Prior unsupervised experience leads to long lasting effects in sensory gating during discrimination learning

As the animal moves in its environment, the brain detects and learns the structure of the surrounding stimuli, independently of the immediate relevance this has for the animal. This experience influences subsequent learning in a manner quantified using paradigms such as latent inhibition or stimulus preconditioning, which measure the effect that unsupervised (not-reinforced) learning has on subsequent reinforced learning. Despite our understanding of the behavioural consequences of prior neutral experience, there is little understanding about the influence of this previous experience on neuronal plasticity. Using latent inhibition, we have shown in mice that learning a two tone discrimination is slower in mice that have had previous neutral exposure to the same or similar tones (<2/3 octave away). Neutral exposure thus elicits profound changes in the brain that influence subsequent learning. To study how previous experience influences experience-dependent plasticity, and better understand the interactions between experience, learning, and plasticity, we recorded sound evoked responses in the auditory cortex of exposed and trained mice. We studied both changes in response magnitude and changes in sensory dynamics, and related both to the differential behavioral effects of different pre-exposure conditions. Here we describe the neuronal changes that paralleled the behavioral findings. We found that discrimination learning led to stronger initial sound-evoked responses and a long-lasting increase in response adaptation and an increase. The first effect was delayed in animals that showed latent inhibition, paralleling behavioural learning. Overall our data reveal that slow changes in behaviour that accompanied learning, paralleled the slow dynamics of experience-dependent plasticity in auditory cortex.