Lebrón Kelimer, Milad Mohammed R, Quirk Gregory J
Department of Physiology, Ponce School of Medicine, Ponce, Puerto Rico 00732, USA.
Learn Mem. 2004 Sep-Oct;11(5):544-8. doi: 10.1101/lm.78604.
Extinction of auditory fear conditioning is thought to form a new memory. We previously found that rats with vmPFC lesions could extinguish fear to the tone within a session, but showed no recall of extinction 24 h later. One interpretation is that the vmPFC is the sole storage site of extinction memory. However, it is also possible that lesioned rats were unable to retrieve extinction memory stored in other structures. To determine if a latent extinction memory could be retrieved with additional training, we repeated the experiment but added an additional 5 d of extinction reminder trials. Replicating our previous findings, vmPFC-lesioned rats extinguished normally on day 1, but showed no recall of extinction on day 2. Over the next 5 d, however, lesioned rats showed significant savings in their rate of re-extinction. Thus, the vmPFC is not the only site where extinction memory is stored. Nevertheless, lesioned rats receiving only two extinction trials per day required twice as many days to initiate extinction as controls. Although recall of extinction is possible without the vmPFC, it is significantly delayed. We suggest that the vmPFC accelerates extinction by permitting access to recently learned extinction trials, thereby maximizing behavioral flexibility.
听觉恐惧条件反射的消退被认为会形成一种新的记忆。我们之前发现，腹内侧前额叶皮层（vmPFC）受损的大鼠在一个实验环节内能够消除对音调的恐惧，但在24小时后却无法回忆起消退情况。一种解释是，vmPFC是消退记忆的唯一存储部位。然而，也有可能是受损大鼠无法提取存储在其他结构中的消退记忆。为了确定通过额外训练是否能够提取潜在的消退记忆，我们重复了实验，但增加了5天的消退提醒试验。重复我们之前的发现，vmPFC受损的大鼠在第1天正常消除恐惧，但在第2天却无法回忆起消退情况。然而，在接下来的5天里，受损大鼠在重新消除恐惧的速度上表现出显著的节省。因此，vmPFC并不是消退记忆存储的唯一部位。尽管如此，每天仅接受两次消退试验的受损大鼠开始消除恐惧所需的天数是对照组的两倍。虽然没有vmPFC也有可能回忆起消退情况，但会显著延迟。我们认为，vmPFC通过允许访问最近学到的消退试验来加速消退，从而最大限度地提高行为灵活性。
