Correlation-based development of ocularly matched orientation and ocular dominance maps: determination of required input activities.
We extend previous models for separate development of ocular dominance and orientation selectivity in cortical layer 4 by exploring conditions permitting combined organization of both properties. These conditions are expressed in terms of functions describing the degree of correlation in the firing of two inputs from the lateral geniculate nucleus (LGN), as a function of their retinotopic separation and their "type" (ON center or OFF center and left eye or right eye). The development of ocular dominance requires that the correlations of an input with other inputs of the same eye be stronger than or equal to its correlations with inputs of the opposite eye and strictly stronger at small retinotopic separations. This must be true after summing correlations with inputs of both center types. The development of orientation-selective simple cells requires that (1) an input's correlations with other inputs of the same center type be stronger than its correlations with inputs of the opposite center type at small retinotopic separation; and (2) this relationship reverse at larger retinotopic separations within an arbor radius (the radius over which LGN cells can project to a common cortical point). This must be true after summing correlations with inputs serving both eyes. For orientations to become matched in the two eyes, correlated activity within the receptive fields must be maximized by specific between-eye alignments of ON and OFF subregions. Thus the correlations between the eyes must differ depending on center type, and this difference must vary with retinotopic separation within an arbor radius. These principles are satisfied by a wide class of correlation functions. Combined development of ocularly matched orientation maps and ocular dominance maps can be achieved either simultaneously or sequentially. In the latter case, the model can produce a correlation between the locations of orientation map singularities and local ocular dominance peaks similar to that observed physiologically. The model's main prediction is that the above correlations should exist among inputs to cortical layer 4 simple cells before vision. In addition, mature simple cells are predicted to have certain relationships between the locations of the ON and OFF subregions of the left and right eyes' receptive fields.
Erwin
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Department of Physiology, University of California, San Francisco, California 94143-0444, USA.
Miller
K D
KD
D000818:Animals; D001931:Brain Mapping; D002415:Cats; D007839:Functional Laterality / Q000502:physiology; D005829:Geniculate Bodies / Q000166:cytology* / Q000502:physiology; D006801:Humans; D008959:Models, Neurological; D009475:Neurons, Afferent / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D013569:Synapses / Q000502:physiology; D013997:Time Factors; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology