Can anyone explain what is wrong with the hypothesis of a largely structural long-term memory store? (i.e., in the synaptome, relying not on individual macromolecules but on the ability of a graph of neurons and synapses to store information)
There’s nothing wrong with it, it’s just that the strength of connections (local synaptic concentration of various neurotransmitters and receptors) has been demonstrated to be just as important as their graph-theoretical structure for long-term memory. Synapses can regulate their strength and maintain the strength over long time periods. The problem that the quoted paragraph is trying to illustrate is that a simple chemical concentration explanation doesn’t cut it since chemicals are being diffused and turned over inside synapses all the time. Thus there must be some mechanism for long-term persistence of memory.
Not only that, but there is evidence that in a lot of brain regions neurons simply connect to whatever cells they touch with the average topology of any region defined by the growth properties of the cell types that exist there. From there, the individual connection strengths are reinforced or worn away or otherwise altered by actual neural activity via changes in membrane, cytoskeleton, kinase, etc activity/composition at the individual synapse (on both sides).
Can anyone explain what is wrong with the hypothesis of a largely structural long-term memory store? (i.e., in the synaptome, relying not on individual macromolecules but on the ability of a graph of neurons and synapses to store information)
There’s nothing wrong with it, it’s just that the strength of connections (local synaptic concentration of various neurotransmitters and receptors) has been demonstrated to be just as important as their graph-theoretical structure for long-term memory. Synapses can regulate their strength and maintain the strength over long time periods. The problem that the quoted paragraph is trying to illustrate is that a simple chemical concentration explanation doesn’t cut it since chemicals are being diffused and turned over inside synapses all the time. Thus there must be some mechanism for long-term persistence of memory.
Not only that, but there is evidence that in a lot of brain regions neurons simply connect to whatever cells they touch with the average topology of any region defined by the growth properties of the cell types that exist there. From there, the individual connection strengths are reinforced or worn away or otherwise altered by actual neural activity via changes in membrane, cytoskeleton, kinase, etc activity/composition at the individual synapse (on both sides).
That was also roughly my mental model, and Wikipedia points in that direction too.