PubMed Health⌕ Search

Biomedical subjects

Kazumi Hirayama

Publications and source records attributed to Kazumi Hirayama.

10 recordsLinked to original sources
PubMed2006

Reactivation of medial temporal lobe and occipital lobe during the retrieval of color information: A positron emission tomography study.

It is widely accepted that memory traces of an event include various types of information about the content of the event and about the circumstances in which the individual experienced it. However, how these various types of information are stored and later retrieved is poorly understood. One hypothesis postulates that the retrieval of specific event information reactivates regions that were active during the encoding of this information, with the aid of binding functions of the medial temporal lobe (MTL) structures. We used positron emission tomography to identify the brain regions related to the encoding and retrieval of color information. Specifically, we assessed whether overlapping activity was found in both the MTL structures and color-related cortical regions during the encoding and retrieval of color information attached with meaningless shapes. During the study, subjects were asked to encode colored (red or green) and achromatic random shapes. At subsequent testing, subjects were presented with only achromatic shapes, which had been presented with or without colors during encoding, and were engaged in retrieval tasks of shapes and colors. Overlapping activity was found in the MTL and occipital lobe (the lingual and inferior occipital gyri) in the right hemisphere during the encoding and retrieval of meaningless shapes with color information compared with those without color information. Although there are some limitations to be considered, the present findings seem to support the view that the retrieval of specific event information is associated with reactivation of both the MTL structures and the regions involved during encoding of the information.

Adult↗
PubMed2005

Different MRI findings for normal elderly and very mild Alzheimer's disease in a community: implications for clinical practice the Tajiri Project.

To investigate magnetic resonance imaging (MRI) findings of very mild dementia, 485 participants were randomly selected in a community. Three hundred and forty participants were of Clinical Dementia Rating (CDR) 0 (healthy), 113 were of CDR 0.5 (questionable dementia), and 32 were of CDR 1 and 2 (including 20 Alzheimer's disease, AD). Cortical atrophy, white matter lesion, etc., were visually assessed. We found that each part of the brain showed atrophy in older adults for CDR 0. For CDR 0.5, the relationships between MRI findings and age were weaker, and for AD, there were no such relationship. Atrophy related with dementia severity was found to be limited to the lateral and medial temporal lobes. For CDR 0.5, amygdala atrophy was the only finding indicating CDR effect but no age effect. The amygdala or anterior entorhinal atrophy is important for discriminating very mild dementia from normal elderly.

Age Factors↗
PubMed2004

[Visual search training for a case of homonymous field defect with multiple visual dysfunctions].

A 72-year-old right handed man developed right homonymous hemianopia without macular sparing, left homonymous lower quadranopia with macular sparing, cerebral amblyopia, cerebral achromatopsia, impaired form vision, and mild right hemispatial neglect, after multiple cerebral infarctions, involving bilateral occipital cortices. His intelligence and memory were deteriorated moderately. He failed to notice objects located in the affected visual field, because of his severely impaired visual search. When ordinary lighting was used, he showed severe right-sided omissions on the line cancellation test. However, omissions were less marked under the brighter lighting. By using a modified method of Kerkhoff and Vianen (1994), he was trained to make saccadic eye movements toward affected regions to find a target and to search and point at targets arranged randomly. As the sensitivity for contrast of isoluminante red and green stimuli was preserved well at high spatial frequencies despite the decreaced contrast sensitivity for brightness, we used green targets as the training stimuli. After the training, search field and pointing range that could be covered by the patient increased in size for both green and white targets, and daily activities improved. Moreover, after the training, he no longer showed discrepancy in line cancellation performances between ordinary and brighter lighting conditions. In the follow up period, the search field and the performance on the line cancellation test were maintained, while the performance of pointing targets array declined. The family members complained of mild re-deterioration of daily activities. Then, the training for searching and pointing re-introduced at home. After the training, his pointing performance and daily activities, evaluated by questionnaires to his family members, improved again. In conclusion, it was suggested that disordered visual search after a homonymous field defect can be treated effectively, even if multiple visual dysfunctions were associated.

