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T O Videen

Publications and source records attributed to T O Videen.

At least 37 records · Page 2Linked to original sources
PubMed1998

Blood-to-brain glucose transport and cerebral glucose metabolism are not reduced in poorly controlled type 1 diabetes.

To test the hypothesis that blood-to-brain glucose transport is reduced in poorly controlled type 1 diabetes, we studied seven patients with a mean (+/- SD) HbA1c level of 10.1 +/- 1.2% and nine nondiabetic subjects during hyperinsulinemic, mildly hypoglycemic (approximately 3.6 mmol/l, approximately 65 mg/dl) glucose clamps. Blood-to-brain glucose transport and cerebral glucose metabolism were calculated from rate constants derived from blood and brain time-activity curves--the latter determined by positron emission tomography (PET)--after intravenous injection of [1-(11)C]glucose using a model that includes a fourth rate constant to account for regional egress of 11C metabolites. Cerebral blood flow and cerebral blood volume were determined with intravenous H2(15)O and inhaled C(15)O, respectively, also by PET. At plateau plasma glucose concentrations of 3.6 +/- 0.0 and 3.7 +/- 0.1 mmol/l, rates of blood-to-brain glucose transport were similar in the two groups (23.7 +/- 2.2 and 21.6 +/- 2.9 micromol x 100 g(-1) x min(-1), P = 0.569, in the control subjects and the patients, respectively). There were also no differences in the rates of cerebral glucose metabolism (16.8 +/- 0.8 and 16.3 +/- 1.2 micromol x 100 g(-1) x min(-1), P = 0.693, respectively). Plasma epinephrine (1,380 +/- 340 vs. 450 +/- 170 pmol/l, P = 0.0440) and glucagon (26 +/- 5 vs. 12 +/- 1 pmol/l, P = 0.0300) responses to mild hypoglycemia were reduced in the patients with type 1 diabetes. We conclude that neither blood-to-brain glucose transport nor cerebral glucose metabolism is measurably reduced in people with poorly controlled type 1 diabetes.

Adult↗
PubMed1995

Blood flow changes in human somatosensory cortex during anticipated stimulation.

Positron emission tomography (PET) measurements of brain blood flow were used to monitor changes in the human primary and secondary somatosensory cortices during the period when somatosensory stimuli were expected. In anticipation of either focal or innocuous touching, or localized, painful shocks, blood flow decreased in parts of the primary somatosensory cortex map located outside the representation of the skin area that was the target of the expected stimulus. Specifically, attending to an impending stimulus to the fingers produced a significant decrease in blood flow in the somatosensory zones for the face, whereas attending to stimulation of the toe produced decreases in the zones for the fingers and face. Decreases were more prominent in the side ipsilateral to the location of the expected stimulus. No significant changes in blood flow occurred in the region of the cortex representing the skin locus of the awaited stimulation. These results are concurrent with a model of spatial attention in which potential signal enhancement may rely on generalized suppression of background activity.

Adult↗
PubMed1993

Tactile-vibration-activated foci in insular and parietal-opercular cortex studied with positron emission tomography: mapping the second somatosensory area in humans.

Positron emission tomographic measurements were used to study the distribution of focal changes in cerebral blood flow (CBF) induced by vibrotactile stimulation of the hands and feet in 22 normal humans. Subjects received bolus intravenous saline injections containing approximately 60 mCi 15O-labeled water. Active regions during stimulation were defined relative to resting, nonstimulated states. Scan data from different subjects were averaged after stereotactic standardization. The results identified previously described foci of increased CBF in postrolandic sensory cortex (primary somatosensory cortex) and supplementary motor cortex. New statistical testing procedures provided independent demonstrations of two additional increases in regional CBF, bilaterally, within the sylvian fissure. One site along the parietal operculum corresponded to previous conjectures about a second somatosensory cortical area (SII) in humans. Another site also was found on the insula. No topographic organization was found in either location. The discussion considers these responsive areas to innocuous tactile stimuli in reference to suggestions about a role for SII in the perception of pain.

Adult↗
PubMed1992

Activation of the hippocampus in normal humans: a functional anatomical study of memory.

We studied regional cerebral blood flow using the H2(15)O method while normal subjects performed four similar tasks involving three-letter word beginnings (stems). Prior to each task, subjects studied a list of words. Local blood flow was then monitored during a 40-sec period while subjects (i) silently viewed word stems, (ii) completed stems to form the first words to come to mind, but the stems were not the beginnings of any study words (baseline), (iii) completed stems and half of them could form study words (priming), or (iv) tried to recall study words, and half of the stems could form these words (memory). There were three major findings. (i) The memory task engaged the right hippocampal region when the memory task was compared to either the baseline or the priming condition. The right hemispheric locus suggests that performance is driven by the visual characteristics of the words rather than by semantic or phonetic analysis. (ii) In the priming-minus-baseline comparison, there was reduction in blood flow in the right posterior cortex. (iii) Right prefrontal cortex was activated in the memory-minus-baseline condition. The results provide evidence for selective activation of the human hippocampal region in association with memory function. The results also lead to a suggestion about the neural basis of repetition priming: following presentation of a stimulus, less neural activity is required to process the same stimulus.

