Background: Inner speech has an important role in many human cognitive functions. Even though it has been extensively studied in post-stroke aphasic patients, there is currently no understanding on how slow-growing lesions affect inner speech abilities.
Methods: In the present study we investigated inner speech abilities in a 41-year-old, right-handed man, MN, who was diagnosed with low-grade glioma three years earlier. We tested his performance on a wide range of standard cognitive tests and on four experiments specifically designed to assess inner speech abilities, involving: silent rhyme judgments, syllable discrimination, and identification of words in compounds and names for numbers. Control data were obtained from 10 neurologically intact adults.
Results: The modified t-test revealed that, in comparison with the HC group, MN's silent rhyming was considerably worse (p=0.027), but his performance on the remaining tests was spared (overt rhyming: p=0.136; words in compounds: p=0.288, discerning syllables: p=0.268; discerning words in names for numbers: p=0.48).
Discussion: Overall, our data on inner speech in this particular case of left temporal lobe slow-growing tumor supports the notion that the brain retains considerable potential for functional reorganization. MN's performance on silent rhyming is likely due to a word retrieval deficit (since we used a pictorial paradigm in this task) and exacerbated by verbal working memory deficit.
Conclusion: Given the critical role of inner speech in various mental functions, assessment of this ability in patients with left temporal lobe tumors is highly recommended.