Specific associative representational plasticity in the primary auditory cortex: The role of learning strategy and a function of cortical area gain for memory

A major function of the cortex is to dynamically subserve the content of memory. Growing evidence largely in the realm of auditory learning has described associative representational plasticity (ARP) even at the first stages of cortical involvement in the primary auditory cortex (A1). ARP has all the characteristics of associative memory: it is formed rapidly and specifically for signal stimuli, its induction consolidates without further bouts of training, and it can last over the longest time intervals studied. Thus, activity in A1 is not merely a pure reflection of the sensation of particular sounds, but is cognitively involved in the service of learning and memory. This dissertation propels the conceptualization of learning-related A1 plasticity into a larger functional domain. The findings herein (1) demand the need to reveal behavioral factors that are critical for the development of ARP and (2) illustrate that the functional advantages of ARP consequent to its development after learning are largely unknown, but are in fact determinable. I identified a critical factor for the induction of ARP: learning strategy. Learning strategies are defined as the collection of external cues that animals utilize to solve behavioral problems (e.g., to obtain reward or avoid punishment). Animals can use a variety of strategies to successfully solve problems, even in identical tasks. In A1, a strategy dependent on tone onsets, as opposed to offsets, appears to be critical not only for the induction, but also for the degree of emergent plasticity with learning. It has largely been assumed that the purpose for plasticity is the same as the cause for its development, i.e., to support the learned behavior. However ARP has a general function for memory. Here, I describe that signal-specific gains in representational area in A1 confer an enhancement in the strength of the auditory content of memory. Overall, this dissertation indicates an interaction more complex than has been previously appreciated between learning, memory and the cortical substrates thereof. This includes consideration of cortical representational plasticity dictated by the specific strategies animals use to learn, and the consequent role of signal-specific representational plasticity for the content of memory.