1. C. Inhibitory interneurons in a relay nucleus are activated by three distinct excitatory pathways. Feed-forward inhibition is produced by the afferent fibers of receptors that terminate on the inhibitory interneurons. Feedback inhibition is produced by recurrent collateral axons of neurons in the output pathway from the nucleus. The interneurons in turn inhibit nearby output neurons, creating sharply defined zones of excitatory and inhibitory activity in the nucleus. In this way the most active relay neurons reduce the output of adjacent, less active neurons, permitting a winner-take-all strategy that ensures that only one of two or more competing responses is expressed. Inhibitory interneurons are also activated by neurons in other brain regions such as the cerebral cortex. The descending pathways allow cortical neurons to control the relay of sensory information centrally, providing a mechanism by which attention can select sensory inputs.
Source: Sensory Coding, Principles of Neural Science, Fifth Editon
Citation: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S. Principles of Neural Science, Fifth Editon; 2012 Available at: Accessed: December 22, 2017
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