Non-verbal sound processing in the primary progressive aphasias

Music Perception in Dementia

Despite much recent interest in music and dementia, music perception has not been widely studied across dementia syndromes using an information processing approach. Here we addressed this issue in a cohort of 30 patients representing major dementia syndromes of typical Alzheimer's disease (AD, n = 16), logopenic aphasia (LPA, an Alzheimer variant syndrome; n = 5), and progressive nonfluent aphasia (PNFA; n = 9) in relation to 19 healthy age-matched individuals. We designed a novel neuropsychological battery to assess perception of musical patterns in the dimensions of pitch and temporal information (requiring detection of notes that deviated from the established pattern based on local or global sequence features) and musical scene analysis (requiring detection of a familiar tune within polyphonic harmony). Performance on these tests was referenced to generic auditory (timbral) deviance detection and recognition of familiar tunes and adjusted for general auditory working memory performance. Relative to healthy controls, patients with AD and LPA had group-level deficits of global pitch (melody contour) processing while patients with PNFA as a group had deficits of local (interval) as well as global pitch processing. There was substantial individual variation within syndromic groups. Taking working memory performance into account, no specific deficits of musical temporal processing, timbre processing, musical scene analysis, or tune recognition were identified. The findings suggest that particular aspects of music perception such as pitch pattern analysis may open a window on the processing of information streams in major dementia syndromes. The potential selectivity of musical deficits for particular dementia syndromes and particular dimensions of processing warrants further systematic investigation.

When the Wedding March becomes sad: Semantic memory impairment for music in the semantic variant of primary progressive aphasia

Music can induce particular emotions and activate semantic knowledge. In the semantic variant of primary progressive aphasia (svPPA), semantic memory is impaired as a result of anterior temporal lobe (ATL) atrophy. Semantics is responsible for the encoding and retrieval of factual knowledge about music, including associative and emotional attributes. In the present study, we report the performance of two individuals with svPPA in three experiments. NG with bilateral ATL atrophy and ND with atrophy largely restricted to the left ATL. Experiment 1 assessed the recognition of musical excerpts and both patients were unimpaired. Experiment 2 studied the emotions conveyed by music and only NG showed impaired performance. Experiment 3 tested the association of semantic concepts to musical excerpts and both patients were impaired. These results suggest that the right ATL seems essential for the recognition of emotions conveyed by music and that the left ATL is involved in binding music to semantics. They are in line with the notion that the ATLs are devoted to the binding of different modality-specific properties and suggest that they are also differentially involved in the processing of factual and emotional knowledge associated with music.

Hearing and dementia

Hearing deficits associated with cognitive impairment have attracted much recent interest, motivated by emerging evidence that impaired hearing is a risk factor for cognitive decline. However, dementia and hearing impairment present immense challenges in their own right, and their intersection in the auditory brain remains poorly understood and difficult to assess. Here, we outline a clinically oriented, symptom-based approach to the assessment of hearing in dementias, informed by recent progress in the clinical auditory neuroscience of these diseases. We consider the significance and interpretation of hearing loss and symptoms that point to a disorder of auditory cognition in patients with dementia. We identify key auditory characteristics of some important dementias and conclude with a bedside approach to assessing and managing auditory dysfunction in dementia.

Mapping the Multiple Graded Contributions of the Anterior Temporal Lobe Representational Hub to Abstract and Social Concepts: Evidence from Distortion-corrected fMRI

A growing body of recent convergent evidence indicates that the anterior temporal lobe (ATL) has connectivity-derived graded differences in semantic function: the ventrolateral region appears to be the transmodal, omni-category center-point of the hub whilst secondary contributions come from the peripheries of the hub in a manner that reflects their differential connectivity to different input/output modalities. One of the key challenges for this neurocognitive theory is how different types of concept, especially those with less reliance upon external sensory experience (such as abstract and social concepts), are coded across the graded ATL hub. We were able to answer this key question by using distortion-corrected fMRI to detect functional activations across the entire ATL region and thus to map the neural basis of social and psycholinguistically-matched abstract concepts. Both types of concept engaged a core left-hemisphere semantic network, including the ventrolateral ATL, prefrontal regions and posterior MTG. Additionally, we replicated previous findings of weaker differential activation of the superior and polar ATL for the processing of social stimuli, in addition to the stronger, omni-category activation observed in the vATL. These results are compatible with the view of the ATL as a graded transmodal substrate for the representation of coherent concepts.

Does the sound of a barking dog activate its corresponding visual form? An fMRI investigation of modality-specific semantic access

Much remains to be learned about the neural architecture underlying word meaning. Fully distributed models of semantic memory predict that the sound of a barking dog will conjointly engage a network of distributed sensorimotor spokes. An alternative framework holds that modality-specific features additionally converge within transmodal hubs. Participants underwent functional MRI while covertly naming familiar objects versus newly learned novel objects from only one of their constituent semantic features (visual form, characteristic sound, or point-light motion representation). Relative to the novel object baseline, familiar concepts elicited greater activation within association regions specific to the presentation modality. Furthermore, visual form elicited activation within high-level auditory association cortex. Conversely, environmental sounds elicited activation in regions proximal to visual association cortex. Both conditions commonly engaged a putative hub region within lateral anterior temporal cortex. These results support hybrid semantic models in which local hubs and distributed spokes are dually engaged in service of semantic memory.

The clinical spectrum of sporadic and familial forms of frontotemporal dementia

The term frontotemporal dementia (FTD) describes a clinically, genetically and pathologically diverse group of neurodegenerative disorders. Symptoms of FTD can present in individuals in their 20s through to their 90s, but the mean age at onset is in the sixth decade. The most common presentation is with a change in personality and impaired social conduct (behavioural variant FTD). Less frequently patients present with language problems (primary progressive aphasia). Both of these groups of patients can develop motor features consistent with either motor neuron disease (usually the amyotrophic lateral sclerosis variant) or parkinsonism (most commonly a progressive supranuclear palsy or corticobasal syndrome). In about a third of cases FTD is familial, with mutations in the progranulin, microtubule-associated protein tau and chromosome 9 open reading frame 72 genes being the major causes. Mutations in a number of other genes including TANK-binding kinase 1 are rare causes of familial FTD. This review aims to clarify the often confusing terminology of FTD, and outline the various clinical features and diagnostic criteria of sporadic and familial FTD syndromes. It will also discuss the current major challenges in FTD research and clinical practice, and potential areas for future research. This review clarifies the terminology of frontotemporal dementia (FTD) and summarizes the various clinical features and most recent diagnostic criteria of sporadic and familial FTD syndromes. It also discusses the current major challenges in FTD research and clinical practice, and highlights potential areas for future research.

