Hirokazu Kikuchi

Tohoku University, Sendai, Kagoshima-ken, Japan

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Publications (7)17.45 Total impact

  • Hirokazu Kikuchi, Toshikatsu Fujii
    Nippon rinsho. Japanese journal of clinical medicine 10/2011; 69 Suppl 8:326-30.
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    ABSTRACT: The aim of this study was to characterise the white matter damage involved in idiopathic normal pressure hydrocephalus (INPH) using diffusion tensor imaging (DTI) and the relationship between this damage and clinical presentation. Twenty patients with INPH, 20 patients with Alzheimer's disease and 20 patients with idiopathic Parkinson's disease (as disease control groups) were enrolled in this study. Mean diffusivity (MD) and fractional anisotropy (FA) were determined using DTI, and these measures were analysed to compare the INPH group with the control groups and with certain clinical correlates. On average, the supratentorial white matter presented higher MD and lower FA in the INPH group than in the control groups. In the INPH group, the mean hemispheric FA correlated with some of the clinical measures, whereas the mean hemispheric MD did not. On a voxel-based statistical map, white matter involvement with high MD was localised to the periventricular regions, and white matter involvement with low FA was localised to the corpus callosum and the subcortical regions. The total scores on the Frontal Assessment Battery were correlated with the FA in the frontal and parietal subcortical white matter, and an index of gait disturbance was correlated with the FA in the anterior limb of the left internal capsule and under the left supplementary motor area. DTI revealed the presence of white matter involvement in INPH. Whereas white matter regions with high MD were not related to symptom manifestation, those with low FA were related to motor and cognitive dysfunction in INPH.
    Journal of Neurology 04/2011; 258(11):1949-57. · 3.58 Impact Factor
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    ABSTRACT: Recent evidence suggests that patients with Alzheimer's disease (AD), as compared with normal individuals, exhibit increased false recognition by stimulus repetition in the Deese-Roediger-McDermott (DRM) task or associative recognition memory tasks, probably due to impaired recollection-based monitoring. However, because of possible alternative explanations for the findings of these previous studies, the evidence for impaired recollection-based monitoring in AD patients remains inconclusive. In this study, we employed stimulus repetition in old/new recognition judgments of single-item picture memory without a factor of association between the stimuli and examined whether AD patients showed increased false item recognition as compared with healthy controls. AD patients and healthy controls studied single-item pictures presented either once or three times. They were later asked to make an old/new recognition judgment in response to (a) Same pictures, pictures identical to those seen at encoding, (b) Similar lures, novel pictures similar to but not identical to those seen at encoding, and (c) Dissimilar lures, novel pictures not similar to those seen at encoding. For Same pictures, repeated presentation of stimuli increased the proportion of "old" responses in both groups. For Similar lures, repeated presentation of stimuli increased the rate of "old" responses in AD patients but not in control subjects. The results of the present study clearly demonstrated elevated false recognition by stimulus repetition in single-item recognition in AD patients. The present findings strongly support the view that AD patients are impaired in their ability to use item-specific recollection in order to avoid false recognition.
    Neuropsychologia 03/2011; 49(7):1897-902. · 3.48 Impact Factor
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    ABSTRACT: Frontal lobe dysfunction is believed to be a primary cognitive symptom in idiopathic normal pressure hydrocephalus (iNPH); however, the neuropsychology of this disorder remains to be fully investigated. The objective of this study was to delineate a comprehensive profile of cognitive dysfunction in iNPH and evaluate the effects of cerebrospinal fluid (CSF) shunt surgery on cognitive dysfunction. A total of 32 iNPH patients underwent neuropsychological testing of memory, attention, language, executive function, and visuoperceptual and visuospatial abilities. Of these 32 patients, 26 were reevaluated approximately 1 year following CSF shunt surgery. The same battery of tests was performed on 32 patients with Alzheimer's disease (AD) and 30 healthy elderly controls. The iNPH patients displayed baseline deficits in attention, executive function, memory, and visuoperceptual and visuospatial functions. Impairments of attention, executive function, and visuoperceptual and visuospatial abilities in iNPH patients were more severe than in those with AD, whereas the degree of memory impairment was comparable to that in AD patients. A significant improvement in executive function was observed following shunt surgery. Patients with iNPH are impaired in various aspects of cognition involving both 'frontal' executive functions and 'posterior cortical' functions. Shunt treatment can ameliorate executive dysfunction.
