Wednesday, November 14, 2012

Possible Implications for Musical Processing in Aphasia

Article: Patel, Aniruddh, John Iversen, Marlies Wassenaar and Peter Hagoort. "Musical syntactic processing in agrammatic Broca's aphasia." Aphasiology 22 (2008), (accessed November 12, 2012).

                This article ties into the debate regarding the similarity between linguistic and musical syntactic processing.  Neuroimaging studies of language and music have revealed overlap in the brain’s response to difficult syntactic integrations.  This intuitively makes sense considering both language and music combine discrete elements to form hierarchically structured sequences such as sentences and chord progressions.  However, cases following brain injury, of amusia without aphasia and aphasia without amusia, seem to indicate dissociations between the two processes.  Patel proposes that language and music have distinct syntactic representations where information is permanently stored, but they both draw on a common pool of limited neural resources.  Therefore, injury to an area where language information is permanently stored can lead to loss of speaking ability with music information retained; however, Patel predicts that these individuals will exhibit parallel deficits in both linguistic and musical syntactic processing.   
                Two studies were completed.  The first examines linguistic and musical syntactic processing with linguistic semantic processing also tested in order to check for a relationship between linguistic semantic processing and musical syntactic processing.  The aphasic individuals studied were all native Dutch speakers who had suffered an ischaemic stroke in the left hemisphere of the brain.  They were given both a linguistic and musical task.  The linguistic task consisted of 120 pre-recorded sentences, and the individuals were asked if the sentences were correct.  Incorrect sentences either contained a violation between subject-verb agreement between the first noun and the second verb or a semantic violation, for example, “Anne scratched her name with her tomato on the wooden door”.  The musical task consisted of 60 pop-style chord progressions.  Half contained an out-of-key chord, and the individuals were asked if all tones belonged together.  The aphasic participants’ results were compared to that of a control group and showed a musical syntactic deficit, not as large as the linguistic syntactic deficit but still significant.  Aphasics also performed slightly worse on semantic tasks.
                The second experiment further studied musical syntactic processing in aphasics using harmonic priming.  Harmonic priming tests the influence of preceding harmonic context on the processing of chords.  It occurs when there is a faster reaction time to close verses distant chords in the circle of fifths.  The test contained two distinct variables.  Chords were presented either close or distant in harmonic context, but some chords were in tune and others mistuned, with the upper note of the triad being flat.  The results indicated aphasic participants failed to show a priming effect, meaning that, while the control group responded faster when the chord was close in harmonic context, aphasics did not.  This suggests that their responses were not driven by harmonic knowledge.
                The author recognizes that further research in this field is necessary and offers suggestions for future research.  He recommends testing patrons with specific anterior lesion profiles, experimenting with different linguistic syntactic operations, discovering which kinds of linguistic tasks correlate with performance on musical syntactic tasks, and discovering whether performance on musical tasks correlates with other aspects of language comprehension besides syntax.
                Something I found really interesting about this article is that, apparently, all reported cases of aphasia without amusia involve professional musicians.  Also, their ability to retain music processing abilities after brain injury could be due to the fact that professional musician’s brains differ from those of non-musicians.   They have increased grey matter density in the frontal regions.  Therefore, in a study like Patel’s, it is important that all participants be non musicians which he indicated in his article.  He also makes note of how helpful it would be for localisationist techniques such as fMRI to be applied to comparisons of syntactic processing in language and music.  Patel speculates that neural resources for processing language and music reside in frontal brain regions and representations where information is stored for more challenging processing tasks are in the posterior regions, but this has not yet been proven.  If we knew for certain where specific language and music processing tasks take place in the brain, the relationship between language and music would be much clearer.  This is also why it would be helpful to test individuals who have all been injured in a very specific area of the brain.  Patel predicted that aphasic individuals with “compromised resource networks” from brain injuries would exhibit “parallel deficits in linguistic and musical syntactic processing”; however, it appears that the deficits in people with aphasia are greater in linguistic processing than musical processing since they have more difficulty in processing sentence structure than musical sequences.  While the abilities to process language and music likely do not suffer equally from brain damage in aphasia, there is enough evidence to show a significant decrease in musical processing ability compared to the control group.  Therefore, I think that this is an interesting field that deserves more attention.  Patel concedes that there are many cases of amusia without aphasia reported, but how in depth have these studies been examined?  It is surely possible that these individuals with amusia have some sort of limitation in language processing that they may not be fully aware of.   This may or may not have to do specifically with syntax in language which Patel recognizes in his article.  Information from further investigation into these studies could reveal interesting insights into the connection between language and music processing.

1 comment:

Olenka Slywynska said...

I found a few things in this article very interesting. For one thing, it is interesting for me that loss of musical syntactic processing can happen along with linguistic syntactic processing in certain lesions, since often music is used therapeutically to retrieve language after brain injury. Thus I assumed that amusia and aphasia would not occur together. However, I just read an article by Hartley, Turry and Raghavan that musical syntactic processing was shown by MEG to occur in Broca’s area. So this would make sense- that a left sided lesion would affect both. But then it is interesting, as you say, that no musicians have had amusia with aphasia. I suppose it is true that professional musicians process music differently than non-professionals.

Finally, I found the idea of testing linguistic semantic as well as syntactic processing in Brocas area neat. It seems that decoding where in the brain different speech capabilities occur is very relevant in knowing how certain lesions will affect an individual. It again emphasizes the complexity of the brain- how in just speech, there are so many areas involved in production and comprehension.