The neural underpinnings of pure word deafness following left temporal damage
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1
Università di Trento, CIMeC (Centro Interdipartimentale Mente/Cervello), Italy
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2
SCA Associates, Italy
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3
King's College London, NatBrainLab, United Kingdom
Introduction
Pure word deafness (PWD) is characterized by the isolated loss of auditory speech processing, in the presence of normal comprehension of written language, and of normal spoken and written production. Its most frequent cause is a bilateral temporal damage, although cases with unilateral lesion have been occasionally reported. In unilateral cases, a combined cortical/subcortical left temporal damage has been proposed, resulting in a double disconnect between the auditory cortex and Wernicke’s area in the left hemisphere (intra-hemispheric disconnection) and between auditory cortex and Wernicke’s area in the left hemisphere and their contralateral counterparts on the right hemisphere (inter-hemispheric disconnection) (Geschwind, 1965).
Historical cases with demonstrated lesion at the autopsy provided anatomical evidence compatible with a disconnection mechanism (Liepmann, 1898), but their descriptions of the underlying cognitive impairments were rather sketchy. Subsequent reports supported the disconnection account on purely functional grounds, (e.g. based on the reversal of the Right-Ear Advantage (REA) in dichotic listening tasks) (Saffran, Marin & Yeni-Komshian, 1976), but lacked a clear anatomical/neuroradiological evidence. In a recent case, spared transcallosal temporal connections ruled out disconnection, but no information on intratemporal connection was provided (Slevc, Martin, Hamilton & Joanisse, 2011).
We report here the first extensive reconstruction of white matter connectivity in a patient with unilateral temporal damage and an isolated form of PWD. Fibre pathways were reconstructed via advanced diffusion tractography based on a spherical deconvolution algorithm and both intra-hemispheric and inter-hemispheric disconnection mechanisms tested.
Case report
Patient FCO, a 38-yr old, right-handed woman, showed a circumscribed left temporal damage (Heschl’s gyrus, anterior Superior Temporal Gyrus, posterior Insula) on structural MRI images. Assessment performed 3 years after the onset of symptoms showed normal pure tone audiometry and AER whereas vocal audiometry was indicative of a cortical damage.
Results
The patient’s isolated auditory speech processing disorder was characterized by marked REA reversal on the dichotic listening test (Figure 1) with normal performances on tasks for music and environmental sounds recognition, written language comprehension, speech production and writing.
Tractography showed intact left acoustic radiations and partial reconstructions of callosal streamlines between primary auditory cortices and between Wernicke’s area and its right-hemisphere homologue. Connections between primary auditory cortex and Wernicke’s area were totally absent.
Discussion
Our functional and structural findings converge in support of disconnection as the most likely mechanism underlying the isolated word deafness reported by a woman with a small left unilateral lesion. The occurrence of PWD following the left temporal damage indicates an asymmetrical lateralization in the early stages of cortical word processing.
References
Geschwind, N. (1965). Disconnection syndromes in animals and man. Brain, 88, 237–94.
Liepmann, H. (1898). Ein Fall von reiner Sprachtaubheit. In: Psychiatrische Abhandlungen (Wernicke, C., Ed.).
Saffran, E.M., Marin, O.S., & Yeni-Komshian, G.H. (1976a). An analysis of speech perception in word deafness. Brain and Language, 3(2), 209–228.
Slevc, L.R., Martin, R.C., Hamilton, A.C., & Joanisse, M.F. (2011). Speech perception, rapid temporal processing, and the left hemisphere: a case study of unilateral pure word deafness. Neuropsychologia, 49(2), 216–230.
Keywords:
Pure word deafness,
disconnection syndromes,
Spherical Deconvolution,
Dichotic listening tasks,
Computational hemispheric asymmetries
Conference:
54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.
Presentation Type:
Platform Sessions
Topic:
Academy of Aphasia
Citation:
Maffei
C,
Capasso
R,
Cazzolli
G,
Dell'Acqua
F,
Catani
M and
Miceli
G
(2016). The neural underpinnings of pure word deafness following left temporal damage.
Front. Psychol.
Conference Abstract:
54th Annual Academy of Aphasia Meeting.
doi: 10.3389/conf.fpsyg.2016.68.00050
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Received:
28 Apr 2016;
Published Online:
15 Aug 2016.
*
Correspondence:
Prof. Gabriele Miceli, Università di Trento, CIMeC (Centro Interdipartimentale Mente/Cervello), Rovereto, TN, 38068, Italy, gabriele.miceli@unitn.it