Activity Changes in the Human Brain Due to Vibratory Stimulation of the Hand Studied with Positron Emission Tomography

Abstract

With positron emission tomography (PET) one can measure the activity of neuronal populations in the human brain indirectly by measurements of the regional cerebral blood flow (rCBF) or of the regional metabolic rate of glucose (rCMRGlu) or oxygen (rCMRO₂) (Raichle 1987). The accurate localization of functional information in the PET images demands, however, integration with additional anatomical information from computerized tomography (CT) or magnetic resonance imaging (MRI). Usually, the changes in rCBF or rCMRGlu that are specifically induced by physiological or psychological stimulation are compared with the resting control state (Roland and Larsen 1976; Mazziotta et al. 1981). Rest is, however, also a specific functional state of brain activity, which in the electroencephalogram is characterized by the expression of a-activity in the parietooccipital leads and in rCBF measurements by high flow in prefrontal areas (Ingvar 1979). Furthermore, PET studies have shown that in rest the mean global CBF and CMRGlu are higher than during sleep (Heiss et al. 1985; Marquet et al. 1990) but lower than during cognitive tasks (Cameron et al. 1990; Roland et al. 1987) and unchanged during simple motor and sensory activation tasks (Fox and Raichle 1984; Fox et al. 1987). These observations raise two questions: (1) Does brain work activate numerous regions? (2) Does brain work depress the activity of neuronal populations?.