An investigation into asymmetrical cortical regulation of salivary S-IgA in conscious man using transcranial magnetic stimulation

Abstract

Transcranial magnetic stimulation (TMS) can activate discrete areas of the cerebral cortex through the intact skull of healthy conscious volunteers. A magnetic coil generates a brief and focused magnetic field that penetrates the skull to activate the specific area of cerebral cortex beneath. This non-invasive procedure is painless, well tolerated by participants and now widely used to explore brain function. We used TMS to investigate asymmetrical cortical regulatory influences on one aspect of immune function: secretion of the antibody immunoglobulin A (S-IgA) into saliva. The right and left temporo-parietal-occipital cortex of 16 healthy, conscious subjects was stimulated on two different occasions, at least 1 week apart. There was an immediate increase in S-IgA concentration following both right and left stimulation. Saliva volume was reduced immediately post-right but not left stimulation. When secretion (μg/min) of S-IgA was calculated (controlling for changing saliva volume) an increase was apparent following left but not right hemisphere stimulation. Furthermore, a significant difference between the relationship between S-IgA concentration and volume of saliva post-left and right stimulation was observed. We conclude that TMS can be used as a tool to investigate cortical regulation of autonomic and immune function in healthy, conscious human subjects and that secretion of saliva and S-IgA is differentially affected by stimulation of the left and right cerebral cortex.