Role of the PAG in the Exercise Pressor Reflex during Varying Intensity of Activity

Abstract

Emerging evidence reports that the periaqueductal grey (PAG) in humans could be a major site for controlling the cardiovascular response to exercise. We previously hypothesised that the PAG is part of the subcortical neurocircuitry involved in the exercise pressor reflex. It is well known that as exercise intensity increases, the magnitude of the elevation of blood pressure from resting levels also increases. In order to identify whether the PAG has a role in controlling the magnitude of this increase, we assessed the spectral changes in local field potentials (LFPs) recorded from both the PAG and the thalamus in a patient who had undergone neurosurgery for the implantation of deep brain stimulating electrodes for the treatment of chronic pain. The patient was asked to perform light exercise (bicep curls), followed by arterial occlusion of the exercised limb in order to artificially stimulate the pressor response. The protocol was performed with a 2kg weight attached to the patient's wrist, and was then repeated with a 4kg weight. The PAG was compared to the thalamus i.e. the control area. The PAG showed significant increases in LFP power at frequencies from 4–12Hz (p<0.001) during occlusion following both 2kg exercise and 4kg exercise. However, in this case study, there did not appear to be a direct relationship between exercise intensity and neural activity. No change in thalamus activity was observed during occlusion.