fMRI reveals two distinct cerebral networks subserving speech motor control.

BACKGROUND: There are few data on the cerebral organization of motor aspects of speech production and the pathomechanisms of dysarthric deficits subsequent to brain lesions and diseases. The authors used fMRI to further examine the neural basis of speech motor control. METHODS AND RESULTS: In eight healthy volunteers, fMRI was performed during syllable repetitions synchronized to click trains (2 to 6 Hz; vs a passive listening task). Bilateral hemodynamic responses emerged at the level of the mesiofrontal and sensorimotor cortex, putamen/pallidum, thalamus, and cerebellum (two distinct activation spots at either side). In contrast, dorsolateral premotor cortex and anterior insula showed left-sided activation. Calculation of rate/response functions revealed a negative linear relationship between repetition frequency and blood oxygen level-dependent (BOLD) signal change within the striatum, whereas both cerebellar hemispheres exhibited a step-wise increase of activation at approximately 3 Hz. Analysis of the temporal dynamics of the BOLD effect found the various cortical and subcortical brain regions engaged in speech motor control to be organized into two separate networks (medial and dorsolateral premotor cortex, anterior insula, and superior cerebellum vs sensorimotor cortex, basal ganglia, and inferior cerebellum). CONCLUSION: These data provide evidence for two levels of speech motor control bound, most presumably, to motor preparation and execution processes. They also help to explain clinical observations such as an unimpaired or even accelerated speaking rate in Parkinson disease and slowed speech tempo, which does not fall below a rate of 3 Hz, in cerebellar disorders.

Identification of emotional intonation evaluated by fMRI.

During acoustic communication among human beings, emotional information can be expressed both by the propositional content of verbal utterances and by the modulation of speech melody (affective prosody). It is well established that linguistic processing is bound predominantly to the left hemisphere of the brain. By contrast, the encoding of emotional intonation has been assumed to depend specifically upon right-sided cerebral structures. However, prior clinical and functional imaging studies yielded discrepant data with respect to interhemispheric lateralization and intrahemispheric localization of brain regions contributing to processing of affective prosody. In order to delineate the cerebral network engaged in the perception of emotional tone, functional magnetic resonance imaging (fMRI) was performed during recognition of prosodic expressions of five different basic emotions (happy, sad, angry, fearful, and disgusted) and during phonetic monitoring of the same stimuli. As compared to baseline at rest, both tasks yielded widespread bilateral hemodynamic responses within frontal, temporal, and parietal areas, the thalamus, and the cerebellum. A comparison of the respective activation maps, however, revealed comprehension of affective prosody to be bound to a distinct right-hemisphere pattern of activation, encompassing posterior superior temporal sulcus (Brodmann Area [BA] 22), dorsolateral (BA 44/45), and orbitobasal (BA 47) frontal areas. Activation within left-sided speech areas, in contrast, was observed during the phonetic task. These findings indicate that partially distinct cerebral networks subserve processing of phonetic and intonational information during speech perception.

Distinct frontal regions subserve evaluation of linguistic and emotional aspects of speech intonation.

In addition to the propositional content of verbal utterances, significant linguistic and emotional information is conveyed by the tone of speech. To differentiate brain regions subserving processing of linguistic and affective aspects of intonation, discrimination of sentences differing in linguistic accentuation and emotional expressiveness was evaluated by functional magnetic resonance imaging. Both tasks yielded rightward lateralization of hemodynamic responses at the level of the dorsolateral frontal cortex as well as bilateral thalamic and temporal activation. Processing of linguistic and affective intonation, thus, seems to be supported by overlapping neural networks comprising partially right-sided brain regions. Comparison of hemodynamic activation during the two different tasks, however, revealed bilateral orbito-frontal responses restricted to the affective condition as opposed to activation of the left lateral inferior frontal gyrus confined to evaluation of linguistic intonation. These findings indicate that distinct frontal regions contribute to higher level processing of intonational information depending on its communicational function. In line with other components of language processing, discrimination of linguistic accentuation seems to be lateralized to the left inferior-lateral frontal region whereas bilateral orbito-frontal areas subserve evaluation of emotional expressiveness.

Dysphonia subsequent to severe traumatic brain injury: comparative perceptual, acoustic and electroglottographic analyses.

