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Predicting
the Anisotropy of Lateral Connections in the Visual Cortex from the Distribution
of Singular Points in the Pattern of Orientation Columns
Laboratory for Visual
Neurocomputing |
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It is known that
neurons in the visual cortex selectively respond to the inclination (orientation)
of the contour lines of visual images, and that the optimally responsive orientation
changes continuously along the cortical surface, indicating a pattern of orientation
columns. The pattern of orientation columns is also characterized by the presence
of singular points around which the optimal orientation changes by 180 degrees.
So far, it has been shown by the optical recordings from area 17 in monkeys and
cats that clockwise and counterclockwise singular points tend to be collocated
alternately. In this study, we carefully examined the distribution of singular
points for optimal orientations near the areas 17/18 border of cats, using the
intrinsic optical recording technique. As a result, near the interareal boundary
singular points of the same type tend to be arranged parallel to the boundary
(Fig. A), and it was confirmed that this tendency is statistically significant.
It is thought that the observed pattern is formed to maximize the orthogonality
of the orientation columns and the area 17/18 border. We also conducted computer
simulation based on a simple model of orientation column formation assuming anisotropic
lateral connections in the cortex. We could reproduce the same tendency of arrangement
of singular points as observed in our experiment. This suggests that there are
anisotropic lateral connections near the interareal boundary. |
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Fig.
A |
Pattern
of orientation columns obtained from the optical recording. The area sandwiched
by the two dashed lines indicates the transition zone between areas 17 and 18.
The optimal orientations are represented by the colors. |
Fig.
B |
Pattern
of orientation columns obtained from the simulation when the excitatory lateral
connections are elongated in the vertical direction on paper. We can see the tendency
that singular points of the same type are arranged horizontally. |
Ohki,
K., Matsuda, Y., Ajima, A., Kim, D.-S., Tanaka, S. Arrangement of Orientation
Pinwheel Centers around Area 17/18 Transition Zone in Cat Visual Cortex Cerebral
Cortex 10, pp593-601, Jun (2000)
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