Adult↗
PubMed1992

Blinded clinical evaluation of positron emission tomography for diagnosis of probable Alzheimer's disease.

We evaluated the sensitivity and specificity of positron emission tomography for diagnosis of probable Alzheimer's disease under conditions similar to those encountered in the routine clinical practice of nuclear medicine. We obtained tomographic images of regional cerebral blood flow from three groups of subjects: (1) 13 subjects, ages 69 to 84, who had probable Alzheimer's disease diagnosed by validated clinical criteria; (2) 15 subjects, ages 57 to 77, who had Parkinson's disease without dementia; and (3) 11 subjects, ages 65 to 83, who were normal. Three blinded reviewers, who had not previously seen the images, categorized them as normal, bilateral temporoparietal flow defects typical of Alzheimer's disease, or other abnormality. Consensus interpretation demonstrated sensitivity of 0.38 (5/13) and specificity of 0.88 (23/26) for identifying patients with probable Alzheimer's disease. Thus, the criterion of bilateral temporoparietal reduction in cerebral blood flow used in this study did not have sufficient sensitivity to be of clinical value. While other criteria may be developed to improve diagnostic accuracy, clinical utility can be established only by testing for validity in patients with a full spectrum of complicating neurologic and psychiatric conditions for whom diagnosis is uncertain and who are then followed longitudinally to determine clinical outcome or pathologic findings.

Aged↗
PubMed1992

A functional anatomical study of unipolar depression.

The functional neuroanatomy of unipolar major depression was investigated using positron emission tomography to measure differences in regional cerebral blood flow (BF). A relatively homogeneous subject group was obtained using criteria for familial pure depressive disease (FPDD), which are based upon family history as well as upon symptoms and course. Because of the absence of certain knowledge about the pathophysiology of mood disorders and their underlying functional neuroanatomy, we used data obtained from the subtraction of composite images from one-half of depressed and control subjects to identify candidate regions of interest. The major cortical region defined in this manner was statistically tested on a second set of subjects. Using this strategy, we found increased BF in an area that extended from the left ventrolateral prefrontal cortex onto the medial prefrontal cortical surface. Based upon the connectivity between these portions of the prefrontal cortex and the amygdala and evidence that the amygdala is involved in emotional modulation, activity was measured in the left amygdala and found to be significantly increased in the depressed group. A separate group of subjects with FPDD who were currently asymptomatic were also imaged to determine whether these findings represented abnormalities associated with the depressed state, or with a trait difference that might underlie the tendency to become depressed. Only the depressed group had increased activity in the left prefrontal cortex, suggesting that this abnormality represents a state marker of FPDD. Both the depressed and the remitted groups demonstrated increased activity in the left amygdala, though this difference achieved significance only in the depressed group. This suggests that the abnormality involving the left amygdala may represent a trait marker of FPDD, though further assessment in a larger sample size is necessary to establish this. These data along with other evidence suggest that a circuit involving the prefrontal cortex, amygdala, and related parts of the striatum, pallidum, and medial thalamus is involved in the functional neuroanatomy of depression.

Adult↗
PubMed1988

Regional correction of positron emission tomography data for the effects of cerebral atrophy.

Given the low spatial resolution of positron emission tomography (PET), regional measurements of neural tissue are often inaccurate because of the presence of non-neural elements and to mixtures of different tissue types within the volume of space influencing the measurements. These effects are significant in scans of brains both with and without atrophy, but are particularly significant when comparing measurements of brains with atrophy with those of normals, as is typically done in studies of aging and dementia. Previous attempts to correct for cerebral atrophy have been limited to global measurements. Using computer simulations, we illustrate the effects of atrophy and describe a method for correcting regional PET data to represent units of actual neural tissue volume.

Atrophy↗
PubMed1987

Brain blood volume, flow, and oxygen utilization measured with 15O radiotracers and positron emission tomography: revised metabolic computations.

We have revised our methods for calculating regional blood volume, flow, oxygen extraction, and oxygen utilization from positron emission tomography data obtained using 15O-labeled radiotracers. These revisions include radioactive decay explicitly within the model equations instead of requiring all measured activity to be corrected for decay prior to incorporation in the equations. The revised equations yield small but significant differences in the computed values.