We tested the applicability of the Goettinger Hoarseness Diagram (GHD) for quantitative evaluation of voice disorders after severe traumatic brain injury (TBI) and compared the obtained data with those from established voice analysis systems such as the Multi-Dimensional Voice Program (MDVP), electroglottography (EGG) and perceptual ratings using sustained vowel productions from 10 patients with TBI dysarthrophonia at late stages postinjury and of 10 healthy control speakers. Statistical analyses revealed significant intergroup differences with respect to various acoustic and perceptual measures, i.e., irregularity component, noise component, noise-to-harmonic ratio, shimmer, jitter, roughness, creakiness, strained-strangledness, hypernasality. By contrast, the considered EGG estimates, i.e., open quotient and speed quotient, did not allow for separation of patients and controls. In addition, the two GHD components exhibited close correlations to perceived roughness and creakiness, on the one hand, and breathiness and, to some degree, nasality, on the other, whereas the MDVP parameters failed to differentiate between these two perceptual modes of phonation.

Contralaterality of cortical auditory processing at the level of the M50/M100 complex and the mismatch field: a whole-head magnetoencephalography study.

Humans show a stronger cortical representation of auditory input at the opposite hemisphere each. To specify the temporal aspects of this contralaterality effect within the domain of speech stimuli, the present study recorded a series of evoked magnetic fields (M50, M100, mismatch field) subsequent to monaural application of stop consonant-vowel syllables using whole-head magnetoencephalography (MEG). The M50 components exhibited a skewed shape of cross-symmetrical distribution in terms of an initial maximum peak succeeded by a knot over the contralateral and a reversed pattern over the ipsilateral temporal lobe. Most presumably, this pattern of evoked fields reflects two distinct stages of central-auditory processing: (a) initial excitation of the larger contralateral and the smaller ipsilateral projection area of the stimulated ear; (b) subsequent transcallosal activation of the residual neurons, i.e. the targets of the non-stimulated ear, at either side. Previous studies using non-speech stimuli found contralaterality of central-auditory processing to extend to the M100 field. In contrast, a larger amplitude of ipsilateral M100 as compared to the respective opposite deflection emerged after stimulation of either ear. Finally, the computed magnetic analogues of mismatch negativity failed any significant laterality effects. These data provide first evidence for a distinct pattern of hemispheric differences at the level of the M50/M100 complex subsequent to monaural application of speech stimuli.

Neural correlates of duplex perception: a whole-head magnetencephalography study.

Simultaneous experience of the same acoustic stimulus in two distinct phenomenological modes, e.g. as a speech-like and as a non-speech event, is referred to as duplex perception (DP). The most widely investigated DP paradigm splits each of the stop consonant-vowel (CV) syllables /ga/ and /da/ into an isolated formant transient (chirp) and the remaining sound structure (base). The present study recorded mismatch fields in response to a series of dichotically applied base and chirp components using whole-head magnetencephalography (MEG). Preattentive mismatch fields showed larger amplitudes in response to contralateral deviants. During attention to the fused percept /da/, the left ear deviants chirps elicited an enhanced and posteriorly shifted dipole field over the ipsilateral hemisphere. These data provide first neurophysiological evidence that the integration of acoustic stimulus elements into a coherent syllable representation constitutes a distinct stage of left-hemisphere speech sound encoding.

Cortical activation patterns of affective speech processing depend on concurrent demands on the subvocal rehearsal system. A DC-potential study.

In order to delineate brain regions specifically involved in the processing of affective components of spoken language (affective or emotive prosody), we conducted two event-related potential experiments. Cortical activation patterns were assessed by recordings of direct current components of the EEG signal from the scalp. Right-handed subjects discriminated pairs of declarative sentences with either happy, sad or neutral intonation. Each stimulus pair was derived from two identical original utterances that, due to digital signal manipulations, slightly differed in fundamental frequency (F0) range or in duration of stressed syllables. In the first experiment, subjects were asked: (i) to denote the original emotional category of each sentence pair and (ii) to decide which of the two items displayed stronger emotional expressiveness. Participants in the second experiment were asked to repeat the utterances using inner speech during stimulus presentation in addition to the discrimination task. In the absence of inner speech, a predominant activation of right frontal regions was observed, irrespective of emotional category. In the second experiment, a bilateral activation with left frontal preponderance emerged from discrimination during additional performance of inner speech. Compared with the first experiment, a new pattern of acoustic signal processing arose. A relative decrease of brain activity during processing of F0 stimulus variants was observed together with increased activation during discrimination of duration-manipulated sentence pairs. Analysis of behavioural data revealed no significant differences in evaluation of expressiveness between the two experiments. We conclude that the topographical shift of cortical activity originates from left hemisphere (LH) mechanisms of speech processing that centre around the subvocal rehearsal system as an articulatory control component of the phonological loop. A strong coupling of acoustic input and (planned) verbal output channel in the LH is initiated by subvocal articulatory activity like inner speech. These neural networks may provide interpretations of verbal acoustic signals in terms of motor programs and facilitate continuous control of speech output by comparing the signal produced with that intended. Most likely, information on motor aspects of suprasegmental signal characteristics contributes to the evaluation of affective components of spoken language. In consequence, the right hemisphere (RH) holds a merely relative dominance, both for processing of F0 and for evaluation of emotional significance of sensory input. Psychophysically, an important determinant on expression of lateralization patterns seems to be given by the degree of communicative demands such as solely perceptive (RH) or perceptive and verbal-expressive (RH and LH).

