What it is
Researchers trained head-fixed mice to categorize the temporal rate of amplitude-modulated noise while longitudinally imaging L5 ET extratelencephalic neurons alongside comparison L2/3 neurons and L5 IT intratelencephalic neurons. With learning, only the L5 ET neurons reshaped their tuning and developed robust, categorical responses, while the L2/3 and L5 IT populations did not. The categorical code was present during the task and absent during passive listening in the same neurons on the same day, indicating context-gated expression. A generalized linear model confirmed that the categorical selectivity reflected sensory encoding rather than motor confounds, and although all populations carried choice signals, those signals were strongest in the L5 ET neurons.
Why it matters
Auditory cortex has long been implicated in perceptual categorization, but the cell-type-specific circuits that implement category learning were unknown. Isolating L5 ET neurons, the deep-layer channel that projects out of cortex, shows where a learned category forms and how it is selectively routed to downstream targets.
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Filed underneuroscience, auditory cortex, perceptual categorization, cortical circuits, two-photon imaging
