Samenvatting
SummaryForeign Accent Syndrome or FAS is a motor speech disorder that causes patients to start
speaking their mother tongue with an accent that is perceived as non-native. The impression
of a ‘foreign’ accent is the consequence of segmental and suprasegmental
changes occurring in the maternal language. FAS is usually the result of brain damage
(often a stroke). However, in recent years, there has been an increasing amount of reports
on FAS in association with psychiatric disorders, or developmental disorders. In
this dissertation, we have tried to establish an in-depth neurolinguistic analysis of three
different variants of FAS: neurogenic FAS, developmental FAS and psychogenic FAS.
In Chapter 1, we gave a historical overview of FAS from its first attestation by
Pierre Marie (1907) to the formulation of the operational definition and the FAS criteria
by Harry Whitaker (1982). Subsequently, we introduced the taxonomic distinction developed by Verhoeven and Mariën (2010), who described the four FAS variants: neurogenic, developmental, psychogenic and mixed FAS. This dissociation served as a
common thread for the layout of the current dissertation. Afterwards, we presented an
overview of the linguistic, cognitive, and computational explanations for the mechanisms inducing FAS. These theories were the main ideas against which the results in the
subsequent chapters were evaluated. We ended this chapter with an overview of the
research objectives of this dissertation.
In Chapter 2 we focused on the neurogenic FAS variant. The chapter constituted
a detailed review of the vascular FAS cases published between 1907 and October 2016. We focused on the vascular FAS cases, because these provide the best lesion-behavior correlations. We investigated the demographic data (gender, linguistic background etc.), lesion location , linguistic characteristics, associated cognitive impairments, comorbid speech- and/or language disorders, and onset and remission. We concluded that vascular FAS affects mainly monolingual women, who usually suffered structural damage affecting the premotor cortex, the motor cortex, the insula or the basal ganglia. In terms of the linguistic characteristics there was a preponderance of vowel elongation, vowel fronting, raising, backing and lowering, consonant substitution and consonant omission. On the suprasegmental level, speech was characterized by a slow speech rate, altered rhythm and intonation. The results also showed that vascular FAS is infrequently associated with cognitive deficits, although it often co-occurs with other speech- and language disorders (primarily aphasia). The onset of FAS is usually acute (occurring within 3 weeks after a stroke). Conclusions with respect to prognosis could not be made as the remission data were only irregularly provided. A comparison with ataxic dysarthria and apraxia of speech demonstrated that vascular FAS shares an important amount of perceptual characteristics with these motor speech disorders. After evaluation of the pathophysiology in conjunction with the clinically attested characteristics it is concluded in this chapter that vascular FAS most likely is a dual component disorder. The disruption in connectivity between areas associated with planning and/or execution of speech, usually affecting the cortico-striato-pallidal-thalamic pathways, can explain the clinical phenotype of vascular FAS.
In Chapter 3 we presented two new cases of foreign accent syndrome after posterior
fossa lesions. The speech characteristics of both patients showed resemblances with
apraxia of speech and ataxic dysarthria. The speech disturbances and cognitive deficits were explained in light of a disruption in the cerebellar connections with (pre-)frontal areas, and the hypothesis is raised whether FAS can be the result of consequent disruptions in feedforward and feedback motor speech control (in which the cerebellum plays a mediating role). An alternative hypothesis is that maladaptive compensation by unaffected brain areas, for instance the contralateral cerebellum (in case 2), plays a role.
In Chapter 4, we described the case of a 17-year-old Belgian boy with developmental
FAS and comorbid developmental apraxia of speech (DAS). The neuropsychological
and neurolinguistic investigations demonstrated that the patient had a normal
IQ, but impaired planning and graphomotor skills (visuo-constructional dyspraxia),
set-shifting and goal-oriented cognitive strategies. The patient underwent a Tc-99m-
ECD SPECT scan. This revealed a significant hypoperfusion in the prefrontal and medial
frontal regions, and in the lateral temporal regions. The hypoperfusion in the right
cerebellum almost reached significance. We argued that the linguistic deficits (FAS and
DAS) as well as the isolated visuo-constructional dyspraxia can be interpreted as the
functional expression of the retained hypoperfusions, affecting areas involved in linguistic and non-linguistic tasks involving planning (speech, but also graphomotor
plans for writing), attention and execution. The deficits in combination with the SPECT
scan again underline the importance of intact cerebro-cerebellar functional
communication.
In Chapter 5 we reviewed all of the assumed psychogenic FAS cases published
between 1907 and July 2014. The cases were analyzed for largely the same aspects as the vascular FAS patients, i.e. demographic data, etiologies, FAS characteristics (segmental and suprasegmental), associated cognitive impairments, comorbid speech- and/or language disorders and onset and remission data. The results demonstrated that psychogenic FAS predominantly affects monolingual women, that the disorder often cooccurs with a mental disorder and that FAS onset is usually associated with exacerbations in the context of an associated psychopathology. In cases in which the patient did not believe the FAS to be of psychogenic origin, the onset of the FAS was often considered particularly late compared to the incident the patient him-/herself held responsible for inciting the FAS (see also Chapter 7). The associated linguistic characteristics were
primarily vowel elongations, additions, and fronting, and at the consonant level:
omissions and substitutions. At the suprasegmental level, speech was marked by an
abnormal intonation, a slow speech rate and an altered speech rhythm. The psychogenic patients showed a diverse set of cognitive impairments affecting memory, attention, executive functions, processing speed, intelligence, fine motor skills and
visuospatial skills. These impairments were often directly associated with the psychopathology.
In case of doubt, the hypothesis of cogniform disorder – a cognitive disorder of a somatoform nature – was raised. Comorbid speech and/or language disorders were
very specific. Patients sometimes went through a period of mutism and developed
grammatical disorders. Symptom evolution was different from the one found in vascular FAS: speech symptoms fluctuated frequently over time, sometimes in association with psychiatric exacerbations. Lastly, we found that psychogenic FAS usually recedes simultaneously with the resolution of the associated psychiatric disorder (often pharmacologically induced), or spontaneously.
In Chapter 6 we discussed the case of a 40-year-old, non-aphasic, polyglot
Belgian woman with a history of drug addiction and psychiatric problems. In February
2010, she acutely developed a foreign accent of sudden onset in her first language
(French). Speech was relatively fluent, although the patient sometimes spoke in a stutter-like manner and she had a marked grammatical output disorder. The initial psychodiagnostic assessment disclosed indications for a conversion disorder, although the diagnosis could not be formally objectified. After three years, the patient's accent suddenly receded after a general anesthesia for an appendectomy. Her grammatical output disorder however, remained present, although only in the writing of her first language (French). We conducted a perceptual accent rating experiment in which the raters were native speakers of French. They confirmed that the patient sounded foreign. Based on the irregularities within the neurolinguistic profile, the psychiatric traits, and the sudden spontaneous recovery affecting only one modality, we concluded that the patient suffered a FAS of psychogenic origin.
In Chapter 7 we presented the case of a 33-year-old, French-speaking Belgian
woman who was involved in a car accident as a pedestrian. She developed a German/
Flemish-like accent approximately six months after the incident. Based on the neuroimaging data in the acute phase, structural brain damage was formally excluded. The neuropsychological investigations revealed poor executive functions, processing
speed, attention and verbal memory. We explained these deficits in the context of a
post-concussion syndrome. We did not formally rule out cogniform deficits: the fact
that the patient was implicated in litigation when she consulted the department, warranted such a hypothesis. Importantly, the accent – which fluctuated over time – was first noticed when the patient was dismissed from work. The psychodiagnostic evaluation disclosed that there were indications for a borderline personality although a formal diagnosis could not be made. We equally performed a perceptual accent rating experiment same methodology as in chapter 6 – which confirmed that the patient was perceived as a non-native speaker of French by a group of native French-speaking raters.
Specifically, the symptom evolution, including delayed onset and psychodiagnostic
findings in the absence of neurological disorder, argued in favor of a diagnosis of psychogenic
FAS.
In Chapter 8, we discuss the case of a 28-year-old Dutch-speaking woman from
the Netherlands who developed FAS two weeks after she slipped and fell down the
staircase. Medical history revealed that around the same time, the patient had started
displaying very disoriented behavior and had visual hallucinations. The FAS was unlike any previously published case: when in stress, the accented speech was interspersed
with German(-like) words and structures (language mixing and switching) and sometimes evolved to neologistic jargon speech. Apart from a borderline low intelligence, the formal psychodiagnostic tests did not lead to the diagnosis of a psychiatric disorder. The contradictory findings in the neurolinguistic tableau, in conjunction with her psychiatric and speech symptoms, were strongly indicative of an underlying psychogenic etiology.
In Chapter 9 we discussed the main research findings of this dissertation. In this
final chapter we compare the three types of FAS that were described and discussed in
this dissertation. The status of FAS as a motor speech disorder at the level of execution and planning is evaluated as well as the role of the cerebellum in its pathophysiology.
We end the chapter concluding that the term ‘foreign accent syndrome’, as coined by
Whitaker, is a misnomer.
| Datum prijs | 18 mei 2017 |
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| Originele taal | English |
| Prijsuitreikende instantie |
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| Begeleider | Peter Marien (Promotor), Roelien Bastiaanse (Promotor) & Verhoeven Jo (Promotor) |