Abstract
Anatomical studies propose that the primate auditory cortex contains more fields than have actually been functionally confirmed or described. Spatially resolved functional magnetic resonance imaging (fMRI) with carefully designed acoustical stimulation could be ideally suited to extend our understanding of the processing within these fields. However, after numerous experiments in humans, many auditory fields remain poorly characterized. Imaging the macaque monkey is of particular interest as these species have a richer set of anatomical and neurophysiological data to clarify the source of the imaged activity. We functionally mapped the auditory cortex of behaving and of anesthetized macaque monkeys with high resolution fMRI. By optimizing our imaging and stimulation procedures, we obtained robust activity throughout auditory cortex using tonal and band-passed noise sounds. Then, by varying the frequency content of the sounds, spatially specific activity patterns were observed over this region. As a result, the activity patterns could be assigned to many auditory cortical fields, including those whose functional properties were previously undescribed. The results provide an extensive functional tessellation of the macaque auditory cortex and suggest that 11 fields contain neurons tuned for the frequency of sounds. This study provides functional support for a model where three fields in primary auditory cortex are surrounded by eight neighboring “belt” fields in non-primary auditory cortex. The findings can now guide neurophysiological recordings in the monkey to expand our understanding of the processing within these fields. Additionally, this work will improve fMRI investigations of the human auditory cortex.
Highlights
The primate brain consists of numerous fields with specific roles in sensing and perceiving the environment
The anatomical evidence for the existence of a particular functional field remains unconfirmed. This leaves us with an incomplete understanding of auditory cortex, and impedes our understanding of subsequent processing relying on input from these auditory cortical fields (ACF), such as by fields specialized for processing communication sounds or those involved in integrating information from the different senses
Our initial goal was to activate a large region of the macaque auditory cortex upon which many ACFs could be functionally localized and described
Summary
The primate brain consists of numerous fields with specific roles in sensing and perceiving the environment. Concerning the cortical regions involved in the perception of sound, anatomical studies suggest that there are around a dozen auditory cortical fields (ACFs) [1,2,3,4,5]. For many of the fields either their role in acoustical processing comes from limited functional evidence in select primate species or is unknown In the latter case, the anatomical evidence for the existence of a particular functional field remains unconfirmed. The anatomical evidence for the existence of a particular functional field remains unconfirmed This leaves us with an incomplete understanding of auditory cortex, and impedes our understanding of subsequent processing relying on input from these ACFs, such as by fields specialized for processing communication sounds or those involved in integrating information from the different senses
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