Neural circuits in auditory and audiovisual memory

Working memory is the ability to employ recently seen or heard stimuli and apply them to changing cognitive context. Although much is known about language processing and visual working memory, the neurobiological basis of auditory working memory is less clear. Historically, part of the problem has been the difficulty in obtaining a robust animal model to study auditory short-term memory. In recent years there has been neurophysiological and lesion studies indicating a cortical network involving both temporal and frontal cortices. Studies specifically targeting the role of the prefrontal cortex (PFC) in auditory working memory have suggested that dorsal and ventral prefrontal regions perform different roles during the processing of auditory mnemonic information, with the dorsolateral PFC performing similar functions for both auditory and visual working memory. In contrast, the ventrolateral PFC (VLPFC), which contains cells that respond robustly to auditory stimuli and that process both face and vocal stimuli may be an essential locus for both auditory and audiovisual working memory. These findings suggest a critical role for the VLPFC in the processing, integrating, and retaining of communication information. This article is part of a Special Issue entitled SI: Auditory working memory.

Core auditory processing deficits in primary progressive aphasia

The extent to which non-linguistic auditory processing deficits may contribute to the phenomenology of primary progressive aphasia is not established. Using non-linguistic stimuli devoid of meaning we assessed three key domains of auditory processing (pitch, timing and timbre) in a consecutive series of 18 patients with primary progressive aphasia (eight with semantic variant, six with non-fluent/agrammatic variant, and four with logopenic variant), as well as 28 age-matched healthy controls. We further examined whether performance on the psychoacoustic tasks in the three domains related to the patients’ speech and language and neuropsychological profile. At the group level, patients were significantly impaired in the three domains. Patients had the most marked deficits within the rhythm domain for the processing of short sequences of up to seven tones. Patients with the non-fluent variant showed the most pronounced deficits at the group and the individual level. A subset of patients with the semantic variant were also impaired, though less severely. The patients with the logopenic variant did not show any significant impairments. Significant deficits in the non-fluent and the semantic variant remained after partialling out effects of executive dysfunction. Performance on a subset of the psychoacoustic tests correlated with conventional verbal repetition tests. In sum, a core central auditory impairment exists in primary progressive aphasia for non-linguistic stimuli. While the non-fluent variant is clinically characterized by a motor speech deficit (output problem), perceptual processing of tone sequences is clearly deficient. This may indicate the co-occurrence in the non-fluent variant of a deficit in working memory for auditory objects. Parsimoniously we propose that auditory timing pathways are altered, which are used in common for processing acoustic sequence structure in both speech output and acoustic input.

Nonverbal auditory working memory: Can music indicate the capacity?

Different working memory (WM) mechanisms that underlie words, tones, and timbres have been proposed in previous studies. In this regard, the present study developed a WM test with nonverbal sounds and compared it to the conventional verbal WM test. A total of twenty-five, non-music major, right-handed college students were presented with four different types of sounds (words, syllables, pitches, timbres) that varied from two to eight digits in length. Both accuracy and oxygenated hemoglobin (oxyHb) were measured. The results showed significant effects of number of targets on accuracy and sound type on oxyHb. A further analysis showed prefrontal asymmetry with pitch being processed by the right hemisphere (RH) and timbre by the left hemisphere (LH). These findings suggest a potential for employing musical sounds (i.e., pitch and timbre) as a complementary stimuli for conventional nonverbal WM tests, which can additionally examine its asymmetrical roles in the prefrontal regions.

Auditory rehabilitation after stroke: treatment of auditory processing disorders in stroke patients with personal frequency-modulated (FM) systems

PURPOSE

Auditory disability due to impaired auditory processing (AP) despite normal pure-tone thresholds is common after stroke, and it leads to isolation, reduced quality of life and physical decline. There are currently no proven remedial interventions for AP deficits in stroke patients. This is the first study to investigate the benefits of personal frequency-modulated (FM) systems in stroke patients with disordered AP.

METHODS

Fifty stroke patients had baseline audiological assessments, AP tests and completed the (modified) Amsterdam Inventory for Auditory Disability and Hearing Handicap Inventory for Elderly questionnaires. Nine out of these 50 patients were diagnosed with disordered AP based on severe deficits in understanding speech in background noise but with normal pure-tone thresholds. These nine patients underwent spatial speech-in-noise testing in a sound-attenuating chamber (the "crescent of sound") with and without FM systems.

RESULTS

The signal-to-noise ratio (SNR) for 50% correct speech recognition performance was measured with speech presented from 0° azimuth and competing babble from ±90° azimuth. Spatial release from masking (SRM) was defined as the difference between SNRs measured with co-located speech and babble and SNRs measured with spatially separated speech and babble. The SRM significantly improved when babble was spatially separated from target speech, while the patients had the FM systems in their ears compared to without the FM systems.

CONCLUSIONS

Personal FM systems may substantially improve speech-in-noise deficits in stroke patients who are not eligible for conventional hearing aids. FMs are feasible in stroke patients and show promise to address impaired AP after stroke. Implications for Rehabilitation This is the first study to investigate the benefits of personal frequency-modulated (FM) systems in stroke patients with disordered AP. All cases significantly improved speech perception in noise with the FM systems, when noise was spatially separated from the speech signal by 90° compared with unaided listening. Personal FM systems are feasible in stroke patients, and may be of benefit in just under 20% of this population, who are not eligible for conventional hearing aids.

