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. 1998 Apr 15;508(Pt 2):523–548. doi: 10.1111/j.1469-7793.1998.00523.x

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© The Physiological Society 1998

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A, connectivity scheme: the model assumes that two types of thalamic inputs (‘on’ centre represented by ○, and ‘off’ centre by ) converge monosynaptically or disynaptically (through inhibitory smooth interneurons of the S1 class) on layer IV spiny stellate cells and layer II-III pyramidal cells of the S2 class. The size of each symbol represents the relative efficacy of synaptic transmission. For the sake of clarity only a subset of the global envelope of geniculate inputs is represented. Excitatory intracortical connections which convey mixed ‘on’ and ‘off’ information are represented by open triangles. The two S2 cells linked by reciprocal connections belong to the same isofunctional column and share common inputs of both geniculate and cortical origin. The RFs depicted in B-D represent the spatial distribution of excitatory and inhibitory inputs to the S2 cell. B, the distribution of RF centres of a small proportion of the geniculate inputs to the S2 cell are shown as a cross-section of the cortical RF width. The RFs of strong and weak excitatory LGN afferents, the size of which indicates their relative synaptic efficacy, were displaced vertically for the sake of clarity. Each position of the RF of the cortical cell is fed by both ‘on’ and ‘off’ inputs. C, S1 cells also receive mixed ‘on’ and ‘off’ inputs from the LGN. However, one of these inputs predominates over the entire RF, the ‘off’ for the S1 ‘off’ cell type and the ‘on’ for the S1 ‘on’ cell type. Reciprocal inhibitory connections (thick terminal segments) between these cells are responsible for their antagonist response. In addition, these cells receive excitatory intracortical input from spiny S2 cells, and through a local recurrent loop send an inhibitory feedback onto the same group of cells. D, supragranular and granular cells of the S2 type make reciprocal connections with each other. The S2 RF schematized here has separate ‘on’ and ‘off’ fields and a central overlap zone of variable extent, characteristic of simple cells. Since the two S2 cells share common inputs, their RFs are identical.

Inline graphic — A, connectivity scheme: the model assumes that two types of thalamic inputs (‘on’ centre represented by ○, and ‘off’ centre by ) converge monosynaptically or disynaptically (through inhibitory smooth interneurons of the S1 class) on layer IV spiny stellate cells and layer II-III pyramidal cells of the S2 class. The size of each symbol represents the relative efficacy of synaptic transmission. For the sake of clarity only a subset of the global envelope of geniculate inputs is represented. Excitatory intracortical connections which convey mixed ‘on’ and ‘off’ information are represented by open triangles. The two S2 cells linked by reciprocal connections belong to the same isofunctional column and share common inputs of both geniculate and cortical origin. The RFs depicted in B-D represent the spatial distribution of excitatory and inhibitory inputs to the S2 cell. B, the distribution of RF centres of a small proportion of the geniculate inputs to the S2 cell are shown as a cross-section of the cortical RF width. The RFs of strong and weak excitatory LGN afferents, the size of which indicates their relative synaptic efficacy, were displaced vertically for the sake of clarity. Each position of the RF of the cortical cell is fed by both ‘on’ and ‘off’ inputs. C, S1 cells also receive mixed ‘on’ and ‘off’ inputs from the LGN. However, one of these inputs predominates over the entire RF, the ‘off’ for the S1 ‘off’ cell type and the ‘on’ for the S1 ‘on’ cell type. Reciprocal inhibitory connections (thick terminal segments) between these cells are responsible for their antagonist response. In addition, these cells receive excitatory intracortical input from spiny S2 cells, and through a local recurrent loop send an inhibitory feedback onto the same group of cells. D, supragranular and granular cells of the S2 type make reciprocal connections with each other. The S2 RF schematized here has separate ‘on’ and ‘off’ fields and a central overlap zone of variable extent, characteristic of simple cells. Since the two S2 cells share common inputs, their RFs are identical.