"Stick out your tongue": tongue protrusion in neocortex and hypothalamic damaged rats.

Easily administered tests, analogues to the human neurological "stick out your tongue" tests, were devised to assess tongue use in normal, lateral hypothalamic (LH) and decorticate rats. LH and decorticate rats showed loss of tongue protrusion and licking immediately after surgery. Even though LH rats did not recover spontaneous eating dry food and drinking water, they showed extensive recovery of tongue protrusion and use. Decorticate rats regained the ability to eat dry food and drink water, but they showed minimal recovery of tongue protrusion and use. Comparisons of rats with variously located circumscribed neocortical lesions showed maximal tongue protrusion deficits followed orbital frontal cortex ablations. The results show: (1) that the tests developed and described are useful for routine examination of rats that have feeding abnormalities; (2) the feeding abnormalities of decorticate and LH rats can be dissociated; and (3) the orbital frontal cortex and corticofugal pathways passing through or adjacent to the LH may play a special role in the control of tongue and mouth use.