Biomedical subjects

Tetsuya Iidaka

Publications and source records attributed to Tetsuya Iidaka.

16 recordsLinked to original sources

PubMed2006

Volume of left amygdala subregion predicted temperamental trait of harm avoidance in female young subjects. A voxel-based morphometry study.

We investigated the relationship between temperamental predisposition and brain structure by using a standard questionnaire and high-resolution T1-weighted magnetic resonance image (MRI) in normal young volunteers. Fifty-six subjects completed the Japanese version of the Temperament and Character Inventory (TCI, 125 items) and underwent an MRI acquisition of the brain. The gray matter (GM) was extracted from the whole brain image of the subjects and normalized to the standard brain template using statistical parametric mapping and the optimized voxel-based morphometry (VBM) method. When the score on the harm avoidance (HA) subscale was used as a dependent variable, the multiple regression analysis revealed that the HA score positively correlated with the volume of the part of left amygdala. The region-of-interest analysis showed that the correlation was significant in the female subjects but not in the male subjects. The correlation was significant even after the effects of age, depression score, and total GM volume were taken into account. The differential correlation between the sexes may be caused by differences in hormonal condition and the vulnerability of women to socio-psychological stress. In addition, the novelty seeking (NS) score positively correlated with the GM of the left middle frontal gyrus. The volume of the tail of the right caudate nucleus positively correlated with the reward dependence (RD) score. With regard to the NS and RD scores, no significant sex difference was observed in the correlation. These results indicate that the temperamental traits measured using the questionnaire may have a morphological basis in the human brain.

Adult↗

PubMed2006

Frontoparietal network involved in successful retrieval from episodic memory. Spatial and temporal analyses using fMRI and ERP.

The neural basis for successful recognition of previously studied items, referred to as "retrieval success," has been investigated using either neuroimaging or brain potentials; however, few studies have used both modalities. Our study combined event-related functional magnetic resonance imaging (fMRI) and event-related potential (ERP) in separate groups of subjects. The neural responses were measured while the subjects performed an old/new recognition task with pictures that had been previously studied in either a deep- or shallow-encoding condition. The fMRI experiment showed that among the frontoparietal regions involved in retrieval success, the inferior frontal gyrus and intraparietal sulcus were crucial to conscious recollection because the activity of these regions was influenced by the depth of memory at encoding. The activity of the right parietal region in response to a repeated item was modulated by the repetition lag, indicating that this area would be critical to familiarity-based judgment. The results of structural equation modeling revealed that the functional connectivity among the regions in the left hemisphere was more significant than that in the right hemisphere. The results of the ERP experiment and independent component analysis paralleled those of the fMRI experiment and demonstrated that the repeated item produced an earlier peak than the hit item by approximately 50 ms.

Brain Mapping↗

PubMed2006

Regional cerebral blood flow changes in depression after electroconvulsive therapy.

A large number of studies have documented regional cerebral blood flow (rCBF) abnormalities in depression. A smaller yet significant number of studies have examined changes in rCBF before and after treatment. The findings, however, have been variable with regard to changes before and after electroconvulsive therapy (ECT). A consecutive series of patients (n=10) with drug-resistant major depressive episode according to DSM-IV with 17-item Hamilton Rating Scale for Depression (HRSD) scores greater than or equal to 14 gave their informed consent and were studied with technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (99mTc-ECD SPECT) before and after a course of ECT. The results were analyzed with statistical parametric mapping version 99. No region showed significant positive correlations between rCBF patterns of changes and HRSD changes, but three clusters emerged as showing significant negative correlations. These regions corresponded with left frontopolar gyrus, left amygdala, globus pallidus and nucleus accumbens, and left superior temporal gyrus. It was speculated that ECT affected both the prefrontal cortex, commonly assumed to be involved in depression, and the amygdala, known to play a central role in the processing of emotional stimuli, through the limbic-cortical-striatal-pallidal-thalamic circuit.

