May
02
2006

A little bit of color can go a long way


A Human Eye: Courtesy Wikipedia Images

Have your eyes ever played a trick on you? Perhaps you thought you saw something moving but it was a figment of your imagination. Researchers at the Salk Institute have recently suggested that two neurological pathways come together enabling superb motion detection.

Our brains rely on neural pathways to detect motion. This past April, researchers at the Salk Institute of Biological Studies have found a specific neural circuit playing a vital role in the ability to detect motion. The outer layer of the brain, named the cortex, plays an important role in motion recognition. Up till now, it has been believed that motion perception is not influenced by color and fine details. However, the idea of motion perception is becoming more colorful!

Our eyes have the duty of breaking down daily images we come across. These images are broken down into three divisions: color, position and brightness. Each of these categories has specialized pathways transmitting seen images from our eyes to our brain. The pathway transmitting color and fine spatial detail is named the parvocellular pathway. The magnocellular pathway detects low contrast and rapid changes. Lastly the visual cortex uses information from both the parvocellular and magnocellular to compute motion, shape and color.


Camouflaged lizard: Consider the motion of a slowly moving lizard camouflaged against leaves and twigs: the M pathway wouldn’t recognize the lizard, but the P pathway, detecting color, fine detail, and slow movement, would pick it up. (Photo courtesy Rachel Kramdar)Courtesy Kramdar

The Salk Institute for Biological Studies has challenged the long-standing understanding that the magnocellular and parvocellular are two totally separate pathways. It has commonly been assumed that the magnocelluar pathway is the only pathway that transmits information to the cortical motion processing area called the MT. The MT in turn receives input from the primary visual cortex, which gets its information from the magnocelluar pathway as well. Researchers from the Salk Institute are proposing that the parvocellular pathway has input when detecting motion and also sends information to the primary visual cortex.

Sounds complicated, huh? Well, researchers at the Salk Institute used a rabies virus strain to track neural circuits in reverse. The rabies virus was used because it had special infectious properties allowing scientists to easily discern neurological pathways. They were able to trace neural circuits beginning at the MT back to the magnocellular and parvocellular pathways connecting to the primary visual cortex. The technique is called trans-synaptic tracing. Findings suggested that the magnocellular and parvocellular pathways merged before transmitting visual information to the MT area.

The research team was composed of professor Edward Callaway, graduate student Jonathan Nassi and post-doctoral researcher David Lyon, Ph.D. Callaway commented on the significance of his teams’ findings:

“...People tend to think about detection of fast motion changes. But we also need to detect the motion of things that are moving more slowly. The addition of the parvocellular pathway to the motion systems helps us to see movement of things to which the magnocelluar pathway is blind.”

-From Eurekalert

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