<p>Interesting question! </p>

<p>The paper you read should have inserted an appropriate citation. Moreover, "little input" is a subjective statement and doesn't make much sense in the context, as it can mean that there are few efferent axons (which may still have large effects on retinal functioning), or that the efferent input is relatively unimportant when compared to the afferent visual projections (which may indeed be so). In fact, I think what the authors actually try to say is that there is not much data available on efferent retinal input. </p>

<p>To answer your question: The efferent projections from the brain back to the retina, referred to as <strong>centrifugal projections</strong>, are indeed not extensively studied. The studies done were mainly performed in avian species. However, centrifugal projections have been shown to exist in <strong>monkeys and humans</strong>. In the macaque, they originate in the brain in the <strong>hypothalamus</strong>, and constitute <strong>histaminergic</strong> neurons which are thought to be involved in <strong>regulating blood flow</strong> in the inner plexiform layer of the retina. They may also be involved in <strong>regulating retinal dopaminergic amacrine cells</strong>, at least in mice and other species. Specifically, dopaminergic amacrine cells in the retina may be receiving centrifugal input from the <strong>suprachiasmatic nucleus</strong> (SCN, situated in the hypothalamus) where <strong>circadian rythms</strong> are initiated from melanopsin containing ganglion cells. The dopaminergic amacrine cells in the retina target photoreceptors, horizontal cells and amacrine cells and thereby regulate the retina depending on the state of the <strong>circadian clock</strong>. Most studies are histological in nature and functional data remains scant.  </p>

<p><strong>Reference</strong>:<br>
<a href="http://webvision.med.utah.edu/book/part-iii-retinal-circuits/feedback-loops/" rel="nofollow">Webvision - Feedback Loops (by Helga Kolb)</a>          </p>

CC BY-SA 3.0
2014-12-02T11:11:31.843Z
2014-12-03T00:08:43.503Z
2014-12-03T00:08:43.503Z
AliceD
<p>Gollisch &amp; Meister (2010) state that "the retina receives little efferent input from the brain" (p. 157). Could anyone describe what exactly this "little efferent input" (where it originates, whether it is present in primates, its function ...) is or point me to the relevant literature?</p>

<p>Here is the paper in question:</p>

<p><a href="http://hebb.mit.edu/courses/connectomics/Gollisch%20Meister%20eye%20smarter%20scientists%20believed%20neural%20computations%20circuits%20retina%2010.pdf" rel="nofollow">Gollisch, T., &amp; Meister, M. (2010). Eye smarter than scientists believed: neural computations in circuits of the retina. Neuron, 65, 150–64.</a></p>

CC BY-SA 3.0
2014-12-01T15:14:50.263Z
After a quick google search I would assume it is related to ['efferent nerve fibers'](http://en.wikipedia.org/wiki/Efferent_nerve_fiber), which _I personally_ would then interpret as meaning the eyes get little input from the central nervous system. This from a very superficial non-expert interpretation seems to make sense. :) Good question!
Steven Jeuris
CC BY-SA 3.0
2014-12-01T17:14:06.907Z
Generally, I am aware what "efferent" mean for nervous system. But I wasn't able to find literature on efferent input for retina from the brain. Some say that there is no such input (e.g., "The output from the Lateral Geniculate Nucleus (LGN) to sensory source (retina) does not exist in primate, but this is not always so with other lower animals", http://people.idsia.ch/~luciw/papers/tamd11-weng.pdf), but Gollisch & Meister seem to think that it exists for vertebrates.
Andrey Chetverikov
CC BY-SA 3.0
2014-12-01T17:21:00.730Z
I edited the question to make it more clear
Andrey Chetverikov
CC BY-SA 3.0
2014-12-02T13:54:50.193Z
Two more links that were provided to me on FB:
http://www.ncbi.nlm.nih.gov/pubmed/17059846, http://www.ispsychophysics.org/fd/index.php/proceedings/article/viewFile/573/564
Andrey Chetverikov
<vision><neuroanatomy><neurophysiology>
What is the meaning of "little efferent input" to retina?
Andrey Chetverikov
# What is the meaning of "little efferent input" to retina?

(Asked by: username_0 on 2014-12-01)

Gollisch & Meister (2010) state that "the retina receives little efferent input from the brain" (p. 157). Could anyone describe what exactly this "little efferent input" (where it originates, whether it is present in primates, its function ...) is or point me to the relevant literature?

Here is the paper in question:

[Gollisch, T., & Meister, M. (2010). Eye smarter than scientists believed: neural computations in circuits of the retina. Neuron, 65, 150–64.](http://hebb.mit.edu/courses/connectomics/Gollisch%20Meister%20eye%20smarter%20scientists%20believed%20neural%20computations%20circuits%20retina%2010.pdf)

**Tags:** vision, neuroanatomy, neurophysiology

> **Comments:**
> **username_1**: After a quick google search I would assume it is related to ['efferent nerve fibers'](http://en.wikipedia.org/wiki/Efferent_nerve_fiber), which _I personally_ would then interpret as meaning the eyes get little input from the central nervous system. This from a very superficial non-expert interpretation seems to make sense. :) Good question!  
> **username_0**: Generally, I am aware what "efferent" mean for nervous system. But I wasn't able to find literature on efferent input for retina from the brain. Some say that there is no such input (e.g., "The output from the Lateral Geniculate Nucleus (LGN) to sensory source (retina) does not exist in primate, but this is not always so with other lower animals", http://people.idsia.ch/~luciw/papers/tamd11-weng.pdf), but Gollisch & Meister seem to think that it exists for vertebrates.  
> **username_0**: I edited the question to make it more clear  
> **username_0**: Two more links that were provided to me on FB: http://www.ncbi.nlm.nih.gov/pubmed/17059846, http://www.ispsychophysics.org/fd/index.php/proceedings/article/viewFile/573/564  

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## 1 answers

### Answer by username_2 on 2014-12-02. Score: 5 | Accepted answer

Interesting question!

The paper you read should have inserted an appropriate citation. Moreover, "little input" is a subjective statement and doesn't make much sense in the context, as it can mean that there are few efferent axons (which may still have large effects on retinal functioning), or that the efferent input is relatively unimportant when compared to the afferent visual projections (which may indeed be so). In fact, I think what the authors actually try to say is that there is not much data available on efferent retinal input.

To answer your question: The efferent projections from the brain back to the retina, referred to as **centrifugal projections**, are indeed not extensively studied. The studies done were mainly performed in avian species. However, centrifugal projections have been shown to exist in **monkeys and humans**. In the macaque, they originate in the brain in the **hypothalamus**, and constitute **histaminergic** neurons which are thought to be involved in **regulating blood flow** in the inner plexiform layer of the retina. They may also be involved in **regulating retinal dopaminergic amacrine cells**, at least in mice and other species. Specifically, dopaminergic amacrine cells in the retina may be receiving centrifugal input from the **suprachiasmatic nucleus** (SCN, situated in the hypothalamus) where **circadian rythms** are initiated from melanopsin containing ganglion cells. The dopaminergic amacrine cells in the retina target photoreceptors, horizontal cells and amacrine cells and thereby regulate the retina depending on the state of the **circadian clock**. Most studies are histological in nature and functional data remains scant.

**Reference**:  
[Webvision - Feedback Loops (by Helga Kolb)](http://webvision.med.utah.edu/book/part-iii-retinal-circuits/feedback-loops/)


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