Blood Volume↗
PubMed1986

Penicillin-induced epileptiform activity does not prevent ocular dominance shifts in monocularly deprived kittens.

Epileptiform activity was induced in the visual cortex with penicillin to test whether it would prevent the ocular dominance shift that normally occurs in monocularly deprived kittens. The eyelids of one eye of 5-week-old kittens were sutured shut for several days. During this period, whenever the kittens were in the light, aqueous penicillin in artificial cerebrospinal fluid (CSF) or just CSF was applied in a cylinder mounted over the visual cortex. Electroencephalograms monitored during the period of deprivation indicated nearly continuous interictal spiking in the visual cortex. Extracellular recordings were made of cells in the region directly under the position of the cylinder. 14C-labeled 2-deoxyglucose autoradiography in a control kitten showed that this area had considerably increased metabolism during epileptiform activity. The majority of cortical cells were dominated by the non-deprived eye in both epileptic and control kittens, with no noticeable difference between them. These preliminary observations indicate that the disruption of cortical activity that occurs during interictal epileptiform activity does not prevent the ocular dominance shift in monocularly deprived kittens.

Animals↗
PubMed1985

Substantial reduction of noradrenaline in kitten visual cortex by intraventricular injections of 6-hydroxydopamine does not always prevent ocular dominance shifts after monocular deprivation.

Ten kittens had cannulas inserted into their lateral ventricles for daily injections of 6-hydroxydopamine (6-OHDA). At 5-6 weeks of age one eye was sutured shut, and one week later recordings were made from the visual cortex to assay the ocular dominance of a sample of cells. In six kittens the injections of 6-OHDA were continued until the day before recording, while in four kittens the injections were stopped around the time of eye suture, on the assumption that continued injections of 6-OHDA over several days has effects that are not specific to the noradrenaline (NA) system and that the two procedures might show different results. In all animals the concentration of NA in the visual cortex near the site of recording was reduced by approximately 90%. In all animals the ocular dominance histograms recorded from the visual cortex were shifted so that the majority of cells (83 +/- 13%) were dominated by the open eye. There were no substantial differences between the two groups of experimental animals or between the experimental animals and two control animals that had cannulas implanted and ascorbate alone injected without 6-OHDA. We conclude that the concentration of NA in the visual cortex can be reduced substantially by injections of 6-OHDA into the lateral ventricle without preventing the shift in ocular dominance that usually occurs after suturing shut the eyelids of one eye.

Animals↗
PubMed1985

DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) depletes noradrenaline in kitten visual cortex without altering the effects of monocular deprivation.

Kittens were given N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to deplete cortical noradrenaline (NA) in order to test whether this would affect the results of monocular deprivation. Seven kittens that received DSP-4 systemically had cortical NA depleted by 25 to 98%, and six kittens that received DSP-4 in the lateral ventricle had cortical NA depleted by 72 to 92%. In all of these kittens, suturing shut the eyelids of one eye for 1 to 2 weeks produced a visual cortex in which most neurons responded only or most strongly to the eye that remained open. These results are considered together with previous results from our laboratory on monocular deprivation and NA depletion. There is little difference between the ocular dominance histograms of depleted and undepleted animals and little correlation between the extent of the ocular dominance shift and the extent of NA depletion. We conclude that depletion of cortical NA by itself does not prevent the cortical effects of monocular deprivation and that, where such an effect has been found, it may be due to some other factor.

Amines↗
PubMed1984

Substantial reduction of cortical noradrenaline by lesions of adrenergic pathway does not prevent effects of monocular deprivation.

We tested the theory that depletion of noradrenaline reduces the plasticity of the visual cortex in kittens by using another method of depletion. Lesions were made in the lateral hypothalamus to interrupt fibers in the dorsal noradrenergic bundle going from the locus ceruleus to the telencephalon. The lesions were induced at approximately 3 1/2 weeks of age in kittens; approximately 2 weeks later one eye was sutured shut, and about 10 days after that cells were recorded in the visual cortex. The location of the lesions was verified histologically, and the effect of the lesions was verified by noradrenaline analyses (high pressure liquid chromatography-electrochemistry) of samples from the visual cortex. The noradrenaline content of the visual cortex was reduced by 70 to 90%. However, the majority of cells recorded in the visual cortex could not be driven through the eye that had been sutured closed. The ocular dominance histograms for cells in the visual cortex were indistinguishable from those of kittens that were monocularly deprived for a similar period in the "critical period" and that had normal amounts of noradrenaline in their visual cortex. Therefore, we conclude that reduction of the noradrenaline content of the visual cortex by 70 to 90% is insufficient, by itself, to prevent the physiological changes that occur in the visual cortex after monocular deprivation.

