<p>Development of patterns of synaptic connection contains elements of both outgrowth and pruning. For example, this paper from zebrafish development illustrates both those mechanisms, which appear to be tightly linked:</p>

<blockquote>
  <p>Meyer MP, Smith SJ. 2006. Evidence From in Vivo Imaging That Synaptogenesis Guides the Growth and Branching of Axonal Arbors by Two Distinct Mechanisms. Journal of Neuroscience 26:3604–3614.</p>
</blockquote>

<p>In more advanced animals (e.g. cats), there is also evidence for both outgrowth and pruning:</p>

<blockquote>
  <p>Callaway EM, Katz LC. 1990. Emergence and Refinement of Clustered Horizontal Connections in Cat Striate Cortex. Journal of Neuroscience 10:1134–1153.</p>
</blockquote>

<p>There is also evidence for generation of new neurons in adult humans, which implies that new synaptic connections must be forged to integrate newborn neurons into existing networks:</p>

<blockquote>
  <p>Ericsson et al. 1998. Neurogenesis in the adult human hippocampus. Nature Medicine 4:1313-1317.</p>
</blockquote>

CC BY-SA 3.0
2016-10-14T14:40:39.297Z
2016-10-14T14:40:39.297Z
Dylan Richard Muir
<p>The phrase "fire together, wire together" comes from an explanation of <a href="https://en.wikipedia.org/wiki/Hebbian_theory" rel="nofollow noreferrer">Hebbian Learning</a> and refers to the adaptation of synapses as a response to the firing of already connected neurons. This is one of several <a href="https://en.wikipedia.org/wiki/Synaptic_plasticity" rel="nofollow noreferrer">Synaptic Plasticity</a> mechanisms. Two others that exist are <a href="https://en.wikipedia.org/wiki/Long-term_potentiation" rel="nofollow noreferrer">Long Term Potentiation</a> (strengthening and creation) and <a href="https://en.wikipedia.org/wiki/Long-term_depression" rel="nofollow noreferrer">Long Term Depression</a> (weakening and destruction).</p>

<p>All of these mechanisms are still being researched heavily to understand their detail better. However, I hope this gives you a good starting point.</p>

CC BY-SA 3.0
2016-07-06T21:59:20.800Z
2017-10-31T18:43:26.477Z
2017-10-31T18:43:26.477Z
Seanny123
<p>Are new connections continuously forged in the adult human brain, or do we just start all wired together and then prune until we have something we like?</p>

CC BY-SA 3.0
2016-07-06T17:29:23.090Z
I believe it is a bit of both. But that will likely depend per brain region.
Robin Kramer-ten Have
<neuroscience><theoretical-neuroscience>
Can "fire together, wire together" be undone?
DJG
# Can "fire together, wire together" be undone?

(Asked by: username_0 on 2016-07-06)

Are new connections continuously forged in the adult human brain, or do we just start all wired together and then prune until we have something we like?

**Tags:** neuroscience, theoretical-neuroscience

> **Comments:**
> **username_1**: I believe it is a bit of both. But that will likely depend per brain region.  

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## 2 answers

### Answer by username_2 on 2016-10-14. Score: 3 | Accepted answer

Development of patterns of synaptic connection contains elements of both outgrowth and pruning. For example, this paper from zebrafish development illustrates both those mechanisms, which appear to be tightly linked:

> Meyer MP, Smith SJ. 2006. Evidence From in Vivo Imaging That Synaptogenesis Guides the Growth and Branching of Axonal Arbors by Two Distinct Mechanisms. Journal of Neuroscience 26:3604–3614.

In more advanced animals (e.g. cats), there is also evidence for both outgrowth and pruning:

> Callaway EM, Katz LC. 1990. Emergence and Refinement of Clustered Horizontal Connections in Cat Striate Cortex. Journal of Neuroscience 10:1134–1153.

There is also evidence for generation of new neurons in adult humans, which implies that new synaptic connections must be forged to integrate newborn neurons into existing networks:

> Ericsson et al. 1998. Neurogenesis in the adult human hippocampus. Nature Medicine 4:1313-1317.


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### Answer by username_3 on 2016-07-06. Score: 5

The phrase "fire together, wire together" comes from an explanation of [Hebbian Learning](https://en.wikipedia.org/wiki/Hebbian_theory) and refers to the adaptation of synapses as a response to the firing of already connected neurons. This is one of several [Synaptic Plasticity](https://en.wikipedia.org/wiki/Synaptic_plasticity) mechanisms. Two others that exist are [Long Term Potentiation](https://en.wikipedia.org/wiki/Long-term_potentiation) (strengthening and creation) and [Long Term Depression](https://en.wikipedia.org/wiki/Long-term_depression) (weakening and destruction).

All of these mechanisms are still being researched heavily to understand their detail better. However, I hope this gives you a good starting point.


---

