A computational model of surround suppression based on the circuitry of the lateral geniculate nucleus of the cat

The receptive field of a visual neuron has been traditionally divided in two parts, the classical receptive field (CRF) and the surround. Presentation of a stimulus in the CRF can cause a response of the cell, stimulation of the surround can only modulate the cell's response to stimuli presented in the CRF. An example of such a modulation is surround suppression. This is the phenomenon where the response of a cell is suppressed when the diameter of a grating is extended to the surround of their receptive field. The extent of surround suppression is dependent on the contrast of the stimulus. For stimuli of low contrast, the suppression is generally low while for high contrasts the suppression increases. The extent of surround suppression can additionally depend on the difference in orientation between the grating presented in the CRF and the surrounding annular grating. Several computational models have explained these phenomena by a circuitry, which exclusively lay within Vl or higher visual areas. This may however not be correct, since cells in the LGN already show a similar extent of surround suppression. In addition, an experiment where inhibitory input to cells within V1 was inactivated by iontophoretically administering the GABA(A)-receptor antagonist, bicuculline methiodide, didn't show a significant effect on the shape of the normalized size tuning curve although the response of the V1 cells did decrease. This result also indicates that the extent of surround suppression may be independent on the circuitry within V1. V1 may thus possibly inherit fully or partly the surround suppression from the cells in LGN. In this case the circuitry that causes surround suppression may be fully or partly located in the LGN. In the past a circuitry has been proposed to explain surround suppression in the LGN. It has also been shown in a computational model that this circuitry can explain surround suppression and orientation-selective surround suppression in the LGN. A computational model of this circuitry has been extended here to show that this circuitry can also explain contrast-dependent surround suppression