Recurrent Circuits Amplify Corticofugal Signals and Drive Feedforward Inhibition in the Inferior Colliculus

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Computational Neuroscience

Background:

• The inferior colliculus (IC) is a crucial midbrain center for complex sound perception.
• Descending auditory cortical projections modulate IC activity, influencing feature selectivity and plasticity.
• A paradox exists: corticofugal projections are excitatory, yet often cause net inhibition in the IC.

Purpose of the Study:

• To investigate the mechanism by which excitatory corticofugal inputs generate inhibition in the inferior colliculus.
• To elucidate the role of intracollicular circuitry in mediating descending control of auditory processing.

Main Methods:

• In vitro electrophysiology in acute slices of the inferior colliculus.
• Optogenetic stimulation of corticofugal axons.
• Utilized fluorescent reporter mice to distinguish neuron types.

Main Results:

• Corticofugal excitation was stronger in glutamatergic IC neurons than GABAergic neurons.
• Repetitive corticofugal activity induced spiking in glutamatergic neurons, which then excited local GABAergic neurons.
• This recurrent excitation amplified activity and generated significant local inhibition within the IC.

Conclusions:

• Descending auditory cortical pathways engage intracollicular inhibitory circuits indirectly.
• A novel polysynaptic mechanism explains how excitatory corticofugal inputs lead to inhibition in the IC.
• This pathway allows for sophisticated top-down control of auditory processing, even with sparse direct inhibitory connections.