Mechanisms of physiological gustatory sweating and flushing in the face.

Mechanisms of physiological gustatory sweating and flushing were investigated in 21 patients with a facial nerve lesion compromising parasympathetic outflow to the lacrimal gland, and in 13 patients undergoing diagnostic blockade of the stellate ganglion. Vascular responses and electrodermal activity (which reflects sweating) were monitored on each side of the forehead before and during gustatory stimulation with chillies or Tabasco sauce (derived from chillies). Vascular responses in the cheeks were also monitored in 14 patients with a facial nerve lesion. Sympathetic blockade increased gustatory vasodilatation but prevented gustatory sweating on the blocked side of the forehead. A facial nerve lesion did not affect gustatory sweating in the forehead or vasodilatation in the cheeks. However, a facial nerve lesion impaired vasodilatation in the forehead in all six patients who ate chillies, and also in four of five patients whose blood vessels dilated extensively on the normally-innervated side of the forehead when the patients tasted Tabasco sauce. These findings suggest that sympathetic sudomotor activity mediates physiological gustatory sweating in the forehead, whereas sympathetic vasoconstrictor tone inhibits gustatory vasodilatation in the forehead. A parasympathetic vasodilator reflex in the facial nerve contributes actively to gustatory flushing in the forehead, but some other unidentified mechanism influences vascular responses in the cheeks.