Complex Events Initiated by Individual Spikes in the Human Cerebral Cortex
(A) Single action potentials in a presynaptic (Pre) pyramidal neuron (top) were effective in triggering postsynaptic (Post) action potentials with high-amplitude unitary responses in a postsynaptic axo-axonic cell (aac). The action potentials in the pyramidal neuron resulted in monosynaptic EPSPs in 65% of the trials eliciting second-order action potentials (middle), whereas in 35% of the trials, only subthreshold EPSPs were evoked (bottom). Note that postsynaptic, second-order action potentials in the axo-axonic cell were followed by occasional higher order spikes riding on presumably trisynaptic EPSPs.
(B) Reconstruction of the somatodendritic (red) and axonal (black) arborization of the postsynaptic axo-axonic cell shown in panel (A).
(C) Action potentials in a human axo-axonic cell trigger a sequence of polysynaptic events following a monosynaptic IPSP and a disynaptic EPSP in a postsynaptic pyramidal cell recorded with a low intracellular chloride concentration rendering all IPSPs hyperpolarizing in the two recorded cells. Note that downstream recurrent activity in the network triggers spikes in the axo-axonic cell. Responses of the pyramidal cell are shown as single sweeps (middle) and the average (bottom).