Disruption of lordosis by dorsal midbrain lesions in the golden hamster.

Bilateral lesions of the dorsal midbrain at levels from the anterior to posterior deep tectum abolished lordosis responses to males or manual stimuli. The lesions also blocked reflexive head turning and biting responses to tactile stimulation of the face. Unilateral dorsal midbrain lesions impaired responses to stimuli impinging upon the contralateral body and/or face without affecting lordosis responses to ipsilaterally-applied manual stimuli. The pattern of deficits following unilateral lesions was consistent with the known somatosensory organization of the dorsal midbrain, but the uniform effectiveness of the bilateral lesions placed at any anterior-posterior level of the dorsal midbrain may have been due to bilateral interruption of central gray efferents in addition to deep tectal neuronal damage. Neither bilateral nor unilateral lesions had to involve the central gray to produce their effects.