Non-verbal sound processing in the primary progressive aphasias

Abstract

Little is known about the processing of non-verbal sounds in the primary progressive aphasias. Here, we investigated the processing of complex non-verbal sounds in detail, in a consecutive series of 20 patients with primary progressive aphasia [12 with progressive non-fluent aphasia; eight with semantic dementia]. We designed a novel experimental neuropsychological battery to probe complex sound processing at early perceptual, apperceptive and semantic levels, using within-modality response procedures that minimized other cognitive demands and matching tests in the visual modality. Patients with primary progressive aphasia had deficits of non-verbal sound analysis compared with healthy age-matched individuals. Deficits of auditory early perceptual analysis were more common in progressive non-fluent aphasia, deficits of apperceptive processing occurred in both progressive non-fluent aphasia and semantic dementia, and deficits of semantic processing also occurred in both syndromes, but were relatively modality specific in progressive non-fluent aphasia and part of a more severe generic semantic deficit in semantic dementia. Patients with progressive non-fluent aphasia were more likely to show severe auditory than visual deficits as compared to patients with semantic dementia. These findings argue for the existence of core disorders of complex non-verbal sound perception and recognition in primary progressive aphasia and specific disorders at perceptual and semantic levels of cortical auditory processing in progressive non-fluent aphasia and semantic dementia, respectively.

Figure 1

Schematic of experimental stimuli and presentation sequences (A and B). Schematics of auditory and visual early perceptual stimuli, and the presentation sequence used. (C) Schematic of spectral inversion of a complex sound, as used in the auditory apperceptive test. (D and E) Examples of auditory and visual semantic stimulus pairs, and a schematic of the presentation sequence used. t = time (s).

Figure 2

MRI brain sections showing auditory cortices in PNFA and semantic dementia (SD) patients. Sections of each patient's volumetric T₁-weighted magnetic resonance brain volume are shown. Sections have been tilted to run along the superior temporal plane (STP) to show key auditory cortical areas: the site of primary auditory cortex in Heschl's gyrus (HG), and surrounding non-primary areas in anterior temporal lobe (aTL), posterior superior temporal gyrus and planum temporale (posterior temporal lobe: pTL), insula (ins) and inferior parietal lobe (iPL). For all brain images, the left hemisphere is shown on the left. For reference normal auditory cortical anatomy is shown on the inset sections (lower right) from the brain of a healthy younger individual. Brain images from the PNFA group are shown above and the semantic dementia group below. Above each image is shown the patient's age (left) and clinical disease duration (right) in years at the time of the scan. Within each group brain images have been arranged loosely in order of disease duration; the PNFA group had an older age range and a wider variation in age, and to reflect this, images have been further clustered to show younger patients above and older patients below.

Figure 3

Performance on experimental subtests: raw data. SD = semantic dementia