Patchy intrinsic connections of the ferret primary auditory cortex

Small iontophoretic injections, of the leucoagglutinin extracted from Phaseolus vulgaris (PHA-L), were made at a depth of 600 microns, into the ferret primary auditory cortex (AI). The lectin anterogradely labelled the axons of pyramidal cells located in the upper layers. The axons had collaterals which terminated in 5-8 columns within AI. The columns were 0.25-0.8 mm in diameter and, based on their position, appeared to be in areas of cortex where the cells would have higher and lower as well as equivalent characteristic frequencies to those in the injection site.