Field potentials evoked in the brain stem of the cat by stimulation of the carotid sinus, glossopharyngeal, aortic and superior laryngeal nerves.

1. In a primarily topographical study, the field potentials evoked in the brain stem of the cat by stimulation of the sinus, glossopharyngeal (IX), aortic and superior laryngeal (SLN) nerves have been recorded with glass micro-electrodes.2. Extracellular negative potentials were evoked in the region of the nucleus of the tractus solitarius and in the lateral reticular formation (LRF) by electrical stimulation of all four nerves. There were differences in the form of these potentials amongst the nerves, particularly between sinus-IX and aortic-SLN. The potentials were identified as post-synaptic with early and late components and were sometimes preceded by an afferent volley.3. Extracellular positive potentials were evoked in the subnucleus reticularis medialis medullae oblongatae and the nucleus reticularis gigantocellularis. Intracellularly recorded hyperpolarizations recorded from six cells had the same time course as the extracellular positivity. Spontaneously active cells encountered in these regions were sometimes depressed for the duration of the positivity.4. Each of the above field potentials was maximal in the region of Horsley-Clarke A. P. co-ordinates -10 to -13 mm.5. At A.P. co-ordinates of -15 to -17 mm negativity showing post-tetanic potentiation was evoked, at latencies similar to the negativity in the LRF, in the commissural nucleus of Cajal, the dorsolateral reticular formation and the medial reticulo-spinal tract.6. Negative potentials were evoked in the contralateral LRF.