Reproducibility studies with 11C-DTBZ, a monoamine vesicular transporter inhibitor in healthy human subjects.
(1/970)
The reproducibility of (+/-)-alpha-[11C] dihydrotetrabenazine (DTBZ) measures in PET was studied in 10 healthy human subjects, aged 22-76 y. METHODS: The scan-to-scan variation of several measures used in PET data analysis was determined, including the radioactivity ratio (target-to-reference), plasma-input Logan total distribution volume (DV), plasma-input Logan Bmax/Kd and tissue-input Logan Bmax/Kd values. RESULTS: The radioactivity ratios, plasma-input Bmax/Kd and tissue-input Bmax/Kd all have higher reliability than plasma-input total DV values. In addition, measures using the occipital cortex as the reference region have higher reliability than the same measures using the cerebellum as the reference region. CONCLUSION: Our results show that DTBZ is a reliable PET tracer that provides reproducible in vivo measurement of striatal vesicular monoamine transporter density. In the selection of reference regions for DTBZ PET data analysis, caution must be exercised in circumstances when DTBZ binding in the occipital cortex or the cerebellum may be altered. (+info)
Two similar cases of encephalopathy, possibly a reversible posterior leukoencephalopathy syndrome: serial findings of magnetic resonance imaging, SPECT and angiography.
(2/970)
Two young women who had encephalopathy that resembled reversible posterior leukoencephalopathy syndrome are presented. The brain magnetic resonance imaging (MRI) of these patients exhibited similar T2-high signal lesions, mostly in the white matter of the posterior hemispheres. Xe-SPECT during the patients' symptomatic period showed hypoperfusion in the corresponding areas, and angiography demonstrated irregular narrowing of the posterior cerebral artery. Clinical manifestations subsided soon after treatment, and the abnormal radiological findings also were almost completely resolved. Thus, we concluded that transient hypoperfusion followed by ischemia and cytotoxic edema might have had a pivotal role in these cases. (+info)
Evaluation of dopaminergic presynaptic integrity: 6-[18F]fluoro-L-dopa versus 6-[18F]fluoro-L-m-tyrosine.
(3/970)
The effectiveness of 6-[18F]fluoro-L-m-tyrosine (6FMT) to evaluate dopamine presynaptic integrity was compared to that of 6-[18F]fluoro-L-dopa (6FDOPA) in vivo by positron emission tomography (PET). Six normal and six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkeys received 6FDOPA and 6FMT PET scans on separate occasions with identical scanning protocols. Four measures, the rate of uptake of tracer into striatum using either the arterial input function (Ki) or the activity in the occipital cortex as the input function (Kc), the rate of loss of striatal radioactivity (k(loss)), and an index of "effective turnover" of dopamine (k(loss)/Ki), were obtained for both tracers during extended PET studies. 6-[18F]Fluoro-L-m-tyrosine was as effective as 6FDOPA in separating normals from MPTP-lesioned subjects on the basis of the uptake rate constants Ki and Kc. However, in contrast to 6FDOPA, it was not possible to differentiate the normal from the lesioned animal using k(loss) or k(loss)/Ki for 6FMT. Thus, FMT appears to be a reasonable, highly specific tracer for studying the activity of aromatic dopa decarboxylase enzyme as an index of presynaptic integrity. However, if one is interested in investigating further the metabolic pathway and obtaining an in vivo estimate of the effective turnover of dopamine (after pharmacologic manipulation, for example), 6FDOPA remains the tracer of choice. (+info)
Topographic organization of human visual areas in the absence of input from primary cortex.
(4/970)
Recently, there has been evidence for considerable plasticity in primary sensory areas of adult cortex. In this study, we asked to what extent topographical maps in human extrastriate areas reorganize after damage to a portion of primary visual (striate) cortex, V1. Functional magnetic resonance imaging signals were measured in a subject (G.Y.) with a large calcarine lesion that includes most of primary visual cortex but spares the foveal representation. When foveal stimulation was present, intact cortex in the lesioned occipital lobe exhibited conventional retinotopic organization. Several visual areas could be identified (V1, V2, V3, V3 accessory, and V4 ventral). However, when stimuli were restricted to the blind portion of the visual field, responses were found primarily in dorsal extrastriate areas. Furthermore, cortex that had formerly shown normal topography now represented only the visual field around the lower vertical meridian. Several possible sources for this reorganized activity are considered, including transcallosal connections, direct subcortical projections to extrastriate cortex, and residual inputs from V1 near the margin of the lesion. A scheme is described to explain how the reorganized signals could occur based on changes in the local neural connections. (+info)
Cortical visuomotor integration during eye pursuit and eye-finger pursuit.
