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Resection of putative “Wernicke’s area” is neither necessary nor sufficient to cause “Wernicke’s aphasia” in a neurosurgical population

Poster A40 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall
Also presenting in Poster Slam A, Thursday, October 6, 10:00 - 10:15 am EDT, Regency Ballroom

Deborah F. Levy¹, Matthew K. Leonard¹, Patrick Hullett¹, John P. Andrews¹, Stephen M. Wilson², Mitchel S. Berger¹, Edward F. Chang¹; ¹University of California San Francisco, ²Vanderbilt University Medical Center

“Wernicke’s aphasia” describes a clinical syndrome characterized predominantly by disproportionate impairment to comprehension, classically accompanied by fluent yet paraphasic speech. This syndrome is thought to be caused by damage to “Wernicke’s area”, a term most often used to refer to the posterior third of the superior temporal gyrus (pSTG) and, debatably, aspects of the supramarginal and/or angular gyri. However, the mapping between the two Wernicke-inspired terms is not one-to-one. Inspired by seminal papers by JP Mohr revealing important distinctions between Broca’s area and the region implicated in Broca’s aphasia, here we demonstrate a set of circumstances in which there is a clear lack of correspondence between “Wernicke’s aphasia” and putative “Wernicke’s area”. Drawing from a dataset of 259 individuals, we present 7 cases in which circumscribed resection of the pSTG was performed, along with 21 cases in which a transient Wernicke’s aphasia was induced per the standards of the Western Aphasia Battery (WAB). There was no overlap between these two groups; that is, circumscribed resections of the pSTG did not lead to diagnoses of Wernicke’s aphasia (associating instead with post-surgical deficits in repetition), and diagnoses of Wernicke’s aphasia did not follow from circumscribed resections of the pSTG (associating instead with larger and more anterior resections). Additionally, exact sign tests revealed strikingly preserved single word comprehension relative to sentence comprehension regardless of clinical or anatomical grouping (median advantage for single words: 7.65, p<0.01 in the clinically-defined group; median advantage for single words: 4.30, p=0.02 in the anatomically-defined group), demonstrating inherent multidimensionality within a composite comprehension measure often used in classifications of aphasia. These cases illustrate that the relationship between anatomically defined “Wernicke’s area” and clinically defined “Wernicke’s aphasia” is not strictly causal, and support prior work demonstrating marked variability within aphasia subtype classifications. Though a limitation is the potential for atypical language organization in this population, recent functional imaging work has suggested that reorganization in neurosurgical cohorts is minimal, particularly in cases with late disease onset, as in the majority of cases described here. These findings have implications for clinical practice in that they caution against over-reliance on preconceived notions of “forbidden zones'' and their functions when making surgical decisions. Furthermore, for the cognitive neuroscience of language, these results demonstrate the need for more precise descriptions of both anatomical regions of interest and clinical language profiles, and invite further investigation of the role of the far posterior STG in language.

Topic Areas: Disorders: Acquired, Speech Perception