This is the third part of a study of the article:
Is plasticity of synapses the mechanism of long-term memory storage? By Wickliffe C. Abraham, Owen D. Jones and David L. Glanzman
The SPM hypothesis states the potentiation of the synapses and their changes to be where information is stored.
Potentiation
the increase in strength of the electrical signal caused by the transmission in the synapse
However, it may be possible that instead of this, the information is stored in the connection between cells in a memory circuit that are created from a learning experience.
In this case, LTP would only be needed for the retrieval of the information and not the storage.
Another argument against plasticity for storage is that proteins aren’t stable and have a half like of 2 to 5 days in the adult brain.
Also, it has been found that spines change frequently.
Spine
part of a neuron, in the shape of thorns coming from branches of the neuron, that is involved in a synapse
Though the fact that proteins don’t need to last the full life of the memory is a valid counter argument for the first.
This leads to the cell intrinsic hypothesis of memory storage. In this hypothesis, information is stored inside a cell by stable molecules instead of in a synapse.
Cell intrinsic hypothesis of memory storage
A hypothesis stating that memories are stored on the inside of a cell.
There are several potential mechanisms for it and currently, the most likely is epigenetic storage and particularly DNA methylation.
The arguments for DNA methylation are that it is relatively stable, compact and energy efficient in addition to the possibility of a large storage amount due to the high number of methylation sites on the genome.
It is believed that memory signals modify the DNA of the neuron which will change the neuron’s phenotype. This will then cause the neuron to send certain signals when receiving particular information related to the memory.
Epigenetic
Related to DNA changes that turn genes on and off
DNA methylation
The binding of a methyl group to a part of the DNA to block the transcription of the gene.
Phenotype
Observable traits.
Another suggested mechanism is that of histone modification.
Histone
a protein that creates the structure for DNA to stick to and be shaped into chromosomes ( the figure 8 )
When they bind to acetyl groups, they ease the transcription of the gene to create proteins and do the opposite when they are disconnected.
However, this is less stable than methylation making the first the more likely one.
It is also possible that the mechanism behind storage depends on the type of information and many other factors.
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