The Neuroanatomy of Speech Processing: A Large-scale Lesion Study

Abstract

The neural basis of language has been studied for centuries, yet the networks critically involved in simply identifying or understanding a spoken word remain elusive. Several functional–anatomical models of critical neural substrates of receptive speech have been proposed, including (1) auditory-related regions in the left mid-posterior superior temporal lobe, (2) motor-related regions in the left frontal lobe (in normal and/or noisy conditions), (3) the left anterior superior temporal lobe, or (4) bilateral mid-posterior superior temporal areas. One difficulty in comparing these models is that they often focus on different aspects of the sound-to-meaning pathway and are supported by different types of stimuli and tasks. Two auditory tasks that are typically used in separate studies—syllable discrimination and word comprehension—often yield different conclusions. We assessed syllable discrimination (words and nonwords) and word comprehension (clear speech and with a noise masker) in 158 individuals with focal brain damage: left (n = 113) or right (n = 19) hemisphere stroke, left (n = 18) or right (n = 8) anterior temporal lobectomy, and 26 neurologically intact controls. Discrimination and comprehension tasks are doubly dissociable both behaviorally and neurologically. In support of a bilateral model, clear speech comprehension was near ceiling in 95% of left stroke cases and right temporal damage impaired syllable discrimination. Lesion-symptom mapping analyses for the syllable discrimination and noisy word comprehension tasks each implicated most of the left superior temporal gyrus. Comprehension but not discrimination tasks also implicated the left pMTG, whereas discrimination but not comprehension tasks also implicated more dorsal sensorimotor regions in posterior perisylvian cortex.

Comparing the brain–behaviour relationship in acute and chronic stroke aphasia

“… 14 On the other hand, pMTG is considered a hub within the language network 13 and is part of the lexical-semantic ventral stream; damage to this stream is associated with auditory comprehension deficits. 79 This study confirms the critical role of these regions in language, and as WAB-R AQ is a composite score, it is unsurprising that regions from both dorsal and ventral streams are implicated. There is often progressive degeneration of white matter integrity following stroke, and this may be more notable in the later stages of recovery.…”

Informational Masking in Aging and Brain-lesioned Individuals

“…Locations of stroke-induced lesions were determined by visual inspection of the lesion maps generated (Fig. 4 depicts the overlap of these lesion maps after the lesion maps were transformed into Montreal Neurological Institute template space using standard procedures [ 32 ]). Inspection of the lesion maps yielded the following general categories of lesion locations: N = 49 left cerebral hemisphere, N = 1 right cerebral hemisphere, N = 2 bilateral cerebral hemisphere, N = 1 right cerebellum, N = 1 left cerebellum, and N = 1 brain stem.…”

Dynamics of Functional Networks for Syllable and Word-Level Processing

“…Sublexical contingencies, such as syllable-to-syllable transitions (i.e., syllable-to-syllable transitions are here defined as sublexical syllabic features that have a higher within than between word probability and thus allow the “grouping” of syllables into words), contribute to word processing and have been shown to activate parts of the superior temporal sulcus (STS; Mesgarani et al, 2014 ; Okada & Hickok, 2006 ) and a dorsal-path network ( Hickok & Poeppel, 2007 ). Additionally, parts of the inferior frontal gyrus (IFG) have been suggested to contribute to word-level processing, for example, in sublexical processing tasks reflecting sensory-motor integration ( Burton et al, 2000 ; Moineau et al, 2005 ; Möttönen & Watkins, 2009 ) or in tasks that elicit lexical competition ( Kan et al, 2006 ; Rodd et al, 2015 ; Thompson-Schill et al, 1997 ); whereas it has been argued that the recruitment of frontal motor areas reflects working memory processes rather than speech comprehension per se ( Rogalsky et al, 2022 ).…”