From Sound to Meaning –Dynamic Transformations in Auditory Signal-Processing

How do we make sense of sensory inputs? One important clue may be the central role of selective and predictive attention, by focusing limited resources on behaviorally relevant sensory channels and modulating information flow at multiple stages, to improve perception.Our approach is to study the effect of attention on information processing at the single neuron level in the primary auditory cortex (A1) of animals trained on multiple auditory tasks that require selective attention to task-specific salient spectral frequency or temporal cues. Our results demonstrate that when animals actively attend to a task, their auditory cortical neurons can rapidly change their spectrotemporal filter characteristics to improve the animal’s performance. Thus, cortical sensory filters are not fixed, but are highly adaptive, and show dynamic, task-specific transformations during auditory behavior. To study the broader neural circuits involved in attention, we have initiated research on several other components in the network, including secondary auditory cortical areas, nucleus basalis, and the prefrontal cortex (PFC), a brain area known to play a key role in attention and decision-making. In contrast to A1, PFC responses are largely independent of the acoustic properties of sound, and encode an abstract, categorical representation of sound meaning. Recent studies show that electrical stimulation of PFC can elicit receptive field transformations in A1 neurons very similar to the attentional effects observed during behavior. Our working model suggests a top-down instructive role for PFC, and emphasizes the importance of interactions between multiple brain areas during selective attention that lead to matched auditory cortical filters for attended acoustic stimuli, creating a dynamic, evolving neural representation of task-salient sounds and thus optimizing perception on a moment-to-moment basis.