Memory is content-rich. Thus, in addition to mechanisms of learning and storage, an understanding of memory requires the identification of neural substrates that can represent specific content. My work combines behavioral neuroscience with sensory neurophysiology to reveal how learning-induced plasticity in early sensory cortex meets this criterion. Learning about associations between sensory events and their outcomes changes the organization of neural sensory representations in receptive fields and cortical maps. This kind of representational plasticity occurs even in the adult brain as animals learn and remember.
The primary auditory cortex (A1) is a model for neural substrates of learning when an association involves sound. A1 can encode sound stimulus identity, e.g., by its neural representation of a specific tonal frequency in cortical receptive fields that are sensitive to sound frequency (along with a number of other sound parameters that are also represented in A1). Frequency receptive fields together comprise a tonotopic map. Yet, the tonotopy in A1 can also encode the learned behavioral significance of auditory stimuli – not just its identity. For example, experience-dependent adult plasticity re-organizes A1 to enhance the representation of an auditory signal after learning its importance, e.g., via receptive field shifts towards important sound frequencies, which thereby expand frequency-specific cortical representation of significant sounds in the tonotopic map. Moreover, associative memory is strengthened when the sound’s A1 representation becomes enhanced. A central focus of my work is to investigate the relationship between representational plasticity in A1 and its resulting functions on auditory memory and cognition. For example, recent studies in A1 have revealed that the greater the cortical representational gain, the stronger the memory.