Aged↗
PubMed2003

[Back to the high school days: an abnormal remembering characterized by concurrent as well as alternating feeling to be in the past and present].

After the successful treatment of a hypothalamic germinoma, a 31-year-old right-handed male developed a difficulty in memory and admitted to our department for detailed evaluation. Neuropsychologically he showed no personality change, confabulation, misidentification, delusion or disorientation to physical time. Neither aphasia, dementia or frontal lobe dysfunction was found. However, he showed a moderate degree of anterograde amnesia and a retrograde amnesia for the last 5 years judged by a public events test. Moreover, his temporal markings of a correctly remembered event in the post high school days shifted strongly toward the high school days. This temporal location abnormality was largely limited to the events from the days of his graduation from the high school to the period 5 years prior to the present incident. He felt personal events happened during this period as if they had occurred in the high school days, although he well knew that they actually happened much later. At the same time he felt that memories of the high school days were abnormally vivid and recent. Most interestingly, he was found to have been experiencing a funny feeling that he was living in the high school days and the present at the same time. The feeling occurred either simultaneously or alternatively. In the latter instance, he would suddenly start behaving as if he were a high school student. He would start urging his wife to go to the school together immediately. This behavior would be over in several minutes. His consciousness was clear in these instances and there was no amnesia for these periods. A brain MRI with gadolinium enhancement showed a lesion extending in the hypothalamus, anterior thalamus, basal forebrain and midbrain bilaterally. After eight months this abnormality of temporal sensation disappeared. However, tendency to make the date of public event nearer to the high school period persisted. We hypothesize that impaired temporal estimation for an event recalled from the retrograde memory store and mis-arousal of familiarity evoked at the time of spontaneous recollection are responsible for double feeling of time of an experience. These phenomenon might be attributable to the partial destruction of the Papez' and the basolateral limbic circuits.

Adult↗
PubMed2003

[A case of probable dementia with Lewy bodies presenting with geographic mislocation and nurturing syndrome].

A 83-year-old right handed man developed nurturing syndrome and geographical mislocation (misidentification of places) as a result of dementia with Lewy bodies. He showed parkinsonism, fluctuating cognition, repeated falls, systematic delusions (delusional jealousy with vivid feeling of witness), rapid eye movement sleep behavior disorder, and mild dementia. His brain MRI showed atrophy of bilateral temporal tips and amygdala. A FDG-PET showed decrease of glucose metabolism in right frontal lobe and left temporo-parietal areas. He showed constructional disability, frontal lobe dysfunction, mild deterioration of immediate memory, mild anterograde amnesia, and retrograde amnesia for recent events. Aphasia, apraxia, agnosia, confabulation, or deterioration of facial perception was not noted. He could state the genealogy, ages and recent whereabouts of his relatives, and could state the locations and geographical relationships of his neighboring buildings. He insisted that his father's existence, who had died 52 years ago, although he talked about the episode of his death just before. One month after having a dream that his sick-room was in a fictitious branch of our hospital which located in his neighboring temple, he developed a delusion that his ward was actually in the temple. The former disorder seems to correspond to the nurturing syndrome described by Venneri et al. (2000), and the latter one suggested us that his dream was causally involved in the formation of geographical mis-localization. After Ramachandran's explanation for Capgras' syndrome, we hypothesized that mis-arousal of familiarity evoked by visual perception or memory was attributable to the dysfunction of amygdala, and failure of consistency-checking was caused by the dysfunction of the right frontal lobe.

Aged↗
PubMed2003

[Unawareness for homonymous visual field defect].

