摘要:

AbstractPositron emission tomography (PET) studies of ligand binding lack sufficient anatomical detail to evaluate topographical variations in binding within each of the lobes of the human cerebral cortex. This study employed PET to localize [11C]diprenorphine binding to opioid receptors and magnetic resonance (MR) imaging for defining medial surface structures. Continuous arterial sampling for metabolite corrected [11C]diprenorphine levels and CNS blood flow were used to model the volume of distribution (VDtot) of binding for three subjects. The PET images of VDtotwere coregistered to the MR images for each case and 37 regions of interest were used to calculate VDtot. The VDtotwas averaged for the three cases and coregistered with an MR reconstruction of the medial surface and plotted onto a flat map of this region.The average VDtotshowed that binding was highest in anterior cingulate, rostral cingulofrontal transition, and prefrontal cortices, while binding in caudal parts of anterior cingulate and superior frontal cortices, and posterior cingulate cortex varied from high to low. Three statistical levels of binding were defined in relation to the high binding in perigenual area 24: high and equal to area 24, moderate and significantly lower than area 24 (p<0.01), or low (p<0.001). These levels of binding were plotted onto an unfolded map of the medial cortex. The VDtotwas high in rostral cortex, and a strip of high binding continued caudally on the dorsal lip of the cingulate gyrus. There were patches of high binding in cinguloparietal transition, posterior parietal, and supplementary motor cortices. Four regions had low binding: (1) areas 29 and 30 in the callosal sulcus, (2) fundus of the cingulate sulcus likely involving the cingulate motor areas, (3) fundus of the superior cingulate sulcus involving two divisions of supplementary motor cortex, and (4) sensorimotor cortex on the paracentral lobule. Variations in binding may reflect functional specializations such as low binding in the cingulate motor and visuospatial areas and high levels in areas involved in processing information with affective content. The higher sensitivity of three‐dimensional scanning and coregistration of PET and MR images makes it feasible to analyze single individuals and, by performing pixel‐by‐pixel spectral analysis and generation of parametric maps, statistical analyses are possible. © 1995 Wiley‐L

ISSN:1065-9471    

DOI:10.1002/hbm.460030102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to develop a method for obtaining simultaneous electrophysiological and functional magnetic resonance imaging data. Using phantom experiments and tests on several of the investigators, a method for obtaining simultaneous electrophysiological and fMRI data was developed and then tested in three volunteers including two task activation experiments. It was then applied in a sleep experiment (n = 12). Current limiting resistance and low‐pass filtering were added to the electrophysiological circuit. Potential high frequency current loops were avoided in the electrical layout near the subject. MRI was performed at 1.5 T using conventional and echo planar imaging sequences. There was no evidence of subject injury. Expected correlations were observed between the electrophysiological and fMRI data in the task activation experiments. The fMRI data were not significantly degraded by the electrophysiological apparatus. Alpha waves were detected from within the magnet in seven of the 15 experimental sessions. There was degradation of the electrophysiological data due to ballistocardiographic artifacts (pulsatile whole body motion time‐locked to cardiac activity) which varied between subjects from being minimal to becoming large enough to make detection of alpha waves difficult. We concluded that simultaneous fMRI and electrophysiological recording is possible with minor modifications of standard electrophysiological equipment. Our initial results suggest this can be done safely and without compromise of the fMRI data. The usefulness of this technique for studies of such things as sleep and epilepsy is promising. Applications requiring higher precision electrophysiological data, such as evoked response measurements, may require modifications based on ballistocardiographic effects. © 1995 Wiley‐Lis

ISSN:1065-9471    

DOI:10.1002/hbm.460030103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractRecent data from positron emission tomography (PET) imaging studies suggest the possibility of studying synaptic transmission in vivo in humans. The approach will require a synthesis of two established techniques: brain activation studies (conventionally performed by measuring regional cerebral blood flow or metabolism) and neurotransmitter receptor imaging (using radiolabelled ligands that bind to specific neuroreceptors). By comparing neuroreceptor binding in subjects at rest and while performing an activation task, it may be possible to determine whether a particular neurotransmitter is involved in performance of the task. The underlying principle is that endogenous neurotransmitter competes with the injected radioligand for the same receptors, thereby inhibiting ligand binding. This effect will be even more pronounced during activation, as the synaptic concentration of transmitter rises. Thus, activation of a specific neurotransmitter will be detected as adecreasein specific binding of the radioligand. In this paper we review neurophysiological and biochemical literature to estimate the endogenous neurotransmitter concentration changes that will be expected to occur during an activation task, using the dopamine system as an example. We calculate that the average synaptic dopamine concentration is ≈ 100 nM and that it approximately doubles during activation. This, along with consideration of the concentration of radioligand and affinities of the ligand and dopamine for dopamine receptors, suggests that physiological activation of a specific neurotransmitter system is likely to be detectable with PET. © 1995 Wiley‐Liss,

ISSN:1065-9471    

DOI:10.1002/hbm.460030104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractConsiderable evidence suggests that cognitive state affects local levels of neurotransmitter in the brain. We introduce a compartment model of neuroreceptor ligand kinetics to describe the effect of change in cognitive state on positron emission tomography (PET) signal dynamics. The model is used to establish optimal experimental conditions, timing of activation, and ligand characteristics, for detecting cognitive activation. The model, which follows free and bound endogenous neurotransmitter, describes the PET curve predicted for a single injection of radioligand in the presence or absence of activation. Activation was conceptualized as the performance of a task that raises the level of neurotransmitter that competes for receptor sites with the radioligand. Simulating the dopamine system, for example, required making assumptions regarding the kinetic rate constants for binding/dissociation of endogenous dopamine to/from the receptor and dopamine concentrations in the synapse. Simulations suggest that activation of dopamine should be detectable with PET and the D2 receptor ligand [11C]raclopride, although this ligand might not be optimal. Aspects of experimental design can be modified to optimize the likelihood of detecting neurotransmitter changes. The ideal radioligand for these studies should bind irreversibly to its receptor. Furthermore, the task should commence at injection time and last for at least 7 minutes. Optimal task duration depends on the dynamics of free radioligand in the tissue and can be determined via model simulations for any well‐characterized receptor ligand. Flow effects were shown to be distinguishable from those of neurotransmitter activation. General principles regarding desirable ligand characteristics and activation timing held for both the D2 receptor and the dopamine transporter site. © 1995 Wiley‐Liss,

ISSN:1065-9471    

DOI:10.1002/hbm.460030105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractLocal changes in cerebral hemodynamics are observed within a few hundred milliseconds of changes in neural activity. If hemodynamic responses are mediated by passive diffusion of a spatial signal (from the site of neural activity to the microvessels) then the dynamics of the response suggest a lower limit on the signal's apparent diffusion and elimination. The aim of this work was to estimate these limits and narrow the field of possible candidate substances.A simple biophysical simulation was used to examine how the time course of concentration changes in a spatial signal, at the site of action (microvessels), depends on key diffusion parameters (source geometry, apparent diffusion and elimination half‐life). The simulations suggested (1) that the rise in signal concentration is mostly a function of source geometry and diffusion. Conversely falls in concentration depend on elimination and (2) even when sources are very sparsely distributed Nitric Oxide would have a sufficiently fast diffusion and elimination to signal the early components of activity‐dependent hemodynamic response by passive diffusion. © 1995 Wiley‐Lis

ISSN:1065-9471    

DOI:10.1002/hbm.460030106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1065-9471    

DOI:10.1002/hbm.460030107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1065-9471    

DOI:10.1002/hbm.460030101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY