How Do Barrels Work?
Inhibitory barrel neurons are strongly driven by thalamic inputs. When thalamic neurons in the C2 barreloid fire initially asynchronously, for example when whisker C3 is deflected, inhibitory cells in the C2 barrel fire. Excitatory neurons do so only weakly, if at all. Inhibition quickly dominates the circuit, preventing the excitatory cells from spiking, even if thalamic activity levels eventually become high.
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When the C2 whisker is deflected, large numbers of C2 barreloid neurons fire initially synchronously, activating both inhibitory and excitatory neurons. Because of the positive feedback provided by excitatory-to-excitatory cell synapses, activity within the excitatory population builds rapidly. Within a few milliseconds, this explosive increase in activity is transferred, via synapses from excitatory to inhibitory cells, to the inhibitory population. Now powerfully engaged by both thalamocortical and local excitatory populations, intrabarrel inhibition overwhelms the excitatory response and forces the network back towards its rest state. In the figure, the green, red and gray circles represent populations of neurons. |