Abstract
(Englisch)
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The overall aim of this study is to investigate which brain structures respond to specific reward stimuli. The technique used is radiolabelled water activation studies and positron emission tomography (PET). The patterns of response in healthy controls will serve to compare these with various patient groups. We also propose a comparison between different control groups (male-female, smoker-no-smoker).
According to our results of 1996, we modified last year the research plan by using a different behavioral task in order to find common regions activated in all tasks with money reward and to increase the likelihood to find additional brain regions activated. We have measured regional cerebral blood flow (rCBF) distribution in each subject while performing a prelearned spatial and object delayed response task in two reinforcement conditions and in a baseline condition. The conditions were exactly identical except for the reinforcer used. In the baseline condition, the subjects did not get any feedback for their responses. In the reinforcement conditions, correct responses were either rewarded by money, a prototypical reward for humans, or by a simple 'ok' signal. Stimuli were presented on a computer screen. Responses were made with the right index finger. Subjects were instructed before the scans that they would receive the final indicated sum of money.
In 1998 we have increased and completed our groups of subjects. During the last two years, we have examined the following groups of subjects: 1) a group of 12 parkinsonian patients (PD Patients), 9 men and 3 women, age 41-70 years; 2) a group of 10 older healthy male volunteers, age 43-72 years; 3) a group of 11 older healthy female volunteers, age 43-69; 4) a group of 10 young healthy male volunteers, age 22-43 years; 5) a group of 10 young healthy female volunteers, age 22-32 years; 6) a group of 10 young healthy male volunteers, smokers, age 24-33 years; 7) a group of 9 male heroin addicts, age 23-39 years.
All the subjects are right-handed. None of the subjects of the control groups have a history of neurological or psychiatric disease. The subjects of the first five groups are non-smokers. We also have studied a group of 10 healthy male volunteers executing the task with the left hand in order to exclude a laterality effect and a group of 8 healthy male volunteers doing a control task, where the visual and motor stimulation were kept equal but in which no memory process was possible, in order to understand the task specific activation.
The results showed rCBF increases in right putamen, in right insular cortex, in right cingulum, in right and left cerebellum and in midbrain in the money reward condition in all groups of healthy volunteers. However we found some differences between the different groups of healthy volunteers in the money condition. In the group of young women , we found an rCBF increase in right frontal cortex and in left parahippocampal gyrus in addition to the already mentioned brain regions and no activation of the insular cortex or of the right cingulum. In the group of older women, we found an rCBF increase in right frontal cortex, in right temporal cortex, in left hippocampus, left parahippocampal gyrus and left thalamus. The young smokers showed an rCBF increase in right frontal cortex and in right amygdala. In parkinsonian patients, we didn't find any rCBF increase in the money reinforcement condition. Drug addicts showed an rCBF increase in right nucleus lentiformis, left frontal cortex, left midbrain and right and left cerebellum by comparing the 'ok' reinforcement condition with the money reward condition. No activation was found in the other comparisons with the money condition.
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