Wolfram Ziegler

Consensus Paper: Language and the Cerebellum: an Ongoing Enigma

In less than three decades, the concept “cerebellar neurocognition” has evolved from a mere afterthought to an entirely new and multifaceted area of neuroscientific research. A close interplay between three main strands of contemporary neuroscience induced a substantial modification of the traditional view of the cerebellum as a mere coordinator of autonomic and somatic motor functions. Indeed, the wealth of current evidence derived from detailed neuroanatomical investigations, functional neuroimaging studies with healthy subjects and patients and in-depth neuropsychological assessment of patients with cerebellar disorders shows that the cerebellum has a cardinal role to play in affective regulation, cognitive processing, and linguistic function. Although considerable progress has been made in models of cerebellar function, controversy remains regarding the exact role of the “linguistic cerebellum” in a broad variety of nonmotor language processes. This consensus paper brings together a range of different viewpoints and opinions regarding the contribution of the cerebellum to language function. Recent developments and insights in the nonmotor modulatory role of the cerebellum in language and some related disorders will be discussed. The role of the cerebellum in speech and language perception, in motor speech planning including apraxia of speech, in verbal working memory, in phonological and semantic verbal fluency, in syntax processing, in the dynamics of language production, in reading and in writing will be addressed. In addition, the functional topography of the linguistic cerebellum and the contribution of the deep nuclei to linguistic function will be briefly discussed. As such, a framework for debate and discussion will be offered in this consensus paper.

Syllable Frequency and Syllable Structure in Apraxia of Speech.

Recent accounts of the pathomechanism underlying apraxia of speech (AOS) were based on the speech production model of Levelt, Roelofs, and Meyer, and Meyer (1999)1999. The apraxic impairment was localized to the phonetic encoding level where the model postulates a mental store of motor programs for high-frequency syllables. Varley and Whiteside (2001a) assumed that in patients with AOS syllabic motor programs are no longer accessible and that these patients are required to use a subsyllabic encoding route. In this study, we tested this hypothesis by exploring the influence of syllable frequency and syllable structure on word repetition in 10 patients with AOS. A significant effect of syllable frequency on error rates was found. Moreover, apraxic errors on consonant clusters were influenced by their position relative to syllable boundaries. These results demonstrate that apraxic patients have access to the syllabary, but that they fail to retrieve the syllabic motor patterns correctly. Our findings are incompatible with a subsyllabic route model of apraxia of speech.

Task-related factors in oral motor control: speech and oral diadochokinesis in dysarthria and apraxia of speech.

This study was focused on the potential influence of task-related factors on oral motor performance in patients with speech disorders. Sentence production was compared with a nonspeech oral motor task, i.e., oral diadochokinesis. Perceptual and acoustic measures of speech impairment were used as dependent variables. Between-task comparisons were made for subsamples of a population of 140 patients with different motor speech syndromes, including apraxia of speech and cerebellar dysarthria. In a further analysis subgroups were matched for speaking rate. Overall, dysdiadochokinesis was correlated with the degree of speech impairment, but there was a strong interaction between task type and motor speech syndrome. In particular, cerebellar pathology affected DDK to a relatively greater extent than sentence production, while apraxic pathology spared the ability of repeating syllables at maximum speed.

The role of the left mesial frontal cortex in fluent speech: evidence from a case of left supplementary motor area hemorrhage.

This study reports on a woman who suffered left anterior cerebral artery hemorrhage with a focal lesion undercutting the left supplementary motor area. After almost complete recovery of language the patient was left with dysfluent, halting speech. In a series of four experiments we examined the major factors influencing the patients articulation. There was a significant effect of lexicality and syllabic length on repetition and articulatory learning (Experiments 1 and 2). The number of syllables was also found to influence, in a simple reaction task, onset latencies, but not inter-response times (Experiment 3). On the contrary, articulatory intricacy had no particular effect on either repetition or vocal reaction (Experiments 1 and 3). While repetition of real words was preserved, single word production in word generation tasks was impaired. Rhyme generation and alliteration, both of which rely on phonological processing, were particularly involved, whereas semantic word generation tasks like verb generation and generation of category members were relatively spared (Experiment 4). Control tasks revealed that the observed phonological processing deficit was confined to the condition of generating spoken language output. These experimental findings suggest that the patients dysfluent speech could neither be attributed to a deficit of linguistic processing proper, nor to one of motor execution. Her speech disorder rather resulted from an impairment of initiating sequential articulations, particularly in association with the process of downloading temporarily stored multisyllabic strings from an articulatory buffer. This deficit could obviously be overcome in real word repetition through the use of a semantic lexical route.

Disturbed coarticulation in apraxia of speech: Acoustic evidence

The results of a recent perceptual study (W. Ziegler & D. von Cramon, 1985, Anticipatory coarticulation in a patient with apraxia of speech. Brain and Language 26, 117-130) provided evidence for disturbed coarticulation in verbal apraxia. Further support for this finding is now provided by acoustic analyses. Formant frequencies and LP reflection coefficients were chosen to assess anticipatory vowel-to-vowel coarticulation and vowel anticipation in stop consonants, respectively. These parameters revealed a lack of coarticulatory cohesion in the speech of a patient suffering from verbal apraxia, explainable by a consistent delay in the initiation of anticipatory vowel gestures. The findings are discussed with respect to prosodic features and to theoretical and clinical concepts of verbal apraxia.

