Homing pigeons subjected to section of the anterior commissure can build up two olfactory maps in the deflector lofts.

Pigeons kept in two cages with screens which deflect the wind clockwise (CW) or counter-clockwise (CCW) show corresponding deflections in their initial orientation. In order to determine the nature of this phenomenon, experimental birds were treated as follows: The anterior commissure of the forebrain (AC), which mediates the interhemispheric transfer of olfactory input was sectioned; After surgery, each experimental bird was kept alternately in a CW cage with its right nostril plugged, and in a CCW cage with its left nostril plugged; the two treatments were alternated every 3 days for 69 days before test releases began. In 23 out of 28 cases the experimentals showed CW deflections when released with the right nostril plugged and CCW deflections when released with the left nostril plugged. The controls were intact, and their nostrils were free in each phase of the experiment. They were subdivided into two groups: one group was kept in the CW cage when the experimentals were in the same cage, the other group in the CCW cage when the experimentals stayed there. In the remaining time each group was kept in a fenced loft. The behaviour of controls demonstrated that the time the experimentals had spent in each kind of deflector cage had been long enough to produce the corresponding deflections in initial orientation. Control experiments were then performed on pigeons with the AC sectioned (2 series) and on intact birds (1 series), both maintained in lofts which did not deflect the wind, and released with one nostril plugged. They did not show deflections similar to those of the experimentals.(ABSTRACT TRUNCATED AT 250 WORDS)