title: The effects of lesions to thalamic lateral internal medullary lamina and posterior nuclei on learning, memory and habituation in the rat.
abstract: The behavioral effects of radiofrequency lesions to the lateral internal medullary lamina region (IML) or the posterior region (Po: containing the parafascicular and posterior nuclei) of the thalamus were compared to sham operated controls. Subjects were pre-operatively trained and then tested for post-operative retention of a NMTP task. Whereas the Po-lesion group was impaired only on long delays (60, 90 s), the IML-lesion group was impaired on retention and re-acquisition and demonstrated lower performance at all delays (5-90 s) of the NMTP task. Post-operative training and testing was conducted on three additional tasks: Morris water maze, acoustic startle, and passive avoidance. The IML-lesion group was impaired in finding a hidden and visual platform in the Morris water maze, demonstrated a blunted response but normal habituation to an acoustic startle stimulus, and showed normal retention of a passive avoidance task. On those three tasks, the performance of the Po-lesion group was similar to controls. In the IML-lesion group, neuronal loss resulting from axotomy and/or transneuronal degeneration was observed within nuclei of the midline and anterior thalamus and the mammillary body. These results suggest that lesions to the IML region disrupt a range of cognitive functions and produce pathological destruction in distant brain regions; whereas damage to the posterior thalamus causes spatial delay-sensitive deficits.
authors.affiliation: Neurology Research Services, VA Medical Center, San Diego, CA 92169, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Savage
authors.forename: A J
authors.initials: AJ
authors.lastname: Sweet
authors.forename: R
authors.initials: R
authors.lastname: Castillo
authors.forename: P J
authors.initials: PJ
authors.lastname: Langlais
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000502:physiology; D003463:Cues; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D007858:Learning / Q000502:physiology*; D008297:Male; D018782:Maze Learning / Q000502:physiology; D008568:Memory / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013216:Reflex, Startle / Q000502:physiology; D013787:Thalamic Nuclei / Q000033:anatomy & histology / Q000502:physiology*