Ectopic eyes function without connection to brain: Experiments with tadpoles show ectopic eyes that 'see'

Feb 27, 2013
Researchers at Tufts University have shown that transplanted eyes located far outside the head in a vertebrate animal model can confer vision without a direct neural connection to the brain. In this image, a "blind" tadpole without its native (normal) eyes is able to see using functioning ectopic eye located in tail. Dark area in midsection is the stomach. Credit: Images courtesy of D. Blackiston and M. Levin

For the first time, scientists have shown that transplanted eyes located far outside the head in a vertebrate animal model can confer vision without a direct neural connection to the brain.

Biologists at Tufts University School of Arts and Sciences used a frog model to shed new light – literally – on one of the major questions in regenerative medicine, , and sensory augmentation research.

"One of the big challenges is to understand how the brain and body adapt to large changes in organization," says Douglas J. Blackiston, Ph.D., first author of the paper "Ectopic Eyes Outside the Head in Xenopus Tadpoles Provide For Light-Mediated Learning," in the February 27 issue of the . "Here, our research reveals the brain's remarkable ability, or plasticity, to process visual data coming from misplaced eyes, even when they are located far from the head."

Blackiston is a post-doctoral associate in the laboratory of co-author Michael Levin, Ph.D., professor of biology and director of the Center for Regenerative and at Tufts University.

Levin notes, "A primary goal in medicine is to one day be able to restore the function of damaged or missing sensory structures through the use of biological or artificial replacement components. There are many implications of this study, but the primary one from a medical standpoint is that we may not need to make specific connections to the brain when treating sensory disorders such as blindness."

In this experiment, the team surgically removed donor embryo eye primordia, marked with fluorescent proteins, and grafted them into the posterior region of recipient embryos. This induced the growth of ectopic eyes. The recipients' natural eyes were removed, leaving only the ectopic eyes.

revealed various innervation patterns but none of the animals developed nerves that connected the ectopic eyes to the brain or cranial region.

To determine if the ectopic eyes conveyed visual information, the team developed a computer-controlled visual training system in which quadrants of water were illuminated by either red or blue LED lights. The system could administer a mild electric shock to tadpoles swimming in a particular quadrant. A motion tracking system outfitted with a camera and a computer program allowed the scientists to monitor and record the tadpoles' motion and speed.

Eyes See Without Wiring to Brain

The team made exciting discoveries: Just over 19 percent of the animals with optic nerves that connected to the spine demonstrated learned responses to the lights. They swam away from the red light while the blue light stimulated natural movement.

Their response to the lights elicited during the experiments was no different from that of a control group of tadpoles with natural eyes intact. Furthermore, this response was not demonstrated by eyeless tadpoles or tadpoles that did not receive any electrical shock.

"This has never been shown before," says Levin. "No one would have guessed that eyes on the flank of a tadpole could see, especially when wired only to the spinal cord and not the brain."

The findings suggest a remarkable plasticity in the brain's ability to incorporate signals from various body regions into behavioral programs that had evolved with a specific and different body plan.

"Ectopic eyes performed visual function," says Blackiston. "The brain recognized visual data from eyes that impinged on the spinal cord. We still need to determine if this plasticity in vertebrate brains extends to different ectopic organs or organs appropriate in different species."

One of the most fascinating areas for future investigation, according to Blackiston and Levin, is the question of exactly how the brain recognizes that the electrical signals coming from tissue near the gut is to be interpreted as visual data.

In computer engineering, notes Levin, who majored in computer science and biology as a Tufts undergraduate, this problem is usually solved by a "header"—a piece of metadata attached to a packet of information that indicates its source and type. Whether electric signals from eyes impinging on the spinal cord carry such an identifier of their origin remains a hypothesis to be tested.

Explore further: Bees able to spot which flowers offer best rewards before landing

More information: Blackiston, B. J. and Levin, M. (2013). Ectopic eyes outside the head in Xenopus tadpoles provide sensory data for light-mediated learning. J. Exp. Biol. 216, 1031-1040.

