Friday, November 14, 2008

20 Second Memory Can Save a Life

Earlier in the semester, we talked about certain animals that used specific techniques to escape their predators such as the moths that used the E1 and E2 receptors in their ears to detect how far or close the bat was from them so that they could get away in time. Likewise, Zebrafish larvae use a rare form of memory to get away from its predators' attacks. An experiment performed on the Zebrafish larvae by researchers at the University of California, Berkeley showed that the larvae seem to have the ability to remember a rhythm taught to them by using flashes of light for about 20 seconds after the flashes stop. In the experiment, when the light was flashed the larvae moved their tails according to the beat of the flashes, and when the light was turned off the larvae continued to move its tail in the same exact beat for about 20 seconds longer. Also the brain activity was examined during the flashing and after the flashing stopped, and the results showed that their brains portrayed activity that was adjusted to the rhythm (of the flashes) even after the flashes ceased .

Researchers believe that the Zebrafish larvae use this short span of memory to their advantage. To us humans 20 seconds might mean absolutely nothing but as for the Zebrafish whose greatest fear is being attacked by the dragonfly larvae, 20 seconds mean the chance to live a little longer than expected. Researchers say that the dragonflies' attacks may be somewhat rhythmic and thus by learning the rhythm of their attacks the Zebrafish are able to predict and break away from the next attack.

The article can be found here.

Update: Well the experiment was done to get an in depth idea of how animals keep track of smaller increments of time. For instance we know that many animals regulate their day through their internal biological clock known as the circadian rhythm, but researchers are now interested to know if they are able to perform activities that require them to keep account of smaller periods of time ("like how quickly their predators are approaching," In the specific experiment explained in my article, the researchers saw that the zebrafish larvae flipped their tails every time the light flashed at six second intervals, and even after the lights were turned off they continued to flip their tails at the same rhythm very precisely. Researchers tested the larvae's ability to learn the rhythms at different durations and frequencies of the light flashing and they never failied to learn the pattern. Even though they weren't able to remember the pattern for too long, as a matter of fact no longer than 20 seconds this still proves that they are able to keep track of small intervals of time (in seconds and minutes) and thus can use this to defend themselves from their predators.

Also some of you were confused with how this memory span actually helps them escape from their predators. It is not that the flashing of the lights exactly imitates their predators attacks, but them being able to learn a rhythm helps them predict the next attack and escape as fast as possible. In terms of the zebrafish larvae whose predator is the dragonfly larvae, the 20 second memory span does seem quite beneficial. The dragonfly larvae is known to be very unsuccessful in attacking its prey. So when the dragonfly first misses its prey, it takes them a couple of seconds to
re-adjust and attack again, thus if the dragonfly misses a couple of times it allows the zebrafish to learn the pattern of the attack and predict the next attack and escape accordingly.

Posted by Tazneena Ishaque (9)


At 11:12 PM, Blogger PWH said...

This is really interesting, but I do not quite understand what is happening. If the larvae only remember the flashes 20 seconds after they stop how could that save their life? I get that the dragonfly larvae have rhythmic attacks, but what good does it do if they get attacked after the 20 seconds is up? Do they only learn if the dragonfly larvae miss them and then try to attack within the 20 seconds? It just doesn't seem that it would be that beneficial to them if they have to keep relearning it.

-Tara Quist

At 10:30 AM, Blogger PWH said...

This comment has been removed by the author.

At 10:31 AM, Blogger PWH said...

Are there only certain rhythms that they are able to remember, and as a follow-up question, is the rhythm of the flashing light at all similar to the rhythm of a dragonfly attack?

-Benjamin Spozio

At 1:54 PM, Blogger PWH said...

so they visualize the blinking lights as the dragonfly larvae blinding the light from the sun? Very cool topic though, it makes sense that zebrafish larvae would use some stimuli so simple as blinking light as a signal of danger because their brains are small and undeveloped.

-Joe Alonzo

At 3:07 PM, Anonymous Anonymous said...

How exactly is the attack of the dragonfly rhythmic, and also, how does the flashing of a light mimic an attack? It's a bit hard for me to visualize how learning a rhythm would allow the zebrafish to avoid attack, but maybe I need to see it in action. Interesting post.

Jane de Verges

At 3:36 PM, Anonymous Anonymous said...

This is interesting. What I want to know is, what can they do in those extra 20 secs to escape the predator? Is there anything that can be done to extend the 20 secs memory to be longer?
-Sasha Rogers

At 3:43 PM, Blogger PWH said...

I think I understand what what is happening- Light is flashed at a certain frequency in the environment of the Zebra fish larvae, and the Zebra fish larvae move their tails using the same frequency as the flashing light, and continue for 20 seconds the same frequency of tail movements even after the flashing light has stopped. In you're blog post, the predator that may induce this behavior is a little unclear because you state the predator is a dragonfly at first, then you later refer to the predator as a dragonfly larvae. Overall the whole concept of the Zebra fish larvae memory span is brilliant, with the Zebra fish larvae having such a useful survival mechanism a very early stage of life.

-Kiel Boutelle

At 4:11 PM, Blogger PWH said...

interesting, does this behavior stay with them when they grow up or is it specific to the larvae stage?

Hessom Minaei

At 4:35 PM, Anonymous Anonymous said...

Since dragonfly larvae are the chief predators to these zebrafish larvae and it takes the dragonfly seconds to adjust their attack, this 20 seconds seems like it is plenty of time to elude most capture. I wonder if the zebrafish memory increased slowly over time as they were predated by dragonfly larvae, or did they start out with 20 seconds of memory? Maybe each memory space is a kind of pre-adaptation to more memory time?

Allan Eldridge

At 5:51 PM, Anonymous Anonymous said...

This is interesting, but I don't quite understand. You say that the fish can use the information to break away from the next attack, but wouldn't that only be effective if the next attack occured in the next 20 seconds? Or maybe if the fish is observing the dragon larvae attack another fish, he has a better chance of getting away if the the dragonfly switches to attacking him?

-Corinne Delisle

At 10:32 PM, Blogger PWH said...

Interesting post! I am somewhat confused on how a flashing light mimics a dragonfly larva. But it is very interesting how they can remember this rhythm to avoid predators. Does the 20 seconds give the zebra fish larvae a head start before the predator is close enough to attack?

-Carlos A. Varela

At 10:56 PM, Anonymous Anonymous said...

Really interesting article and I really liked your summary and connection to material in the class - it was really helpful in trying to understand the article material! I am curious to know how a dragonfly attacks rhythmically. Do the larvae see someone originally attacked and then move away and why would a dragonfly attack in such a fashion?

Maura Mulvey

At 11:04 PM, Blogger PWH said...

It is amazing that what seems to be such a short memory span can be lifesaving for this species. Is a 20second memory span relatively long for fish? In this experiment, they used flashes of light to create a rhythm. Do you know what sense the rhythmic attacks of the dragonflies appeal to? Interesting article.

-Helen Thi


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