<p>Donald Hebb's postulate only applies when two neurons are already connected. It seems you are asking more specifically, 'when two neurons are not already connected and they want to connect, how and why?' Correct?</p>

<p>In this case, we do not know. StrangeLoop mentions it is due to the location of the neurons and the spreading of activation. Yes these might be the case but evidence is extremely limited.</p>

<p>It may be the case that correlated activation of two neurons instigates the formation of a synapse between them. It may also be the case that synapses form <a href="http://www.ncbi.nlm.nih.gov/pubmed/20646057" rel="noreferrer">completely randomly</a> and plasticity takes advantage of any new synapses (don't forget <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3018773/" rel="noreferrer">anti-hebbian</a>). It may also be a combination of both. We do not know.</p>

<p>We further do not know concretely what happens in the reverse; for example, what causes a synapse to be eliminated, is it activity driven or a stochastic process?</p>

<p>Some recent evidence showed that spine generation and elimination are <a href="http://www.nature.com/nature/journal/v483/n7387/full/nature10792.html" rel="noreferrer">related to 'learning' and 'unlearning'</a>. This suggests that activity driven plasticity can form/eliminate synapses, but my previous reference shows strong evidence that formation/elimination are stochastic -- hence we do not know!</p>

<p>Another thing which is not clear from your question, as James mentions, is at what age you are considering. Early development of synapses is <a href="http://en.wikipedia.org/wiki/Synaptogenesis#Synapse_Formation_Specificity" rel="noreferrer">more well understood</a> and it may be the case that during early development a group of mechanisms determine why/where/how a synapse forms/eliminates and during adult another set of mechanisms are in charge.</p>

<p>For example, in the early post-natal visual system, <a href="http://www.ncbi.nlm.nih.gov/pubmed/671298" rel="noreferrer">it is found that cells have responses with similar properties as adult; however, later on in development visual experience is required to maintain these properties</a>. <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2822731/" rel="noreferrer">Furthermore, these changes must occur within a critical period for activity-dependent plasticity.</a></p>

CC BY-SA 3.0
2014-09-30T09:14:38.377Z
2014-10-03T00:08:10.627Z
2014-10-03T00:08:10.627Z
dogAwakeCat
<p>I have been reading about neuron creation, guidance cues and all sorts of highly complex mechanisms used to allow one neuron axon to extend or connect - but to what end?</p>

<p><em>Why</em> does <em>one</em> neuron end up connecting to another? <em>(instead of all the others)</em></p>

CC BY-SA 3.0
2014-09-19T11:35:15.173Z
Are you asking for a certain neurobiological mechanism or making a philosophical question implying some sort of decision making?
Lazaros Mitskopoulos
CC BY-SA 3.0
2014-09-19T11:42:18.997Z
I'm after the effect of the biological mechanism - i.e. I know there are factors inside and outside the neuron which the mechanism consists of - but I want to know what the effect is. E.g. Complex mechanism inside a neuron cause an action potential but the overall effect is an addition  - "neural integration". I want to know the effect of neuron guidance/axon growth etc for a single neuron.
James
<neuroscience><theoretical-neuroscience>
Why does a neuron choose to connect to another?
James
# Why does a neuron choose to connect to another?

(Asked by: username_0 on 2014-09-19)

I have been reading about neuron creation, guidance cues and all sorts of highly complex mechanisms used to allow one neuron axon to extend or connect - but to what end?

*Why* does *one* neuron end up connecting to another? *(instead of all the others)*

**Tags:** neuroscience, theoretical-neuroscience

> **Comments:**
> **username_1**: Are you asking for a certain neurobiological mechanism or making a philosophical question implying some sort of decision making?  
> **username_0**: I'm after the effect of the biological mechanism - i.e. I know there are factors inside and outside the neuron which the mechanism consists of - but I want to know what the effect is. E.g. Complex mechanism inside a neuron cause an action potential but the overall effect is an addition  - "neural integration". I want to know the effect of neuron guidance/axon growth etc for a single neuron.  

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## 1 answers

### Answer by username_2 on 2014-09-30. Score: 8 | Accepted answer

Donald Hebb's postulate only applies when two neurons are already connected. It seems you are asking more specifically, 'when two neurons are not already connected and they want to connect, how and why?' Correct?

In this case, we do not know. StrangeLoop mentions it is due to the location of the neurons and the spreading of activation. Yes these might be the case but evidence is extremely limited.

It may be the case that correlated activation of two neurons instigates the formation of a synapse between them. It may also be the case that synapses form [completely randomly](http://www.ncbi.nlm.nih.gov/pubmed/20646057) and plasticity takes advantage of any new synapses (don't forget [anti-hebbian](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3018773/)). It may also be a combination of both. We do not know.

We further do not know concretely what happens in the reverse; for example, what causes a synapse to be eliminated, is it activity driven or a stochastic process?

Some recent evidence showed that spine generation and elimination are [related to 'learning' and 'unlearning'](http://www.nature.com/nature/journal/v483/n7387/full/nature10792.html). This suggests that activity driven plasticity can form/eliminate synapses, but my previous reference shows strong evidence that formation/elimination are stochastic -- hence we do not know!

Another thing which is not clear from your question, as username_0 mentions, is at what age you are considering. Early development of synapses is [more well understood](http://en.wikipedia.org/wiki/Synaptogenesis#Synapse_Formation_Specificity) and it may be the case that during early development a group of mechanisms determine why/where/how a synapse forms/eliminates and during adult another set of mechanisms are in charge.

For example, in the early post-natal visual system, [it is found that cells have responses with similar properties as adult; however, later on in development visual experience is required to maintain these properties](http://www.ncbi.nlm.nih.gov/pubmed/671298). [Furthermore, these changes must occur within a critical period for activity-dependent plasticity.](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2822731/)


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