Participation of thalamic nuclei in the elaboration of conditioned avoidance reflexes of rats. V. Lesions of the nucleus mediodorsalis.

Hooded rats of the Long-Evans strain with isolated bilateral lesions of the nucleus mediodorsalis thalami (MD) were not able to avoid foot-shocks in a simple runway and in the jumping test. They even did not move and showed no emotional reactions during the conditioned stimulus. The lesions did not change spontaneous behaviour, motor patterns or the thresholds of pain reactivity. The animals displayed less spontaneous and goal-directed orienting responses. The possible participation of MD in a functional system realizing certain kinds of prognosis is discussed.