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VendicarE
1.6 / 5 (7) Feb 27, 2013
I don't find this particularly surprising.

The eye is conveying very limited sensory information to the existing nervous system and the brain of the tadpole, being more complex than that of the average TeaPublican, is capable of processing it as tactile or some other stimulation and learn to respond to various flavors of stimulus from the eye.
Zep Tepi
1.8 / 5 (5) Feb 27, 2013
I dont see how this means they 'saw' =)

MrVibrating
1 / 5 (4) Feb 27, 2013
Surely the metadata is implicit in the bandwidth size, spectral range and interplay of frequency components that characterise the signals from a given modality?

(ie. if it looks and acts like a certain form of information, maybe it is?)

This also came to mind:

http://medicalxpr...ain.html

Huns
1 / 5 (5) Feb 27, 2013
This looks like simple stimulus-response to me. The animal has learned to associate input from the grafted eye with the pain of being shocked. This doesn't mean that it "sees" anything, but that when the state of the neural network includes certain patterns (which happen to originate in the eye, but could be just about anything else) that it should avoid those. Pattern recognition is the primary task of any animal's brain. I would not suppose anything more convoluted than this.
Tausch
1.6 / 5 (7) Feb 27, 2013
Simplified Hint:
During open brain surgery the awake patient is asked what he/she is experiencing during questioning.

The brain surgeon has applied a generic electric potential to an area of the brain with a probe.

The patient's response is a function of location - where the generic electric potential is applied.

Still in the dark?
More Hints:
All brains...except Tea-publicans... undergo countless dress rehearsals and dry trial runs before a single sensory function ever gets to delivery the real McCoy - light, sound, touch, smell, taste, and all other sensory functions belonging to life.

Still in the dark?
I'm not getting pay to do their research, you know.
And I want them very much to test their hypothesis.
And then to contact me.
Why?
Because they will still be in dark.
C_elegans
2.3 / 5 (3) Feb 27, 2013
Pattern recognition is the primary task of any animal's brain. I would not suppose anything more convoluted than this.


So it's not worth investigating further? If we can identify the genes and molecules enabling ectopic wiring of eyes on a frog tail, then maybe we could enhance its effect. There are currently developed prosthetics that translate vision into electrical impulses on a patients tongue, and those participants can indeed see high contrast images. We can detect activity in the visual cortex of these patients (the region where the brain forms images). How are the electrical patterns being diverted from neurons in the tongue to the visual cortex? We probably should do more to understand the process of neural integration, and ectopic eyes are a convenient model system for doing just that.

http://en.wikiped...rainport
Tausch
1 / 5 (3) Feb 27, 2013
in [the] dark.
Tausch
1 / 5 (3) Feb 27, 2013
pay=paid
Typos, grr.
Yes. Do more to understand the process of neural integration. It's all there to be discovered and revealed. You will love how nature works. When it works. There are exceptions when life forms have political affiliations.
VendicarE
1 / 5 (3) Feb 28, 2013
Quite the contrary. I think they should start experimenting with lower order organisms like American Conservatives.

Vivisection comes to mind. How do those things work?

"So it's not worth investigating further?" - C elegans
temporal_A
1 / 5 (2) Feb 28, 2013
"No one would have guessed that eyes on the flank of a tadpole could see..." That is not true. Many scientists (including me) have guessed and knew this (even at the age of 7 yrs old I knew that it was possible.) It is well known that the sensory/nervous system can be activated by many technological/biological ways. If this signal manages to get to the brain, the brain will adapt and "notice" and "interpret" the signal. Scientist have managed to make blind people see via their tongue. Some blind people can "see" shapes and gauge distance with their ears as bats do...and there are much greater examples too. This science is not new and advancing, thanks to researchers as in the article.
Tausch
1 / 5 (2) Mar 01, 2013
I have a voicegram for the 'brain'. I don't need a header for any of all existing senses.
Why?
All pathways for all senses go to the brain. Now matter how convoluted paths are, those paths all arrive at the brain.
Why?
Because no matter what "header" —a piece of metadata attached to a packet of information that indicates its source and type - you have, the brain does not give a shit from where that information comes or what that information is.

