Sympathetic activity at rest and motor brain areas: FDG-PET study.

Although recent studies identified brain areas which are involved in short term activation of the sympathetic nervous system, little is known about brain mechanisms which generate the individual variability of basal autonomic activity. In this fluorodeoxyglucose positron emission tomography study (FDG-PET), we aimed to identify brain regions, which covary with function parameters of the autonomic nervous system at rest. Therefore, FDG-PET (Siemens, Germany) was performed twice in 14 healthy resting subjects (7 m, 7 f; mean age 29.5 years) while different parameters of autonomic function were assessed simultaneously: Blood pressure, heart rate, power spectra of heart rate variability (HF/LF ratio) and plasma catecholamines. In order to control for attention, subjects had to focus visual affective neutral presentations during the experiment. Correlation analysis was performed as a region of interest analysis using SPM2 software (p<0.001 uncorrected). Sympathetic activity at rest varied substantially between subjects. There were significant positive correlations between increase of regional cerebral glucose metabolism (rCGM) of the heads of caudate nuclei on both sides and the HF/LF ratio of heart rate variability. Furthermore, significant negative correlations between both heart rate and plasma catecholamines and rCGM decreases of caudate nuclei heads were found. In addition, there was a positive correlation between plasma catecholamines and primary motor cortex activation. Autonomic nervous system at rest seems to be partially interlocked with activity of motor brain regions - the caudate nuclei and the motor cortex. This might have clinical implications for the understanding of stress-related disorders, which are frequently accompanied by increased sympathetic activity as well as muscle tone.