A physiological signature of sound meaning in dementia

The meaning of sensory objects is often behaviourally and biologically salient and decoding of semantic salience is potentially vulnerable in dementia. However, it remains unclear how sensory semantic processing is linked to physiological mechanisms for coding object salience and how that linkage is affected by neurodegenerative diseases. Here we addressed this issue using the paradigm of complex sounds. We used pupillometry to compare physiological responses to real versus synthetic nonverbal sounds in patients with canonical dementia syndromes (behavioural variant frontotemporal dementia – bvFTD, semantic dementia – SD; progressive nonfluent aphasia – PNFA; typical Alzheimer's disease – AD) relative to healthy older individuals. Nonverbal auditory semantic competence was assessed using a novel within-modality sound classification task and neuroanatomical associations of pupillary responses were assessed using voxel-based morphometry (VBM) of patients' brain MR images. After taking affective stimulus factors into account, patients with SD and AD showed significantly increased pupil responses to real versus synthetic sounds relative to healthy controls. The bvFTD, SD and AD groups had a nonverbal auditory semantic deficit relative to healthy controls and nonverbal auditory semantic performance was inversely correlated with the magnitude of the enhanced pupil response to real versus synthetic sounds across the patient cohort. A region of interest analysis demonstrated neuroanatomical associations of overall pupil reactivity and differential pupil reactivity to sound semantic content in superior colliculus and left anterior temporal cortex respectively. Our findings suggest that autonomic coding of auditory semantic ambiguity in the setting of a damaged semantic system may constitute a novel physiological signature of neurodegenerative diseases.

Pain and temperature processing in dementia: a clinical and neuroanatomical analysis

Symptoms suggesting altered pain and temperature processing have been described in dementia diseases. Using a semi-structured caregiver questionnaire and MRI voxel-based morphometry in patients with frontotemporal degeneration or Alzheimer’s disease, Fletcher et al. show that these symptoms are underpinned by atrophy in a distributed thalamo-temporo-insular network implicated in somatosensory processing.

Symptoms suggesting altered processing of pain and temperature have been described in dementia diseases and may contribute importantly to clinical phenotypes, particularly in the frontotemporal lobar degeneration spectrum, but the basis for these symptoms has not been characterized in detail. Here we analysed pain and temperature symptoms using a semi-structured caregiver questionnaire recording altered behavioural responsiveness to pain or temperature for a cohort of patients with frontotemporal lobar degeneration (n = 58, 25 female, aged 52–84 years, representing the major clinical syndromes and representative pathogenic mutations in the C9orf72 and MAPT genes) and a comparison cohort of patients with amnestic Alzheimer’s disease (n = 20, eight female, aged 53–74 years). Neuroanatomical associations were assessed using blinded visual rating and voxel-based morphometry of patients’ brain magnetic resonance images. Certain syndromic signatures were identified: pain and temperature symptoms were particularly prevalent in behavioural variant frontotemporal dementia (71% of cases) and semantic dementia (65% of cases) and in association with C9orf72 mutations (6/6 cases), but also developed in Alzheimer’s disease (45% of cases) and progressive non-fluent aphasia (25% of cases). While altered temperature responsiveness was more common than altered pain responsiveness across syndromes, blunted responsiveness to pain and temperature was particularly associated with behavioural variant frontotemporal dementia (40% of symptomatic cases) and heightened responsiveness with semantic dementia (73% of symptomatic cases) and Alzheimer’s disease (78% of symptomatic cases). In the voxel-based morphometry analysis of the frontotemporal lobar degeneration cohort, pain and temperature symptoms were associated with grey matter loss in a right-lateralized network including insula (P < 0.05 corrected for multiple voxel-wise comparisons within the prespecified anatomical region of interest) and anterior temporal cortex (P < 0.001 uncorrected over whole brain) previously implicated in processing homeostatic signals. Pain and temperature symptoms accompanying C9orf72 mutations were specifically associated with posterior thalamic atrophy (P < 0.05 corrected for multiple voxel-wise comparisons within the prespecified anatomical region of interest). Together the findings suggest candidate cognitive and neuroanatomical bases for these salient but under-appreciated phenotypic features of the dementias, with wider implications for the homeostatic pathophysiology and clinical management of neurodegenerative diseases.

Physiological phenotyping of dementias using emotional sounds

INTRODUCTION

Emotional behavioral disturbances are hallmarks of many dementias but their pathophysiology is poorly understood. Here we addressed this issue using the paradigm of emotionally salient sounds.

METHODS

Pupil responses and affective valence ratings for nonverbal sounds of varying emotional salience were assessed in patients with behavioral variant frontotemporal dementia (bvFTD) (n = 14), semantic dementia (SD) (n = 10), progressive nonfluent aphasia (PNFA) (n = 12), and AD (n = 10) versus healthy age-matched individuals (n = 26).

RESULTS

Referenced to healthy individuals, overall autonomic reactivity to sound was normal in Alzheimer's disease (AD) but reduced in other syndromes. Patients with bvFTD, SD, and AD showed altered coupling between pupillary and affective behavioral responses to emotionally salient sounds.

DISCUSSION

Emotional sounds are a useful model system for analyzing how dementias affect the processing of salient environmental signals, with implications for defining pathophysiological mechanisms and novel biomarker development.

Auditory hedonic phenotypes in dementia: A behavioural and neuroanatomical analysis

Patients with dementia may exhibit abnormally altered liking for environmental sounds and music but such altered auditory hedonic responses have not been studied systematically. Here we addressed this issue in a cohort of 73 patients representing major canonical dementia syndromes (behavioural variant frontotemporal dementia (bvFTD), semantic dementia (SD), progressive nonfluent aphasia (PNFA) amnestic Alzheimer's disease (AD)) using a semi-structured caregiver behavioural questionnaire and voxel-based morphometry (VBM) of patients' brain MR images. Behavioural responses signalling abnormal aversion to environmental sounds, aversion to music or heightened pleasure in music (‘musicophilia’) occurred in around half of the cohort but showed clear syndromic and genetic segregation, occurring in most patients with bvFTD but infrequently in PNFA and more commonly in association with MAPT than C9orf72 mutations. Aversion to sounds was the exclusive auditory phenotype in AD whereas more complex phenotypes including musicophilia were common in bvFTD and SD. Auditory hedonic alterations correlated with grey matter loss in a common, distributed, right-lateralised network including antero-mesial temporal lobe, insula, anterior cingulate and nucleus accumbens. Our findings suggest that abnormalities of auditory hedonic processing are a significant issue in common dementias. Sounds may constitute a novel probe of brain mechanisms for emotional salience coding that are targeted by neurodegenerative disease.

