Figure 1.
Reconstruction of a biocytin-filled chandelier cell from a mouse neocortical brain slice. Soma and dendrites labeled in blue, axon arbor in red. Chandelier cells have characteristic terminal portions of their axon, which form short vertical rows of boutons resembling candlesticks. Each candlestick innervates a single axon initial segment of a pyramidal cell.
Figure 2.
Hypothesized Propagation of Activity in Human Neocortex
An action potential in a pyramidal neuron (cell 1) elicits a spike in a chandelier cell (2) via a strong connection, in turn evoking a third-order spike in a downstream pyramidal cell (3). This spike results in a trisynaptic EPSP being recorded in a postsynaptic pyramidal cell (cell 4, event A). At the same time, cell 3 drives both a basket cell (5) and chandelier cell (6) to threshold. The basket cell evokes a hyperpolarizing IPSP on the postsynaptically recorded pyramidal cell (cell 4, event B), four synapses removed from the original spike. The spiking chandelier cell (6) triggers yet another pyramidal neuron to fire (7), which produces an EPSP on the recorded neuron (cell 4, event C), five synapses away from the original spike. The result seen in the postsynaptic pyramidal neuron (cell 4) is a delayed EPSP-IPSP-EPSP sequence (events A, B, and C), traveling through three, four, and five synapses respectively. Molnár et al. propose that polysynaptic pathways similar to this one can be activated by a single action potential in a cortical pyramidal cell.