Feed-Forward versus Feedback Inhibition in a Basic Olfactory Circuit
Fig 7
Simplified model with sine-wave input and single cells representing each cell population illustrates phase locking across a range of inhibitory synaptic strengths.
Single cells: projection neuron (PN, green), Kenyon cell (KC, orange), lateral horn neuron (LHN, blue), giant GABAergic neuron (GGN, red). (A) Structure of the circuit. (B, Left) Feedback (FB) inhibitory model shows cells fired in the same order regardless of inhibitory synaptic strengths, although the KC, LHN, and GGN do fire slightly later as the inhibitory synapses were strengthened. (B, Right) Feed-forward (FF) inhibitory model: since GGN responses were determined by PN and not KCs, GGN does not phase shift. KC and LHN responses changed phase as inhibitory synaptic strength varied. KCs and LHNs fired after GGN for all values of inhibition except the weakest ones.