Harvard brain images: Cat versus rat

Scientists can now see how neurons in animal brains react to different visual stimuli. Alzheimer's might not be far behind.

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Have you ever wondered what's passing through your kitten's mind? Microscopy techniques pioneered at Harvard Medical School can now give you an answer.


Photo: Harvard Medical School
Time lapse images reveal how
neurons react to visual stimuli
such as moving diagonal lines.

Researchers at the university have captured images from living animal brains, a milestone in trying to understand how neurons interact with each other inside the brain. Ultimately, the technique could be used to analyze neurodegenerative diseases like Alzheimer's.

Time lapse images released earlier this month provide a close-up of the neural circuits that produce vision in cats and rats. The subject animals were shown different pictures of black and white stripes in horizontal, vertical and diagonal patterns. The different patterns caused different groups of neurons to fire, represented by lights blinking off and on in the images.

"This technique allows us to see the brain seeing," R. Clay Reid, a professor of neurobiology at HMS, said in a statement.

Scientists have captured images of live neurons in the past but typically could only view a few cells at a time. This new technique, which can create images of larger tissue regions, could help researchers understand how--on a large scale--neurons work together to coordinate higher-level functions. It will also give researchers a deeper understanding of brain structure.

In a cat, for instance, researchers found that neurons sharing the same characteristic--such as increased sensitivity to slanted (rather than vertical) lines--are grouped together in the brain. Narrow borders separate nerve types.

To obtain the images, Reid and research fellow Kenichi Ohki filled neurons in cats and rats with a dye that glows when calcium levels in the animal rises, a sign that neuron activity is increasing. They then illuminated the cells with a high-powered laser and used an advanced microscope to create the time lapse images.

The nerve cells captured in the images are from the visual cortex responding to image fragments. Some regions fire when the animal sees horizontal lines; others fire off when leftward or rightward movement is perceived.

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