O'Connor K N, Allison T L, Rosenfield M E, Moore J W
Department of Psychology, University of Massachusetts, Amherst 01003, USA.
Exp Brain Res. 1997 Mar;113(3):534-56. doi: 10.1007/pl00005605.
In classical trace conditioning the acquisition of a conditioned response (CR) is possible even though an interval (the trace interval) elapses between the conditioned stimulus (CS) and unconditioned stimulus (US). This implies that some neural representation of the CS (the stimulus trace) is able to support association between the two stimuli. The medial geniculate nucleus (MGN), particularly the medial division (mMGN), has been identified as one site in the auditory pathway where associative related changes in neural activity occur. If neurons in the MGN are involved in such a sensory trace and in acquisition of a CR, then it is expected that activity following an acoustic CS should be related to both stimulus and response. This study examined the extracellular activity of single units in the MGN during differential auditory trace conditioning of the rabbit nictitating membrane response (NMR). Two 150-ms tones (600 Hz and 1200 Hz) served as CS+ and CS-, and the US was periorbital electrostimulation. Changes in activity during the stimulus and trace interval were largest in the medial and dorsal MGN divisions on CS+ trials and on trials in which a CR was made. Examination of probe stimuli of short (50 ms) and long (600 ms) duration suggested that both CR latency and activity changes in the trace interval were related to stimulus duration and time-locked to stimulus offset. Comparisons of neural activity on the basis of fast or slow CR responses revealed different patterns of response--activity on fast CR trials was generally greater and tended to occur earlier. These results suggest that MGN neurons are involved in the maintenance of a sensory memory trace and possibly play a part in CR generation and timing.
在经典痕迹条件反射中，即使在条件刺激（CS）和非条件刺激（US）之间存在一个间隔（痕迹间隔），条件反应（CR）的习得也是可能的。这意味着CS的某种神经表征（刺激痕迹）能够支持两种刺激之间的关联。内侧膝状体核（MGN），特别是内侧部分（mMGN），已被确定为听觉通路中神经活动发生联想相关变化的一个部位。如果MGN中的神经元参与了这样的感觉痕迹以及CR的习得，那么可以预期，听觉CS之后的活动应该与刺激和反应都相关。本研究在兔瞬膜反应（NMR）的差异听觉痕迹条件反射过程中，检测了MGN中单个神经元的细胞外活动。两个150毫秒的音调（600赫兹和1200赫兹）分别作为CS+和CS-，US为眶周电刺激。在CS+试验和出现CR的试验中，刺激和痕迹间隔期间的活动变化在内侧和背侧MGN分区中最大。对短（50毫秒）和长（600毫秒）持续时间的探测刺激的检查表明，CR潜伏期和痕迹间隔中的活动变化都与刺激持续时间相关，并与刺激偏移时间锁定。根据快速或慢速CR反应对神经活动进行比较，发现了不同的反应模式——快速CR试验中的活动通常更大，且倾向于更早出现。这些结果表明，MGN神经元参与了感觉记忆痕迹的维持，并且可能在CR的产生和定时中发挥作用。
