Comparison of glucose metabolism and cerebral blood flow during cortical motor activation.

Regions of cerebral cortex activated in normal subjects making simple, repetitive, voluntary wrist movements were studied with positron emission tomography (PET). The regional cerebral metabolic rate of glucose utilization was studied with 2-[18F]fluoro-2-deoxy-D-glucose (FDG), and regional cerebral blood flow was studied with 15O-labeled water. No significant activation was found with the cerebral metabolic rate studies. Studies of regional cerebral blood flow showed significant activation of the contralateral sensorimotor cortex region of 42%, of the ipsilateral sensorimotor cortex region of 19%, and of the medial frontal cortex of 30% compared with the resting state. Increases in blood flow in the contralateral sensorimotor cortex and medial frontal cortex were visible on every activated scan. Measurement of regional cerebral blood flow seems to be more sensitive than regional cerebral metabolic rate of glucose utilization for studying cortical activation with voluntary movement.

Studies of sensory and motor cortex physiology: with observations on akinesia in Parkinson's disease.

Magnetic stimulation of the brain can be used to investigate sensory and motor physiology and pathophysiology in intact humans. Although uncommon, it is possible for magnetic stimulation over sensorimotor cortex to produce paresthesis. With magnetic stimulation, it is also possible to block the conscious sensation of an electrical shock delivered to the index finger. The magnetic stimulus must be delivered in the interval from 300 msec before to 200 msec after the cutaneous shock and must be delivered over the contralateral hand region of the sensorimotor cortex. In a reaction time situation, the expected voluntary response may be delayed by a magnetic stimulus delivered over the sensorimotor cortex just before the movement. With the use of a relatively weak magnetic stimulus that does not produce a motor evoked potential (MEP) when the body part is at rest, but that will produce a response when the body part is activated, the reaction time can be divided into two periods. In the first period, there is no MEP and the motor cortex remains 'inexcitable'. In the second period, there is a gradual increase in MEP amplitude even though the voluntary electromyographic activity has not yet appeared. This 'excitable' period indicates the activation of motor cortex before the motor command is delivered. Application of this technique to the analysis of prolonged reaction time (akinesia) in patients with Parkinson's disease shows that the excitable period is prolonged. This describes the mechanism underlying the difficulty in the generation of a motor command in these patients.

The effects of smoking and cigarette nicotine content on smokers' preparation and performance of a psychosocially stressful task.

This study examined the effects of tobacco smoking and cigarette nicotine content on four dimensions of emotional behavior (peripheral autonomic, electrocortical, cognitive, and overt motor) during both the preparation for and the performance of a psychosocially stressful task (extemporaneous speaking). Three groups of experienced smokers either did not smoke, smoked a low-nicotine cigarette, or smoked a high-nicotine cigarette while they were preparing to perform the speaking task. All subjects reported prior to the experiment that they did experience smoking as relaxing and that they did experience a stronger desire to smoke under a variety of negative affective states compared to a variety of positive affective states. In spite of these verbal reports, however, neither the smoking ritual nor the nicotine content of the cigarette smoked had a significant effect on any of the four dimensions of the emotional behavior studied during either the preparation for or the performance of the task. These results were discussed in terms of previous psychophysiological studies utilizing different types of stressors and behavioral indices of emotion.