BRAIN-STEM NEURONS AND POSTGANGLIONIC SYMPATHETIC-NERVES - DOES CORRELATION MEAN CONNECTION

Short-term correlations in activity have been widely used as evidence to connect brainstem units with postganglionic sympathetic nerves. The se may be detected by spike-triggered averaging, cross correlation or coherence analysis. The specificity of this type of evidence has been investigated by cross-correlating the activity of identified cutaneous vasoconstrictor postganglionic fibres with that of medullary premotor neurones of like and of unlike functional type, as determined by phys iological testing (preoptic warming), in anaesthetised cats. Single me dullary premotor neurones of both types were recorded from the subretr ofacial nucleus: they were identified by their barosensitivity and, in most cases, their spinally projecting axons. By the test criteria cho sen, the correlation method gave both false-positive and false-negativ e results as commonly as it gave correct ones. We conclude that it is not a reliable way to determine brainstem-postganglionic connectivity.