The correlation between the spike activity and the waves of surface ECoG was studied in the visual and motor cortex of alert non-immobilized rabbits. A comparison was made between the forms of the obtained correlation functions for the cells with different horizontal and vertical distances between them. The analysis revealed the similarity of such functions in neurones of V-VI cortical layers, situated vertically under each other along the microelectrode track. Similar in form statistic connections between the ECoG and the background spike activity were also found, beginning with the depth of 1.000 mc, in the neurones situated at the same horizontal cortical level; however, with the increased distance between the cells the degree of similarity of these connections decreases in a non-linear way. On the basis of the obtained data a conclusion is made that the tangential sizes of the background functional ensembles of the cortical neurones are within the range of 140-300 mc.