Adult↗

PubMed2006

High-dose of multiple antipsychotics and cognitive function in schizophrenia: the effect of dose-reduction.

We evaluated the effect of antipsychotic dose-reduction on the neurocognitive function of 17 schizophrenic patients (11 male and 6 female, mean age=42.4+/-11.3) who have been taking high-doses of multiple conventional antipsychotics. The mean (+/-SD) of total daily antipsychotic doses (in mg/day, chlorpromazine-equivalent) was 2,253 (+/-668) at baseline, which was reduced to 1,315 (+/-276). Possible changes in neurocognitive function were assessed using Wisconsin card sorting test (WCST) and continuous performance test (CPT). As controls, we examined WCST and CPT in 6 schizophrenic patients (4 male and 2 female, mean age=47.7+/-14.2) who had been taking high-doses of multiple antipsychotics (mean daily antipsychotic dose=1,753+/-165 mg) and declined to change their antipsychotic regimen. In WCST, the mean number of total correct answers significantly increased (53.2+/-16.3 vs. 63.8+/-19.6, P=0.035, Wilcoxon signed rank test); perseverative errors significantly decreased (54.4+/-27.3 vs. 35.4+/-20.1, P=0.013, Wilcoxon signed rank test) after the antipsychotic dose-reduction. In contrast, the control group showed no significant difference between the two WCST performances conducted with a three-month interval. The improvements in WCST performance significantly correlated with the decreases in PANSS negative syndrome score in the subject patients. No significant change was observed in CPT performances in either group. Our preliminary data shows that, in schizophrenic patients taking high-doses of multiple conventional antipsychotics, dose-reduction might lead to improvements in cognitive functions.

Adult↗

PubMed2006

Hemodynamic and electrophysiological relationship involved in human face processing: evidence from a combined fMRI-ERP study.

Functional magnetic resonance imaging (fMRI) and event-related potential (ERP) experiments were conducted in the same group of subjects and with an identical task paradigm to investigate a possible relationship between hemodynamic and electrophysiological responses within the brain. The subjects were instructed to judge whether visually presented stimuli were faces or houses and then press the corresponding button. Functional MRI identified face- and house-related regions in the lateral and medial part of the fusiform gyrus, respectively, while ERP showed significantly greater N170 negativity for face than for house stimuli in the temporo-occipital electrodes. Correlation analysis between the BOLD signal in the fusiform gyrus and ERP parameters demonstrated a close relationship between the signal and both latency and amplitude of N170 across the subjects. These correlations may indicate that the variation in cognitive demand and hemodynamic responses during the face/house discrimination task is coupled with the variation of N170 peak latency/amplitude across the subjects. Thus, integrative analysis of spatial and temporal information obtained from the two experimental modalities may help in studying neural correlates involved in a particular cognitive task.

Adult↗

PubMed2006

Gamma band activity and its synchronization reflect the dysfunctional emotional processing in alexithymic persons.

In the present study, we investigated the gamma band response and its phase synchrony between electrodes in alexithymia, which is characterized by a disability in identifying and describing feelings. Individuals with high and low alexithymia scores were selected according to the scores on the 20-item Toronto Alexithymia Scale. EEG was recorded from alexithymic and nonalexithymic persons viewing emotionally negative or neutral stimuli. Nonalexithymic persons exhibited increased gamma band power and phase synchronization at the 400-450-ms time window when processing emotionally negative stimuli. Neither enhanced gamma band power nor phase synchronization was observed in alexithymic persons in the negative emotion condition. These results suggest that gamma band activity reflects emotional processing, and alexithymic persons may have a deficit in communication between brain regions or in the utilization of memory or emotional information during the processing of emotional stimuli.

Adult↗

PubMed2005

Association of neural and physiological responses during voluntary emotion suppression.

