Department of Psychology, University of Maryland College Park, College Park, Maryland 20742, USA.
J Neurosci. 2012 Sep 19;32(38):13137-44. doi: 10.1523/JNEUROSCI.2393-12.2012.
Normal aging has been associated with an increased propensity to wait for rewards. When this is tested experimentally, rewards are typically offered at increasing delays. In this setting, persistent responding for delayed rewards in aged rats could reflect either changes in the evaluation of delayed rewards or diminished learning, perhaps due to the loss of subcortical teaching signals induced by changes in reward; the loss or diminution of such teaching signals would result in slower learning with progressive delay of reward, which would appear as persistent responding. Such teaching signals have commonly been reported in phasic firing of midbrain dopamine neurons; however, similar signals have also been found in reward-responsive neurons in the basolateral amygdala (ABL). Unlike dopaminergic teaching signals, those in ABL seem to reflect surprise, increasing when reward is either better or worse than expected. Accordingly, activity is correlated with attentional responses and with the speed of learning after surprising increases or decreases in reward. Here we examined whether these attention-related teaching signals might be altered in normal aging. Young (3-6 months) and aged (22-26 months) male Long-Evans rats were trained on a discounting task used previously to demonstrate these signals. As expected, aged rats were less sensitive to delays, and this change was associated with a loss of attentional changes in orienting behavior and neural activity. These results indicate that normal aging alters teaching signals in the ABL. Changes in these teaching signals may contribute to a host of age-related cognitive changes.
正常衰老与等待奖励的倾向增加有关。当在实验中进行测试时，奖励通常会随着延迟的增加而提供。在这种情况下，老年大鼠对延迟奖励的持续反应可能反映了延迟奖励评估的变化或学习能力的下降，这可能是由于奖励引起的皮质下教学信号的丧失或减少；这种教学信号的丧失或减少会导致随着奖励的延迟逐渐学习速度变慢，这会表现为持续反应。这些教学信号通常在中脑多巴胺神经元的相位发射中被报道；然而，在杏仁核基底外侧（ABL）中的奖赏反应神经元中也发现了类似的信号。与多巴胺能教学信号不同，ABL 中的信号似乎反映了惊讶，当奖励好于或差于预期时，信号会增加。因此，活动与注意力反应和奖励意外增加或减少后的学习速度相关。在这里，我们研究了这些与注意力相关的教学信号在正常衰老过程中是否会发生变化。年轻（3-6 个月）和老年（22-26 个月）雄性 Long-Evans 大鼠在以前用于证明这些信号的折扣任务上进行了训练。正如预期的那样，老年大鼠对延迟的敏感性降低，这种变化与定向行为和神经活动的注意力变化丧失有关。这些结果表明，正常衰老会改变 ABL 中的教学信号。这些教学信号的变化可能导致一系列与年龄相关的认知变化。