So now your information is there at the brain without a header.
Now what?
It's a voicegram. Remember? You are standing in front of a building (the brain) with 100 billion open windows(neurons) and the only 'header' you got was the path that you had to take to brain (the building.)
So now what?
You shout. It's a voicegram, remember? Whatever the information, every window receives that information.
So now what?
So now it's time for you to search for your header.
Why?
Because you want to test a hypothesis.
Why?
I have no idea.
Gpnum
3 / 5 (2) Mar 02, 2013
This looks like simple stimulus-response to me. The animal has learned to associate input from the grafted eye with the pain of being shocked. This doesn't mean that it "sees" anything, but that when the state of the neural network includes certain patterns (which happen to originate in the eye, but could be just about anything else) that it should avoid those. Pattern recognition is the primary task of any animal's brain. I would not suppose anything more convoluted than this.


Exactly.
The signal generated by the eye doesn't need to be interpreted as visual information to explain the tadpole behavior, it just needs to send a different signal for red and blue light.
Tausch
1 / 5 (3) Mar 02, 2013
Exactly. The signal generated by the eye doesn't need to be interpreted as visual information to explain the tadpole behavior, it just needs to send a different signal for red and blue light.


Exactly. I will ask the editor to delete the following in the above article so no one sees a contradiction to both of your conclusions:
Their response to the lights elicited during the experiments was no different from that of a control group of tadpoles with natural eyes intact. Furthermore, this response was not demonstrated by eyeless tadpoles or tadpoles that did not receive any electrical shock.


Like the customer, the reader is always right.
That careless researcher! How dare he write something to contradict your conclusions and no less your findings!

On behalf of this researcher, I apologize for my colleague.
Won't happen again. Please forgive us.

Moebius
2.3 / 5 (3) Mar 03, 2013
When you connect a stimulus to an input it probably isn't going to change the input's function, it will just be registered as another stimulus. If that spinal nerve was conveying touch then the new eye was probably felt as touch with qualities modified by color.
betterexists
1 / 5 (3) Mar 03, 2013
Far better is to incorporate "Inner Ear" (Cochlea) of Mammals in suitable animals
betterexists
1 / 5 (3) Mar 03, 2013
I also prefer to see an eye put deep on the back of a Goat in its Fetal stage. Once it is born ....if it blinks at flash light focused on the eye....Eureka
Tausch
1 / 5 (3) Mar 03, 2013
You all are asserting that information that acts (an event occurs), has a header.
In all of computational science this is standard.
In all of nature this is never the case.
The hypothesis is testable.
Wait and see.
Huns
1 / 5 (3) Mar 03, 2013
Simplified Hint:
During open brain surgery the awake patient is asked what he/she is experiencing during questioning.

The brain surgeon has applied a generic electric potential to an area of the brain with a probe.

The patient's response is a function of location - where the generic electric potential is applied.

Still in the dark?
More Hints:
All brains...except Tea-publicans... undergo countless dress rehearsals and dry trial runs before a single sensory function ever gets to delivery the real McCoy - light, sound, touch, smell, taste, and all other sensory functions belonging to life.

Still in the dark?
I'm not getting pay to do their research, you know.
And I want them very much to test their hypothesis.
And then to contact me.
Why?
Because they will still be in dark.

Why do you need to inject political opinions into a discussion on biology?
Huns
1 / 5 (3) Mar 03, 2013
Exactly. I will ask the editor to delete the following in the above article so no one sees a contradiction to both of your conclusions:

They responded in the same way, but that doesn't prove that the grafted animals processed the data in their visual cortices, or using any pathway involved in sight.