Learning-induced gain modulation in L2/3 pyramidal neurons qualitatively changes the local interactions.

<p>(A) In the experiment <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000617#pcbi.1000617-Crist2" target="_blank">[10]</a>, monkeys were performing either a fixation task (top) or a bisection task (bottom) while the activity of a supra-granular V1 neuron was recorded in response to a two line stimulus in a side-by-side configuration. One of the two lines is centered in the receptive field (sketched by the square) of the recorded neuron. (B) Activity of the corresponding model L2/3 pyramidal neuron mimicking the recorded supra-granular neuron for different positions of the flanking line, with individual curves normalized by the activity with flanking line at . Top: During pure fixation or before training (modeled by a non-modulated circuitry, gain ), the response of the central neuron is suppressed by the flanking line via global inhibition. Bottom: When performing the bisection task at a nearby location in the trained hemisphere (modeled by a top-down induced gain increase of the L2/3 pyramidal neurons from to ) the lateral suppression turns into strong excitation at random positions due to the enhanced competition within the stochastically modulated network. (C) Modulation indices for the ‘bisection task’ (gain ) versus ‘fixation task’ (gain ). The <i>modulation index</i> is defined as the normalized difference between the maximal and minimal response of the recorded L2/3 pyramidal neuron, each evaluated for the different positions of the flanking line (as represented in B, see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000617#s4" target="_blank">Materials and Methods</a>). Evaluation for neurons in stochastic network configurations shows that the modulation index under the bisection condition is significantly larger than under the fixation condition ( for paired t-test with ), as it is also observed in the experiment (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1000617#pcbi.1000617-Crist2" target="_blank">[10]</a> with , , ).