Distinct core thalamocortical pathways to central and dorsal primary auditory cortex

The cat primary auditory cortex (AI) is usually assumed to form one continuous functional region. However, the dorsal and central parts of the AI iso-frequency domain contain neurons that have distinct response properties to acoustic stimuli. In this study, we asked whether neurons projecting to dorsal versus central regions of AI originate in different parts of the medial geniculate body (MGB). Spike rate responses to variations in the sound level and frequency of pure tones were used to measure characteristic frequency (CF) and frequency resolution. These were mapped with high spatial density in order to place retrograde tracers into matching frequency regions of the central narrow-band region (cNB) and dorsal AI. Labeled neurons projecting to these two parts of AI were concentrated in the middle and rostral thirds of the MGB, respectively. There was little evidence that differences in dorsal and central AI function could be due to convergent input from cells outside the ventral division of the MGB (MGBv). Instead, inputs arising from different locations along the caudal-to-rostral dimension of MGBv represent potential sources of response differences between central and dorsal sub-regions of AI.