Dementias show differential physiological responses to salient sounds

Abnormal responsiveness to salient sensory signals is often a prominent feature of dementia diseases, particularly the frontotemporal lobar degenerations, but has been little studied. Here we assessed processing of one important class of salient signals, looming sounds, in canonical dementia syndromes. We manipulated tones using intensity cues to create percepts of salient approaching ("looming") or less salient withdrawing sounds. Pupil dilatation responses and behavioral rating responses to these stimuli were compared in patients fulfilling consensus criteria for dementia syndromes (semantic dementia, n = 10; behavioral variant frontotemporal dementia, n = 16, progressive nonfluent aphasia, n = 12; amnestic Alzheimer's disease, n = 10) and a cohort of 26 healthy age-matched individuals. Approaching sounds were rated as more salient than withdrawing sounds by healthy older individuals but this behavioral response to salience did not differentiate healthy individuals from patients with dementia syndromes. Pupil responses to approaching sounds were greater than responses to withdrawing sounds in healthy older individuals and in patients with semantic dementia: this differential pupil response was reduced in patients with progressive nonfluent aphasia and Alzheimer's disease relative both to the healthy control and semantic dementia groups, and did not correlate with nonverbal auditory semantic function. Autonomic responses to auditory salience are differentially affected by dementias and may constitute a novel biomarker of these diseases.

Identification of environmental sounds and melodies in syndromes of anterior temporal lobe degeneration

Recognition of nonverbal sounds in semantic dementia and other syndromes of anterior temporal lobe degeneration may determine clinical symptoms and help to define phenotypic profiles. However, nonverbal auditory semantic function has not been widely studied in these syndromes. Here we investigated semantic processing in two key nonverbal auditory domains – environmental sounds and melodies – in patients with semantic dementia (SD group; n = 9) and in patients with anterior temporal lobe atrophy presenting with behavioural decline (TL group; n = 7, including four cases with MAPT mutations) in relation to healthy older controls (n = 20). We assessed auditory semantic performance in each domain using novel, uniform within-modality neuropsychological procedures that determined sound identification based on semantic classification of sound pairs. Both the SD and TL groups showed comparable overall impairments of environmental sound and melody identification; individual patients generally showed superior identification of environmental sounds than melodies, however relative sparing of melody over environmental sound identification also occurred in both groups. Our findings suggest that nonverbal auditory semantic impairment is a common feature of neurodegenerative syndromes with anterior temporal lobe atrophy. However, the profile of auditory domain involvement varies substantially between individuals.

•

Nonverbal auditory processing is an understudied area of semantic memory.

•

We assessed novel auditory semantic tasks in patients with temporal lobe atrophy.

•

Environmental sound and music processing were comparably impaired across the cohort.

•

Individual patients may show relative sparing of melody processing.

•

Nonverbal auditory deficits integrally accompany temporal lobe degeneration.

The undiscovered syndrome: Macdonald Critchley's case of semantic dementia

Semantic dementia is a unique clinicopathological syndrome in the frontotemporal lobar degeneration spectrum. It is characterized by progressive and relatively selective impairment of semantic memory, associated with asymmetric antero-inferior temporal lobe atrophy. Although the syndrome became widely recognized only in the 1980s, descriptions of cases with typical features of semantic dementia have been on record for over a century. Here, we draw attention to a well documented historical case of a patient with features that would have fulfilled current consensus criteria for semantic dementia, as reconstructed from the notes made by her neurologist, Macdonald Critchley, in 1938. This case raises a number of issues concerning the nosology of the semantic dementia syndrome and the potential value of archived case material.

Auditory spatial processing in Alzheimer's disease

The location and motion of sounds in space are important cues for encoding the auditory world. Spatial processing is a core component of auditory scene analysis, a cognitively demanding function that is vulnerable in Alzheimer's disease. Here we designed a novel neuropsychological battery based on a virtual space paradigm to assess auditory spatial processing in patient cohorts with clinically typical Alzheimer's disease (n = 20) and its major variant syndrome, posterior cortical atrophy (n = 12) in relation to healthy older controls (n = 26). We assessed three dimensions of auditory spatial function: externalized versus non-externalized sound discrimination, moving versus stationary sound discrimination and stationary auditory spatial position discrimination, together with non-spatial auditory and visual spatial control tasks. Neuroanatomical correlates of auditory spatial processing were assessed using voxel-based morphometry. Relative to healthy older controls, both patient groups exhibited impairments in detection of auditory motion, and stationary sound position discrimination. The posterior cortical atrophy group showed greater impairment for auditory motion processing and the processing of a non-spatial control complex auditory property (timbre) than the typical Alzheimer's disease group. Voxel-based morphometry in the patient cohort revealed grey matter correlates of auditory motion detection and spatial position discrimination in right inferior parietal cortex and precuneus, respectively. These findings delineate auditory spatial processing deficits in typical and posterior Alzheimer's disease phenotypes that are related to posterior cortical regions involved in both syndromic variants and modulated by the syndromic profile of brain degeneration. Auditory spatial deficits contribute to impaired spatial awareness in Alzheimer's disease and may constitute a novel perceptual model for probing brain network disintegration across the Alzheimer's disease syndromic spectrum.

Auditory agnosia

Auditory agnosia refers to impairments in sound perception and identification despite intact hearing, cognitive functioning, and language abilities (reading, writing, and speaking). Auditory agnosia can be general, affecting all types of sound perception, or can be (relatively) specific to a particular domain. Verbal auditory agnosia (also known as (pure) word deafness) refers to deficits specific to speech processing, environmental sound agnosia refers to difficulties confined to non-speech environmental sounds, and amusia refers to deficits confined to music. These deficits can be apperceptive, affecting basic perceptual processes, or associative, affecting the relation of a perceived auditory object to its meaning. This chapter discusses what is known about the behavioral symptoms and lesion correlates of these different types of auditory agnosia (focusing especially on verbal auditory agnosia), evidence for the role of a rapid temporal processing deficit in some aspects of auditory agnosia, and the few attempts to treat the perceptual deficits associated with auditory agnosia. A clear picture of auditory agnosia has been slow to emerge, hampered by the considerable heterogeneity in behavioral deficits, associated brain damage, and variable assessments across cases. Despite this lack of clarity, these striking deficits in complex sound processing continue to inform our understanding of auditory perception and cognition.