BACKGROUND: There was no report which dealt with the relationship between emotional state, degree of defective visual search, severity of hemianopic dyslexia, the episode when the patient became aware of the defect, and unawareness of visual loss in homonymous hemifield. OBJECTIVE: To investigate the relationship between degree of awareness and those factors that might be responsible for the unawareness, including the aspects listed above. METHODS: Four patients with visual field defects caused by a brain lesion after a stroke was investigated. Self rating of emotional state, search performance for an object among many placed on a table, and for text reading, as well as visual field, visual positive phenomena, and hemispatial neglect were evaluated. Degree of unawareness for field loss was evaluated by modified version of the method of Bisiach et al. (1985). In addition, the episodes when the patient became aware of the defect were asked. RESULT: In accordance with the previous studies, we found no relationship between the degree of awareness of field defect and anatomic lesions, co-existence of hemispatial neglect, or the degree of awareness of hemiplegia. However, the patient with neglect was unaware of their troubles in vision at all, whereas the patients without neglect were aware of the troubles but misinterpreted them as problems of the eyes including acuity. In accordance with previous studies, co-existence of visual hallucinations or illusions seemed to be associated with awareness of visual field defect. No relationship was found between the degree of awareness of field defect and emotional state, degree of field loss, degree of defective visual search, or severity of hemianopic dyslexia. Their responses to the inquiry about the degree of awareness of field defect were not consistent. Thus, the awareness of the field defect seemed to be difficult to be kept firmly in their mind. On the other hand, the patients could remember the episode when they became aware of the defect for the first time, being able to specify time, place, and situation. CONCLUSION: Levine (1990) suggested that the sensory loss in this sort of patients was never phenomenally immediate but instead must be discovered by observation and inference. Non-specificity of the lesion, qualitative difference in awareness between the patient with and without hemispatial neglect, association of positive visual phenomena and awareness, fluctuation of awareness, and dependence of awareness on personal experiences found in our patients, can be explained with this 'discovery' hypothesis.

Aged↗
PubMed2002

Contrast sensitivity of patients with severe motor and intellectual disabilities and cerebral visual impairment.

We attempt to evaluate the residual visual capacities of nine patients (seven males and two females; age range 4 to 35 years, mean 13.8 +/- 9.98) with cerebral visual impairment coupled with severe motor and intellectual disabilities by their contrast sensitivities to sine-wave gratings. Two methods were used for detecting the occurrence of ocular responses to stimuli: (1) detection of optokinetic nystagmus to drifting sinusoidal gratings by naked-eye observation and electronystagmography and (2) detection of ocular pursuit for a drifting Gabor patch by naked-eye observation. We succeeded in measuring the sensitivities of eight cases. For the remaining one case, only the Gabor method could be applied. Most cases showed low contrast sensitivity in both higher (2 and 4 cycles/degree) and lower (0.125 and 0.25 cycles/degree) spatial frequencies and relatively high contrast sensitivity in the middle (0.5 and 1 cycle/degree) range of spatial frequencies. We conclude that the residual visual capacities of patients with severe motor and intellectual disabilities and cerebral visual impairment can be measured fairly accurately by these behavioral methods.

Adolescent↗
PubMed2002

[A case of pure anarithmetia associated with disability in processing of abstract spatial relationship].

A 35-year-old right handed man developed pure anarithmetia after an left parieto-occipital subcortical hemorrhage. His intelligence, memory, language, and construction ability were all within normal limits. No hemispatial neglect, agraphia, finger agnosia, or right-left disorientation were noted. He showed no impairments in reading numbers aloud, pointing to written numbers, writing numbers to dictation, decomposition of numbers, estimation of numbers of dots, reading and writing of arithmetic signs, comprehension of arithmetic signs, appreciation of number values, appreciation of dots' number, counting aloud, alignment numbers, comprehension of the commulative law and the distributive law, retrieval of the table value (ku-ku), immediate memory for arithmetic problems, and use of electric calculator. He showed, however, remarkable difficulty even in addition and subtraction between one figure digits, and used counting on his fingers or intuitive strategy to solve the problems even when he could solve them. He could not execute multiplication and division, if the problems required other than the table value (ku-ku). Thus, he seemed to have difficulties in both of elemental arithmetic facts and calculating procedures. In addition, his backward digit span and reading of analogue clocks were deteriorated, and he showed logico-grammatical disorder of Luria. Our case supports the notion that there is a neural system which was shared in part between processing of abstract spatial relationship and calculation.

Adult↗