Inside a moth’s brain

Posted by Synnøve Ressem

The moth species Heliothis virescense is only a few centimetres long, but it is every cotton farmer’s nightmare. These insects thrive in cotton fields, where they do roughly NOK 14 billion in damage annually.

It is estimated that at least 10 000 people die each year as a direct consequence of chemical pesticides. One goal of insect research is to develop biological controls for the world’s worst insect pests, thus reducing the use of pesticides.

But if you are going to fight the enemy, you have to know the enemy. That is one of the reasons that researchers in NTNU’s Department of Biology are doing advanced brain surgery on this tiny insect. Another reason is that what happens in a moth’s brain is not so different from what happens in the human brain. That means understanding the insect’s senses, learning capabilities and memory will help increase our understanding of how the human brain works.

Norwegian researchers moths
Photo credit: Ole Morten Melgård

PhD candidate Bjarte Bye Løfaldli and Dr. Pål Kvello are studying the sense of smell, memory and taste in insects. They have invited this Gemini journalist into their little operating room, where a greyish yellow moth is stuck into a wax lump under a strong microscope, ready for microsurgery.

The sound of a brain

Through the microscope, I look into two huge eyes. My gaze continues to a scalpel, which cuts into the head and exposes the insect’s brain. A glass electrode, with a tip less than one micrometre, is filled with a contrast fluid and inserted into the grey-white tissue of the brain.

“There’s no anesthesia. Isn’t it unbearably painful?”

“Not at all,” replies surgeon Kvello calmly, and notes the new data in a notebook. “Insects have no pain receptors, nor do they have the cognitive traits needed to experience pain the way we do. The experience of pain is created in the brain. Insects don’t have a system that can convey information about pain,” Kvello assures me.

A moment later I’m sitting in front of a computer screen with headphones on, and I’m experiencing something amazing: I’m listening to recordings of a moth’s brain at work – or more formally, the sound of the signals from the brain cells. The sound is unique, it can best be described as a kind of ticking. The signals come in an even beat, like a relaxed pulse.

Sugar Kick

Suddenly the brain activity explodes with insane speed and strength.

“The moth just got a sugar rush,” explains Kvello.

The point of this research is to understand how the neural network in the olfactory system is constructed, and how signals between the cells are mediated. The signals have to be decoded, which is done by putting electrodes into the individual neurons that make up the network. This makes it possible to see and hear the signals when they pass through the individual nerve cell on the way to the other cells that it has contact with.

The signals are sent when the cell is stimulated by a scent that the nerve cell helps to inform the brain about. In this case, the trigger is sugar. When the stimulation is done, the scientists inject a fluorescent dye into the brain. The dye lights up under a light of a specific wavelength. Thus, the researchers can see the cell and the brain structures to which it is connected.

An average brain

In the last part of the experiment the brain is cut out and prepared. Now scientists can peek at every single cell under a microscope. Their efforts have enabled them to create an entire deck of cards with images, which together show the cell in three dimensions. These images are used to reconstruct the cells and create a three-dimensional model of them.

moth brain illustration
Moth brain model. The blue areas are the primary smell centre. Learning and memory take place in areas that are coloured green. The protrusions on the sides are the visual areas, otherwise known as eyes. Illustration: NTNU Department of Biology

“We have collected many such nerve cell models, each from different individuals. We wanted to visualize them together. In collaboration with a researcher in Germany, we have managed to construct a standard brain model. We can call it an ‘average’ brain,” says Løfaldli.

The researchers used other brains that they had removed that were filled with dye to make three-dimensional models, just as they did with the neurons. The positions of brain structures, volumes and surfaces were compared using an algorithm in a computer program. This gave them an average that was the basis for the standard model.

“Now we can take a nerve cell from any moth from the species we are studying, and put it into the brain model, in exactly the same place as it was in the original brain. By inserting several nerve cells, we can see how they are positioned relative to each other, how they interact with each other, and thus how the network is put together,” explains Løfaldli and Kvello.

“When we put together this information with information from the signals, we know what one cell in the network told the other cells. Thus we can see how our decoded signal is transmitted in the network.”

From insects to humans

Scientists now know exactly which part of the brain works with what. The moth’s brain contains about one million nerve cells. In comparison, the human brain has more than one hundred billion nerve cells.

“The moth’s odour system is a micro-network with a relatively low number and few types of neurons. That makes it a good model for understanding how the brain works. Researchers who study human brains have to be reasonably satisfied with seeing images of the brain without being able to go into certain nerve cells. We have the great advantage that we can study the entire neural network in a brain that is intact. That enables us to see how individual cells work and interact with each other,” says Løfaldli.

He is confident that the project will generate new information about how the senses are involved in learning and memory, not only in insects, but in all mammals, including our two-legged variety.

Professor May-Britt Moser at the Kavli Institute at NTNU, one of the world’s foremost scholars on the biology of memory, agrees.

“Brain cells in insects and higher animals use largely the same cellular mechanisms. Each species didn’t keep reinventing the wheel as they evolved. Therefore, studies of insects and snails provide us with important information about the human brain in the end,” she confirms.

Smell, taste, learning

Løfaldli and Kvello work in a research group led by Professor Hanna Mustaparta, who is an expert on the neurobiology of insects.

“This is primarily basic research,” Mustaparta explains. “We want to find out how both people and animals are able to detect scents and flavour precursors. Learning and memory are also very important in this context.”
She believes that insects are excellent models for this type of research. They have well-developed senses of smell and taste, which are crucial for them to survive.

“More than two-thirds of all species on Earth are insects. This great diversity has resulted in amazing environmental adaptations. It allows us to determine both the mechanisms that are common to all, and mechanisms that have particularly evolved in certain species. We compare the mechanisms in other animals and humans. That gives us an understanding of smell and taste in a broader context,” says Mustaparta.

Featured image: A magnified picture of a moth with its brain exposed (inserted into the picture). The moth is two centimetres long, and the brain is smaller than a pinhead.
Photo credit: NTNU Department of Biology

Synnøve Ressem works as a science journalist at GEMINI magazine, and has been a journalist for 23 years. She is employeed by the Norwegian University of Science and Technology in Trondheim.

August 24, 2010

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