Figure 3.

Gating mechanisms involving inhibition. As in figure 2, in all circuits, information is transmitted from cortical area A to area B by projections labeled “*,” while the gating signal controlling the mechanism is conveyed by an axon labeled “G.” (A) Gating by shunting inhibition. The gating signal triggers inhibitory interneurons that shunt area B pyramidal neuron activity, keeping set A input from triggering set B neurons, and therefore closing the gate. (B) Gating by inhibition modulation in a network where excitation and inhibition compensate each other. The gate is closed by default, but can be opened by the gating signal, which reduces the strength of the inhibition in B, and allows excitatory neurons present there to fire (Modified from Vogels and Abbott, 2009). (C) Gating by network rhythms. Cortical sets A and B, in addition to sender and receiver neurons, also contain densely interconnected inhibitory, fast-spiking interneurons capable of producing stable oscillatory activity at a frequency of about 40 Hz (represented on the figure by a wavy background). By changing the phase of the oscillations in group A relative to those in group B, a gating axon could control the amount of activity evoked in B by input from A, as is illustrated by the histogram on the right (data in histogram modified from Cardin et al., 2009).