Abstract
In many ways, the complement of cell subtypes determines the information processing that a local brain circuit can perform. For example, the balance of excitatory and inhibitory (E/I) signaling within a brain region contributes to response magnitude and specificity in ways that influence the effectiveness of information processing. An extreme example of response changes to sensory information occur across Critical Periods (CPs). In primary mammalian visual cortex, GAD65 and parvalbumin inhibitory cell types in particular control experience-dependent responses during a CP. Here, we test how the density of GAD65- and parvalbumin-expressing cells may inform on a CP for complex behavioral learning. Juvenile male zebra finch songbirds (females cannot sing) learn to sing through coordinated sensory, sensorimotor, and motor learning processes distributed throughout a well-defined neural network. There is a CP for sensory learning, the process by which a young male forms a memory of his “tutor’s” song, which is then used to guide the young bird’s emerging song structure. We quantified the effect of sex and experience with a tutor on the cell densities of GAD65- and parvalbumin-expressing cells across major nodes of the song network, using ages that span the CP for tutor song memorization. As a resource, we also include whole-brain mapping data for both genes. Results indicate that inhibitory cell populations differ across sex, age, and experiential conditions, but not always in the ways we predicted.
Highlights
Balanced excitatory and inhibitory (E/I) signaling is a widespread neural feature that facilitates informational integration and cognitive function[1]
Inhibitory cell types, GAD65 and parvalbumin in particular, are sufficient to gate an extreme example of developmental switches in experience-dependent plasticity: Critical Periods (CPs)
We asked if the density of these two cell types in major areas of a neural network required for developmental song learning in the zebra finch songbird are consistent with a CP for tutor song memorization and the distributed learning that occurs throughout the network
Summary
Balanced excitatory and inhibitory (E/I) signaling is a widespread neural feature that facilitates informational integration and cognitive function[1]. Despite hearing song all day every day, male zebra finches can only use song they hear during the juvenile phase that spans approximately Posthatch day (P) 30–65 to shape the structure of their own song (Fig. 1a)[11,12,13,14,15] (but see[16]) This limited learning phase meets the criteria for a CP because males that do not hear song P30–65 can use a song they experience later to guide their song structure; learning song prevents future learning whereas lack of learning permits late learning[17,18]. We asked how GAD65- and parvalbumin-expressing cell populations changed in major nodes of the network for developmental song learning. The combination of age, sex, and prior tutor experience determines whether or not a bird can memorize tutor song and sing, these conditions permit associations between GAD- and parvalbumin- expressing cell populations and brain function and behavior. Future work can expand on these first findings by investigating additional inhibitory cell subtypes and measuring dynamic firing properties of these cell populations
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