A model for the intracortical origin of orientation preference and tuning in macaque striate cortex

We report results of numerical simulations for a model of generation of ori entation selectivity in macaque striate cortex. In contrast to previous mod els, where the initial orientation bias is generated by convergent genicula te input to simple cells and subsequently sharpened by lateral circuits, ou r approach is based on anisotropic intracortical excitatory connections whi ch provide both the initial orientation bias and its subsequent amplificati on. Our study shows that the emerging response properties are similar to th e response properties that are observed experimentally, hence the hypothesi s of an intracortical generation of orientation bias is a sensible alternat ive to the notion of an afferent bias by convergent geniculocortical projec tion patterns. In contrast to models based on an afferent orientation bias, however, the "intracortical hypothesis" predicts that orientation tuning g radually evolves from an initially nonoriented response and a complete loss of orientation tuning when the recurrent excitation is blocked, but new ex periments must be designed to unambiguously decide between both hypotheses.