Figure 5. Thalamocortical FFI by PV neurons imposes coincidence detection.

A. Thalamocortical neurons synapse onto both excitatory principal cells (PC) and PV neurons. Thalamocortical connections are stronger onto PV than PC neurons. B. FFI by PV INs curtails TC mediated EPSPs on PCs leaving a narrow temporal window of opportunity for excitatory inputs to summate. Consequently, near synchronous inputs are required for efficient summation of EPSPs and to drive action potential firing on the PC. C. Weakening of PV INs FFI by short-term depression of TC synaptic inputs onto PV cells and PV INs outputs to PC (Gabernet et al., 2005). These two steps of adaptation weaken FFI more than direct feed-forward excitation of PC neurons. D. Weakening of FFI by modulation of PV IN output synapses. Both GABAB receptor-activation by NGFCs (Chittajallu et al., 2013) and muscarinic receptor-activation by acetylcholine (Kruglikov and Rudy, 2008) reduce inhibitory outputs to PCs. E. Relationship between the summation of EPSPs on PCs and their temporal difference for different strengths of FFI. As FFI is weakened, asynchronous inputs can summate more effectively (Pouille and Scanziani, 2001). F. FFI regulates the gain of PC populations. As excitatory drive increases, PV cells recruitment increases at a higher rate than the recruitment of excitatory cells. This will prevent PC population from saturation and will allow a wider dynamic range of the local PC population than if inhibition was absent (dotted line) (Pouille et al., 2009).