Detecting motion in vision

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A team of Washington University vision researchers is the first to identify a specific type of cell in the eye that appears to be responsible for the ability to detect motion. Studying retinas in mice, the researchers identified a specific type of cell that transmits information when the retina detects moving objects. When something is moving in the visual field, those cells send signals to other cells that then transmit the information to the brain. Those signals can help mice avoid predators. For humans, understanding how those cells transmit signals may aid in the development of artificial retinas for people who cannot see.

IT?S KIND OF AMAZING THAT THE EYE?S RETINA CAN DETECT AND DISTINGUISH MOVING OBJECTS IN OUR FIELD OF VISION BECAUSE OUR EYES, HEADS AND BODIES ALSO ARE MOVING. SO SOMEHOW, RETINAL CELLS HAVE TO DISTINGUISH BETWEEN OUR MOVEMENTS AND THE MOVEMENTS OF OBJECTS IN THE WORLD AROUND US. AND NOW RESEARCHERS AT WASHINGTON UNIVERSITY SCHOOL OF MEDICINE IN ST. LOUIS HAVE IDENTIFIED A CIRCUIT IN THE MOUSE RETINA THAT?S INVOLVED IN THAT OBJECT-MOTION DETECTION, AND THEIR DISCOVERY EVENTUALLY COULD PAY DIVIDENDS FOR PEOPLE WHO HAVE VISION LOSS AND WHO ONE DAY MAY BE CANDIDATES FOR ARTIFICIAL RETINAS. JIM DRYDEN REPORTS?

WASHINGTON UNIVERSITY VISUAL SCIENTIST DANIEL KERSCHENSTEINER SAYS IT?S SUSPRISING HOW RELATIVELY LITTLE IS KNOWN ABOUT HOW THE CELLS IN THE EYES TRANSMIT MESSAGES TO THE BRAIN. SCIENTISTS KNOW THAT THE RODS AND CONES IN THE RETINA CONVERT LIGHT INTO IMPULSES THAT ARE CARRIED BY OTHER CELLS TO THE BRAIN. THE LAST MESSENGERS TO TRANSMIT SIGNALS TO THE BRAIN ARE CALLED GANGLION CELLS.

(act):15o/c understanding vision

The brain doesn?t see light. The brain only sees the spike
trains of these 20 or so types of ganglion cells. In that sense,
understanding what these spike trains tell us about the visual
world is fundamental to understanding vision.

BUT THERE ARE A COUPLE OF KEY STEPS BETWEEN THE RODS AND CONES AND THE GANGLION CELLS. IN FACT, KERSCHENSTEINER SAYS THERE ARE ABOUT 90 DIFFERENT CELL TYPES IN THE RETINA, AND VERY LITTLE IS UNDERSTOOD ABOUT WHAT MOST OF THEM DO. IN THESE EXPERIMENTS, KERSCHENSTEINER AND HIS COLLEAGUES WERE LOOKING TO IDENTIFY CELLS THAT DETECT MOTION IN THE VISUAL FIELD.

(act):15o/c image moves

It was realized several years ago now that there?s already such
an output from the retina that distinguishes between movements
of objects within a visual scene, but remains silent when the
whole image moves.
TAHNBEE KIM, A GRADUATE STUDENT IN KIRSCHENSTEINER?S LAB, IDENTIFIED A SPECIFIC CELL TYPE IN THE INNER RETINA, A TYPE OF CELL CALLED AN AMACRINE CELL, THAT KERSCHENSTEINER SAYS IS KEY TO OBJECT-MOTION DETECTION.

(act):13o/c avoid cars

One of the purposes of this is to draw our attention to regions
of the visual world where something moves, and one can imagine
why that might be useful if you want to survive in a world with
predators or avoid cars.

THEY USED A TECHNIQUE CALLED 2-PHOTON IMAGING TO CHART HOW VISUAL IMPULSES TRAVELED FROM THE PHOTORECEPTOR CELLS TO THE INNER RETINA, WHERE SPECIFIC AMACRINE CELLS CARRIED SIGNALS TO GANGLION CELLS AND THEN, TO THE BRAIN. AND WHEN THEY INTERRUPTED COMMUNICATION BETWEEN THESE SPECIFIC AMACRINE CELLS AND GANGLION CELLS, THE MOUSE RETINA COULD NO LONGER DETECT OBJECT MOTION.

(act):08o/c ganglion cell

We removed their ability to ?speak.? They can?t release?they
can?t package the neurotransmitter in the vesicle, and thus,
they can?t ?talk? to the ganglion cell.

KERSCHENSTEINER SAYS IT?S IMPORTANT TO UNDERSTAND WHAT ACTIVATES PARTICULAR RETINAL CELLS AND ALLOWS THEM TO COMMUNICATE VISUAL SIGNALS TO THE BRAIN. HE SAYS THAT UNDERSTANDING IS ESSENTIAL IF ARTIFICIAL RETINAS ARE EVER GOING TO BE ABLE TO RESTORE SIGHT IN PEOPLE WHO HAVE LOST VISION.

(act):21o/c the brain

Several retinal prostheses are being tested. If photoreceptors
are lost, or other elements of the retina are lost, the idea is
can we replace what the retina does by electronics and then
send this signal to the brain? But that presupposes that you
understand what the retina does and what it tells the brain.

AND THAT?S WHAT STUDIES LIKE THIS ONE ARE TRYING TO FIGURE OUT. THE NEW RESEARCH IS PUBLISHED ONLINE IN THE JOURNAL eLIFE. I?M JIM DRYDEN

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