Carter Ronald McKell, Hofstotter Constanze, Tsuchiya Naotsugu, Koch Christof
Division of Biology and Engineering and Applied Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2003 Feb 4;100(3):1399-404. doi: 10.1073/pnas.0334049100. Epub 2003 Jan 27.
Previous studies of associative learning implicate higher-level cognitive processes in some forms of classical conditioning. An ongoing debate is concerned with the extent to which attention and awareness are necessary for trace but not delay eye-blink conditioning [Clark, R. E. & Squire, L. R. (1998) Science 280, 77-81; Lovibond, P. F. & Shanks, D. (2002) J. Exp. Psychol. Anim. Behav. Processes 28, 38-42]. In trace conditioning, a short interval is interposed between the termination of the conditioned stimulus (CS) and the onset of the unconditioned stimulus (US). In delay conditioning, the CS and US overlap. We here investigate the extent to which human classical fear conditioning depends on working memory. Subjects had to carry out an n-back task, requiring tracking an item 1 or 2 back in a sequentially presented list of numbers, while simultaneously being tested for their ability to associate auditory cues with shocks under a variety of conditions (single-cue versus differential; delay versus trace; no task versus 0-, 1-, and 2-back). Differential delay conditioning proved to be more resilient than differential trace conditioning but does show a reduction due to task interference similar in slope to that found in trace conditioning. Explicit knowledge of the stimulus contingency facilitates but does not guarantee trace conditioning. Only the single-cue delay protocol shows conditioning during the more difficult working memory task. Our findings suggest that the larger the cognitive demands on the system, the less likely conditioning occurs. A postexperimental questionnaire showed a positive correlation between conditioning and awareness for differential trace conditioning extinction.
先前关于联想学习的研究表明，在某些形式的经典条件反射中涉及更高层次的认知过程。目前正在进行的一场辩论关注的是，在痕迹性而非延迟性眨眼条件反射中，注意力和意识在多大程度上是必要的[克拉克，R.E. & 斯夸尔，L.R.（1998年）《科学》280卷，77 - 81页；洛夫邦德，P.F. & 尚克斯，D.（2002年）《实验心理学：动物行为过程》28卷，38 - 42页]。在痕迹性条件反射中，条件刺激（CS）终止与无条件刺激（US）开始之间插入一个短暂的间隔。在延迟性条件反射中，CS和US重叠。我们在此研究人类经典恐惧条件反射在多大程度上依赖于工作记忆。受试者必须执行一个n - 回溯任务，即要求在按顺序呈现的数字列表中追踪1个或2个数字之前出现的数字，同时在各种条件下（单线索与差异；延迟与痕迹；无任务与0 - 回溯、1 - 回溯和2 - 回溯）测试他们将听觉线索与电击相关联的能力。事实证明，差异延迟性条件反射比差异痕迹性条件反射更具弹性，但由于任务干扰确实也表现出减少，其斜率与在痕迹性条件反射中发现的相似。对刺激偶然性的明确了解有助于但不能保证痕迹性条件反射。只有单线索延迟方案在更困难的工作记忆任务期间显示出条件反射。我们的研究结果表明，对系统的认知要求越高，条件反射发生的可能性就越小。实验后的问卷调查显示，差异痕迹性条件反射消退的条件反射与意识之间存在正相关。