Recent neuroimaging studies have shown that several prefrontal regions play critical roles in inhibiting activation of limbic regions during voluntary emotion regulation. The present study aimed to confirm prior findings and to extend them by identifying the frontal neural circuitry associated with regulation of peripheral physiological responses during voluntary emotion suppression. Ten healthy female subjects were presented with affectively positive, neutral, and negative pictures in each of an Attending and Suppression task. Regional cerebral blood-flow changes were measured using 15O-water positron emission tomography, and autonomic (heart rate: HR, skin conductance response: SCR) and endocrine (adrenocorticotropic hormone: ACTH) indices were measured during both tasks. The left amygdala and the right anterior temporal pole were activated during the Attending task, whereas activation was observed in the left lateral prefrontal cortex (LPFC), including the adjacent medial prefrontal cortex (MPFC), and medial orbitofrontal cortex (MOFC) during the Suppression task. In the Attending task, activation in the amygdala and MOFC positively correlated with magnitudes of the SCR and ACTH responses. Emotion suppression elicited enhancement of SCR and the strength of the effect positively correlated with activation in the MOFC. These results suggest that the MOFC plays a pivotal role in top-down regulation of peripheral physiological responses accompanying emotional experiences.

Adrenocorticotropic Hormone↗

PubMed2005

A variant C178T in the regulatory region of the serotonin receptor gene HTR3A modulates neural activation in the human amygdala.

Converging evidence in neurophysiological and neuroimaging studies has suggested that the limbic and prefrontal systems play important roles in emotion and cognition. These structures are activated when we see a human face, assuming that we automatically evaluate the biological significance of the stimuli. The serotonin (5-HT) system within the brain has been tied to various behaviors such as mood and anxiety and to the biology of neuropsychiatric disorders. To investigate the link between the 5-HT system and limbic/prefrontal activity, normal subjects (n = 26) who underwent functional magnetic resonance imaging and faced recognition tasks were genotyped for the single nucleotide polymorphism C178T in the regulatory region of the serotonin receptor type 3 gene (HTR3A). We found that the subjects with C/C alleles had greater activity in the amygdala and dorsal and medial prefrontal cortices than those with C/T alleles. The C/C group also showed a faster reaction time during the task than the C/T group. The temperamental predisposition of the subjects had a significant correlation with brain activity in the C/C group. The genotype effect in the right amygdala and prefrontal cortex was largest during the first run of the experiment. These results indicate that the C178T variation in the HTR3A has a critical influence on the amygdaloid activity and on human face processing, probably through regulation of the receptor expression. The present study may contribute to elucidating a possible link among genes, the brain, and behavior in normal populations and may help reveal the biological basis of neuropsychiatric disorders.

Adult↗

PubMed2005

Linking semantic priming effect in functional MRI and event-related potentials.

The aim of this study is to examine the neural substrates involved in semantic priming using a combined event-related functional magnetic resonance imaging (fMRI) and event-related potentials (ERP) study. Twelve subjects were instructed to judge whether the presented target word was a real word or a nonword. Under the related condition, target words were preceded by a semantically related prime word. On the other hand, under the unrelated condition, prime words did not have semantic relatedness with the target word. The reaction time for reaching a judgment was longer under the unrelated condition than under the related condition, indicating that the recognition of target words is promoted by semantic priming under the related condition. In the fMRI results, we found reduced activity in the dorsal and ventral left inferior frontal gyrus, the anterior cingulate, and left superior temporal cortex for related versus unrelated conditions (i.e., the repetition suppression effect). ERP analysis revealed that the amplitude of the N400 component was reduced under the related condition compared with the unrelated condition (i.e., the N400 priming effect). Correlation analysis between the BOLD repetition suppression effect and the N400 priming effect decomposed by independent component analysis (ICA) across subjects showed significant correlation in the left superior temporal gyrus. This finding is consistent with the recent MEG data suggesting that the source of N400 is judged to be the bilateral superior temporal lobe. We discussed this finding herein in relation to the modulation of access to the phonological representation caused by semantic priming.

Adult↗

PubMed2005

Dissociation of conscious and unconscious repetition priming effect on event-related potentials.

