Controversy

Memory transfer was a biological process proposed by James V. McConnell and others in the 1960s. Memory transfer proposes a chemical basis for memory termed memory RNA which can be passed down through flesh instead of an intact nervous system. Since RNA encodes information[1] living cells produce and modify RNA in reaction to external events, it might also be used in neurons to record stimuli.[2][3][4] This explained the results of McConnell's experiments in which planarians retained memory of acquired information after regeneration. Memory transfer through memory RNA is not currently a well-accepted explanation and McConnell's experiments proved to be largely irreproducible.[5]

In McConnell's experiments, he classically conditioned planarians to contract their bodies upon exposure to light by pairing it with an electric shock.[6][5] The planarians retained this acquired information after being sliced and regenerated, even after multiple slicings to produce a planarian where none of the original trained planarian was present.[5] The same held true after the planarians were ground up and fed to untrained cannibalistic planarians, usually Dugesia dorotocephala.[5][7] As the nervous system was fragmented but the nucleic acids were not, this seemed to indicate the existence of memory RNA[5] but it was later suggested that only sensitization was transferred,[6] or that no transfer occurred and the effect was due to stress hormones in the donor or pheromone trails left on dirty lab glass.[2] However, other experiments seem to support the original findings in that some memories may be stored outside the brain.[1][8][9]

https://en.wikipedia.org/wiki/Memory_transfer

Current Science

https://journals.biologists.com/jeb/article/216/20/3799/11714/An-automated-training-paradigm-reveals-long-term

Planarian flatworms are a popular system for research into the molecular mechanisms that enable these complex organisms to regenerate their entire body, including the brain. Classical data suggest that they may also be capable of long-term memory. Thus, the planarian system may offer the unique opportunity to study brain regeneration and memory in the same animal. To establish a system for the investigation of the dynamics of memory in a regenerating brain, we developed a computerized training and testing paradigm that avoided the many issues that confounded previous, manual attempts to train planarians. We then used this new system to train flatworms in an environmental familiarization protocol. We show that worms exhibit environmental familiarization, and that this memory persists for at least 14 days – long enough for the brain to regenerate. We further show that trained, decapitated planarians exhibit evidence of memory retrieval in a savings paradigm after regenerating a new head. Our work establishes a foundation for objective, high-throughput assays in this molecularly tractable model system that will shed light on the fundamental interface between body patterning and stored memories. We propose planarians as key emerging model species for mechanistic investigations of the encoding of specific memories in biological tissues. Moreover, this system is lik ely to have important implications for the biomedicine of stem-cell-derived treatments of degenerative brain disorders in human adults.