Fig. 5.

Mexican-hat-type connectivity depends on dendritic disinhibition of P cells. (a) Average synaptic currents of different types to P neurons in a bell-shaped persistent activity pattern. Recurrent excitation from P cells is localized; recurrent inhibition from PV neurons is maximal, whereas inhibition from CB neurons shows a dip at the center of the bump. (b) Summation of synaptic currents from P and PV cells is almost flat. (c) When the synaptic contribution from CB neurons is also included, the total synaptic current shows a Mexican-hat-type shape, with local excitation and lateral inhibition. (d) The average membrane potential of a conductance-based P cell increases with its firing rate. Therefore, the driving force (V_P – E_inh) of the inhibitory synaptic current mediated by PV cells and the current itself (as shown in a) is about twice as large at the peak of the bump (where neurons fire at ≈30 Hz) than on the sides (where neurons are inactive).