    Dementia and geriatric cognitive disorders extra. 01/2011; 1(1):202-11.
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    ABSTRACT: Gait disturbance is the most common symptom in idiopathic normal-pressure hydrocephalus (iNPH). However, its pathophysiology in iNPH has not been clarified. Some researchers have hypothesized that the mesencephalic locomotor region, which is a functionally defined area in the brainstem playing an important role in locomotion, is involved in the development of gait disturbance in iNPH. The purpose of the study was to investigate whether the midbrain is involved in the manifestation of gait disturbance in iNPH. Twenty-one iNPH patients who showed clinical improvements after shunt surgery were studied. Brain magnetic resonance imaging (MRI) was performed and clinical symptoms were assessed before and 1 year after surgery. Gait disturbance was assessed by the Timed Up and Go test and gait subcategory of the iNPH Grading Scale, a validated assessment tool for iNPH symptoms. Anteroposterior, left-to-right diameter and cross-sectional areas of the midbrain were measured at the inferior collicular level of axial images in MRI. The diameters and cross-sectional area of the midbrain at baseline did not show significant correlation with gait assessments at baseline (Spearman's correlation). The midbrain measurement did not show significant difference between the baseline and postoperative values (paired t test), and its change rates did not show significant correlation with the change (rates) of the gait assessments. In this study there were no findings to suggest involvement of the midbrain in the manifestation of gait disturbance in iNPH. The hypothesis that the mesencephalic locomotor region is involved in the manifestation of gait disturbance in iNPH needs to be reconsidered.
    Journal of Neurology 12/2010; 258(5):820-5. · 3.58 Impact Factor
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    ABSTRACT: To investigate volumetric changes of the brain and cerebrospinal fluid (CSF) spaces after shunt surgery in shunt-responsive idiopathic normal-pressure hydrocephalus (iNPH), and correlations between the changes and postoperative clinical improvements. Twenty-one patients with shunt-responsive iNPH were studied. Magnetic resonance imaging (MRI) of the brain was performed before and 1year after surgery, and clinical symptoms were assessed by the iNPH Grading Scale, a validated assessment tool of the triad of iNPH, the Modified Rankin Scale, the Timed Up and Go Test, and neuropsychological tests including the Mini-Mental State Examination. The volumes of the left cerebral hemisphere, infratentorial brain, ventricles, and suprasylvian and infrasylvian subarachnoid CSF spaces were measured using an MRI-based volumetric technique. The volumes of the cerebral hemisphere and infratentorial brain did not change significantly after shunt surgery (p=0.231, 0.109, respectively). The volumes of the ventricles and infrasylvian subarachnoid CSF spaces were significantly decreased (p<0.0001, <0.05, respectively), with a mean change rate of -26.1% and -4.5%, respectively. The volumes of the suprasylvian subarachnoid CSF spaces increased significantly (p<0.0001), with a mean change rate of 43.5%. The decrease in ventricular volumes was significantly correlated with clinical improvement.
    Journal of the neurological sciences 09/2010; 296(1-2):7-12. · 2.32 Impact Factor
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    ABSTRACT: Dissociative amnesia usually follows a stressful event and cannot be attributable to explicit brain damage. It is thought to reflect a reversible deficit in memory retrieval probably due to memory repression. However, the neural mechanisms underlying this condition are not clear. We used fMRI to investigate neural activity associated with memory retrieval in two patients with dissociative amnesia. For each patient, three categories of face photographs and three categories of people's names corresponding to the photographs were prepared: those of "recognizable" high school friends who were acquainted with and recognizable to the patients, those of "unrecognizable" colleagues who were actually acquainted with but unrecognizable to the patients due to their memory impairments, and "control" distracters who were unacquainted with the patients. During fMRI, the patients were visually presented with these stimuli and asked to indicate whether they were personally acquainted with them. In the comparison of the unrecognizable condition with the recognizable condition, we found increased activity in the pFC and decreased activity in the hippocampus in both patients. After treatment for retrograde amnesia, the altered pattern of brain activation disappeared in one patient whose retrograde memories were recovered, whereas it remained unchanged in the other patient whose retrograde memories were not recovered. Our findings provide direct evidence that memory repression in dissociative amnesia is associated with an altered pattern of neural activity, and they suggest the possibility that the pFC has an important role in inhibiting the activity of the hippocampus in memory repression.
    Journal of Cognitive Neuroscience 04/2009; 22(3):602-13. · 4.49 Impact Factor