The role of horizontal intracortical connections in "long-range" spatial interactions

Abstract

Previous studies have used a conservative definition of CRF size, the minimum response field (MRF). But MRF measurement misses parts of the CRF that are too insensitive to generate spikes when stimulated alone. We have measured the size of the CRF in macaque V1 neurons using a grating summation technique. On average the MRF underestimates the area of the CRF by a factor of 4 at high contrast. At low contrast, the suppressive surround is weakened and the area of summation increases by an additional factor of 6. Using published visuotopic maps, we projected our measured CRFs onto the cortical surface, and found that the majority have radii that correspond to horizontal cortical distances of 2-6 mm.