Abstract

Electrical deep brain stimulation (DBS) in humans has previously been shown to alter cardiovascular parameters such as blood pressure, pulse pressure and the response of blood pressure to standing. An alteration in the autonomic nervous system is likely to be responsible for these changes. We have directly recorded sympathetic nerve activity (MSNA) in humans with deep brain stimulating electrodes during on/off stimulation phases of subcortical structures known to modulate arterial blood pressure. Patients undergoing deep brain stimulation of the periaqueductal gray (PAG) and subthalamic nucleus (STN) for chronic neuropathic pain and Parkinson’s disease, respectively, were selected. Our results on the effects of DBS on the STN and PAG show differentiated changes in sympathetic outflow during on/off stimulation periods, which are reflected in a differentiated hemodynamic response. While it is not known how the differentiated control of sympathetic discharge probability and strength is brought about, it has been suggested that baroreflex modulation of sympathetic outflow occurs at two CNS locations. The dorsal PAG which is involved in pain regulation and cardiovascular control is also a major site in processing fear and anxiety. Single vasoconstrictor fibre firing probability during rest was recently shown to be increased in patients with panic disorder. A shift towards a greater number of high amplitudes and hence number of fibres firing together as observed during PAG stimulation is in keeping with these findings. Our STN results also suggest this area is an important part of the neurocircuitry controlling the arterial baroreflex.