Abnormal brain activity in social reward learning in children with autism spectrum disorder: an fMRI study.

PURPOSE: We aimed to determine whether Autism Spectrum Disorder (ASD) would show neural abnormality of the social reward system using functional MRI (fMRI). MATERIALS AND METHODS: 27 ASDs and 12 typically developing controls (TDCs) participated in this study. The social reward task was developed, and all participants performed the task during fMRI scanning. RESULTS: ASDs and TDCs with a social reward learning effect were selected on the basis of behavior data. We found significant differences in brain activation between the ASDs and TDCs showing a social reward learning effect. Compared with the TDCs, the ASDs showed reduced activity in the right dorsolateral prefrontal cortex, right orbitofrontal cortex, right parietal lobe, and occipital lobe; however, they showed increased activity in the right parahippocampal gyrus and superior temporal gyrus. CONCLUSION: These findings suggest that there might be neural abnormality of the social reward learning system of ASDs. Although this study has several potential limitations, it presents novel findings in the different neural mechanisms of social reward learning in children with ASD and a possible useful biomarker of high-functioning ASDs.

Abnormal activation of the social brain network in children with autism spectrum disorder: an FMRI study.

OBJECTIVE: The aim of this study is to investigate abnormal findings of social brain network in Korean children with autism spectrum disorder (ASD) compared with typically developing children (TDC). METHODS: Functional magnetic resonance imaging (fMRI) was performed to examine brain activations during the processing of emotional faces (happy, fearful, and neutral) in 17 children with ASD, 24 TDC. RESULTS: When emotional face stimuli were given to children with ASD, various areas of the social brain relevant to social cognition showed reduced activation. Specifically, ASD children exhibited less activation in the right amygdala (AMY), right superior temporal sulcus (STS) and right inferior frontal gyrus (IFG) than TDC group when fearful faces were shown. Activation of left insular cortex and right IFG in response to happy faces was less in the ASD group. Similar findings were also found in left superior insular gyrus and right insula in case of neutral stimulation. CONCLUSION: These findings suggest that children with ASD have different processing of social and emotional experience at the neural level. In other words, the deficit of social cognition in ASD could be explained by the deterioration of the capacity for visual analysis of emotional faces, the subsequent inner imitation through mirror neuron system (MNS), and the ability to transmit it to the limbic system and to process the transmitted emotion.

A pulse artifact removal method considering artifact variations in the simultaneous recording of EEG and fMRI.

A simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) can provide high spatiotemporal information of brain activity. However, a proper analysis of the EEG signals is often hindered by various artifacts. In particular, pulse artifact (PA) induced from the heartbeat of a subject interferes with reliable measurements of the EEG signal. A new PA removal method that takes into account the delay variation between the heartbeat and PA and the window size variation in PA is presented in order to improve the detection and suppression of PA in EEG signals. A PA is classified into either a normal PA or a deformed PA. Only normal PAs are averaged to generate a PA template that is used to remove PAs from the measured EEG signals. The performance of the proposed method was evaluated by simulated data and real EEG measurements from epilepsy patients. The results are compared with those from conventional methods.

Involvement of the anterior thalamic radiation in boys with high functioning autism spectrum disorders: a Diffusion Tensor Imaging study.

BACKGROUND: Autism has been hypothesized to reflect neuronal disconnection. Several recent reports implicate the key thalamic relay nuclei and cortico-thalamic connectivity in the pathophysiology of autism. Accordingly, we aimed to focus on evaluating the integrity of the thalamic radiation and sought to replicate prior white matter findings in Korean boys with high-functioning autism spectrum disorders (ASD) using Diffusion Tensor Imaging (DTI). METHODS: We compared fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) in 17 boys with ASD and 17 typically developing controls in the anterior thalamic radiation (ATR), superior thalamic radiation (STR), posterior thalamic radiation (PTR), corpus callosum (CC), uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF). RESULTS: The two groups were group-matched on age, IQ, handedness and head circumference. In whole-brain voxel-wise analyses, FA was significantly reduced and MD was significantly increased in the right ATR, CC, and left UF in subjects with ASD (p<0.05, corrected). We found significantly lower FA in right and left ATR, CC, left UF and right and left ILF and significantly higher MD values of the CC in the ASD group in region of interest-based analyses. We also observed significantly higher RD values of right and left ATR, CC, left UF, left ILF in subjects with ASD compared to typically developing boys and significantly lower AD values of both ILF. Right ATR and right UF FA was significantly negatively correlated with total SRS score within the ASD group (r=-.56, p=.02). CONCLUSIONS: Our preliminary findings support evidence implicating disturbances in the thalamo-frontal connections in autism. These findings highlight the role of hypoconnectivity between the frontal cortex and thalamus in ASD.

