Neurophysiological properties of magnetic cells in the pigeon's visual system

Single unit electrical activity was recorded extracellularly in the nucleus of the basal optic root (nBOR) and in the optic tectum under earth-strength magnetic stimulation. Units in the nBOR which were stimulated while the eyes were illuminated by light of different wavelengths exhibited peaks of magnetic responsiveness at 503 nm and 582 nm. Magnetically directional selective cells were found in the stratum griseum et fibrosum superficiale of the optic tectum. They also showed directional selectivity to dynamic photic stimuli. Response peaks varied with the orientation of the pigeon in the horizontal plane. This confirmed that the magnetic responses contained directional information. The results suggest that the receptor and neural organisation of the pigeon's visual system provides an adequate substrate for the detection and elaboration of magnetic compass information.