Relation of olfactory bulb and cortex. I. Spatial variation of bulbocortical interdependence.

Traces of extracellular electrical activity were simultaneously recorded from multiple electrode sites of the olfactory bulb and cortex of 10 alert, minimally restrained rabbits. Rhythmic bursts of 35-85 cps activity appeared concurrently in both structures on the inspiratory phase of a respiratory slow wave. Bulbocortical correlation was significantly higher during bursts than during interburst segments. Four conditions were expected to indicate interdependence of a bulbar and a cortical recording site: (1) a common bulbar and cortical burst frequency; (2) high bulbocortical burst correlation; (3) low bulbocortical burst phase dispersion; and (4) correlation between bulbar and cortical burst amplitudes. Pairs of sites were found which satisfied all 4 conditions. Mean bulbocortical correlation was inversely related to phase dispersion over all the site pairs examined. Significant variation in both correlation and phase dispersion was found with location of the recording sites in the bulb and in the cortex. Sites in the olfactory bulb thus differed significantly in their relation with cortical sites, and likewise, cortical sites differed significantly in their relation with bulbar sites. It is concluded that interdependence between the olfactory bulb and cortex can be detected in the relation of their field potentials and that the interdependence is spatially non-uniform.