Abstract
Neural representation in the auditory cortex is rapidly modulated by both top-down attention and bottom-up stimulus properties, in order to improve perception in a given context. Learning-induced, pre-attentive, map plasticity has been also studied in the anesthetized cortex; however, little attention has been paid to rapid, context-dependent modulation. We hypothesize that context-specific learning leads to pre-attentively modulated, multiplex representation in the auditory cortex. Here, we investigate map plasticity in the auditory cortices of anesthetized rats conditioned in a context-dependent manner, such that a conditioned stimulus (CS) of a 20-kHz tone and an unconditioned stimulus (US) of a mild electrical shock were associated only under a noisy auditory context, but not in silence. After the conditioning, although no distinct plasticity was found in the tonotopic map, tone-evoked responses were more noise-resistive than pre-conditioning. Yet, the conditioned group showed a reduced spread of activation to each tone with noise, but not with silence, associated with a sharpening of frequency tuning. The encoding accuracy index of neurons showed that conditioning deteriorated the accuracy of tone-frequency representations in noisy condition at off-CS regions, but not at CS regions, suggesting that arbitrary tones around the frequency of the CS were more likely perceived as the CS in a specific context, where CS was associated with US. These results together demonstrate that learning-induced plasticity in the auditory cortex occurs in a context-dependent manner.
Highlights
State-dependent neural representation is found in both the sensory (e.g., [1,2,3]) and motor systems [4], suggesting that neurons multiplex their function to perform different analyses according to context
We performed a context-dependent auditory fear conditioning, in which a mild electrical foot shock as unconditioned stimulus (US) was associated with 20kHz conditioned stimulus (CS) tone under the noise condition, while only the CS was presented in the silent condition
We demonstrated that this conditioning changed both behavior and auditory cortical activities in a context-dependent manner
Summary
State-dependent neural representation is found in both the sensory (e.g., [1,2,3]) and motor systems [4], suggesting that neurons multiplex their function to perform different analyses according to context. Pre-attentively (under anesthesia), the receptive fields are rapidly modulated by bottom-up stimulus properties [8] such as stimulus density [9], bandwidth [10], envelope [11], and context [12] Such context-dependent modulation of receptive fields is critically involved for contrast gain control [13], possibly through synaptic depression [14], [15] and/or other network mechanisms [11], [16]. Past experiences such as passive sound exposure and active learning influence the pre-attentive cortical representation (for reviews: [17,18,19]). Little attention has been paid to the rapid, context-dependent modulation of such plasticity
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