Encoding of temporal speech features (formant transients) during binaural and dichotic stimulus application: a whole-head magnetencephalography study.

Spoken-word recognition depends upon the encoding of relevant 'information bearing elements' of the acoustic speech signal. For example, relatively rapid shifts of spectral energy distribution (formant transients) cue the perception of stop consonant-vowel (CV) syllables such as /ba/, /ga/, and /da/. A variety of data indicate left-hemisphere superiority with respect to the processing of formant transients. To further delineate the underlying neurophysiological mechanisms, evoked cortical fields in response to CV syllables (oddball design; frequent stimulus=binaural /ga/; four deviant constellations: Binaural /ba/, binaural /da/, left /da/ (left ear deviant)-right /ga/, right /da/ (right ear deviant)-left /ga/) were recorded by means of whole-head magnetencephalography (MEG; 151 channels) under two different conditions of attentional demands (visual distraction versus reaction to prespecified stimuli). (a) During binaural stimulus presentation attention toward target events resulted in a significantly enhanced mismatch field (MMNm, magnetic analogue to the mismatch negativity) over the left as compared to the right hemisphere. In contrast, preattentive processing of the CV syllables failed MMNm lateralization effects. (b) Dichotic application of /da/ elicited a larger contralateral MMNm amplitude in subjects with right ear advantage (REA) at behavioral testing. In addition, right ear deviants yielded a stronger ipsilateral response than the left ear cognates. Taken together, these data indicate bilateral preattentive processing and subsequent attention-related predominant left-hemisphere encoding of formant transients at the level of the supratemporal plane. Furthermore, REA during dichotic application of CV syllables seems to be linked to functional dissociation of the two hemispheres during auditory processing.

Stroboscopic articulography using fast magnetic resonance imaging.

A method to display dynamic aspects of vocal tract configuration during speech production by means of fast magnetic resonance imaging is presented. Data acquisition during repetitive movement relies on a stroboscopy-like procedure. The time resolution achieved is 120 images s-1 in a selected plane. As compared with other techniques of kinematic measurements of speech motor processes, this procedure allows for visualization of the temporal and spatial coordination of all relevant articulators, e.g. the entire tongue, the velum and the lower vocal tract. As an example, the method was applied to repetitions of stop consonant-vowel-nasal syllables.

Lip-jaw and tongue-jaw coordination during rate-controlled syllable repetitions.

The present study investigated the relationship between functionally relevant compound gestures and single-articulator component movements of the jaw and the constrictors lower lip and tongue tip during rate-controlled syllable repetitions. In nine healthy speakers, the effects of speaking rate (3 vs 5 Hz), place of articulation, and vowel type during stop consonant-vowel repetitions (/pa/, /pi/, /ta/, /ti/) on the amplitude and peak velocity of differential jaw and constrictor opening-closing movements were measured by means of electromagnetic articulography. Rather than homogeneously scaled compound gestures, the results suggest distinct control mechanisms for the jaw and the constrictors. In particular, jaw amplitude was closely linked to vowel height during bilabial articulation, whereas the lower lip component amplitude turned out to be predominantly rate sensitive. However, the observed variability across subjects and conditions does not support the assumption that single-articulator gestures directly correspond to basic phonological units. The nonhomogeneous effects of speech rate on articulatory subsystem parameters indicate that single structures are differentially rate sensitive. On average, an increase in speech rate resulted in a more or less proportional increase of the steepness of peak velocity/amplitude scaling for jaw movements, whereas the constrictors were less rate sensitive in this respect. Negative covariation across repetitions between jaw and constrictor amplitudes has been considered an indicator of motor equivalence. Although significant in some cases, such a relationship was not consistently observed across subjects. Considering systematic sources of variability such as vowel height, speech rate, and subjects, jaw-constrictor amplitude correlations showed a nonhomogeneous pattern strongly depending on place of articulation.

