risk of cardiovascular disease is known to be increased in obstructive sleep apnea syndrome (OSAS). Its mechanism can be explained by the observation that the sympathetic tone increases due to repetitive apneas accompanied by hypoxias and arousals during sleep. Heart rate variability (HRV) representing cardiac autonomic function is mediated by respiratory sinus arrhythmia, baroreflex-related fluctuation, and thermoregulation-related fluctuation. We evaluated the heart rate variability of OSAS patients during night to assess their relationship with the severity of the symptoms. We studied overnight polysomnographies of 59 male untreated OSAS patients with moderate to severe symptoms (mean age 45.4+/- 11.7 yr, apnea-hypopnea index [AHI]=43.2+/-23.4 events per hour, and AHI >15). Moderate (mean age 47.1+/-9.4 yr, AHI=15-30, n=22) and severe (mean age 44.5 +/-12.9 yr, AHI >30, n=37) OSAS patients were compared for the indices derived from time and frequency domain analysis of HRV, AHI, oxygen desaturation event index (ODI), arousal index (ArI), and sleep parameters. As a result, the severe OSAS group showed higher mean powers of total frequency (TF) (p=0.012), very low frequency (VLF) (p= 0.038), and low frequency (LF) (p=0.002) than the moderate OSAS group. The LF/HF ratio (p=0.005) was higher in the severe group compared to that of the moderate group. On the time domain analysis, the HRV triangular index (p=0.026) of severe OSAS group was significantly higher. AHI was correlated best with the LF/HF ratio (r(p))=0.610, p<0.001) of all the HRV indices. According to the results, the frequency domain indices tended to reveal the difference between the groups better than time domain indices. Especially the LF/HF ratio was thought to be the most useful parameter to estimate the degree of AHI in OSAS patients.