Figure 7.

Feedback shapes the cortical landscape according to context. Framework for how feedback pathways may contribute to flexible sensory-motor processing. Top panels illustrate hierarchically-arranged cortical nodes with input regions at the bottom and output regions at the top. Blue arrows represent sensory inputs (bottom) or cortical outputs (top). Blue nodes represent highly active regions whereas yellow nodes represent less active regions. Black lines represent the structural and functional connectivity between nodes, with thicker lines depicting stronger connectivity. Bottom panels are energy landscape representations of the above networks. The height of each contour reflects the energy barrier of propagating into that region. (A) If signal processing between cortical regions is defined only by feedforward connections, then sensory-motor processing will always follow the strongest connections. (B) Different contexts, such as goal-direction or self-generated movement, can propagate along feedback and laterals pathways [green lines (excitatory) and red lines (inhibitory)]. Consequently, these top-down signals modulate which input and output nodes are enhanced or suppressed, thereby altering the coupling strengths between cortical regions (black lines). The same input signal may now be routed to diverse outputs, as appropriate for the current context. As illustrated in the bottom panels, modulations of activity levels within individual regions and coupling strengths between regions change the contours of the cortical landscape, favoring different input-output trajectories.