Hearing and music in dementia

Music is a complex acoustic signal that relies on a number of different brain and cognitive processes to create the sensation of hearing. Changes in hearing function are generally not a major focus of concern for persons with a majority of neurodegenerative diseases associated with dementia, such as Alzheimer disease (AD). However, changes in the processing of sounds may be an early, and possibly preclinical, feature of AD and other neurodegenerative diseases. The aim of this chapter is to review the current state of knowledge concerning hearing and music perception in persons who have a dementia as a result of a neurodegenerative disease. The review focuses on both peripheral and central auditory processing in common neurodegenerative diseases, with a particular focus on the processing of music and other non-verbal sounds. The chapter also reviews music interventions used for persons with neurodegenerative diseases.

Acquired amusia

Recent developments in the cognitive neuroscience of music suggest that a further review of the topic of amusia is timely. In this chapter, we first consider previous taxonomies of amusia and propose a fresh framework for understanding the amusias, essentially as disorders of cognitive information processing. We critically review current cognitive and neuroanatomic findings in the published literature on amusia. We assess the extent to which the clinical and neuropsychologic evidence in amusia can be reconciled; both with the information-processing framework we propose, and with the picture of the brain organization of music and language processing emerging from cognitive neuroscience and functional neuroimaging studies. The balance of evidence suggests that the amusias can be understood as disorders of musical object cognition targeting separable levels of an information-processing hierarchy and underpinned by specific brain network dysfunction. The neuroanatomic associations of the amusias show substantial overlap with brain networks that process speech; however, this convergence leaves scope for separable brain mechanisms based on altered connectivity and dynamics across culprit networks. The study of the amusias contributes to an increasingly complex picture of the musical brain that transcends any simple dichotomy between music and speech or other complex sounds.

Dissociating the semantic function of two neighbouring subregions in the left lateral anterior temporal lobe

We used fMRI in 35 healthy participants to investigate how two neighbouring subregions in the lateral anterior temporal lobe (LATL) contribute to semantic matching and object naming. Four different levels of processing were considered: (A) recognition of the object concepts; (B) search for semantic associations related to object stimuli; (C) retrieval of semantic concepts of interest; and (D) retrieval of stimulus specific concepts as required for naming. During semantic association matching on picture stimuli or heard object names, we found that activation in both subregions was higher when the objects were semantically related (mug-kettle) than unrelated (car-teapot). This is consistent with both LATL subregions playing a role in (C), the successful retrieval of amodal semantic concepts. In addition, one subregion was more activated for object naming than matching semantically related objects, consistent with (D), the retrieval of a specific concept for naming. We discuss the implications of these novel findings for cognitive models of semantic processing and left anterior temporal lobe function.

Delayed auditory feedback simulates features of nonfluent primary progressive aphasia

The pathophysiology of nonfluent primary progressive aphasia (nfvPPA) remains poorly understood. Here, we compared quantitatively speech parameters in patients with nfvPPA versus healthy older individuals under altered auditory feedback, which has been shown to modulate normal speech output. Patients (n = 15) and healthy volunteers (n = 17) were recorded while reading aloud under delayed auditory feedback [DAF] with latency 0, 50 or 200 ms and under DAF at 200 ms plus 0.5 octave upward pitch shift. DAF in healthy older individuals was associated with reduced speech rate and emergence of speech sound errors, particularly at latency 200 ms. Up to a third of the healthy older group under DAF showed speech slowing and frequency of speech sound errors within the range of the nfvPPA cohort. Our findings suggest that (in addition to any anterior, primary language output disorder) these key features of nfvPPA may reflect distorted speech input signal processing, as simulated by DAF. DAF may constitute a novel candidate pathophysiological model of posterior dorsal cortical language pathway dysfunction in nfvPPA.

•

The pathophysiology of nonfluent progressive aphasia (nfvPPA) is poorly understood.

•

Delayed auditory feedback (DAF) disrupts speech output in some normal listeners.

•

We compared quantitatively speech in nvfPPA with DAF in healthy older individuals.

•

Around a third of healthy older individuals under DAF developed features of nvfPPA.

•

DAF is a candidate pathophysiological model of dorsal pathway dysfunction in nfvPPA.

Neurocognitive insights on conceptual knowledge and its breakdown

Conceptual knowledge reflects our multi-modal 'semantic database'. As such, it brings meaning to all verbal and non-verbal stimuli, is the foundation for verbal and non-verbal expression and provides the basis for computing appropriate semantic generalizations. Multiple disciplines (e.g. philosophy, cognitive science, cognitive neuroscience and behavioural neurology) have striven to answer the questions of how concepts are formed, how they are represented in the brain and how they break down differentially in various neurological patient groups. A long-standing and prominent hypothesis is that concepts are distilled from our multi-modal verbal and non-verbal experience such that sensation in one modality (e.g. the smell of an apple) not only activates the intramodality long-term knowledge, but also reactivates the relevant intermodality information about that item (i.e. all the things you know about and can do with an apple). This multi-modal view of conceptualization fits with contemporary functional neuroimaging studies that observe systematic variation of activation across different modality-specific association regions dependent on the conceptual category or type of information. A second vein of interdisciplinary work argues, however, that even a smorgasbord of multi-modal features is insufficient to build coherent, generalizable concepts. Instead, an additional process or intermediate representation is required. Recent multidisciplinary work, which combines neuropsychology, neuroscience and computational models, offers evidence that conceptualization follows from a combination of modality-specific sources of information plus a transmodal 'hub' representational system that is supported primarily by regions within the anterior temporal lobe, bilaterally.

