Dynamic state and the receptive field transformation in the lemniscal auditory thalamocortical system

In an effort to understand how ecological and communication sounds are processed in the mammalian auditory system, neuroscientists, have investigated neural connectivity and response properties in dozens of areas from the cochlea to the auditory cortex. However, little attention has been given to the functional role of connections between different areas. Two central structures, the medial geniculate body of the thalamus (MGB) and the auditory cortex, are considered essential for the processing of complex auditory signals such as vocalizations. Specifically, the substructure of the MGB that sends high-fidelity discriminative auditory information to the cortex is the ventral division (MGBv), which projects heavily to the primary auditory cortex (AI). An understanding of the MGBv-AI interaction, for both its ethological significance and its commonality with other systems, would deepen our understanding of the neurobiological bases of mammalian sensation. We recorded hundreds of single neurons in the MGBv and AI of the anesthetized cat. The focus of this dissertation is the functional role of the MGBv-AI thalamocortical transformation in the spectral and temporal coding of sounds.; Although each of the four chapters may be read independently, they are arranged in a logically sequential order. The first chapter shows how powerful dynamic state transitions in the thalamocortical network can be controlled with carefully designed, naturalistic stimuli. The second chapter presents a thorough comparison of simultaneously recorded thalamic and cortical cells across spectral, temporal, spectrotemporal, and aural stimulus domains. While this chapter compares all thalamic versus all cortical cells, it does not consider functional connections between individual neurons. Such monosynaptic connections and the variety of their convergence patterns are taken up in Chapter 3, where we describe how some response properties are faithfully preserved from thalamus to cortex while others are created intracortically. Finally, the last chapter analyzes the functional thalamocortical connections on a more quantitative, spike-by-spike basis. This allows us to address the amount of information a given thalamic cell contributes to its cortical target, and how other inputs cooperate to influence the spectrotemporal character of that information.