A Neural Representation of Pitch Salience in Nonprimary Human Auditory Cortex Revealed with Functional Magnetic Resonance Imaging
3 years ago
Sounds that have similar structure but a different perceived pitch cause the same types of fMRI responses in most auditory brain regions (including primary auditory cortex). But activity in anterior, non-primary auditory cortex (anterolateral Heschl's gyrus) did correlate with perceived pitch. Anterior non-primary auditory cortex is responsible for computing pitch.
Even in the abstract the author points out the fundamental assumptions in fMRI so the reader can judge for herself whether to accept the final interpretation. (Disclaimer: I work with the first author)
The idea behind the study is so simple it's surprising this hasn't been done before. Specificity of non-primary auditory cortex activity is interesting. Does it imply that pitch information isn't fed back in any way to primary auditory areas?
This kind of paper often comes with strong claims about a certain brain area being the first one in a circuit to process a certain type of information. But the author here was careful with his language not to overstate the results.
The claim that non primary cortex is the first to show pitch correlates is dependent on the assumption that nonsignificant activation differences in subcortical/primary cortical areas imply that those areas don't process pitch. But how do you judge that pitch isn't just encoded there in a way not detectable by fMRI? For example temporal coding hasn't been shown to have an fMRI correlate, but it definitely is a form of place coding in hippocampus. Could pitch be rate coded in primary cortex? To be fair, the author acknowledges this issue. But it's not clear how to get around it.