Modeling the Emergence of Whisker Direction Maps in Rat Barrel Cortex
A At t = 5,000, direction maps in each supra-barrel were compared to the template pinwheel (inset) and classed as somatotopically correct pinwheels (the example map has a ‘pinwheelness’ score of 0.9), somatotopically inverted pinwheels (example score -0.9) or not pinwheels (score 0.2), as described in Results. When there is no correlation between the direction in which each whisker is stimulated during training (), pinwheel maps emerge in each supra-barrel, but they are equally likely to rotate clockwise or counter-clockwise. When such a correlation is present in the inputs (), the number of supra-barrels containing pinwheels that rotate in a somatotopically consistent way increases to a maximum of 76%. Surprisingly, perfectly correlated inputs () degrade pinwheel quality. B This behavior is reflected in a plot of absolute ‘pinwheelness’ scores, in which all but the scores for progress over training iterations (t = 0, 500, 1,000, 2,000, 3,000, 4,000 in progressive dashed lines) toward good scores at t = 5,000 (solid line). Scores are highest for , suggesting that networks trade a bias to maximize pinwheelness for one towards somatotopic alignment as is increased. C shows that pinwheels rotating in the correct direction become aligned to the somatotopic template, with a final circular standard deviation for .