Deep-layer neurons in mice link sound categories to choices

After training, one group of auditory-cortex neurons formed sound categories that depended on active behavior.

Editorial illustration — not from the study.

Researchers trained head-fixed mice to categorize amplitude-modulated noise according to its temporal rate while repeatedly imaging neurons in the auditory cortex. They compared deep-layer L5 extratelencephalic neurons with neurons in layers 2/3 and another deep-layer group, L5 intratelencephalic neurons.

With learning, the L5 extratelencephalic neurons changed their sound tuning and developed clear category responses. The same neurons showed this code during the task but not when the mice passively listened to the sounds, indicating that the representation depended on the behavioral context.

How sound categories formed

L5 extratelencephalic neurons developed pronounced changes in sound tuning as the mice learned the categorization task. They formed robust categorical responses, unlike the layer 2/3 and L5 intratelencephalic comparison populations.

The category responses appeared while the mice were engaged in the task and disappeared during passive listening on the same day. A generalized linear model, used to separate sound-related signals from choice-related signals, indicated that the categorical responses reflected sensory encoding rather than movement. All three neuron populations carried choice signals, but these signals were strongest in the L5 extratelencephalic neurons.

Why the pathway matters

The findings identify a specific group of deep-layer auditory-cortex neurons that combines information about sound categories with signals related to behavioral choices. Because these neurons project to targets outside the telencephalon, they may provide an output route through which the auditory cortex passes behaviorally relevant information to downstream brain regions. The study helps narrow the search for the circuits that connect sensory categorization with action selection.

Evidence and caveats

The study used longitudinal two-photon imaging in trained, head-fixed mice and compared three auditory-cortex neuron populations. The researchers also used a statistical model to distinguish sensory signals from choice-related signals. The results show associations between neural activity, learned sound categories and choices; they do not by themselves establish that L5 extratelencephalic neurons are required for categorization or directly cause the animals’ choices. The abstract does not report the number of mice or neurons, and the task involved one type of sound categorization in mice, so the findings may not generalize to other sensory tasks or to humans.

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