Spastic dysarthria after acquired brain injury: An acoustic study

CVC syllables, sustained fricatives and rapid diphthong repetitions were examined in ten patients with spastic dysarthria following closed head trauma and cerebro-vascular accident. Speech samples were evaluated hy acoustic-signal processing. The data obtained/or segment durations, vowel quality, and plosive realisations revealed a disproportionate impairment in gross movements of the tongue back as compared to the tongue blade. In the milder cases target configurations could often be realised to an acoustically normal extent, yet at the expense of production time. This and the abnormalities in diphthong repetitions suggested that the faculty of accelerating the moving structures was limited in the observed spastic dysarthrics. Control of fine forces, however, was not generally impaired.

Apraxia of speech.

Publisher Summary Apraxia of speech is described as an impairment of the capacity to program the movements of the articulators for the purpose of speaking. Patients with apraxia of speech may present with a broad variety of clinical signs, depending on the severity of their speech impairment and the pattern of accompanying aphasic symptoms. In its most severe form, apraxia of speech may result in a total inability to voluntarily produce even a single word, syllable, or speech sound (apraxic mutism). The primary cause of apraxic speech impairment is left hemisphere stroke. The great majority of patients with apraxia of speech have suffered from infarction or hemorrhage of the left middle cerebral artery (central cortical branch) and its perforating arteries, or of the left lateral lenticulostriate arteries. Other etiologies can also cause apraxia of speech, e.g., traumatic brain injury, hematoma caused by arteriovenous malformation, or brain tumor. Brocas attempt at localizing the “faculty of articulate language” has often been considered as the birth of modern neuropsychology. The treatment of persisting apraxia of speech is a notorious therapeutic challenge. In clinical practice, speech therapists dispense a variety of well established treatment techniques, but there is only little empirical support for their effectiveness.

Balance and motor speech impairment in essential tremor

The pathogenesis of essential tremor (ET) is still under debate. Several lines of evidence indicate that ET is associated with cerebellar dysfunction. The aim of the present study was to find corroborating evidence for this claim by investigating balance and speech impairments in patients with ET. In addition, the effect of deep brain stimulation (DBS) on balance and speech function was studied. A group of 25 ET patients including 18 with postural and/or simple kinetic tremor (ETpt) and seven ET patients with additional clinical signs of cerebellar dysfunction (ETc) was compared to 25 healthy controls. In addition, 12 ET patients with thalamic DBS participated in the study. Balance control was assessed during gait and stance including tandem gait performed on a treadmill as well as static and dynamic posturography. Motor speech control was analyzed through syllable repetition tasks. Signs of balance impairment were found in early stages and advanced stages of ET. During locomotion, ET patients exhibited an increased number of missteps and shortened stride length with tandem gait. ETc patients and, to a lesser extent, ETpt patients had increased postural instability in dynamic posturography conditions that are sensitive to vestibular or vestibulocerebellar dysfunction. ETc but not ETpt patients exhibited significantly increased syllable durations. DBS had no discernable effect on speech performance or balance control. We conclude that the deficits in balance as well as the subclinical signs of dysarthria in a subset of patients confirm and extend previous findings that ET is associated with an impairment of the cerebellum.

Anticipatory coarticulation in a patient with apraxia of speech

Articulatory anticipation of vowel gestures was assessed in an apraxic patient, a dysarthric patient, and three normal speakers. The technique of assessment included perceptual identification of gated speech stimuli. The speech material consisted of /getVte/ utterances with the target vowels /i/, /y/, and /u/. In the case of the apraxic patient the gated vowels were identified at a later instant relative to the preceding plosion burst than in the normal speakers. This result was interpreted as reflecting a delayed onset of coarticulatory gestures, in particular lip rounding. The identification rates for the dysarthrics vowels rather reflected the general reduction of this patients vowel space.

Syllable frequency and syllable structure in the spontaneous speech production of patients with apraxia of speech

Background: The sublexical factors syllable frequency and syllable structure are known to influence error rates in patients with apraxia of speech (e.g., Aichert & Ziegler, 2004; Romani & Galluzzi, 2005). To our knowledge, these factors have almost exclusively been examined by single‐word production paradigms. However, performance on single‐word tasks is not necessarily a good predictor of spontaneous speech production, since the generation of conversational speech involves specific conditions and additional demands. This might influence the weights of syllable frequency and syllable structure in explanations of the accuracy of speech production in apraxic speakers. Aims: Our aim was to determine if the spontaneous speech production of patients with apraxia of speech (AOS) is influenced by the factors syllable frequency and syllable structure. The two research questions that guided our investigation were: (1) Are the distribution properties of syllables in spontaneous speech different in patients with AOS compared to unimpaired speakers? (2) Do the factors syllable frequency and syllable structure affect articulatory accuracy in the spontaneous speech of patients with AOS? Methods & Procedures: Three patients with AOS and 15 neurologically unimpaired control persons produced samples of spontaneous speech with a minimum of 1000 syllables each. Structure and frequency counts were made on the basis of the German CELEX database. Outcomes & Results: The distribution properties of the spontaneous speech samples were similar in the apraxic speakers and the unimpaired controls. In all three patients the proportion of errors was significantly higher on low‐ than on high‐frequency syllables. In two patients a significant effect even persisted when any confound with syllable structure was ruled out. Syllable structure effects were only found within the low‐frequency syllables. Conclusions: Syllable frequency and syllable structure play a decisive role with respect to articulatory accuracy in the spontaneous speech production of patients with AOS. The first author of this study was supported by a grant from the DFG ‐ German research council (ZI 469/10‐2). We would also like to thank the ReHa‐Hilfe e.V. for their support. We are grateful to our colleagues from the Neuropsychological Clinic, Munich‐Bogenhausen Hospital, Munich, and to the staff from the speech therapy departments at the Rehabilitation Hospitals Bad Heilbrunn and Bad Aibling for their collaboration on clinical issues. We would also like to express our gratitude to all participants.