Wernicke's area revisited: parallel streams and word processing

Auditory word-form recognition was originally proposed by Wernicke to occur within left superior temporal gyrus (STG), later further specified to be in posterior STG. To account for clinical observations (specifically paraphasia), Wernicke proposed his sensory speech center was also essential for correcting output from frontal speech-motor regions. Recent work, in contrast, has established a role for anterior STG, part of the auditory ventral stream, in the recognition of species-specific vocalizations in nonhuman primates and word-form recognition in humans. Recent work also suggests monitoring self-produced speech and motor control are associated with posterior STG, part of the auditory dorsal stream. Working without quantitative methods or evidence of sensory cortex' hierarchical organization, Wernicke co-localized functions that today appear dissociable. "Wernicke's area" thus may be better construed as two cortical modules, an auditory word-form area (AWFA) in the auditory ventral stream and an "inner speech area" in the auditory dorsal stream.

Agnosia for accents in primary progressive aphasia

As an example of complex auditory signal processing, the analysis of accented speech is potentially vulnerable in the progressive aphasias. However, the brain basis of accent processing and the effects of neurodegenerative disease on this processing are not well understood. Here we undertook a detailed neuropsychological study of a patient, AA with progressive nonfluent aphasia, in whom agnosia for accents was a prominent clinical feature. We designed a battery to assess AA's ability to process accents in relation to other complex auditory signals. AA's performance was compared with a cohort of 12 healthy age and gender matched control participants and with a second patient, PA, who had semantic dementia with phonagnosia and prosopagnosia but no reported difficulties with accent processing. Relative to healthy controls, the patients showed distinct profiles of accent agnosia. AA showed markedly impaired ability to distinguish change in an individual's accent despite being able to discriminate phonemes and voices (apperceptive accent agnosia); and in addition, a severe deficit of accent identification. In contrast, PA was able to perceive changes in accents, phonemes and voices normally, but showed a relatively mild deficit of accent identification (associative accent agnosia). Both patients showed deficits of voice and environmental sound identification, however PA showed an additional deficit of face identification whereas AA was able to identify (though not name) faces normally. These profiles suggest that AA has conjoint (or interacting) deficits involving both apperceptive and semantic processing of accents, while PA has a primary semantic (associative) deficit affecting accents along with other kinds of auditory objects and extending beyond the auditory modality. Brain MRI revealed left peri-Sylvian atrophy in case AA and relatively focal asymmetric (predominantly right sided) temporal lobe atrophy in case PA. These cases provide further evidence for the fractionation of brain mechanisms for complex sound analysis, and for the stratification of progressive aphasia syndromes according to the signature of nonverbal auditory deficits they produce.

Language, executive function and social cognition in the diagnosis of frontotemporal dementia syndromes

Frontotemporal dementia (FTD) represents a spectrum of non-Alzheimer's degenerative conditions associated with focal atrophy of the frontal and/or temporal lobes. Frontal and temporal regions of the brain have been shown to be strongly involved in executive function, social cognition and language processing and, thus, deficits in these domains are frequently seen in patients with FTD or may even be hallmarks of a specific FTD subtype (i.e. relatively selective and progressive language impairment in primary progressive aphasia). In this review we have attempted to delineate how language, executive function, and social cognition may contribute to the diagnosis of FTD syndromes, namely the behavioural variant FTD as well as the language variants of FTD including the three subtypes of primary progressive aphasia (PPA): non-fluent/agrammatic, semantic and logopenic. This review also addresses the extent to which deficits in these cognitive areas contribute to the differential diagnosis of FTD versus Alzheimer's disease (AD). Finally, early clinical determinants of pathology are briefly discussed and contemporary challenges to the diagnosis of FTD are presented.

Clinical diagnostic criteria and classification controversies in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) can manifest as a spectrum of clinical syndromes, ranging from behavioural impairment to language or motor dysfunction. Recently, revised diagnostic criteria have been proposed for the behavioural and progressive aphasia syndromes associated with frontotemporal degeneration. The present review will summarize these diagnostic guidelines and highlight some lingering controversies in the classification of FTLD clinical syndromes. We will discuss common tools and methods used to identify the insidious changes of behavioural variant frontotemporal dementia (bvFTD), the value of new, patient-based tasks of orbitofrontal function, and the issue of a benign or 'phenocopy' variant of bvFTD. With regard to primary progressive aphasia (PPA), we will discuss the scope of the semantic disorder in semantic-variant PPA, the nature of the speech disorder in non-fluent, agrammatic PPA, and the preliminary utility of a logopenic PPA classification.

The language profile of posterior cortical atrophy

BACKGROUND

Posterior cortical atrophy (PCA) is typically considered to be a visual syndrome, primarily characterised by progressive impairment of visuoperceptual and visuospatial skills. However, patients commonly describe early difficulties with word retrieval. This paper details the first systematic analysis of linguistic function in PCA. Characterising and quantifying the aphasia associated with PCA is important for clarifying diagnostic and selection criteria for clinical and research studies.

METHODS

15 patients with PCA, seven patients with logopenic/phonological aphasia (LPA) and 18 age matched healthy participants completed a detailed battery of linguistic tests evaluating auditory input processing, repetition and working memory, lexical and grammatical comprehension, single word retrieval and fluency, and spontaneous speech.

RESULTS

Relative to healthy controls, PCA patients exhibited language impairments across all of the domains examined, but with anomia, reduced phonemic fluency and slowed speech rate the most prominent deficits. PCA performance most closely resembled that of LPA patients on tests of auditory input processing, repetition and digit span, but was relatively stronger on tasks of comprehension and spontaneous speech.

CONCLUSIONS

The study demonstrates that in addition to the well reported degradation of vision, literacy and numeracy, PCA is characterised by progressive oral language dysfunction with prominent word retrieval difficulties. Overlap in the linguistic profiles of PCA and LPA, which are both most commonly caused by Alzheimer's disease, further emphasises the notion of a phenotypic continuum between typical and atypical manifestations of the disease. Clarifying the boundaries between Alzheimer's disease phenotypes has important implications for diagnosis, clinical trial recruitment and investigations into biological factors driving phenotypic heterogeneity in Alzheimer's disease. Rehabilitation strategies to ameliorate the phonological deficit in PCA are required.

