Abstract
You've probably heard about differences between the left brain and the right brain in people. Did you ever wonder where that came from? Do other animals have specialized brain hemispheres too? One hypothesis has it that brain lateralization evolved as a survival mechanism in animals with eyes on the sides of their heads. One eye could focus on finding food, while the other watched out for predators. This project tests that hypothesis by looking for left-right bias in feeding behavior in lizards.Summary
Objective
The goal of this project is to see if lizards exhibit a bias for striking either to the left or to the right when feeding.Introduction
There is a large body of evidence indicating that, in most people, the two halves of the human brain are specialized for different functions. In other words, there is evidence for lateralization (sidedness) of brain function. The goal of this project is to look for evidence of lateralization in another animal, the lizard. By studying the behavior of animals besides humans, we can hope to gain an understanding of when and how lateralization of brain function evolved. This broad approach is called comparative neuroscience, because comparisons are made between the brains and behavior of different species.
The earliest evidence for lateralization of brain function in humans came from studies of people who had brain damage on one side of the brain due to injury or stroke. The most obvious finding was that each side of the brain controlled the opposite side of the body. Damage to the left side of the brain can cause loss of sensation, weakness, or paralysis in body parts on the right side of the body. Conversely, damage to the right side of the brain can cause loss of sensation, weakness, or paralysis in body parts on the left side of the body.
Another finding was that damage to the left hemisphere of the brain frequently caused the injured person to experience difficulty in producing or understanding language. Some patients might be able to understand language (as evidenced by their ability to act in response to a question or request), but be unable to give a spoken response. Other patients might be able to speak, but when they did, the grammar was so garbled that they could not be understood. Collectively, these different types of problems with language production, comprehension, or both are called aphasia. In the majority of people, the brain areas specialized for language are in the left side of the brain. Some people (anywhere from 5 to 40% of the population) have a right-hemisphere specialization for language, or both hemispheres involved in language production and comprehension (Chudler et al., date unknown, Brain Australia, 2003).
Damage to the right side of the brain tended to cause problems with spatial perception. For example, patients with damage to the right hemisphere might ignore sensory stimulation that occurred on their left side. When asked to draw a clock face, they might draw a complete circle, but then put all of the clock numbers on the right-hand half of the clock face. The symptoms could even extend to the patient's perception of their own body. For example, they might neglect to shave the left side of the face, or to dress the left side of the body. They might not even recognize the limbs on the left side of the body as their own. Patients with right hemisphere strokes may also lack awareness of or insight into their condition (Brain Australia, 2003).
The finding of brain lateralization in humans leads curious scientists to wonder how and why such specialization of the two brain hemispheres evolved. Comparative neuroscience can be used to try to answer these types of questions. One hypothesis about the evolutionary significance of brain lateralization is that it helped to prevent conflict of response between the two hemispheres. For example, consider animals with laterally-placed eyes (like most birds and lizards). In these animals, each eye is mostly concerned with only one half of the visual field. The left eye (which projects to the right side of the brain), looks at the left half of visual space, and the right eye (which projects to the left side of the brain) looks at the right half of visual space. Therefore, the reasoning goes, if one brain hemisphere is dominant for a certain survival behavior (avoiding predators, for example), and the other is dominant for a complementary survival behavior (finding food, for example), then conflicts between survival behaviors are more easily avoided (Bisazza et al., 1998).
Previous studies have found evidence for lateralization of escape behavior, communication between members of a single species, paw preference, feeding behavior, and aggressive responses (Bisazza et al., 1998). In this project, you will study feeding behavior in lizards to see if there is a bias to one side or the other when the lizard strikes at food.
Terms and Concepts
To do this project, you should do research that enables you to understand the following terms and concepts:- Brain lateralization (i.e., left-brain, right-brain specialization)
- Comparative neuroscience
- Visual fields in lizards
Questions
- Which side of the brain controls the left side of a lizard's body?
- Which side of the brain controls the right side of a lizard's body?
Bibliography
- For information on brain lateralization in humans, see:
- Chudler, E., et al., date unknown. 'Oh Say Can You Say:' The Brain and Language, Neuroscience for Kids, University of Washington, Seattle. Retrieved April 24, 2007.
- Brain Australia, 2003. What Are the Effects of Stroke? The Brain Foundation, Australia. Retrieved April 24, 2007.
- For information on brain lateralization in animals, see:
Rogers, L.R., date unknown. Survival with an Asymmetrical Brain, School of Biological Sciences, University of New England, New South Wales, Australia. Retrieved April 24, 2007. - For an advanced article on the evolution of brain asymmetry, see:
Bisazza, A., L.J. Rogers and G. Vallortigara, 1998. "The Origins of Cerebral Asymmetry: A Review of Evidence of Behavioural and Brain Lateralization in Fishes, Reptiles and Amphibians," Neuroscience and Biobehavioural Reviews 22 (3): 411–426.
Materials and Equipment
To do this experiment you will need the following materials and equipment:- Lizard. You can use your own pet lizard or get one from a pet store. A kit is also available from Carolina Biological (item #: 147252).
- The kit includes a large terrarium with a light, soil, moss, tropical plants, anole (American chameleon), and misting bottle.
- Test (or home) cage with transparent top
- Live crickets, available from a pet store or Carolina Biological, item #: 143550
- Video camera
- Tripod
- Monitor for video playback
- Plastic wrap
- Ruler
- Marker
- Protractor
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Experimental Procedure
- Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
- Set up the video camera on a tripod so that you can record the lizard's movements inside its cage.
- Place a small number of crickets in the cage. Record the lizard's movements with the video camera.
- Collect enough video recordings so that you can analyze 40 separate feeding events. Each time the lizard strikes at a cricket counts as one event, whether or not the lizard succeeds in catching the cricket.
- Play back the video tape on a monitor to measure the direction of the strike for each feeding event.
- Cover the monitor with a sheet of plastic wrap.
- Identify the time point on the video when the lizard made its first move toward the target cricket.
- At this time point, mark the centerline of the lizard's head with a marker and ruler. The centerline should be perpendicular a line connecting the centers of the two eyes, and halfway in between the two eyes.
- Advance the tape frame by frame. Relative to the centerline you drew, does the lizard move to the left, to the right, or straight ahead in order to strike at the target cricket?
- Was the strike successful or not?
- Analyze at least 40 separate feeding events. You will need to collect data on many separate days to reach this number.
- Is the lizard more likely to strike to the left or to the right? Or are strikes to each side about equally likely?
- Is the lizard more likely to succeed when striking to the left or to the right? Or are strikes to each side about equally successful?
Ask an Expert
Variations
- Data from a single lizard is interesting, but the experiment would be even better if you collected data from multiple lizards. Maybe you could team up with other lizard owners, either locally or over the Internet in order to get data from multiple animals. (Make sure to get approval from your parents first.)
- For experiments on brain lateralization in other pets, see these Science Buddies projects:
Careers
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