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Thalamic label patterns suggest primary and ventral auditory fields are distinct core regions
Douglas A Storace1, Nathan C Higgins, Heather L Read
1Psychology, Behavioral Neuroscience Division, University of Connecticut, Storrs, Connecticut 06269, USA.
The Journal of Comparative Neurology
|March 17, 2010
Summary
Rat auditory cortex, like primate auditory cortex, has multiple core regions. This study used functional imaging and retrograde tracers to map connections between the medial geniculate body and auditory cortex areas A1 and VAF.
Area of Science:
- Neuroscience
- Auditory System Research
- Comparative Anatomy
Background:
- Primate auditory cortex is hierarchically organized into core and belt regions based on thalamic connections and response properties.
- Core regions receive unimodal input from the ventral medial geniculate body (MGBv), while belt regions receive cross-modal input from outside the MGBv.
- Previous work identified distinct response properties in rat primary auditory cortex (A1) and ventral auditory field (VAF), but their classification as core or belt remained unclear.
Purpose of the Study:
- To investigate the anatomical connections of rat auditory cortex areas A1 and VAF with the medial geniculate body (MGB).
- To determine if rat auditory cortex exhibits a hierarchical organization similar to primates, with distinct core regions.
- To clarify the classification of VAF as a core or belt auditory cortex based on its thalamic input.
Main Methods:
- High-resolution functional imaging was used to map metabolic responses to auditory stimuli (tones).
- Retrograde tracer injections were guided by functional imaging into A1 and VAF.
- The size, density, and location of retrogradely labeled neurons in the MGB were analyzed based on their cortical projection target and position within the MGB.
Main Results:
- Neurons projecting to A1 and VAF were located in the same MGB subdivisions but in distinct rostral (A1) and caudal (VAF) locations.
- A small overlap (<3%) of projections to both A1 and VAF was observed.
- VAF-projecting neurons were smaller than A1-projecting neurons in the dorsal (MGBd) and suprageniculate (SG) nuclei, indicating soma size varies with location and target.
- The majority (>70%) of neurons projecting to both A1 and VAF were located in the MGBv.
Conclusions:
- The distinct anatomical connection profiles of A1 and VAF with the MGB suggest that rat auditory cortex, similar to primate auditory cortex, comprises multiple distinct core regions.
- These findings support a hierarchical organization model for the rat auditory system.
- The study provides crucial anatomical evidence for classifying VAF within the core auditory processing stream.
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