Tamaki Miyamoto

A fronto-parietal network for chewing of gum: a study on human subjects with functional magnetic resonance imaging.

The purpose of this study is to investigate human brain activity during mastication using fMRI. Twelve right-handed normal subjects performed two tasks: chewing of gum at their own pace, and imitating the movements of chewing gum. In order to reveal which areas of the brain are more strongly activated while chewing gum, we performed the conjunction analyses of gum chewing minus sham chewing with gum chewing minus rest. The common activity in the orofacial sensorimotor and premotor cortex was subtracted out since it was common to both tasks, but there were some differences in activity in some prefrontal and posterior parietal cortex areas. Our results suggest that a fronto-parietal network for mastication exists and may contribute to higher cognitive information processing.

Psychotic episodes during Zonisamide treatment

Several articles have appeared over the last years devoted to mental side effects during zonisamide (ZNS) treatment. In this study, we were particularly interested in psychotic episodes. Seventy-four epileptic patients with a history of ZNS treatment were surveyed retrospectively over the period spanning 1 March 1984 to 30 June 1994. They were divided into two groups according to the presence or absence of psychotic episodes during ZNS treatment. We analysed various factors pertaining to psychotic episodes during ZNS treatment. Of the 74 patients 14 had psychotic episodes. We found that the incidence of psychotic episodes during ZNS treatment was several times higher than the previously reported prevalence of epileptic psychosis, and that the risk of psychotic episodes was higher in young patients. In 13 patients, psychotic episodes occurred within a few years of commencement of ZNS. In children, obsessive-compulsive symptoms appeared to be related to psychotic episodes. It is important to terminate ZNS as soon as possible if psychotic episodes develop and never restart, even if seizures become worse. It cannot definitely be proved that ZNS causes psychotic episodes, as information on mental side effects during ZNS monotherapy is scant, but it does appear likely that ZNS contributes to psychotic episodes during polytherapy.

Saccular stimulation of the human cortex: A functional magnetic resonance imaging study

Recent imaging studies have reported the projection of semicircular canal signals onto wide regions of the cerebral cortex but little is known about otolith projections onto the cerebral cortex. We used functional magnetic resonance imaging (fMRI) to investigate the activation of the cortex by loud clicks that selectively stimulate the sacculus. Twelve normal volunteers were presented with auditory stimuli via an earphone containing a piezo electric element. High-intensity [maximum volume of 120 dB (SPL)] or low-intensity [maximum volume of 110 dB (SPL)] clicks were delivered at a frequency of 1 Hz and lasted 1 ms. We first checked that the high-intensity, but not low-intensity, clicks stimulated the sacculus by determining the vestibular evoked myogenic potentials. We then analyzed two task conditions (high- and low-intensity clicks) in a boxcar paradigm. We obtained gradient echo echo-planar images by using a 1.5 T MRI system. We analyzed the fMRI time series data with SPM2. High-intensity clicks activated wide areas of the cortex, namely, the frontal lobe (prefrontal cortex, premotor cortex, and frontal eye fields), parietal lobe (the region around the intraparietal sulcus, temporo-parietal junction, and paracentral lobule), and cingulate cortex. These areas are similar to those reported in previous imaging studies that analyzed the cortical responses to the activation of the semicircular canals. Thus, semicircular canal and otolith/saccular signals may be processed in similar regions of the human cortex.

Cerebral activation related to the control of mastication during changes in food hardness.

To investigate the neural network involved in the control of mastication during changes in food hardness, we employed functional magnetic resonance imaging while 15 healthy subjects chewed gum whose hardness was changed by chewing. By comparing the areas activated when the hardness of the bolus varied widely with those seen when the hardness of the bolus had stabilized, we identified selective activations of the supplementary motor area, the dorsolateral prefrontal cortex, the superior temporal gyrus of the left hemisphere, and the premotor area and inferior parietal lobule of the right hemisphere. These findings indicate that these areas are probably related to processes linking sensory input and motor output involved in the change of hardness food during mastication.

Microstructural White Matter Abnormalities of Multiple System Atrophy: In Vivo Topographic Illustration by Using Diffusion-Tensor MR Imaging

PURPOSE To determine whether diffusion-tensor (DT) imaging can demonstrate microstructural white matter abnormalities of multiple system atrophy (MSA) and to correlate these imaging findings with clinical signs and symptoms. MATERIALS AND METHODS Institutional review board approval and written informed consent were obtained. DT imaging was performed in 16 patients with MSA with predominant cerebellar symptoms (MSA-C) (mean age, 60.0 years + or - 5.1 [standard deviation]; range, 51-69 years) and 16 age-matched healthy subjects. Fractional anisotropy (FA) and mean diffusivity (MD) were compared voxel-by-voxel between the two groups by using a two-sample t test. Overlap maps were created to illustrate areas with FA and MD alterations. Correlation between DT imaging indexes and Barthel index score, scale for assessment and rating of ataxia (SARA) score, severity of orthostatic hypotension, age of disease onset, and disease duration was tested by using Spearman rank or Pearson product-moment correlation analysis. T2-weighted and proton density-weighted images of the patients were visually assessed. RESULTS Widespread areas of FA reduction and MD elevation were observed in supra- and infratentorial white matter structures in patients with MSA (P < .05, false discovery rate corrected). Significant correlation (P < .01) between DT imaging indexes and Barthel index score, SARA score, severity of orthostatic hypotension, and disease duration was observed for multiple areas with FA and/or MD alterations. T2-weighted and proton density-weighted images showed no significant abnormality in supratentorial white matter. CONCLUSION DT imaging may help identify the microstructural white matter abnormalities of MSA-C. DT imaging may be useful for severity assessment of MSA-C.