Speech disorders following severe traumatic brain injury: kinematic analysis of syllable repetitions using electromagnetic articulography.

Using electromagnetic articulography, the lips, the tip of the tongue, and the tongue dorsum were tracked during repetitions of the syllables [pa], [ta] and [ka] in 10 speakers with dysarthria following severe traumatic brain injury and in 10 age-matched control subjects. When asked to produce the syllable trains as fast as possible, the patient group showed a rather homogeneous pattern of movement abnormalities including prolonged syllable durations and reduced peak velocity/amplitude ratios. Most presumably, limited speed generation gives rise to the impaired ability to increase speech rate. During the habitual speaking condition, reduced velocity/amplitude ratios were restricted to the tongue tip and tongue dorsum. Obviously, the tongue and the lips are differentially affected in dysarthria following severe traumatic brain injury.

Differential impact of periodic and aperiodic speech-like acoustic signals on magnetic M50/M100 fields.

Voiced and unvoiced sounds, characterized by a periodic or aperiodic acoustic structure, respectively, represent two basic information-bearing elements of the speech signal. Using whole-head magnetencephalography (MEG), magnetic fields (M50/M100) in response to synthetic vowel-like as well as noise-like signals matched in spectral envelope were recorded in 20 subjects. Aperiodic events gave rise to increased M50 concomitant with reduced M100 activity as compared to their periodic cognates. Attention toward the auditory channel enhanced the effects of signal periodicity. These data provide first evidence that speech-relevant acoustic features differentially affect evoked magnetic fields as early as the M50 component. Conceivably, the M50 field reflects an ongoing monitoring process whereas the M100 component is bound to more specific operations such as detection of signal periodicity.

Preattentive processing of consonant vowel syllables at the level of the supratemporal plane: a whole-head magnetencephalography study.

A variety of clinical and experimental data indicate superiority of the left hemisphere with respect to the encoding of dynamic aspects of the acoustic speech signal such as formant transients, i.e., fast changes of spectral energy distribution across a few tens of milliseconds, which cue the perception of stop consonant vowel syllables. Using an oddball design, the present study recorded auditory evoked magnetic fields by means of a whole-head device in response to vowels as well as syllable-like structures. Both the N1m component (=the magnetic equivalent to the N1 response of the electroencephalogram (EEG)) and various difference waves between the magnetic fields to standard and respective rare events (MMNm=magnetic mismatch negativity) were calculated. (a) Vowel mismatch (/a/ against /e/) resulted in an enlarged N1m amplitude reflecting, most presumably, peripheral adaptation processes. (b) As concerns lateralized responses to syllable-like structures, only the shortest transient duration (=10 ms) elicited a significantly enhanced MMNm at the left side. Conceivably, the observed hemispheric difference contributes to prelexical parsing of the auditory signal rather than the encoding of linguistic categories.

A cerebellar-like terminal and postural tremor induced in normal man by transcranial magnetic stimulation.

Trains of repetitive transcranial magnetic stimulation (TMS) at 10-30 Hz and intensities of 90-120% motor threshold were delivered through a figure of eight coil over the motor cortex while normal subjects made either rapid, self-terminated (ballistic) wrist movements or maintained the position of their wrist at a fixed angle. Movement kinematics and EMG activity in antagonistic forearm muscles were analysed. In the ballistic task, repetitive TMS had little effect on the velocity or acceleration of the initial segment of the movement, although it induced large terminal oscillations (tremor) around the target position at frequencies between 4.4 and 7.2 Hz. The likelihood that tremor would occur increased with increasing stimulus intensities or frequencies. It was maximal with stimulation over the forearm area, and decreased with stimulation over the leg area, or over parietal sites; there was no tremor during stimulation of cervical nerve roots. The frequency of the induced tremor was independent of the rate of stimulation and did not depend on the presence of excitatory and inhibitory motor responses to the stimulus. Stimulation could also induce tremor of the same frequency in the fixed task, but only during co-contraction of forearm muscles. The amplitude of tremor was proportional to the level of co-contraction. Clinically, the tremor induced by repetitive TMS appeared very similar to cerebellar tremors. In order to confirm this we investigated two cerebellar patients, one with autosomal dominant cerebellar ataxia and the other with multiple sclerosis. Both of them had a terminal tremor of 6-7 Hz in the wrist movement task. In the holding task, the amplitude of their postural tremor increased with the level of co-contraction in forearm muscles. Since the frequency of repetitive TMS-induced tremor was independent of stimulus parameters, we conclude that it represents some intrinsic property of the CNS. We suggest that the tremor is caused by disruption of cortical processes involved in terminating a voluntary movement or maintaining a posture. Similarities to cerebellar patients suggest that repetitive TMS may cause tremor by interfering with adaptive cerebellar afferent inflow to motor cortex. Repetitive TMS-induced tremor, therefore, may represent a model of some forms of cerebellar tremor in man.

