Figure 1: Schematic of the two-stage recurrent circuit model.

Solid and dashed lines represent excitatory and inhibitory connections, respectively. Principal excitatory neurons are denoted by y, modulatory excitatory neurons by u, and modulatory inhibitory neurons by a and q. Subscripts 1 and 2 designate neurons in visual areas V1 and V2, respectively. z₁ denotes the input drive from the LGN to V1, a weighted sum of the responses of LGN neurons. Parameters β₁ and γ₁ modulate the input and feedback gain to V1, respectively.