Synchronization and sensitivity enhancement of the Hodgkin-Huxley neurons due to inhibitory inputs

Recent experimental results imply that inhibitory postsynaptic potentials c an play a functional role in realizing synchronization of neuronal firing i n the brain. In order to examine the relation between inhibition and synchr onous firing of neurons theoretically, we analyze possible effects of synch ronization and sensitivity enhancement caused by inhibitory inputs to neuro ns with a biologically realistic model of the Hodgkin-Huxley equations. The result shows that, after an inhibitory spike, the firing probability of a single postsynaptic neuron exposed to random excitatory background activity oscillates with time. The oscillation of the firing probability can be rel ated to synchronous firing of neurons receiving an inhibitory spike simulta neously. Further, we show that when an inhibitory spike input precedes an e xcitatory spike input, the presence of such preceding inhibition raises the firing probability peak of the neuron after the excitatory input. The resu lt indicates that an inhibitory spike input can enhance the sensitivity of the postsynaptic neuron to the following excitatory spike input. Two neural network models based on these effects on postsynaptic neurons caused by in hibitory inputs are proposed to demonstrate possible mechanisms of detectin g particular spatiotemporal spike patterns.