Biophysical Network Modelling of the dLGN Circuit: Different Effects of Triadic and Axonal Inhibition on Visual Responses of Relay Cells
Fig 5
Illustration of two pathways for triadic inhibition of relay cells (RCs).
Curves show membrane potentials of the IN dendrite (panels B,D) at the distal synapse position (blue dot in panel A) and in RC soma (panels C,E), respectively. (A) Illustration of interneuron (IN) with triadic connection with RC shown as open circle. (B) Single incoming GC spike input to distal (triadic) synapse (time stamp tsyn = 1 ms denoted as red bar in small display on top) triggers a large postsynaptic response in distal IN dendrite, effectively resulting in a dendritic action potential. (C) Same GC input spike as in (B) now also projecting to the RC partner of the triadic circuit with a short time delay resulting in direct triadic inhibition of the RC (starting at time shown as blue time-stamp bar above): without inhibition the GC input to the RC cell gives an immediate RC action potential (red curve), while no action potential occurs if the excitatory input is accompanied by direct triadic inhibition (black curve). (D) Back-propagating action potential in IN dendrite(s) triggered by a strong synapse input to the IN soma (activation time tsyn = –8 ms, gmax = 300 nS, Esyn = 10 mV, τ = 1 ms, Isyn(t) = gmax ⋅ exp(−(t − tsyn)/τ) ⋅ (Vm − Esyn) for t ≥ tsyn). For illustration purposes, the distal activation of the IN dendrite by the GC input is here absent, i.e., wGIt = 0. (E) Same GC input spike as in panels B and C now also projecting to an RC cell, gives an RC action potential both without (red curve) and with soma-driven triadic inhibition (black curve) as the inhibition occurs too late (blue time-stamp bar above) to prevent action-potential firing in the RC.