Temporal and spectral aspects of coarticulation in ataxic dysarthria: an acoustic analysis.

In order to analyze the impact of cerebellar disorders on temporal and spectral aspects of coarticulation, 9 individuals with cerebellar dysfunction and 9 controls were asked to produce test sentences comprising a target vowel (V = [a], [i], or [u]) within a schwa-t-V-t-schwa environment. The control speakers were investigated both at their habitual speech tempo and under a slow speaking condition. The squared distances between averaged FFT spectra served as a quantitative estimate of target-induced coarticulation, a method that can be applied to consonants as well as vowels, and which avoids the shortcomings of formant analysis. In order to test the significance of coarticulation effects at the level of individual speakers and to obtain F values as a further measure of the strength of coarticulation, multivariate tests of target effects were performed, with the first 6 principal components derived from the spectra of each speaker. First, inconsistent patterns of anticipatory vowel-to-vowel (W) interactions emerged across individuals, and neither significant group differences nor any effects of speech rate could be detected. The underlying control mechanisms thus seem to be segment-linked subject-specific specifications of the pretarget vowel, uncompromised by cerebellar dysfunction. Second, all participants exhibited highly significant anticipatory [t(h)]-to-vowel (CV) coarticulation. This effect was slightly smaller in the cerebellar group than in the control group, which can be at least partially explained by reduced spectral distances among the 3 target vowels. Speech rate did not influence the CV effects of the control group. As concerns temporal aspects of coarticulation, no significant group differences emerged in terms of length adjustments of the pretarget consonant to the intrinsic duration of the target vowel. Third, ataxic speakers showed a tendency toward enlarged perseverative vowel-to-[t(h)] (VC) and W effects if their slow speech rate was taken into account. Retentive coarticulation turned out to be similar in slow ataxic speakers and in fast-speaking controls. However, significant attenuation of these effects emerged in the latter group under the condition of decreased speech tempo. In summary, these results corroborate the suggestion of different mechanisms of gestural overlap in the temporal domain: Whereas perseverative coarticulation, presumably, reflects biomechanical or motor constraints, anticipation seems to represent higher level phonetic processing.

Cerebellar contributions to the perception of temporal cues within the speech and nonspeech domain.

A previous study (Ackermann, Gräber, Hertrich, & Daum, 1997) reported impaired phoneme identification in cerebellar disorders, provided that categorization depended on temporal cues. In order to further clarify the underlying mechanism of the observed deficit, the present study performed a discrimination and identification task in cerebellar patients using two-tone sequences of variable pause length. Cerebellar dysfunctions were found to compromise the discrimination of time intervals extending in duration from 10 to 150 ms, a range covering the length of acoustic speech segments. In contrast, categorization of the same stimuli as a "short" or "long pause" turned out to be unimpaired. These findings, along with the data of the previous investigation, indicate, first, that the cerebellum participates in the perceptual processing of speech and nonspeech stimuli and, second, that this organ might act as a back-up mechanism, extending the storage capacities of the "auditory analyzer" extracting temporal cues from acoustic signals.

Hemispheric lateralization of the neural encoding of temporal speech features: a whole-head magnetencephalography study.