Differential activation of face memory encoding tasks in alcohol-dependent patients compared to healthy subjects: an fMRI study.

It has been hypothesized that the right hemisphere of the brain is more sensitive to alcohol-related damage than the left hemisphere. The present study tested this hypothesis, using functional MRI to determine whether the pattern for right hemispheric activity is different for alcohol-dependent patients, compared to normal healthy individuals. Two different types of memory encoding tasks were performed separately: word and face encoding for both alcohol-dependent patients and normal healthy volunteers. The data for the normal volunteers indicate that the left prefrontal region is more active during word encoding, whereas the right parahippocampal region is more active during face encoding. The results for the patient data, however, demonstrated left lateralization in the prefrontal area during word encoding, while right lateralization in the parahippocampal region during face encoding was not observed. Therefore, alcoholism appears to have no influence on left hemispheric activity, since the activation pattern was similar to that observed for normal healthy persons. However, the absence of right hemispheric lateralization in alcohol-dependent patients is consistent with the hypothesis that the right hemisphere is more vulnerable to alcohol-related damage than the left hemisphere.

Susceptibility compensated fMRI study using a tailored RF echo planar imaging sequence.

PURPOSE: To implement a method using a tailored radiofrequency (TRF) pulse with a quadratic phase profile to recover susceptibility-induced signal losses in gradient-recalled echo-planar images (EPI). MATERIALS AND METHODS: A functional magnetic resonance imaging (fMRI) experiment for compensation of susceptibility artifacts, known as the TRF pulse EPI sequence (TRF-EPI), was used. TRF pulse compensates the susceptibility effect with a reduced signal-to-noise ratio (SNR) to one-half when the maximum phase distribution is 2pi. We demonstrate theoretically that the maximum phase distribution can also be reduced to pi rather than 2pi, improving the SNR accordingly. An analysis was conducted comparing this newly proposed strategy using a standard RF excitation with a linear phase distribution and a quadratic TRF excitation with a pi phase distribution. RESULTS: Thorough experimental comparisons were also made between the TRF quadratic excitation with a pi phase profile and conventional EPI with a standard excitation in human subjects during ventral brain activation. CONCLUSION: With reduced maximum phase distribution in the TRF pulse, signals in the susceptibility-affected areas, such as the orbitofrontal and inferior temporal cortex, were increased, suggesting that the technique could be a useful adjunct to fMRI.

An accurate heart beat detection method in the EKG recorded in fMRI system.

The simultaneous recording of functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG) provides an efficient signal for the high spatiotemporal brain mapping because each modality provides complementary information. The peak detection in the EEG signal measured in the MR scanner is necessary for removal of the ballistocardiac artifact. Especially, it would be affected by the quality of the EKG signal and the variation of the heart beat rate. Therefore, we propose the peak detection method using a K-teager energy operator (K-TEO) as well as further refinement processes in order to detect precise peaks. We applied this technique to the analysis of simulation waves with random noise and abrupt heat beat changes.

Brain activation related to affective dimension during thermal stimulation in humans: a functional magnetic resonance imaging study.

