Salmon P, Tsaltas E, Gray J A
Department of Psychology, Institute of Psychiatry, London, England.
Behav Neural Biol. 1988 Mar;49(2):152-64. doi: 10.1016/s0163-1047(88)90473-6.
Male Sprague-Dawley rats were trained to bar-press for food reward on a successive discrimination involving periods of reward on a variable-interval (VI) 18-s schedule interspersed with periods of extinction. The two components of the schedule were signaled by a steady or a flashing light, counterbalanced between VI and extinction components. Confirming previous findings, the discrimination was easier when the flashing light signaled VI and the steady light signaled extinction, than with the reverse allocation of stimuli. This pattern of results is consistent with a dynamogenic effect of flashing light relative to steady light, facilitating discrimination when the flashing light signals the occasion to respond but impairing discrimination when this stimulus signals the occasion to withhold responding. Given this interpretation of performance in the successive discrimination task, it may be used to test three different hypotheses of the functions of the dorsal noradrenergic bundle (DB): that this subserves learning, selective attention, or behavioral inhibition plus arousal. To examine these hypotheses sham-operated animals were compared to animals in which hippocampal noradrenaline levels had been reduced by 98% and hypothalamic levels by 48% after injection into the DB of the catecholamine-specific neurotoxin, 6-hydroxy-dopamine. The lesioned animals responded more slowly than controls in VI components when these were signaled by the flashing light, and more rapidly than controls in extinction components when these were signaled by the steady light. In consequence, the discrimination was impaired only in the condition (flashing light signaling VI, steady light signaling extinction) which controls found easier. These results are in conflict with predictions from the learning and attentional hypotheses of DB function. They are consistent, however, with a model that attributes behavioral inhibitory functions to the DB projection to the septohippocampal system, and arousing functions to the DB projection to the hypothalamus.
雄性斯普拉格-道利大鼠接受训练，在一个连续辨别任务中通过按压杠杆获取食物奖励，该任务包括在可变间隔（VI）18秒的奖励期与消退期之间交替进行。奖励期和消退期由稳定光或闪烁光指示，在VI期和消退期之间进行了平衡处理。与先前的研究结果一致，当闪烁光指示奖励期（VI）而稳定光指示消退期时，辨别任务比刺激分配相反的情况更容易。这种结果模式与闪烁光相对于稳定光的动力激发效应一致，即当闪烁光指示做出反应的时机时促进辨别，但当该刺激指示抑制反应的时机时损害辨别。基于对连续辨别任务表现的这种解释，它可用于检验关于背侧去甲肾上腺素能束（DB）功能的三种不同假设：即它支持学习、选择性注意或行为抑制加唤醒。为了检验这些假设，将假手术动物与在向DB注射儿茶酚胺特异性神经毒素6-羟基多巴胺后海马去甲肾上腺素水平降低98%且下丘脑水平降低48%的动物进行比较。当由闪烁光指示时，损伤动物在奖励期（VI）部分的反应比对照组慢，而当由稳定光指示时，在消退期部分的反应比对照组快。因此，只有在对照组认为更容易的条件下（闪烁光指示奖励期（VI），稳定光指示消退期）辨别才受损。这些结果与DB功能的学习和注意假设的预测相冲突。然而，它们与一种模型一致，该模型将行为抑制功能归因于DB向隔海马系统的投射，而将唤醒功能归因于DB向下丘脑的投射。
