2

I'm doing some research into how the brain works for a research project.

Often, websites describe that the connection between two neurons strengthens when one of the neurons sends a 'message' to the other, they don't have to both send 'messages' at the same time.

However, I recently watched the video here: https://www.brainfacts.org/thinking-sensing-and-behaving/learning-and-memory/2021/what-memories-are-made-of-100121

An experiment is conducted in the video on a rodent brain, and the results show the the connection is not strengthened when Neuron A sends a 'message' to Neuron B, but only when both Neuron A and B fire at the same time, inducing LTP (Long Term potentiation).

I've tried to look into this, but most websites say the former theory, not explaining the results of the experiment.

So, when does a neural connection strengthen, when LTP occurs, or when just one of the neurons fires?

If they strengthen both of the times, what is the difference between the strengthening and why did the experiment in the video yield the results it did?

Thank you so much for your time!

IntegralPilot
  • 23
  • 4

1 Answers1

1

Long-term potentiation is a form of "synaptic strength" changing.

Specifically, the video you describe seems to be talking about spike-timing dependent plasticity (though I'm not going to bother watching the video; there are plenty of text sources for this information out there).

In classical LTP, synaptic strength increases due to post-synaptic calcium interactions. For these interactions to occur, it's necessary for there to first be a synaptic release of glutamate, which binds postsynaptic AMPA receptors and NMDA receptors (both types of glutamate receptor). AMPA receptors depolarize the cell and make it more likely to fire in the near future. NMDA receptors are a bit more special because they permeable to not only sodium but also calcium, but are typically blocked with a magnesium ion around resting voltages. If the postsynaptic cell subsequently fires an action potential, the depolarization dislodges the magnesium block and allows calcium to enter through NMDA receptors. This calcium signal triggers a further signaling cascade with an end result being more AMPA receptors in the membrane: that means a bigger response at that synapse next time neurotransmitter is released. You can think of this as a special "AND" operation requiring a temporal order.

Often, websites describe that the connection between two neurons strengthens when one of the neurons sends a 'message' to the other, they don't have to both send 'messages' at the same time.

I think these websites are just avoiding getting into the details. If you read a "how-to" manual on how to drive an automobile, it might say you press on the gas pedal to speed up. It's not wrong to say that, even if it simplifies things a lot and doesn't explain what specifically the gas pedal does or that it only works if you have the vehicle in gear and gas in the tank and the engine is on, etc.

Bryan Krause
  • 7,376
  • 3
  • 13
  • 23