Figure 8.

Thalamic gating of information flow between two cortical areas. Information in cortical area A is conveyed to up/down neurons in cortical area B by axons labeled “*.” The up/down neurons are shifted to their up state by gating axon “G” projected by a neuron in an association thalamic nucleus. The remaining connections represented target the thalamic cell. The firing order for the cells, indicated on the figure by small numbers, is as follows. Initially, the activity in cortical area A (0) is confined to this region. However, appropriate firing of neurons in areas A and C (1) can trigger the thalamic projection cell (2), which then switches area B neurons from their down to their up state (3), therefore opening the gate from area A to area B. The activity in areas B and C (4) can however close this gate by silencing the thalamic neuron through inhibitory projections from thalamic reticular nucleus neurons (5). Cell location and connections between cortical layers selected from data in Felleman and Van Essen (1991), Guillery and Sherman (2002), Zikopoulos and Barbas (2006), and Xiao et al. (2009).