An intracellular analysis of visual cortical neurones to moving stimuli: Responses in a co-operative neuronal network
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- Creutzfeldt, O.D., Kuhnt, U. & Benevento, L.A. Exp Brain Res (1974) 21: 251. doi:10.1007/BF00235746
Responses of cortical cells from the foveal and perifoveal visual field representation in area 17 to moving contrasts were analyzed with intracellular records in anesthetized cats. These intracellularly recorded responses were normal in so far as the cells showed typical orientation/direction sensitivity and only short phasic or no responses to diffuse illumination.
With slowly moving bright or dark bars, two types of responses were seen: those with a small excitatory peak and those with a wider excitatory peak. Inhibitory regions outside the excitatory peak were only seen in cells with a small excitatory area. Only very few cells showed inhibitory “flanks” preceding and following the excitation; often inhibition followed the excitation in both the forward and backward direction; sometimes it preceded it in both directions. The inhibition outside the excitatory zone practically always had “dynamic” properties, i.e. was smaller or larger in the two opposite directions of movements.
All cells showed strong inhibition (IPSP's) mixed with excitation while the stimulus moved over the excitatory response field. The degree of inhibition was clearly sensitive to the direction of movement (forward or backward) of an optimally oriented moving stimulus, and could also be different at different orientation/ directions. However, the orientation dependence of intracortical inhibition was often less clear than the differences found between the two opposite directions of an optimally oriented stimulus. Inhibition was more marked during binocular than during monocular stimulation.
The excitatory areas of cortical cells were mostly slightly elongated, but not systematically along the axis of optimal orientation. The diameters of the excitatory fields were similar along the optimal and the non-optimal orientation axes (mean 1.9±0.78 vs. 2.2±0.92°).
It is proposed that the orientation/direction sensitivity of cortical cells is a function of intracortical inhibitory connections with direction/orientation sensitivity rather than only due to the spatial arrangement of excitatory and inhibitory on- or off-center fields. A hypothetical retino-cortical projection map is proposed and it is assumed that direction/orientation sensitive intracortical inhibition is essential for the functional properties of cortical neurones.