Animals↗
PubMed1984

The effect of norepinephrine on visual cortical neurons in kittens and adult cats.

The responses of visual cortical neurons during iontophoresis of norepinephrine (NE) were compared in kittens and adult cats. One type of neuronal "plasticity" (the ability of visual cortical neurons to have their response properties markedly altered during exposure to a restricted visual environment) normally occurs only in young kittens and has been hypothesized to depend on the presence of NE. We investigated this hypothesis in terms of a model of synaptic plasticity which suggested that NE would selectively enhance the evoked responses of neurons and that this enhancement might exist to a greater extent in kittens than in adult cats. The responses of 72% (43 of 60) of all neurons sampled decreased during NE iontophoresis, while the responses of only a few neurons (3 of 60) increased. Reduced activity occurred in roughly equal percentages of simple and complex cells. We also looked for differences in NE modulation of the "signal-to-noise" ratio of neurons. Most neurons had little spontaneous activity, but, of those that did, the signal-to-noise ratio increased in some instances and decreased in others. No difference in any of the effects of NE was observed between kittens and adult cats. The role of NE in cortical plasticity is discussed.

Animals↗
PubMedDate not supplied

Importance of hemodynamic factors in the prognosis of symptomatic carotid occlusion.

CONTEXT: The relative importance of hemodynamic factors in the pathogenesis and treatment of stroke in patients with carotid artery occlusion remains controversial. OBJECTIVE: To test the hypothesis that stage II cerebral hemodynamic failure (increased oxygen extraction measured by positron emission tomography [PET]) distal to symptomatic carotid artery occlusion is an independent risk factor for subsequent stroke in medically treated patients. DESIGN AND SETTING: Prospective, blinded, longitudinal cohort study of patients referred from a group of regional hospitals between 1992 and 1996. PATIENTS: From 419 subjects referred, 81 with previous stroke or transient ischemic attack in the territory of an occluded carotid artery were enrolled. All were followed up to completion of the study, with average follow-up of 31.5 months. MAIN OUTCOME MEASURES: Telephone contact every 6 months recorded the subsequent occurrence of all stroke, ipsilateral ischemic stroke, and death. RESULTS: Stroke occurred in 12 of 39 patients with stage II hemodynamic failure and in 3 of 42 patients without (P = .005); stroke was ipsilateral in 11 of 39 patients with stage II hemodynamic failure and in 2 of 42 patients without (P = .004). Six deaths occurred in each group (P = .94). The age-adjusted relative risk conferred by stage II hemodynamic failure was 6.0 (95% confidence interval [CI], 1.7-21.6) for all stroke and 7.3 (95% CI, 1.6-33.4) for ipsilateral stroke. CONCLUSIONS: Stage II hemodynamic failure defines a subgroup of patients with symptomatic carotid occlusion who are at high risk for subsequent stroke when treated medically. A randomized trial evaluating surgical revascularization in this high-risk subgroup is warranted.

Aged↗
PubMedDate not supplied

Practice-related changes in human brain functional anatomy during nonmotor learning.

Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can be used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.

Adult↗
PubMedDate not supplied

Multiple foci in parietal and frontal cortex activated by rubbing embossed grating patterns across fingerpads: a positron emission tomography study in humans.

Somatosensory representations occupy parietal postcentral gyral (S1) and lateral sulcal-opercular cortex (S2). To address the issue of possible multiple activation foci in these regions and possible differences due to stimulating skin directly or through an imposed tool, we studied changes in cerebral blood flow with positron emission tomography during passive tactile stimulation of one or two fingertips. Restrained fingers were rubbed with embossed gratings using a rotating drum stimulator in 11 subjects. For different scans, gratings touched the skin directly for optimal stimulation of cutaneous receptors (called skin mode stimulation) or indirectly through an imposed guitar plectrum snugly fitted to the same fingers (called tool mode stimulation). The latter was expected to stimulate deep receptors better. Subjects estimated roughness after each scan. Direct skin contact activated statistically validated foci in both hemispheres. On the contralateral side these foci occurred in the anterior and posterior limbs of the postcentral gyrus and on the ipsilateral side only in the posterior limb. Tool mode stimulation activated one contralateral focus that was in the posterior limb of the postcentral gyrus. These results suggest at least two maps for distal fingertips in S1 with the anterior and posterior foci corresponding, respectively, to activations in area 3b and the junction between areas 1 and 2. In contralateral S2, skin mode stimulation activated a peak that was anterior and medial to a focus associated with tool mode stimulation. The magnitude of PET counts contralateral to stimulation was greater in the anterior S1 and the S2 regions during initial scans but reversed to more activation in the posterior S1 during later scans. These short-term practice effects suggest changes in neural activity with stimulus novelty.

Adult↗