The retina receives signals from all over the brain, and that is kind of weird

As a neuroscientist, when I think of the retina I am trained to think of a precise set of neurons that functions like a machine, grinding out the visual basis of the world and sending it on to the brain. It operates independently of the rest of the system with the only feedback coming from muscles that move the eye around and dilate the pupils. So when someone [Philipp Berens] casually mentioned to me that yes, the retina does in fact receive signals from the brain? Well, I was floored.

I suppose I should not have been surprised. In fruit flies, there has been a steady accumulation of evidence that the brain sends signals to the eye to get it ready to compensate for any movement the animal will make. Intuitively, that makes a lot of sense. If you are trying to make sense of the visual world, of course you would want to be able to compensate for any sudden changes that you already know about.

It turns out that there is a huge mass of feedback connections from the brain to the retina in birds and mammals, something termed the centrifugal visual system. And inputs are sent via this system from both visual areas and non-visual areas (olfactory, frontal, limbic, and so on). So imagine – your eye knows about what you are smelling. Why? In order to do what?

The answer, it turns out, is that we don’t know. It sends all sorts of neurotransmitters and neuromodulators. The list of peptides it sends are long (GnRH, NPY, FMRF, VIP, etc) as is the list of regions that send feedback to the retina. It seems as if which regions send feedback to the retina is very species-specific, suggesting something about the environment each animal is in. But why?

This is a post long on questions and short on answers. It is more a reminder that the nice, feedforward systems that we have simple explanations for are really complex, multimodal systems designed to create appropriate behaviors in appropriate circumstances. Also it is a reminder to myself about how little I know about the brain, and how mistaken I am about even the simplest things…

I would love someone more knowledgable than me to pipe up and tell me something functional about what these connections do?

References

Repérant J, Médina M, Ward R, Miceli D, Kenigfest NB, Rio JP, & Vesselkin NP (2007). The evolution of the centrifugal visual system of vertebrates. A cladistic analysis and new hypotheses. Brain research reviews, 53 (1), 161-97 PMID: 17059846

Vereczki, V. The centrifugal visual system of rat. Doctoral Thesis. PDF.

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6 thoughts on “The retina receives signals from all over the brain, and that is kind of weird

  1. Do you mean to say that the retina receives neural feedback from the LGN or elsewhere? Never heard about that. Or are you hinting at indirect feedback through eye fixation, focus and saccades, directed by the FEF?

  2. This is an amazingly interesting concept. Could it be perhaps that receiving information from areas such as, say the olfactory bulb, helps us to know which bipolar cells in our retina to excite and which to inhibit to help sharpen out visual range? Such as we smell a rose and what to find it so we ‘more easily’ see the rose we are looking for because our nose has told us it is there? It would be nice to read some more research on this topic! Thank you for posting!

  3. I think that the idea of thinking of what you see causes neurotransmitters to signal to your retina is complicated. It takes an instant to look at something and realize what it is that your looking at. The neurotransmitters work so fast and I think this is amazing.

  4. Before reading this, I had not thought about the possibility of neurons receiving signals from the brain. It takes some abstract thinking to hypothesize why the brain sends signals to the retina rather than just receive them. I like the idea that Allie had, though. Perhaps, by sending signals to the retina, one can “more easily see” whatever stimulated the brain originally.

  5. Before reading this, I had not thought about the possibility of retinal neurons receiving signals from the brain. It takes some abstract thinking to hypothesize why the brain sends signals to the retina rather than just receive them. I like the idea that Allie had, though. Perhaps, by sending signals to the retina, one can “more easily see” whatever stimulated the brain originally

  6. This post was very surprising to me, I also did not know the brain sent signals to the retina. I guess when you explained that the retinas in fruit flies receive signals from the brain; it made more sense to me. Conceivably, the other senses within our body somehow “prime” our sight to more easily connect what we are sensing. If I touch a soft object without having seen it, maybe my brain sends signals to my retina that narrows down the possible options of what the object could be. This may allow for humans and animals to more quickly recognize objects and make sight more efficient.

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