Poremba A, Gabriel M
Department of Psychology and Institute for Neuroscience, Univsity of Texas, Austin, Texas 78712, USA.
J Neurosci. 1997 Nov 1;17(21):8645-55. doi: 10.1523/JNEUROSCI.17-21-08645.1997.
This study assessed the role of the thalamic medial geniculate (MG) nucleus in discriminative avoidance learning, wherein rabbits acquire a locomotory response to a tone [conditioned stimulus (CS)+] to avoid a foot shock, and they learn to ignore a different tone (CS-) not predictive of foot shock. Limbic (anterior and medial dorsal) thalamic, cingulate cortical, or amygdalar lesions severely impair acquisition, and neurons in these areas develop training-induced activity (TIA): more firing to the CS+ than to the CS-. MG neurons exhibit TIA during learning and project to the amygdala. The MG neurons may supply afferents essential for amygdalar and cingulothalamic TIA and for avoidance learning. To test this hypothesis, bilateral electrolytic or excitotoxic ibotenic acid MG nuclear lesions were induced, and multiunit recording electrodes were chronically implanted into the anterior and posterior cingulate cortex, the anterior-ventral and medial-dorsal thalamic nuclei, and the basolateral nucleus of the amygdala before training. Learning was severely impaired and TIA was abolished in all areas in rabbits with lesions. Thus learning and TIA require the integrity of the MG nucleus. Only damage in the medial MG division was significantly correlated with the learning deficit. The lesions abolished the sensory response of amygdalar neurons, and they attenuated (but did not eliminate) the sensory response of cingulothalamic neurons, suggesting the existence of extra geniculate sources of auditory transmission to the cingulothalamic areas.
本研究评估了丘脑内侧膝状体(MG)核在辨别性回避学习中的作用,在该学习过程中,兔子获得对一种音调[条件刺激(CS +)]的运动反应以避免足部电击,并且它们学会忽略另一种不预示足部电击的不同音调(CS -)。边缘系统(前背侧和内侧背侧)丘脑、扣带回皮质或杏仁核损伤会严重损害学习,并且这些区域的神经元会产生训练诱导活动(TIA):对CS +的放电比对CS -的更多。MG神经元在学习过程中表现出TIA,并投射到杏仁核。MG神经元可能为杏仁核和扣带丘脑TIA以及回避学习提供必需的传入神经。为了验证这一假设,在训练前诱导双侧电解或兴奋性毒性鹅膏蕈氨酸MG核损伤,并将多单元记录电极长期植入前扣带回皮质和后扣带回皮质、丘脑前腹侧核和内侧背侧核以及杏仁核基底外侧核。损伤兔子的所有区域的学习均严重受损且TIA消失。因此,学习和TIA需要MG核的完整性。仅内侧MG分区的损伤与学习缺陷显著相关。这些损伤消除了杏仁核神经元的感觉反应,并减弱(但未消除)扣带丘脑神经元的感觉反应,提示存在向扣带丘脑区域的额外膝状体听觉传导源。