The aim of this study was to identify the activated brain region that is involved with the affective dimension of thermal stimulation (not pain, but innocuous warming) using functional MR imaging. Twelve healthy, right-handed male subjects participated in the study. Thermal stimulation with two different temperatures of 41 degrees C and 34 degrees C was applied to the subjects using a fomentation pack, wrapped around the right lower leg of each subject. On the basis of the subjects' responses after the scanning sessions, the authors were able to observe that the subjects felt "warm" and "slightly pleasant and comfortable" under the 41 degrees C condition. The experimental results indicated that warm stimulation produced a significant increase of activation compared to thermal neutral stimulation in various regions such as contralateral insular, ipsilateral cerebellum, ipsilateral putamen, contralateral middle frontal gyrus, ipsilateral inferior frontal gyrus, contralateral postcentral gyrus, and contralateral paracentral lobule. The activated regions are known to be related to thermal sensory, affective/emotional awareness, cognitive functions, sensory-discrimination, and emotion/affective processing, and so on. These results suggest that an appropriate thermal stimulation can produce a positive emotion and activate emotion/affect related regions of the brain.

Effects of syntactic complexity in L1 and L2; an fMRI study of Korean-English bilinguals.

The neural mechanisms underlying the syntactic processing of sentence comprehension in Korean (L1) and English (L2) by late bilinguals were investigated using functional MRI. The Korean native speakers were asked to read sentences with different levels of syntactic complexity in L1 and L2 and respond to comprehension questions concerning the sentences. The syntactic complexity was varied using a center-embedded sentence "The director that the maid introduced ignored the farmer" or a conjoined sentence "The maid introduced the director and ignored the farmer". It was found that the major areas involved in sentence processing such as the left inferior frontal gyrus (IFG), bilateral inferior parietal gyrus, and occipital lobe including cuneus, and lingual gyrus were commonly activated during the processing of both L1 and L2. However, the pattern of activation was different for L1 and L2 in the left IFG. The amount of activation was greater for embedded sentences than for conjoined sentences in L1 while no difference was found in L2. These results suggest that the cortical areas involved with syntactic processing in L1 and L2 are shared, but that the underlying neural mechanisms are different. The findings of the present study are discussed in comparison with Hasegawa et al.'s (Hasegawa, M., Carpenter, P.A., Just, M.A., 2002. An fMRI study of bilingual sentence comprehension and workload. NeuroImage 15, 647-660.) and Yokoyama et al.'s (Yokoyama, S., Okamoto, H., Miyamoto, T., Yoshimoto, K., Kim, J., Iwata, K., Jeong, H., Uchida, S., Ikuta, N., Sassa, Y., Nakamura, W., Horie, K., Sato, S., Kawashima, R., 2006. Cortical activation in the processing of passive sentences in L1 and L2: An fMRI study. NeuroImage 30, 570-579.) studies which also found common areas of activation but different patterns of activation during the processing of L1 and L2.

Racial distinction of the unknown facial identity recognition mechanism by event-related fMRI.

A body of evidence exists indicating that the function of the fusiform area of the face is selectively involved in the perception of faces, and in particular, in perceiving racial differences. In the present study, we investigated the neural substrates of the face-selective region (the fusiform face area, FFA) in the ventral occipital-temporal cortex and examined their role in case of same-racial face recognition by employing event-related fMRI. Twelve healthy subjects (Oriental-Koreans) performed the familiarity judgment tasks while they were being presented with familiar and unknown faces of Oriental-Koreans and Caucasian-Americans. The results indicate that there are significant differences in perceiving unfamiliar faces between Oriental-Koreans and Caucasian-Americans in the FFA, whereas no significant difference was found between familiar Oriental-Korean and Caucasian-American faces in the same area. This suggests that an effect of same-race superiority exists when the perceived identity is only unfamiliar. The neural responses to Oriental-Koreans versus Caucasian-Americans in Oriental-Korean subjects likely reflect cultural evaluations of social groups as modified by individual experience.

An fMRI study of Chinese character reading and picture naming by native Korean speakers.

Chinese characters appear in the currently used Korean language, and the system used for writing system the Korean language consists of a mixture of the Korean alphabet and Chinese characters. In the present study, neural mechanisms involved in reading a single Chinese character words and naming pictures by Korean native speakers were investigated using a functional magnetic resonance imaging technique. The findings show a right hemispheric dominance within the occipito-temporal and the left middle/medial frontal area for both reading Chinese characters and naming pictures. This should reflect the specific visual processing of reading Chinese characters. Additional activations in inferior frontal and cingulage gyrus were also observed. The activations of inferior parietal region and thalamus are of interest, since we assume that these activations are strongly related to the phonological status of single Chinese character words rather than two character words that are typically used by Korean native speakers.

