Electrical responses to direct and indirect photic stimulation of the pineal gland in the pigeon.

Spontaneous electrical activity was recorded from pineal cells in intact and blinded pigeons. Modification of the activity by photic stimulation applied to the lateral eyes or directly to the pineal gland was observed in both groups of birds. The pattern of responses was different in the blinded compared to the sighted pigeons. In the birds with intact lateral eyes, the majority of responses to light were excitatory while in the blinded group more inhibitory effects were recorded. The results indicate that cells in the pigeon pineal gland retain a photoreceptive capacity although the sensitivity of the responsive units is low.