Impaired integrity of the brain parenchyma in non-geriatric patients with major depressive disorder revealed by diffusion tensor imaging

Diffusion tensor imaging (DTI) is considered to be able to non-invasively quantify white matter integrity. This study aimed to use DTI to evaluate white matter integrity in non-geriatric patients with major depressive disorder (MDD) who were free of antidepressant medication. DTI was performed on 19 non-geriatric patients with MDD, free of antidepressant medication, and 19 age-matched healthy subjects. Voxel-based and histogram analyses were used to compare fractional anisotropy (FA) and mean diffusivity (MD) values between the two groups, using two-sample t tests. The abnormal DTI indices, if any, were tested for correlation with disease duration and severity, using Pearson product-moment correlation analysis. Voxel-based analysis showed clusters with FA decrease at the bilateral frontal white matter, anterior limbs of internal capsule, cerebellum, left putamen and right thalamus of the patients. Histogram analysis revealed lower peak position of FA histograms in the patients. FA values of the abnormal clusters and peak positions of FA histograms of the patients exhibited moderate correlation with disease duration and severity. These results suggest the implication of frontal-subcortical circuits and cerebellum in MDD, and the potential utility of FA in evaluation of brain parenchymal integrity.

Effects of Menstrual Cycle on Plasma Melatonin Level and Sleep Characteristics

It is well known that some clinical symptoms (e.g. psychotic symptoms and epileptic seizures) often aggravate around the time of menstruation. Moreover, the change of subjective sleep feeling throughout the menstrual cycle was reported. Therefore, the menstrual cycle is presumed to affect sleep characteristics and biological rhythm. We investigated a circadian pattern of plasma melatonin and body temperature, and sleep characteristics in the different phases of the menstrual cycle under controlled environmental conditions. In this paper, a part of the results is discussed.

ERPs, Semantic Processing and Age

ERPs (N400, LPC and CNV) were elicited in two sets of subjects grouped according to age (young vs. elderly) using a word-pair category matching paradigm. Each prime consisted of a Japanese noun (constructed from two to four characters of the Hiragana) followed by one Chinese character (Kanji) as the target, this latter representing one of five semantic categories. There were two equally probable target conditions: match or mismatch. Each target was preceded by a prime, either belonging to, or not belonging to, the same semantic category. The subjects were required to respond with a specified button press to the given target according to the condition. We found RTs to be longer in the elderly subjects and under the mismatch condition. N400 amplitude was reduced in the elderly subjects under the mismatch condition and there was no difference between match and mismatch response, which were similar in amplitude to that under match condition for the young subjects. In addition, the CNV amplitudes were larger in the elderly subjects. These results suggested that functional changes in semantic processing through aging (larger semantic networks and diffuse semantic activation) were the cause of this N400 reduction, attributing a subsidiary role to attentional disturbance. We also discuss the importance of taking age-related changes into consideration in clinical studies.

Saccular projections in the human cerebral cortex.

Abstract: The cerebral cortical areas processing saccular information were investigated in human subjects using the fMRI method and loud clicks, which selectively activate the saccule. The results were compared with previous vestibular evoked potential (VEP) studies in anesthetized patients following vestibular nerve stimulation. Nine normal subjects participated in fMRI studies. By comparing the cortical areas activated by a click at 85 dB (auditory activation) with those activated by 102 dB (auditory plus saccular activation), the following cortical areas were selectively activated by saccular stimulation: intraparietal sulcus, frontal eye fields, prefrontal cortex, and postcentral gyrus, in addition to insula, supplementary motor area, and anterior and posterior cingulate cortex. Previous VEP studies also revealed similar activation areas by vestibular nerve stimulation with latencies at 6 ms, suggesting that the shortest pathways for activation of cerebral cortical neurons from the labyrinth are trisynaptic, with a relay in the thalamus. The activated areas are also consistent with results in previous studies using caloric stimulation, which primarily activates horizontal semicircular canals. These results suggest that canal and otolith information is processed largely by similar cortical areas in humans. Multiple cortical areas activated by these studies suggest that these areas are involved in different aspects of processing vestibular information. The saccular projections to the prefrontal and frontal cortex suggest that these areas are involved in planning motor synergies to counteract loss of equilibrium.

Disturbance of semantic processing in temporal lobe epilepsy demonstrated with scalp ERPs

We investigated event-related potentials (N400, LPC and CNV) elicited in temporal lobe epilepsy (TLE) patients and control subjects from scalp electrodes, using a word-pair category matching paradigm. Each prime consisted of a Japanese noun (constructed from 2-4 characters of the Hiragana) followed by a Chinese character (Kanji) as the target, the latter representing one of five semantic categories. There were two equally probable target conditions: match or mismatch. Each target was preceded by a prime, either belonging to, or not belonging to, the same semantic category. The subjects were required to respond with a specified button press to the given target, according to the condition. We found RTs to be longer under the mismatch condition in both subject groups. The N400 amplitude was reduced in TLE subjects under both conditions, although LPC and CNV amplitudes showed no significant differences. These results suggest that scalp N400 is capable of demonstrating disturbance of semantic processing in TLE non-invasively.