The characterization of receptive fields and underlying functional topographies creates a basis for understanding fundamental organizing principles and information processing mechanisms evident in the auditory cortex. It is hypothesized that changes in the immediate acoustic environment in which sounds are embedded in may affect receptive fields and consequently alter the cortical topographies of functional parameters. The goal was to study the effect of differences in signal-to-noise ratio on the excitatory receptive field area and the representation of speech-like signals. In particular, back-ground noise was found to effect the size of the receptive field, as well as dynamic range and response threshold. Continuous background noise significantly affects not only the properties of receptive fields but also their spatial distribution. Differential excitation bandwidth changes due to the effects of contextual backgrounds provide a basis for exploring functional distinctions between classes of neurons defined by their sharpness of tuning. Understanding these functional distinctions may provide insights to cortical processing of complex sounds such as speech. The effects of back-ground noise on the spatial-temporal distribution of responses to speech-like sounds was assessed directly. The study revealed a fairly small effect on the spatial distribution pattern while simple amplitude changes of the signal resulted in more profound changes across AI. The consequences of back-ground noise and signal intensity on related functional cortical maps in the primary auditory cortex reveals different subregions in AI that may provide substrates for different processing tasks, such as signal detection versus signal identification. The relationship of these effects to the columnar organization of AI and the variability of cortical maps may reveal important functional principles with regard to cortico-cortical connectivities and the concept of auditory scene analysis.
Supported by NIH grants DC02260 and NS 34835.