How do our brains enable us to see the many shapes of objects in the world? One idea posed by neuroscientists is that there are different types of neurons in the brain that recognize different elements of shape, such as straight lines, curves, and corners, and that shapes are the result of integrating these different basic elements. However, where these neurons are and how their information is integrated is not well understood.
In the late 1960s, Nobel Laureates Hubel and Wiesel discovered that the first stage of visual information processing in the cortex (primary visual cortex) contains submillimeter-sized functional units called orientation columns. They showed that each column contained neurons responsive to only a certain contour orientation (e.g. neurons in a ‘vertical’ orientation column would respond to the vertical contour of a tall tree but not to the contour of a horizontal tree branch). It was later discovered that the set of all possible orientation columns (0-180 deg) shifted systematically around a point in a ‘pinwheel-like’ fashion. This concept of a single orientation column encoding a single contour orientation has been a cornerstone of sensory systems neuroscience.
In this study, two research teams cooperated to develop a novel, highly precise method of targeting electrodes in the orientation column and accurately determinng their position, so that different regions within single orientation columns could be probed. Using intrinsic signal optical imaging to map the orientation columns, researchers conducted systematic and comprehensive study of the functional properties of neurons in different parts of individual orientation columns. For the first time, they found that within single orientation columns there is a clear distribution of neurons with different functional preferences. Specifically, they found three subdomains, whose functional responses were consistent with the encoding of straight lines, curves, and complex contours, respectively. This suggested that single orientation columns may contain multiple basic elements for building shapes and led to a new concept of the ‘pinwheel-centered orientation hypercolumn’. Thus, their technical advance has led to a new view of the orientation column and of cortical functional architecture. This new finding will also be useful for computational models of shape encoding in the brain.