On October 7, 2019, a research paper entitled "long-term memory is formed immediately without the need for protein synthesis-dependent consolidation in Drosophila" was published in Nature Communications by Yi Zhong’s lab. For the first time, it has been revealed that the "context effect" relies on a kind of context-dependent memory that does not require protein synthesis but can be maintained for almost a lifetime, and the neural mechanism of multi-sensory integration of such memory extraction has been revealed. The research has upended perceptions of long-term memory and inspired scientists to re-understand the nature of memory.
It is common knowledge in the whole field of learning and memory research that the formation of long-term memories requires a memory consolidation process that lasts for several hours and requires the synthesis of new proteins. In Drosophila, the formation of long-term memory requires ten repeated training, each with a 15-minute interval. Long-term memory formed by this training requires several hours to consolidate and lasts more than 7 days. However, a single-cycle training, on the other hand, produces relatively unstable memories that are almost completely forgotten within 24 hours. A paper published today by Yi Zhong's research group has found a kind of context-dependent long-term memory, termed as cLTM. The researchers found that in fruit flies, such memory can be formed immediately with a single training session, and can last for more than 14 days without obvious decay.
Figure 1 Memory retention curves tested with different methods
Surprisingly, the maintenance of this memory does not require the synthesis of new protein, nor does it require the classic fly olfactory learning and memory center, the mushroom body. However, the lateral horn, which is often thought to be responsible for olfactory related innate behavior, connects to multiple brain regions, is required for the cLTM retrieval. Here, the researchers found that retrieving cLTM requires the matching of multiple sensory information in the environment, such as the surrounding light, the temperature, the tactile information between the training and test contextual environments. During cLTM retrieval, this information is integrated into the lateral horn to jointly regulate context-dependent olfactory memory retrieval. These findings shed light on the neural mechanisms of situational effects in psychology, and the long-term maintenance of memories that do not depend on solidified forms of memory inspire us to re-understand the nature of learning and memory
Figure 2 Model of cLTM retrieval: Multisensory integration in the LH