Loops

Eyewire General
#1

IANANS, I am not a neuro-scientist. However, this seems like an interesting question to help the ‘layman’ think more critically about this task. I have noticed on occasion that I will have loops in the neurons. It seems un-intuitive to me that this would be desirable in how the brain is wired. But I figured I would ask if this was actually found in reality and or if it could be used as criterion for connectome-ing.


Turing
#2
Yup, the branches of a neuron sometimes touch each other. I used the word "touch", because they are not connected. Though they may be in contact, they are separated by cell membrane and there's no reason to think that the two ends of the branches "talk" to each other. But, nobody really knows why and how this structure forms and whether there is any functional significance. 

This is often the case between two neurons either. Two neurons can touch each other without making synapse. In fact, discriminating "casual contacts" and actual synapses is one of the challenges we have. So, maxim of the day: all that contacts is not a synapse. 

JK
#3

AFAIK, true loops in neurons are believed to not exist. However, self-touch can happen, and appears to happen in this dataset. And a location of self-touch may sometimes harbor a synapse.  A synapse of a neuron onto itself is known as an “autapse.” 


When neurons are cultured in vitro, they make lots of autapses.  Whether autapses are common in vivo, i.e. under natural conditions, has been more controversial. Here is a review by Bekkers on the subject:
http://119.93.223.179/ScienceDirect/Current%20Biology/08-02/sdarticle_011.pdf

That being said, we don’t know whether the self-touches in this retinal dataset are synaptic contacts. Perhaps we can discuss the problem of synapse identification later.
#4

That’s really interesting, I had never known or considered the possibility of autapses. It makes me wonder what sort of affect that would have. (Amplification loops maybe? To re-up the signal strength.) So thanks for an interesting factoid for the day and something new to ponder while I wire.

Or I could just read the article. Even more interesting. Taking to an electronics metaphor, they could feasibly do many things. Filters and gates are pretty intriguing in a functional sense. Anyway thanks for the info.