Although the neural basis of the unconscious priming effect has previously been investigated, the results of these studies have possibly been contaminated by a conscious priming effect. The aim of the present study was to dissociate the effects of conscious and unconscious priming on event-related potential (ERP) by using the process-dissociation procedure. A prime word was presented briefly, followed by a word-stem, in each trial. Under the inclusion condition, subjects were instructed to complete the word-stem using the prime word, while under the exclusion condition subjects were asked to complete the word-stem with a word not seen as prime. The behavioral priming effect was obtained under both conditions, indicating that the prime words were processed unconsciously and influenced the word-stem completion task. We found that two ERP components were affected by repetition priming. First, the N400 amplitude was decreased by word repetition under the inclusion condition, but not under the exclusion condition. This result suggests that N400 would reflect conscious lexical processing, but not unconscious lexical activation. Second, the negativity at left front lateral region was enhanced by word repetition under the exclusion condition. We discuss this finding herein in relation to the activity of the left inferior prefrontal cortex with regard to word semantic processing.

Adolescent↗

PubMed2004

Spatial frequency of visual image modulates neural responses in the temporo-occipital lobe. An investigation with event-related fMRI.

Our visual environment consists of information ranging from coarse to fine patterns with respect to spatial frequency (SF). Neurophysiological studies using experimental animals have shown that there exist specific SF channels in striate and extrastriate visual cortices. In the present study, we used event-related functional magnetic resonance imaging (fMRI) and healthy subjects to investigate whether manipulation of the SF of visual images modulates neural responses in the temporo-occipital lobes. Subjects were scanned while performing "one-back task" with high-pass or low-pass filtered images of a face and house. We demonstrated that visual attention to the stimuli with high SF more specifically involves cortical activation in the left fusiform gyrus and inferior occipital gyrus as compared to that with low SF. High-SF specificity in the left fusiform gyrus was confirmed by voxel-by-voxel comparison of original images with left-right flipped images. There was no low-SF region in the right hemisphere; however, processing of low-SF images may be category-specific in face- and house-related regions. These results may shed light on the neural correlates of behavioral evidence that high-SF stimuli are handled faster and more accurately when presented to the right visual hemifield than to the left counterpart. The present results were also discussed in a viewpoint of local/global processing and functional asymmetry of cerebral hemispheres.

Adult↗

PubMed2004

Functional association of the amygdala and ventral prefrontal cortex during cognitive evaluation of facial expressions primed by masked angry faces: an event-related fMRI study.

The present study examined the functional association of the amygdala and right ventral prefrontal cortex (PFC) during cognitive evaluation of facial expressions. A situation was created where emotional valence of the stimuli was unconsciously manipulated by using subliminal affective priming. Twelve healthy volunteers were asked to evaluate the facial expressions of a target face (500-ms duration) such as "anger", "neutral", or "happy". All target faces expressed relatively weak anger. Just before the presentation of the target face, a prime of three conditions of 35-ms duration, angry face, neutral face, and white blank was presented. The subjects could not consciously identify the primes in this procedure. Activity in the right amygdala was greater with subliminal presentation of the angry prime compared with subliminal presentation of a neutral face or white-blank stimuli. Most importantly, the degree of activation of the right amygdala was negatively correlated with that of the right ventral PFC only with the anger prime. Furthermore, activation of the amygdala was positively correlated with rate of judgment when the subjects recognized anger in the target faces. These results are discussed in terms of the functional association between the right PFC and the amygdala and its influence on cognitive processing.

Adult↗

PubMed2003

Frontal lobe networks for effective processing of ambiguously expressed emotions in humans.

