When you look at an object, like the picture above, there are many features your brain has the task of processing. Color, texture, and position in space to name a few. Lines and angles are some of the first features to be encoded. The primary visual cortex (aliases- striated cortex and V1), has the task of deciphering these stimuli to create and capture what we perceive as a form. In the photos above, there are lines that run up and down, side to side and the combinations in between. Certain granule and pyramidal cell in the visual cortex get really excited when they see a nice up and down line. For others it’s the 45 degrees that really fires them up. To the right is a color-coded representation of the distribution of up and down cells (green), side to side (red) and so forth.
“Why are they called pinwheels?”
Excellent question. It is a bit of a stretch to see, but in the chaos of color, there is a bit of pattern. The six different orientations come together in certain points known as a singularity forming, albeit rough, a pinwheel shape.
“Why would they orient themselves in such a way?”
Well, there is no clear consensus on this, yet. Some believe these pinwheels may just be the result of some imaging artifacts. In the event they are not artifacts, one possibility… Think of a sonar in a submarine. The line that circulates, the radius, goes around one point to scan as effectively as possible the largest surface area. The cells are laid out as efficiently as possible around conferring points, thus creating a six person consensus of a stimuli. If the cells were instead arranged in bars with just 45 degree-ers in one area far from the 180, horizontal or the 90 vertical guys, there would be the possibility of misinterpreting or completely missing a curve because the cells who are wild about curves are in two bars down the street, unaware of the beautiful curve that just walked in. Thank goodness for pinwheels!
Written and photographed by RAZ: Rebecca A. Zarate, MA, LAT
Projected Image: Yevgeniy B. Sitortin and Aniruddha Das, 2006
Kaschube M., Schnabel M., Lowel S., Coppola D.M., White L.E. & Wolf F. (2010). Universality in the Evolution of Orientation Columns in the Visual Cortex, Science, 330 (6007) 1113-1116. DOI: 10.1126/science.1194869
Adapted from Wikipedia