The auditory frequency-following response (FFR) to complex periodic sounds is used to study the subcortical auditory system, and has been proposed as a biomarker for disorders that feature abnormal sound processing. Despite its value in fundamental and clinical research, the neural origins of the FFR are unclear. Using magnetoencephalography, we observe a strong, right-asymmetric contribution to the FFR from the human auditory cortex at the fundamental frequency of the stimulus, in addition to signal from cochlear nucleus, inferior colliculus and medial geniculate. This finding is highly relevant for our understanding of plasticity and pathology in the auditory system, as well as higher-level cognition such as speech and music processing. It suggests that previous interpretations of the FFR may need re-examination using methods that allow for source separation.

Experiences can alter functional properties of neurons in primary sensory neocortex but it is poorly understood how stimulus-reward associations contribute to these changes. Using in vivo two-photon calcium imaging in mouse primary visual cortex (V1), we show that association of a directional visual stimulus with reward results in broadened orientation tuning and sharpened direction tuning in a stimulus-selective subpopulation of V1 neurons. Neurons with preferred orientations similar, but not identical to, the CSϩ selectively increased their tuning curve bandwidth and thereby exhibited an increased response amplitude at the CSϩ orientation. The increase in response amplitude was observed for a small range of orientations around the CSϩ orientation. A nonuniform spatial distribution of reward effects across the cortical surface was observed, as the spatial distance between pairs of CSϩ tuned neurons was reduced compared with pairs of CSϪ tuned neurons and pairs of control directions or orientations. These data show that, in primary visual cortex, formation of a stimulus-reward association results in selective alterations in stimulus-specific assemblies rather than population-wide effects.

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