Introducing the brain: the plasticity of the single neuron (Introduction)

by David Turell @, Tuesday, August 06, 2019, 20:46 (341 days ago) @ David Turell

Changing synaptic connections is a constant activity:

https://medicalxpress.com/news/2019-08-brain-cells.html

"Brain cells, or neurons, constantly tinker with their circuit connections, a crucial feature that allows the brain to store and process information. While neurons frequently test out new potential partners through transient contacts, only a fraction of fledging junctions, called synapses, are selected to become permanent.

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"The team tracked specially labeled neurons in the visual cortex of mice after normal visual experience, and after two weeks in darkness. To their surprise they saw that spines would routinely arise and then typically disappear again at the same rate regardless of whether the mice were in light or darkness. This careful scrutiny of spines confirmed that experience doesn't matter for spine formation, Nedivi said. That upends a common assumption in the field, which held that experience was necessary for spines to even emerge.

"By keeping track of the presence of PSD95 they could confirm that the synapses that became stabilized during normal visual experience were the ones that had accumulated that protein. But the question remained: How does experience drive PSD95 to the synapse? The team hypothesized that CPG15, which is activity dependent and associated with synapse stabilization, does that job.

***

"Indeed, PSD95 recruitment shot up, as if the animals were exposed to visual experience. This showed that CPG15 not only carries the message of experience in the light, it can actually substitute for it in the dark, essentially "tricking" PSD95 into acting as if experience had called upon it.

"'This is a very exciting result, because it shows that CPG15 is not just required for experience-dependent synapse selection, but it's also sufficient," says Nedivi, "That's unique in relation to all other molecules that are involved in synaptic plasticity."

"In all, the paper's data allowed Nedivi to propose a new model of experience-dependent synapse stabilization: Regardless of neural activity or experience, spines emerge with fledgling excitatory synapses and the receptors needed for further development. If activity and experience send CPG15 their way, that draws in PSD95 and the synapse stabilizes. If experience doesn't involve the synapse, it gets no CPG15, very likely no PSD95 and the spine withers away."

Comment: Plasticity is mediated by complex proteins working together. The problem for us is that we do not know how proteins create function. See today's entry: How much can we know? the protein form/function enigma. There must be a level of control that activates each protein and we do not see that level. Too complex for Darwin-style evolutionary theory. Hasad to be designed.


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