Using a passive oddball design (randomized series of standard [frequent] and deviant [rare] stimuli), the present study investigated the neural encoding of syllables differing in a duration parameter (/da/ = short-lag voice onset time [VOT], /ta/ = long-lag VOT) by means of whole-head magnetencephalography (MEG). Dipolar activities at the level of the supratemporal planes allowed to explain the evoked magnetic fields. The N1m/P2m-complex (magnetic equivalent to the N /P2-wave of the electroencephalogram) in response to standard stimuli showed bilateral symmetric distribution. Furthermore, the latency of P2m significantly depended on VOT. Finally, the mismatch response to the deviant /da/-syllables-which represent in German a very frequent word (English: 'here' or 'there')- evolved significantly earlier in the left hemisphere as compared to the right side. In conclusion, processing speed may be an important aspect of the hemispheric specialization of language.

Phonemic vowel length contrasts in cerebellar disorders.

Apraxia of speech and Broca's aphasia both affect voice onset time (VOT) whereas phonemic vowel length distinctions seem to be preserved. Assuming a close cooperation of anterior perisylvian language zones and the cerebellum with respect to speech timing, a similar profile of segment durations must be expected in ataxic dysarthria. In order to test this hypothesis, patients with cerebellar atrophy or cerebellar ischemia were asked to produce sentence utterances including either one of the German lexial items "Rate" (/ra:t(h)e/, 'installment'), "Ratte" (/rat(h)e/, 'rat'), "Gram" (/gra:m/, 'grief'), "Gramm" (/gram/, 'gramm'), "Taten" (/t(h)atn/, 'actions'), or "Daten" (/datn/, 'data'). At the acoustic signal, the duration of the target vowels /a/ and /a:/ as well as the VOT of the word-initial alveolar stops /d/ and /t/ were determined. In addition, a master tape comprising the target words from patients and controls in randomized order was played to three listeners for perceptual evaluation. In accordance with a previous study, first, the cerebellar subjects presented with a reduced categorical separation of the VOT of voiced and unvoiced stop consonants. Second, vowel length distinctions were only compromised in case of the minimal pair "Gram"/"Gramm." In contrast to "Rate"/"Ratte", production of the former lexical items requires coordination of several orofacial structures. Disruption of vowel length contrasts would, thus, depend upon the complexity of the underlying articulatory pattern.

Auditory perceptual evaluation of rhythm-manipulated and resynthesized sentence utterances obtained from cerebellar patients and normal speakers: A preliminary report.

Alterations of the temporal structure of spoken utterances in terms of lengthened acoustic segments and increased syllabic isochrony seem to represent a salient feature of ataxic dysarthria. The present study addresses the question of whether systematic manipulations of the durational aspects of the acoustic speech signal yield an improvement of perceived dysarthric deficits. Different variants of speech rhythm were imposed on sentence utterances obtained from two patients with ataxic dysarthria and two normal control speakers. For the sake of comparability the pitch contours were standardized by means of linearly interpolated stylized versions. The introduced manipulations significantly influenced the ratings of perceived slowness, dysfluency, and rhythmic adequacy. With respect to estimates of overall intelligibility and naturalness, however, ataxic-dysarthric utterances did not benefit from any synthetic changes. By contrast, utterances of normal speakers were rated less intelligible and somewhat more unnatural when resynthesized with an ataxic rhythm. These results indicate that durational factors play a minor role with respect to the overall speech impairment of ataxic speakers.

Kinematic analysis of articulatory movements in central motor disorders.

The various components of the central motor system are expected to play a similar role in speech production and in upper limb control. Slowed articulatory performance, therefore, must be expected in disorders of the corticobulbar tracts, cerebellum, and basal ganglia. Using an optoelectronic device, the present study recorded lower lip trajectories during production of sentence utterances in patients with Parkinson's disease (PD), Huntington's disease (HD), cerebellar atrophy (CA), and pseudobulbar palsy (PB). The various subject groups showed a similar range of overall motor disability. Patients with CA and PB exhibited slowed movement execution in terms of a reduced ratio of peak velocity to maximum amplitude ("stiffness"). In contrast to upper limb motor control, the lip excursions showed an uncompromised shape of velocity profiles. Two different patterns emerged in HD. A single patient suffering from the akinetic-rigid Westphal variant of this disease had articulatory hypometria, whereas the remaining subjects showed significant bradykinesia under increased temporal demands, concomitant with normal movement amplitudes. The PD patients had unimpaired velocity-displacement relationships. Presumably, biomechanical constraints such as the rather small excursions of articulatory lower lip gestures or the scarce spindle supply of facial muscles account for the observed discrepancies between upper limb and speech motor control in PD.