Single cell activity in chronic unit recording: a quantitative study of the unit amplitude spectrum.

The ratio of standard deviation to mean, of the amplitude spectrum of well resolved single units, is shown to scale exponentially. This scaling is explained on the basis of a consideration of the relationship of extracellular voltage to voltage gradient, in a dendritic neuron model. A method is then advanced to extract, from multi-unit data, normally distributed amplitude spectra which are indistinguishable from those of well resolved single units. This method is suggested as a means of characterizing, in general, the unit activity obtained from chronically implanted preparations.