Poster C46, Friday, August 17, 10:30 am – 12:15 pm, Room 2000AB

Does a discrete lesion to the posterior left Middle temporal gyrus produce a language deficit?

Sonia Brownsett1,2, Kori Ramajoo1,2, Katie McMahon3, Hanna Gauvin1,2, Greig de Zubicaray1,2;1Faculty of Health, School - Psychology and Counselling, QUT, 2Institute of Health Biomedical Innovation, QUT, 3Faculty of Health, School - Clinical Sciences

Introduction: The role of the posterior middle temporal gyrus (pMTG) in semantic and language skills remains elusive. Citing lesion evidence from stroke patients, Hickok (1) argues that this region has long been associated with auditory comprehension deficits, suggesting that it’s role in auditory comprehension is at a lexical-semantic level (2,3) or ‘mapping sound onto meaning’ (1,2,4) or a ‘conceptual access mechanism’ (Hickok, 2009). According to Turken and Dronkers (5) “even a small lesion in a strategic place such as the MTG would have far more serious ramifications than a comparable lesion elsewhere in the network”. Given the neurovascular architecture, stroke lesions involving the pMTG typically also include additional perisylvian regions, it is therefore a challenge to draw conclusions about the role of this region from stroke data alone. We present data from a single case study of a patient with a discrete tumour resection involving the pMTG. Methods: A 49-year-old right-handed male had a unilateral grade 4 tumour resected. A T1- and T2- flair weighted MRI image was acquired on a 3T Siemens TRIO scanner. The tumour resection was isolated to the posterior middle temporal gyrus. A battery of assessments investigating residual language, speech and semantic skills were completed to investigate the impact of removal of this posterior cortical tissue on language processing. The patient was not receiving adjunctive treatment but had recently begun taking levetiracetam following an isolated seizure. Results: The participant presented with normal non-verbal cognitive skills and recognition memory of faces. He performed within normal limits on a range of auditory repetition tasks (at word and nonword, digit and sentence levels). Manipulating frequency, imageability and word length did not impact on repetition abilities. Auditory comprehension was also within normal limits, as was reading abilities. Investigating semantic skills specifically, he performed within normal limits on picture and word versions of the camel and cactus test and on most subtests of the Cambridge semantic battery including non-verbal auditory semantics, comprehension, naming, living versus non-living and word fluency. However, the patient presented with an isolated semantic deficit on a synonym judgement task, specifically for low frequency and low imageability items. Conclusion: We present data that demonstrates that damage to the posterior MTG does not produce a comprehension deficit per se. This unique single-case study suggests a relatively circumscribed role for the posterior MTG in abstract semantic retrieval in high-level written synonym judgement rather than either auditory comprehension or amodal semantics. The data presented here does not support notions of a small lesion to the MTG having serious ramifications for the language network (cf. 5) or that this region is associated with auditory comprehension deficits at a lexical-semantic level (cf. 1,2,3,4).

Topic Area: Language Disorders