Stokes K A, Best P J
Department of Psychology, University of Virginia, Charlottesville 22903.
Behav Neural Biol. 1990 May;53(3):334-45. doi: 10.1016/0163-1047(90)90198-f.
Previous results indicating that radial maze performance in animals with mediodorsal thalamic lesions is deficient cannot exclude the possibility that these impairments are due to altered motor mechanisms (response biases). The present study sought to eliminate this potentially confounding variable by using a procedure which tests memory for serial position. This procedure involved experimenter-controlled arm entry (number and order) on a radial arm maze. Following this sequence, animals were presented with one previously entered arm along with an arm not yet visited on that trial. Avoidance of the previously entered arm constituted memory for the prior sequence. Thus, this task represents a form of a win-shift or nonmatching-to-sample task. Seven animals were given ibotenic acid lesions of the mediodorsal nucleus and nine others were given sham operations; 2 weeks later testing in the above procedure was conducted. Results indicated that, although control subjects could differentiate between entered and unentered arms without difficulty, animals with lesions were unable to exhibit this distinction. Much of their memory for arms previously entered in a sequence was at chance level, regardless of the placement of the tested arm in the sequence. Some tendency toward increased errors with longer sequences of arm entries was noted. This may indicate that animals with lesions were susceptible to proactive interference from previous choices. Regardless, even without the opportunity to develop or exhibit response biases, animals lesioned in the mediodorsal nucleus were unable to perform this win-shift task reliably. Thus, discrimination among maze arms is impaired after lesion of the mediodorsal nucleus and this impairment is independent of the motor response patterns which emerge during solution of a conventional radial maze task.
先前的结果表明，丘脑背内侧核损伤动物在放射状迷宫中的表现存在缺陷，但这些损伤可能是由于运动机制改变（反应偏差）所致，这一可能性无法排除。本研究试图通过使用一种测试序列位置记忆的程序来消除这一潜在的混杂变量。该程序包括在放射状臂迷宫中由实验者控制臂的进入（数量和顺序）。按照这个顺序，给动物呈现一个之前进入过的臂和一个在该试验中尚未访问过的臂。避开之前进入过的臂构成了对先前序列的记忆。因此，这个任务代表了一种赢-转移或非匹配样本任务的形式。七只动物接受了丘脑背内侧核的鹅膏蕈氨酸损伤，另外九只接受了假手术；两周后，按照上述程序进行测试。结果表明，虽然对照组动物能够轻松区分进入过和未进入过的臂，但损伤组动物无法表现出这种区分。它们对先前按顺序进入过的臂的记忆大多处于随机水平，无论测试臂在序列中的位置如何。随着臂进入序列变长，错误有增加的趋势。这可能表明损伤组动物容易受到先前选择的前摄干扰。无论如何，即使没有机会形成或表现出反应偏差，丘脑背内侧核损伤的动物也无法可靠地完成这个赢-转移任务。因此，丘脑背内侧核损伤后，对迷宫臂的辨别能力受损，且这种损伤与传统放射状迷宫任务解决过程中出现的运动反应模式无关。
