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W Schiffer

Publications and source records attributed to W Schiffer.

6 recordsLinked to original sources
PubMed1999

Task-specific deactivation patterns in functional magnetic resonance imaging.

In general, image analysis of cognitive experiments using functional magnetic resonance imaging techniques has emphasized those regions of the brain where increases in signal intensity, with regard to the reference state, are associated with activation. Nevertheless, a number of recent papers have shown that there are areas of deactivation as well. In this study, we have used a univariate analysis and echo-planar functional magnetic resonance imaging to address the relationship of the reference state to the deactivations. We employed two dichotomous covert tasks, orthographic lexical retrieval and pure visual retrieval, to contrast with the reference state (baseline) of silent counting. Our analysis yielded extensive, task-specific landscapes of regional incremental and decremental responses. We have specifically demonstrated that the decremental responses are not due to activation in the reference state. We have also demonstrated that they are not an artifact of a specific part of the image analysis, and propose that they represent a physiological, task specific signal that should be considered an integral component of neural networks representing brain function.

Adult↗
PubMed1998

Effect of a haloperidol challenge on regional brain metabolism in neuroleptic-responsive and nonresponsive schizophrenic patients.

OBJECTIVE: The CNS metabolic response to a neuroleptic challenge in treatment-responsive and nonresponsive schizophrenic patients was measured in order to examine the relation between treatment outcome and the capacity to alter neurochemical function in response to acute receptor blockade. METHOD: Positron emission tomography (PET) and [18F]fluorodeoxyglucose (FDG) were used to measure regional cerebral metabolism in seven schizophrenic patients judged to have been responsive to drug treatment previously and seven nonresponsive schizophrenic patients after a drug-free period of at least 3 weeks (baseline) and again 12 hours after administration of 5.0 mg of haloperidol. RESULTS: The haloperidol challenge caused widespread decreases in absolute metabolism in the nonresponsive patients but not the responsive patients. These group differences reflect the findings on the second (challenge) scans, since metabolic values at baseline were not statistically different in the two groups. The pattern of decreased metabolic activity in the nonresponders after the haloperidol challenge is similar to that previously observed in normal subjects. CONCLUSIONS: The metabolic response to drug challenge separates treatment responders from nonresponders and normal subjects. The results suggest that subtyping of schizophrenia (and other psychiatric disorders) can be achieved by measuring the physiologic response to a pharmacologic challenge in vivo with chemical brain-imaging techniques.

Adult↗
PubMed1975

[Studies on the degree of hypoxic and pharmacological coronary dilation (author's transl)].

On 11 isolated dog hearts, perfused with arterial blood of a donor dog, the degree of hypoxic dilatation and the maximum coronary blood flow achieved by adenosine were compared. The maximum coronary blood flow under adenosine infusion amounted to 455ml/minx100g, that means an increase of about 600% of the normal flow. If coronary venous pO2 was below 5mm Hg coronary blood flow was increased to 420ml/minx100g, which is 93% of the pharmacologically achieved maximum increase of the coronary blood flow. The difference between the maximum hypoxic and the maximum pharmacological dilatation is due to the method; it is caused by an increase of the extravascular component of coronary resistance under the influence of catecholamines in the case of hypoxic dilatation. It is pointed out that in order to achieve a maximum hypoxic dilatation oxygen pressure has to be below the critical value. It can be concluded that the intravascular component of coronary resistance is as low under hypoxic as under pharmacological dilatation.

Adenosine↗
PubMed1975

[The effect of increased extracellular calcium concentration on the hypoxic and pharmacologic hyperemia of skeletal muscle].

The influence of an increased Ca concentration on reactive hyperemia, work induced vasodilation and pharmacologically induced dilation (adenosine, nifedipine, verapamil) was studied in the blood perfused gastrocnemius of dogs. Reactive hyperemia, work induced vasodilation and increased blood flow by administration of adenosine could not be influenced by increased extracellular Ca concentrations. A Ca antagonism was demonstrated for nifedipine and verapamil, especially with regard to a diminution of the drug eff.

Adenosine↗