Event related fMRI studies of voluntary and inhibited eye blinking using a time marker of EOG.

Electrooculogram (EOG) measurements, along with infrared measurements, are commonly used to record eye blinking during functional magnetic resonance imaging (fMRI). We report herein, on the use of EOG in measuring voluntary and inhibited eye blinking during echo planar imaging (EPI) in an MR scanner. The inhibited eye blinking occurred during the period, in which subjects were requested not to blink their eyes. After the removal of gradient-field induced artifacts from the EOG signal, the waveform of the EOG clearly showed both voluntary and inhibited eye blinking. Using these data, each voluntary or inhibited eye-blinking event was used as the temporal cue for an event related fMRI. Activation of the bilateral parahippocampal, precentral gyrus and left supplementary motor area was observed for voluntary eye blinking, whereas the medial/superior frontal, precentral, cingulate, precuneus, and superior temporal gyrus appears to be involved in inhibited eye blinking. Based on these experimental results, we propose that the precentral gyrus is responsible for both voluntary and inhibited eye blinking. The parietal area (precuneus and superior temporal gyrus) appears to be exclusively related to inhibited eye blinking.

Brain activation of reading korean words and recognizing pictures by Korean native speakers: a functional magnetic resonance imaging study.

Even though the Korean words are characterized as phonemes like other alphabetic languages, their shape resembles much more morphemes like Chinese characters. The main purpose of the study is to explore neural mechanisms of reading Korean words and recognizing pictures by Korean native speakers using functional magnetic resonance imaging technique. In the experimental results, the authors could see commonly activated areas in occipito-temporal region bilaterally, whereas frontal and temporal region was activated only while reading Korean words. Left middle frontal activation of Korean words was regarded to be involved in the phonological and semantic processing. Right anterior cingulate (BA 32) activation seems to be related with language and sound organization and superior temporal (BA 29) activation might be involved in the processing of phonological system to which tonal information is attached. Right medial frontal (BA 8) activation was reported in the results. The authors suggest the activation of this area is related with nonverbal visual higher order control or visuospatial analysis of Korean words in their experimental tasks.

The influence of face similarity in the case of the perception of morphed self-face.

The purpose of the study was to examine if differences in behavioral effects in terms of facial self-recognition, compared to other identity recognition (familiar, strange) exist. Morphed versions of three facial identities were used in the experiment. The subject's own face was morphed with an unknown identity. A face of a highly familar person and of a stranger were also morphed in the same manner. This morphing procedure was repeated six times for each identity, but with six different unknown faces, in which three of the unknown faces were rated as being similar and the other three as dissimilar. The reaction times and categorical boundaries were then measured. The major finding of the study was that there were significant delayed mean reaction times for the morphed images of version "self versus similarly rated unknown faces" in contrast to the images of "self versus dissimilarly rated unknown faces" only. No significant differences were found in any of the other morphed versions. The authors interpret this result as being uniquely associated to the facial self-recognition and suggest that this association might be related to the "self effect."

Neural correlates of eye blinking; improved by simultaneous fMRI and EOG measurement.

Neural correlates of eye blink in healthy human subjects can be investigated using functional magnetic resonance imaging. However, the focus of most previous studies has been on intentional eye blinking. The goal of the present study was to examine the neural correlates of spontaneous eye blinking with the help of EOG measurements during data acquisition of fMRI. After the removal of the pulse artifact in the EOG signal, EOG waveform clearly indicates eye blinking, which was equivalent to those measured outside of the MRI scanner. On the basis of this detection, each blinking event can be used as a temporal cue for the event-related fMRI. In a comparison, we also investigated the neural correlates of blink inhibition. Based on the brain activation pattern, the activation of the bilateral parahippocampal, the visual cortex was commonly observed for both conditions. The additional activation of the precentral gyrus, corresponding to blink inhibition, and the right medial frontal gyrus, corresponding to spontaneous blinking were observed. Based on these results, we conclude that the medial frontal gyrus is responsible for spontaneous eye blinking, whereas precentral activation appears to be related to blink inhibition.

Neural mechanisms of Korean word reading: a functional magnetic resonance imaging study.

The use of functional magnetic resonance imaging permits the collection of brain activation patterns when native Korean speakers (12 persons as subjects) read Korean words and Chinese characters. The Korean language uses both alphabetic Korean words and logographic Chinese characters in its writing system. Our experimental results show that the activation patterns obtained for reading Chinese characters by Korean native speakers involve neural mechanisms that are similar to Chinese native speakers; i.e. strong left-lateralized middle frontal cortex activation. For the case of Korean word reading, the activation pattern in the bilateral fusiform gyrus, left middle frontal gyrus, left superior temporal gyrus, right mid temporal gyrus, precentral gyrus, and insula was observed. This suggests that the activation pattern for Korean word reading appears to corroborate with that of alphabetic words at the general level. A further noteworthy finding of our study is the strong activation of the posterior part of the right dorsolateral prefrontal cortex (BA 8). The right hemispheric BA 8 belongs to the visual higher order control area and we propose that this area should be responsible for processing of visuospatial (surface form) information of Korean words.

Analysis of functional MRI data based on an estimation of the hemodynamic response in the human brain.

Functional magnetic resonance imaging (fMRI) data is usually analyzed using hemodynamic response data formulated with the aid of a gamma function. An fMRI response to stimuli can be mathematically modeled by convolution of the hemodynamic response and the presented stimulus. This approach is based on a linear system analysis. However, it is known that most biological systems are nonlinear and the nature of the hemodynamic response depends on both the subjects and brain regions under study. In this work, we estimated the hemodynamic responses of the fusiform face area (FFA) and the primary visual area (V1) using 1st- and 2nd-order Volterra kernels. The estimated hemodynamic responses were used to analyze fMRI data obtained from the corresponding regions. The results of the analysis of fMRI data using the estimated hemodynamic responses show a more significant activation than is obtained by conventional analysis using the hemodynamic response modeled by gamma function.

Spatiotemporal brain activation pattern during word/picture perception by native Koreans.

The purpose of this study is to explore spatiotemporal brain activation patterns during perception of words from three different languages (Korean, English, Chinese) and pictures. Using 64 channel event-related potential (ERP) recording and source localization using distributed source model, we investigated, with high temporal resolution, whether similar or different spatiotemporal patterns of brain activation are involved in the perception of words of different languages and/or pictures. Experimental results seem to corroborate left hemispheric dominance in language processing, and temporal/spatial characteristics in word perception revealed by previous ERP and neuroimaging studies. Observed differences in spatial pattern of activation at specific time periods between English and Korean, and Korean and Chinese, could be explained in terms of required visual pattern analysis due to the orthographic characteristics of each language.

Improved ballistocardiac artifact removal from the electroencephalogram recorded in fMRI.

The simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance image (fMRI) is a promising tool that is capable of providing high spatiotemporal brain mapping, with each modality supplying complementary information. One of the major barriers to obtain high-quality simultaneous EEG/fMRI data is that pulsatile activity due to the heartbeat induces significant artifacts in the EEG. The purpose of this study was to develop a novel algorithm for removing heartbeat artifact, thus overcoming problems associated with previous methods. Our method consists of a mean artifact wave form subtraction, the selective removal of wavelet coefficients, and a recursive least-square adaptive filtering. The recursive least-square adaptive filtering operates without dedicated sensor for the reference signal, and only when the mean subtraction and wavelet-based noise removal is not satisfactory. The performance of our system has been assessed using simulated data based on experimental data of various spectral characteristics, and actual experimental data of alpha-wave-dominant normal EEG and epileptic EEG.

Brain regions sensitive to the face inversion effect: a functional magnetic resonance imaging study in humans.

Perception of upright faces relies on configural processing. Therefore recognition of inverted, compared to upright faces is impaired. In a functional magnetic resonance imaging experiment we investigated the neural correlate of a face inversion task. Thirteen healthy subjects were presented with a equal number of upright and inverted faces alternating with a low level baseline with an upright and inverted picture of an abstract symbol. Brain activation was calculated for upright minus inverted faces. For this differential contrast, we found a signal change in the right superior temporal sulcus and right insula. Configural properties are processed in a network comprising right superior temporal and insular cortex.