Cross-correlation of ventrolateral inspiratory neurons in the cat.

The ventrolateral region in the medulla of cats was explored with pairs of microelectrodes with tip separations from 100 to 300 micron such that extracellular potentials of pairs of near-neighboring neurons were recorded simultaneously. At least one neuron of each pair was antidromically activated from the spinal cord. Cross-correlation histograms were computed and showed the existence of short-term synchronization of firing for 8 of 20 neuron pairs (40%). The primary feature of the cross-correlation histograms was, typically, asymmetrical peaks on each side of time zero. The peaks were dissimilar, one low and broad, the other high and narrow, and occurred within a millisecond of time zero. Poststimulus histograms computed for one of the pair, during antidromic activation of the other, indicated a possible interaction between the neurons in one case but not in another. The results are suggestive of neuronal interactions among the late-firing inspiratory neurons of the nucleus retroambigualis but are not conclusive.