Amygdaloid unit activity changes induced by inhibitory avoidance learning

• Main Authors: Chun-Hui Chang, 張鈞惠
• Other Authors: Chen-Tung Yen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/55183795285069129323

碩士 === 國立臺灣大學 === 動物學研究所 === 91 === This study examined the functional role of the amygdala in two versions of inhibitory avoidance tasks, the step-down avoidance motivated by heat and the step-through avoidance motivated by electric shock, with single-unit recording during task sessions. Long-Evans rats successfully acquired these two conditioning paradigms. Rats were divided into the experimental group (n = 8) and the control group (n = 5). Briefly, rats in the experimental group were allowed to adapt the task environment three times, then received the conditioning session, and followed by the test session. Rats in the control group received the unconditioned noxious stimuli in an environment distinct from the original task apparatus. Changes in the neuronal response showed that as the animal got used to the task environment from the first-entry session to the habituated session (the third-entry), neuronal firing rates in the amygdala decreased. After the conditioning session, firing rates increased again in the experimental group, but not in the control group. These results imply that the amygdala may code information by neuronal firing rates. The role of the primary somatosensory cortex in these two tasks was unclear. Data obtained from the experimental group showed that in the step-down avoidance task, firing rates decreased from the first-entry session to the habituated session, and showed further decrement in the test session. This result implies that the primary somatosensory cortex may not be involved in the step-down conditioning process. However, in the step-through avoidance task, firing rates decreased from the first-entry session to the habituated session and increased again in the test session, which implies that the primary somatosensory cortex may be involved in the step-through conditioning process. We failed to find changes in the synchronization among neurons after the conditioning session between the primary somatosensory cortex and the amygdala. Inhibitory avoidance learning may engage both the operant component and the classical component. The present data combined with the lesion data obtained in our lab suggest that the operant component dominated in the step-down avoidance task, and the classical component is an important factor in learning the step-through avoidance task. Our experiment design failed to yield supporting evidence for more involvement of the right amygdala than the left one. It is possible that the neurons in the amygdala are functionally segregated, but this notion needs further examination. We found out that the theta rhythm dominates as the rats entered the task apparatus from the waiting cage, and rats in the experimental group showed dominant theta rhythm in both the waiting cage and the task apparatus after conditioning. Since theta rhythm correlates with awake and alert state in the amygdala, these results imply that the rats in the experimental group may stay alert even in the waiting cage after the conditioning session. From previous related studies, although the amygdala may not be the storage site of long-term memory in this kind of inhibitory avoidance learning, we suggest that the amygdala could pivot avoidance behavior through increase in population firing rate, at least within one day after the conditioning session. Further, the animal may adopt different strategies in acquiring the two inhibitory avoidance tasks: learning in the step-down avoidance task was coped with more active behavior than in the step-through avoidance task.