Behavioral/Systems/Cognitive Exploiting Development to Evaluate Auditory Encoding of Amplitude Modulation

During development, detection for many percepts matures gradually. This provides a natural system in which to investigate the neural mechanisms underlying performance differences: those aspects of neural activity that mature in conjunction with behavioral perfor-mance are more likely to subserve detection. In principle, the limitations on performance could be attributable to either immature sensory encoding mechanisms or an immature decoding of an already-mature sensory representation. To evaluate these alternatives in awake gerbil auditory cortex, we measured neural detection of sinusoidally amplitude-modulated (sAM) stimuli, for which behavioral detection thresholds display a prolonged maturation. A comparison of single-unit responses in juveniles and adults revealed that encoding of static toneswas adult like in juveniles, but responses to sAMdepthwere immature. Since perceptual performancemay reflect the activity of an animal’s most sensitive neurons, we analyzed the d prime curves of single neurons and found an equivalent percentage withhighly sensitive thresholds in juvenile andadult animals. In contrast, perceptual performancemay reflect thepoolingof information from neurons with a range of sensitivities. We evaluated a pooling model that assumes convergence of a population of inputs at a downstreamtargetneuronand foundpoorer sAMdetection thresholds for juveniles. Thus, if sAMdetection is basedon themost sensitive neurons, then immature behavioral performance is best explained by an immature decoding mechanism. However, if sAM detection is based on a population response, then immature detection thresholds are more likely caused by an inadequate sensory representation