Transformation from sound to meaning in the ferret auditory cortex

Abstract: How do we make sense of the sounds we hear? We propose that there is a transformation from sound to meaning in the brain, which includes multiple steps from an initial, faithful encoding of incoming spectrotemporal acoustic patterns to further stages where the relevant auditory objects are recognized, categorized and associated with task or context-specific behavioral meaning and appropriate responses. We have explored this set of transformations by studying adaptive changes in neuronal responses in auditory cortex (AC) as animals selectively attend to specific acoustic targets in different task conditions. We have found that the tuning properties of A1 neurons can be altered in a task-specific fashion, enhancing their ability to encode the attended, task-relevant spectral and temporal features of the current task. This rapid task-related receptive field plasticity (RFP) enhances the contrast between foreground (task-relevant) and background (task-irrelevant) stimuli. The magnitude of these RFP effects is greatly heightened in higher order AC areas. Although there are multiple topdown projections to AC, we are currently investigating the contribution of frontal cortex in mediating RFP. Auditory responsive cells in dorsolateral frontal cortex (dlFC) show gated, adaptive, highly selective encoding of task-relevant target stimuli in a simple tone detect task. In other tasks involving auditory memory, some dlFC neurons show persistent responses for relevant, over-learned stimuli, even in passive listening conditions. We propose that dlFC contributes to sensory discrimination by keeping track of task goals, selectively attending to the class of task-relevant stimuli, and biasing sensory cortex in favor of task-relevant stimuli by reshaping acoustic filter properties of AC neurons. These results support the idea that dlFC and AC are part of a larger broad auditory attention network that uses multiple topdown projections, neuromodulators and an array of plasticity mechanisms to optimize processing of relevant stimuli during auditory attention and facilitate audiomotor integration.