Hidden word learning capacity through orthography in aphasia

Leena M. Tuomiranta, Estela Càmara, Seán Froudist Walsh, Pablo Ripollés, Jani P. Saunavaara, Riitta Parkkola, Nadine Martin, Antoni Rodríguez-Fornells, Matti Laine

Research output: Contribution to journalArticlepeer-review

Abstract

The ability to learn to use new words is thought to depend on the integrity of the left dorsal temporo-frontal speech processing pathway. We tested this assumption in a chronic aphasic individual (AA) with an extensive left temporal lesion using a new-word learning paradigm. She exhibited severe phonological problems and Magnetic Resonance Imaging (MRI) suggested a complete disconnection of this left-sided white-matter pathway comprising the arcuate fasciculus (AF). Diffusion imaging tractography confirmed the disconnection of the direct segment and the posterior indirect segment of her left AF, essential components of the left dorsal speech processing pathway. Despite her left-hemispheric damage and moderate aphasia, AA learned to name and maintain the novel words in her active vocabulary on par with healthy controls up to 6 months after learning. This exceeds previous demonstrations of word learning ability in aphasia. Interestingly, AA's preserved word learning ability was modality-specific as it was observed exclusively for written words. Functional magnetic resonance imaging (fMRI) revealed that in contrast to normals, AA showed a significantly right-lateralized activation pattern in the temporal and parietal regions when engaged in reading. Moreover, learning of visually presented novel word-picture pairs also activated the right temporal lobe in AA. Both AA and the controls showed increased activation during learning of novel versus familiar word-picture pairs in the hippocampus, an area critical for associative learning. AA's structural and functional imaging results suggest that in a literate person, a right-hemispheric network can provide an effective alternative route for learning of novel active vocabulary. Importantly, AA's previously undetected word learning ability translated directly into therapy, as she could use written input also to successfully re-learn and maintain familiar words that she had lost due to her left hemisphere lesion.

Original languageEnglish (US)
Pages (from-to)174-191
Number of pages18
JournalCortex
Volume50
DOIs
StatePublished - Jan 1 2015

Keywords

  • Anomia
  • Aphasia
  • Aphasia treatment
  • Learning
  • Vocabulary

ASJC Scopus subject areas

  • Neuropsychology and Physiological Psychology
  • Experimental and Cognitive Psychology
  • Cognitive Neuroscience

Fingerprint Dive into the research topics of 'Hidden word learning capacity through orthography in aphasia'. Together they form a unique fingerprint.

Cite this