This study examines the neural substrates involved in the recognition of ambiguous facial expressions using functional magnetic resonance imaging. Subjects performed two tasks, one in which they judged facial expressions and another in which they identified gender. Subtraction between ambiguous expression and clear expression conditions revealed the activation of anterior cingulate (ACC), medial frontal (MeFG) and bilateral inferior frontal gyrus (IFG). Structural equation modeling showed that the functional connectivity between these areas was greater with the ambiguous expressions than with the clear ones. The activation of the ACC, MeFG, and right IFG was greater with ambiguous expressions than with ambiguous gender. These results suggest that the neural network involving these frontal regions plays a crucial role in the processing of the ambiguously expressed facial emotions.

Adult↗

PubMed2003

Dissociable neural responses in the hippocampus to the retrieval of facial identity and emotion: an event-related fMRI study.

In studies with brain-damaged patients and experimental animals, the medial temporal lobe, including the hippocampus and parahippocampal gyrus, has been found to play a critical role in establishing declarative or episodic memory. We measured the neural response in these structures, using event-related functional magnetic resonance imaging, while six healthy subjects performed the retrieval task for facial identity and emotion, respectively. Under the identity condition, the subjects participated in a yes/no recognition test for neutral faces learned before the scanning. Under the emotion condition, the subjects learned the faces with positive or negative expression and retrieved their expressions from neutral cue faces. The results showed that the left hippocampus is primarily involved in the identification of learned faces, and that the adjacent parahippocampal gyrus responds more to target than to distracter events. These results indicate a specific engagement of the left hippocampal regions in conscious recollection and identification of physiognomic facial features. The activity in the right hippocampus increased under both the identity and emotion conditions. The present results may relate with the functional model of face recognition in which the left hemisphere contributes to the processing of detailed features and the right hemisphere is efficient in the processing of global features.

Adult↗

PubMed2003

Interaction of prime and target in the subliminal affective priming effect.

It has been found that an emotional stimulus such as a facial expression presented subliminally can affect subsequent information processing and behavior, usually by shifting evaluation of a subsequent stimulus to a valence congruent with the previous stimulus. This phenomenon is called subliminal affective priming. The present study was conducted to replicate and expand previous findings by investigating interaction of primes and targets in the affective priming effect. Two conditions were used. Prime (subliminal presentation 35 msec.) of an angry face of a woman and a No Prime control condition. Just after presentation of the prime, an ambiguous angry face or an emotionally neutral face was presented above the threshold of awareness (500 msec.). 12 female undergraduate women judged categories of facial expressions (Anger, Neutral, or Happiness) for the target faces. Analysis indicated that the Anger primes significantly facilitated judgment of anger for the ambiguous angry faces; however, the priming effect of the Anger primes was not observed for neutral faces. Consequently, the present finding suggested that a subliminal affective priming effect should be more prominent when affective valence of primes and targets is congruent.

Adult↗

PubMed2002

Age-related differences in the medial temporal lobe responses to emotional faces as revealed by fMRI.

Age-related differences involved in the neural substrates of emotional face perception were investigated in young and old healthy volunteers. The subjects were scanned using functional magnetic resonance imaging while they were judging the gender of faces with negative, positive, or neutral emotional valence. The results showed that both the predominant activation in young subjects and reduced activity in old subjects contributed to a significant age difference in the left amygdala during the perception of negative faces. Activity in the right parahippocampal gyrus during the perception of positive faces diminished with advancing age. Neural activity in the angular gyrus and lingual gyrus of the right hemisphere was reduced in the old subjects during the perception of positive faces. There was no region where old subjects had greater activity than young subjects during the task. In old subjects, the overall activity in the right hippocampus during the task correlated negatively with age, whereas the activity in the right parahippocampal gyrus correlated positively with neuropsychological performance. There was no significant correlation between subjects' characteristics and signal change in young subjects. These results indicate the age-associated vulnerability of the medial temporal lobe structures including the amygdala, hippocampus, and parahippocampal gyrus during face perception. The dissociation with reduced activity in the left amygdala and the right parahippocampal gyrus may suggest that aging differentially affects neural responses to faces with negative or positive emotional valence. The parieto-occipital lobe, which has been found to be involved in face processing, also showed a functional decline associated with aging.

Adult↗