When a memory is recalled, it becomes vulnerable again. this is because it must be:

Re-consolidated

Explanation:

Re-consolidated is a process or phenomenon in which already consolidated memory again consolidated and recalled by the memories. It is done because of to strengthen the memory and to modify that memory already stored in the memory.

Individuals need many retrievals to take memory for long years in the long term memory. This process depends on how much deeper the processing occurs in memory. The retrieval could occur at an increasing level of the interval. The re-consolidation process may change the initial process of memory.  

So that when the memory is re-consolidated, it again vulnerable.  

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