The degraded concept representation system in semantic dementia: damage to pan-modal hub, then visual spoke

The core clinical feature of semantic dementia is a progressive yet selective degradation of conceptual knowledge. Understanding the cognitive and neuroanatomical basis for this deficit is a key challenge for both clinical and basic science. Some researchers attribute the deficit to damage to pan-modal conceptual representations that are independent of any particular sensory-motor modality and are represented in the ventrolateral anterior temporal lobes. Others claim that damage to modality-specific visual feature representations in the occipitotemporal 'ventral stream' is responsible. In the present study, we tested the hypothesis that concept degradation in semantic dementia involves a combination of these pan-modal and modality-specific elements. We investigated factors influencing knowledge of object concepts by analysing 43 sets of picture-naming data from patients with semantic dementia. We found a strong influence of two pan-modal factors: highly familiar and typical items were named more accurately than less familiar/atypical items at all stages of the disorder. Items associated with rich sensory-motor information were also named more successfully at all stages, and this effect was present for sound/motion knowledge and tactile/action knowledge when these modalities were studied separately. However, there was no advantage for items rich in visual colour/form characteristics; instead, this factor had an increasingly negative impact in the later stages of the disorder. We propose that these results are best explained by a combination of (i) degradation of modality-independent conceptual representations, which is present throughout the disorder and is a consequence of atrophy focused on the ventrolateral anterior temporal lobes; and (ii) a later additional deficit for concepts that depend heavily on visual colour/form information, caused by the spreading of atrophy to posterior ventral temporal regions specialized for representing this information. This explanation is consistent with a graded hub-and-spoke model of conceptual knowledge, in which there is a gradual convergence of information along the temporal lobes, with visual attributes represented in the posterior cortex giving way to pan-modal representations in the anterior areas.

Both the Middle Temporal Gyrus and the Ventral Anterior Temporal Area Are Crucial for Multimodal Semantic Processing: Distortion-corrected fMRI Evidence for a Double Gradient of Information Convergence in the Temporal Lobes

Most contemporary theories of semantic memory assume that concepts are formed from the distillation of information arising in distinct sensory and verbal modalities. The neural basis of this distillation or convergence of information was the focus of this study. Specifically, we explored two commonly posed hypotheses: (a) that the human middle temporal gyrus (MTG) provides a crucial semantic interface given the fact that it interposes auditory and visual processing streams and (b) that the anterior temporal region—especially its ventral surface (vATL)—provides a critical region for the multimodal integration of information. By utilizing distortion-corrected fMRI and an established semantic association assessment (commonly used in neuropsychological investigations), we compared the activation patterns observed for both the verbal and nonverbal versions of the same task. The results are consistent with the two hypotheses simultaneously: Both MTG and vATL are activated in common for word and picture semantic processing. Additional planned, ROI analyses show that this result follows from two principal axes of convergence in the temporal lobe: both lateral (toward MTG) and longitudinal (toward the anterior temporal lobe).

Accent processing in dementia

Accented speech conveys important nonverbal information about the speaker as well as presenting the brain with the problem of decoding a non-canonical auditory signal. The processing of non-native accents has seldom been studied in neurodegenerative disease and its brain basis remains poorly understood. Here we investigated the processing of non-native international and regional accents of English in cohorts of patients with Alzheimer's disease (AD; n=20) and progressive nonfluent aphasia (PNFA; n=6) in relation to healthy older control subjects (n=35). A novel battery was designed to assess accent comprehension and recognition and all subjects had a general neuropsychological assessment. Neuroanatomical associations of accent processing performance were assessed using voxel-based morphometry on MR brain images within the larger AD group. Compared with healthy controls, both the AD and PNFA groups showed deficits of non-native accent recognition and the PNFA group showed reduced comprehension of words spoken in international accents compared with a Southern English accent. At individual subject level deficits were observed more consistently in the PNFA group, and the disease groups showed different patterns of accent comprehension impairment (generally more marked for sentences in AD and for single words in PNFA). Within the AD group, grey matter associations of accent comprehension and recognition were identified in the anterior superior temporal lobe. The findings suggest that accent processing deficits may constitute signatures of neurodegenerative disease with potentially broader implications for understanding how these diseases affect vocal communication under challenging listening conditions.

Nonverbal sound processing in semantic dementia: a functional MRI study

Semantic dementia (SD) is a unique neurodegenerative syndrome accompanied by relatively selective loss of the meaning of objects and concepts. The brain mechanisms that underpin the syndrome have not been defined: a better understanding of these mechanisms would inform our understanding of both the organisation of the human semantic system and its vulnerability to neurodegenerative disease. In this fMRI study, we investigated brain correlates of sensory object processing in nine patients with SD compared with healthy control subjects, using the paradigm of nonverbal sound. Compared with healthy controls, patients with SD showed differential activation of cortical areas surrounding the superior temporal sulcus, both for perceptual processing of spectrotemporally complex but meaningless sounds and for semantic processing of environmental sound category (animal sounds versus tool sounds). Our findings suggest that defective processing of sound objects in SD spans pre-semantic perceptual processing and semantic category formation. This disease model illustrates that antero-lateral temporal cortical mechanisms are critical for representing and differentiating sound categories. The breakdown of these mechanisms constitutes a network-level functional signature of this neurodegenerative disease.

Structural neuroanatomy of tinnitus and hyperacusis in semantic dementia

INTRODUCTION

Tinnitus and hyperacusis are common symptoms of excessive auditory perception in the general population; however, their anatomical substrates and disease associations continue to be defined.

PATIENTS

with semantic dementia (SemD) frequently report tinnitus and hyperacusis but the significance and basis for these symptoms have not been elucidated.

METHODS

43 patients with a diagnosis of SemD attending a specialist cognitive disorders clinic were retrospectively studied. 14 patients (32% of the cohort) reported at least moderately severe chronic auditory symptoms: seven had tinnitus and a further seven had hyperacusis, and all had brain MRI while symptomatic. MRI data from SemD patients with and without auditory symptoms were compared using voxel based morphometry in order to identify neuroanatomical associations of tinnitus and hyperacusis.

RESULTS

Compared with SemD patients with no history of auditory symptoms, patients with tinnitus or hyperacusis had relative preservation of grey matter in the posterior superior temporal lobe and reduced grey matter in the orbitofrontal cortex and medial geniculate nucleus.