(5/970)
To elucidate cortical mechanisms of visuomotor integration, we recorded whole-scalp neuromagnetic signals from six normal volunteers while they were viewing a black dot moving linearly at the speed of 4 degrees /sec within a virtual rectangle. The dot changed its direction randomly once every 0.3-2 sec. The subject either (1) fixated a cross in the center of the screen (eye fixation task), (2) followed the moving dot with the eyes (eye pursuit task), or (3) followed the dot with both the eyes and the right index finger (eye-finger pursuit task). Prominent magnetic signals, triggered by the changes of the direction of the dot, were seen in all conditions, but they were clearly enhanced by the tasks and were strongest during the eye-finger pursuit task and over the anterior inferior parietal lobule (aIPL). Source modeling indicated activation of aIPL [Brodmann's area (BA) 40], the posterosuperior parietal lobule (SPL; BA 7), the dorsolateral frontal cortex (DLF; BA 6), and the occipital cortex (BA 18/19). The activation first peaked in the occipital areas, then in the aIPL and DLF, and some 50 msec later in the SPL. Our results suggest that all these areas are involved in visuomotor transformation, with aIPL playing a crucial role in this process. (+info)
Unidirectional dyslexia in a polyglot.
(6/970)
Alexia is usually seen after ischaemic insults to the dominant parietal lobe. A patient is described with a particular alexia to reading Hebrew (right to left), whereas no alexia was noted when reading in English. This deficit evolved after a hypertensive right occipitoparietal intracerebral haemorrhage, and resolved gradually over the ensuing year as the haematoma was resorbed. The deficit suggests the existence of a separate, language associated, neuronal network within the right hemisphere important to different language reading modes. (+info)
Elementary visual hallucinations, blindness, and headache in idiopathic occipital epilepsy: differentiation from migraine.
(7/970)
This is a qualitative and chronological analysis of ictal and postictal symptoms, frequency of seizures, family history, response to treatment, and prognosis in nine patients with idiopathic occipital epilepsy and visual seizures. Ictal elementary visual hallucinations are stereotyped for each patient, usually lasting for seconds. They consist of mainly multiple, bright coloured, small circular spots, circles, or balls. Mostly, they appear in a temporal hemifield often moving contralaterally or in the centre where they may be flashing. They may multiply and increase in size in the course of the seizure and may progress to other non-visual occipital seizure symptoms and more rarely to extra-occipital manifestations and convulsions. Blindness occurs usually from the beginning and postictal headache, often indistinguishable from migraine, is common. It is concluded that elementary visual hallucinations in occipital seizures are entirely different from visual aura of migraine when individual elements of colour, shape, size, location, movement, speed of development, duration, and progress are synthesised together. Postictal headache does not show preference for those with a family history of migraine. Most of the patients are misdiagnosed as having migraine with aura, basilar migraine, acephalgic migraine, or migralepsy simply because physicians are not properly informed of differential diagnostic criteria. As a result, treatment may be delayed for years. Response to carbamazepine is excellent and seizures may remit. (+info)
Spatial characteristics of cerebral polyopia: a case study.
(8/970)
A 41-year-old woman showed bilateral monocular polyopia and an incomplete, right-sided homonymous hemianopia following bilateral cerebral strokes confirmed by neuroimaging. She was tested with briefly-presented visual stimuli to determine whether her polyopic images varied with visual field position of stimuli which evoked them. Stimuli close to her scotoma elicited polyopic images at shorter latency and higher probability than did stimuli more distant from it. RS could maintain stable fixation on small stimuli, suggesting that eye movements were not responsible for her polyopia. We discuss the possibility that cerebral polyopia is due to recoding of visual receptive fields in primary visual cortex and that bilateral occipital lesions are a causative factor in the genesis of the disorder. (+info)