Pure word deafness following left temporal damage: Behavioral and neuroanatomical evidence from a new case

Abstract

Pure Word Deafness (PWD) is a rare disorder, characterized by selective loss of speech input processing. Its most common cause is temporal damage to the primary auditory cortex of both hemispheres, but it has been reported also following unilateral lesions. In unilateral cases, PWD has been attributed to the disconnection of Wernicke's area from both right and left primary auditory cortex. Here we report behavioral and neuroimaging evidence from a new case of left unilateral PWD with both cortical and white matter damage due to a relatively small stroke lesion in the left temporal gyrus. Selective impairment in auditory language processing was accompanied by intact processing of nonspeech sounds and normal speech, reading and writing. Performance on dichotic listening was characterized by a reversal of the right-ear advantage typically observed in healthy subjects. Cortical thickness and gyral volume were severely reduced in the left superior temporal gyrus (STG), although abnormalities were not uniformly distributed and residual intact cortical areas were detected, for example in the medial portion of the Heschl's gyrus. Diffusion tractography documented partial damage to the acoustic radiations (AR), callosal temporal connections and intralobar tracts dedicated to single words comprehension. Behavioral and neuroimaging results in this case are difficult to integrate in a pure cortical or disconnection framework, as damage to primary auditory cortex in the left STG was only partial and Wernicke's area was not completely isolated from left or right-hemisphere input. On the basis of our findings we suggest that in this case of PWD, concurrent partial topological (cortical) and disconnection mechanisms have contributed to a selective impairment of speech sounds. The discrepancy between speech and non-speech sounds suggests selective damage to a language-specific left lateralized network involved in phoneme processing.

Separating the Causes of Listening Difficulties in Children

“…The end result of the second block is a set of identified (whether correctly or incorrectly) speech sounds. Having a block dedicated to the identification of speech sounds is consistent with certain cortical lesions that adversely affect the recognition of speech sounds, but not any other sounds ( Maffei et al 2017 ).…”

A Missing Connection: A Review of the Macrostructural Anatomy and Tractography of the Acoustic Radiation

“…In addition to variability across studies, low reproducibility across subjects is also reported. Some groups have been able to reconstruct AR tracts on both hemispheres on 100% of subjects (Behrens et al, 2007; Profant et al, 2014; Maffei et al, 2017). In contrast, even when using similar diffusion models (e.g., ball-and-stick), other studies report reconstructions successful in both hemispheres in much lower proportions, such as 35–50% (Crippa et al, 2010) or 71–86% (Javad et al, 2014).…”

“…Damage to the auditory regions, most often the result of brain infarct or traumatic injury, has been associated generally with rare auditory syndromes, such as verbal auditory agnosia (Shivashankar et al, 2001), environmental auditory agnosia (Taniwaki et al, 2000), and cerebral (or central) deafness (Griffiths, 2002). However, until now, only one study investigated the extent of WM damage to the AR in a patient suffering from verbal auditory agnosia (Maffei et al, 2017). Investigating the extent of damage to the AR in patients suffering speech-related comprehension deficits would potentially enhance our understanding of the involvement of the AR in language processing.…”

A review of brain regions and associated post-concussion symptoms

“…The medial geniculate bodies have also been known to facilitate the efficient transmission of auditory linguistic signals in speech to preserve and perceive environmental sounds ( 175 ). Pathology associated with the medial geniculate body is generalized auditory agnosia and a reduced ability to understand auditory inputs ( 171 , 176 ). Partially because of the close connection between the medial geniculate bodies and other subcortical structures such as the hippocampus and amygdala, a rodent model traumatic brain injury study found abnormally increased activity in the medial geniculate bodies in connection to auditory-induced post-traumatic stress and amygdala dysfunction ( 177 ).…”

“…Studies have shown that damage to acoustic radiation is associated with hearing and language disorders, auditory processing deficits, and decreased speech comprehension ( 174 ). More serious damage could lead to cortical (central) deafness ( 117 , 149 ), environmental sound agnosia, total auditory agnosia of all sounds ( 149 ), or verbal deafness (word agnosia) ( 175 , 176 ). Additionally, an individual can experience auditory hallucinations (i.e., the experience of hearing music in the absence of any external stimuli) ( 150 ) or tinnitus ( 234 ).…”