CONCLUSIONS

Tinnitus and hyperacusis may be a significant issue in SemD. Neuroanatomical evidence in SemD supports previous work implicating a distributed cortico-subcortical auditory and limbic network in the pathogenesis of these abnormal auditory percepts.

Primary progressive aphasias and their contribution to the contemporary knowledge about the brain-language relationship

Primary progressive aphasia (PPA), typically resulting from a neurodegenerative disease such as frontotemporal dementia/Pick Complex or Alzheimer's disease, is a heterogeneous clinical condition characterized by a progressive loss of specific language functions with initial sparing of other cognitive domains. Based on the constellation of symptoms, PPA has been classified into a nonfluent, semantic, or logopenic variant. This review of the literature aims to characterize the speech and language impairment, cognition, neuroimaging, pathology, genetics, and epidemiology associated with each of these variants. Some therapeutic recommendations, theoretical implications, and directions for future research have been also provided.

Semantic dementia: a specific network-opathy

Semantic dementia (SD) is a unique syndrome in the frontotemporal lobar degeneration spectrum. Typically presenting as a progressive, fluent anomic aphasia, SD is the paradigmatic disorder of semantic memory with a characteristic anatomical profile of asymmetric, selective antero-inferior temporal lobe atrophy. Histopathologically, most cases show a specific pattern of abnormal deposition of protein TDP-43. This relatively close clinical, anatomical and pathological correspondence suggests SD as a promising target for future therapeutic trials. Here, we discuss outstanding nosological and neurobiological challenges posed by the syndrome and propose a pathophysiological model of SD based on sequential, regionally determined disintegration of a vulnerable neural network.

Auditory object cognition in dementia

The cognition of nonverbal sounds in dementia has been relatively little explored. Here we undertook a systematic study of nonverbal sound processing in patient groups with canonical dementia syndromes comprising clinically diagnosed typical amnestic Alzheimer's disease (AD; n = 21), progressive nonfluent aphasia (PNFA; n = 5), logopenic progressive aphasia (LPA; n = 7) and aphasia in association with a progranulin gene mutation (GAA; n = 1), and in healthy age-matched controls (n = 20). Based on a cognitive framework treating complex sounds as ‘auditory objects’, we designed a novel neuropsychological battery to probe auditory object cognition at early perceptual (sub-object), object representational (apperceptive) and semantic levels. All patients had assessments of peripheral hearing and general neuropsychological functions in addition to the experimental auditory battery. While a number of aspects of auditory object analysis were impaired across patient groups and were influenced by general executive (working memory) capacity, certain auditory deficits had some specificity for particular dementia syndromes. Patients with AD had a disproportionate deficit of auditory apperception but preserved timbre processing. Patients with PNFA had salient deficits of timbre and auditory semantic processing, but intact auditory size and apperceptive processing. Patients with LPA had a generalised auditory deficit that was influenced by working memory function. In contrast, the patient with GAA showed substantial preservation of auditory function, but a mild deficit of pitch direction processing and a more severe deficit of auditory apperception. The findings provide evidence for separable stages of auditory object analysis and separable profiles of impaired auditory object cognition in different dementia syndromes.

Central auditory disorders: toward a neuropsychology of auditory objects

PURPOSE OF REVIEW

Analysis of the auditory environment, source identification and vocal communication all require efficient brain mechanisms for disambiguating, representing and understanding complex natural sounds as 'auditory objects'. Failure of these mechanisms leads to a diverse spectrum of clinical deficits. Here we review current evidence concerning the phenomenology, mechanisms and brain substrates of auditory agnosias and related disorders of auditory object processing.

RECENT FINDINGS

Analysis of lesions causing auditory object deficits has revealed certain broad anatomical correlations: deficient parsing of the auditory scene is associated with lesions involving the parieto-temporal junction, while selective disorders of sound recognition occur with more anterior temporal lobe or extra-temporal damage. Distributed neural networks have been increasingly implicated in the pathogenesis of such disorders as developmental dyslexia, congenital amusia and tinnitus. Auditory category deficits may arise from defective interaction of spectrotemporal encoding and executive and mnestic processes. Dedicated brain mechanisms are likely to process specialized sound objects such as voices and melodies.

SUMMARY

Emerging empirical evidence suggests a clinically relevant, hierarchical and modular neuropsychological model of auditory object processing that provides a framework for understanding auditory agnosias and makes specific predictions to direct future work.

Receptive prosody in nonfluent primary progressive aphasias

Introduction

Prosody has been little studied in the primary progressive aphasias (PPAs), a group of neurodegenerative disorders presenting with progressive language impairment.

Methods

Here we conducted a systematic investigation of different dimensions of prosody processing (acoustic, linguistic and emotional) in a cohort of 19 patients with nonfluent PPA syndromes (11 with progressive nonfluent aphasia, PNFA; five with progressive logopenic/phonological aphasia, LPA; three with progranulin-associated aphasia, GRN-PPA) compared with a group of healthy older controls. Voxel-based morphometry (VBM) was used to identify neuroanatomical associations of prosodic functions.

Results

Broadly comparable receptive prosodic deficits were exhibited by the PNFA, LPA and GRN-PPA subgroups, for acoustic, linguistic and affective dimensions of prosodic analysis. Discrimination of prosodic contours was significantly more impaired than discrimination of simple acoustic cues, and discrimination of intonation was significantly more impaired than discrimination of stress at phrasal level. Recognition of vocal emotions was more impaired than recognition of facial expressions for the PPA cohort, and recognition of certain emotions (in particular, disgust and fear) was relatively more impaired than others (sadness, surprise). VBM revealed atrophy associated with acoustic and linguistic prosody impairments in a distributed cortical network including areas likely to be involved in perceptual analysis of vocalisations (posterior temporal and inferior parietal cortices) and working memory (fronto-parietal circuitry). Grey matter associations of emotional prosody processing were identified for negative emotions (disgust, fear, sadness) in a broadly overlapping network of frontal, temporal, limbic and parietal areas.

Conclusions

Taken together, the findings show that receptive prosody is impaired in nonfluent PPA syndromes, and suggest a generic early perceptual deficit of prosodic signal analysis with additional relatively specific deficits (recognition of particular vocal emotions).