Telencephalic removal and tonic immobility in the domestic hen (Gallus Domesticus )

The number of inductions and the duration of tonic immobility (TI) was measured in Brown Leghorn hens which were either sham-operated or had total removal of the telencephalon. The overall duration of TI was shorter in sham-operated birds than in decerebrates. The duration of TI decreased significantly in both groups when they were given one trial daily for 7 consecutive days but this was not seen when the birds received 5 trials in rapid succession. The number of inductions necessary to produce TI in decerebrate hens did not differ significantly with repeated testing but sham-operated birds were less susceptible to induction by the 7th trial when tested daily. In contrast, testing the birds in rapid succession had no effect. The possible role of the telencephalon in TI was discussed.