Vertical organization in the visual cortex (area 17) in the cat

Summary1.Responses of cortical cells in the cat's area 17 (central and paracentral area), recorded successively during electrode penetrations perpendicular to the surface, were averaged (PSTH). All cells recorded during one penetration were stimulated with the same stimulus, a slowly moving light or dark slit oriented optimally for the first cell recorded. Comparisons between successively recorded cells were completed by simultaneous recordings from two neurones with the same microelectrode tip. Eye movements as an error were excluded by simultaneous recording of a geniculate cell throughout a cortical penetration.2.The centers of excitatory receptive fields (ERFs) of simultaneously or successively recorded cells during a penetration may be separated by more than 4°. The mean scatter around a column average is 0.81±0.99° in both directions. The scatter is independent of the recording depth. Whereas the optimal orientation of cells recorded during one penetration was generally similar, the optimal direction (forward and backward movement of an optimally oriented stimulus) was variable.3.The ERF diameters as determined from the PSTH were between <0.5° and 7.5°. During each penetration, cells with small (up to 3.0°) and large (>3.0°) ERFs could be discriminated. The inhibitory fields (determined with the conditioning method of Bishop, Coombs and Henry, 1971) were between 2.0 and 8.5° along both the optimal and the non-optimal orientation axis of a cell. The borders of inhibitory fields of cells collected during one penetration were also scattered though overlapping.4.Response analysis of simultaneously and successively recorded cells with different stimuli indicated that, in spite of considerable ERF-overlap, cells with small ERFs had separate excitatory inputs and that intracortical excitatory connections between cells recorded during one penetration were improbable.5.The ERFs of cells with large ERFs covered a field approximately corresponding to the fields of cells with small ERFs. But a convergent input from many small ERF cells to single large ERF cells was excluded because of the incompatible functional properties of both types of cells, which correspond to some extent to simple and complex cells respectively.6.It is concluded that cells within cortical cylinders are not connected through excitatory contacts with each other and that most cells in area 17 are excited by individual excitatory geniculate or cortical inputs. Inhibitory connections seem to be the most important intracortical connections.7.In an Appendix it is shown that anatomical and physiological data do not support significant excitatory convergence of specific geniculate afferents on cortical neurones.