From Single Cells and Columns to Cortical Networks: Coincidence Detection and Synaptic Transmission
While patch pipettes were initially designed to record elementary current events, the whole-cell and cell-attached recording configurations proved useful tools also for examining signaling within and between neurons. I will first summarize work on electrical signaling within single neurons, describing communication between their dendritic compartments, soma, and nerve terminals via forward and backward propagating action potentials. Dendritic excitability endows neurons with a capacity for coincidence detection of spatially separated subthreshold inputs, which is broadcast to other cells by the initiation of action potential bursts (AP bursts). AP bursts can trigger target cell-specific release mechanisms at different terminals of the same neuron and result in the induction of synaptic plasticity if pre- and postsynaptic AP bursts coincide. But what are the roles of active dendritic excitability in behaving animals? To answer this question, I will highlight the functional architecture of an averaged cortical column in the vibrissal (whisker) field of somatosensory cortex (vS1) and compare synaptic and unit responses of major cortical output neurons in layer 5 with responses of afferent neurons in primary somatosensory thalamus and one efferent target. The occurrence of AP bursts suggests that coincidence detection mechanisms operate in vivo; three-dimensional reconstructions indicate that combinations of thalamocortical and intra-columnar inputs could activate dendritic coincidence detection mechanisms. Recordings from efferent targets reveal the importance of AP bursts for signal transfer to these cells. vS1 cortex thus appears to transform the afferent sensory code, at least partially, from a rate to an interval (burst) code.
Bert Sakmann shared the 1991 Nobel Prize in Physiology or Medicine “for discoveries concerning the function of single ion channels in cells.”
17 November 2016, 12:00 (Thursday, 6th week, Michaelmas 2016)
The Oxford Martin School
Professor Bert Sakmann (Max Planck Institute of Neurobiology)
Department of Physiology, Anatomy and Genetics (DPAG)
Members of the University only