Movement-related skin strain associated with goal-oriented lip actions.

It is generally accepted that sensory input contributes to the generation of natural movements. In most motor systems, muscle spindles, tendon organs, joint receptors, and cutaneous mechanoreceptors may provide proprioceptive information. However, the perioral area of the human face lacks muscle spindles, tendon organs, and joint receptors and is therefore a model system for the study of cutaneous afferent contributions to proprioception. This investigation examined a series of skin strains associated with lower-lip movements in human subjects to determine if such strains, which serve as stimuli for cutaneous mechanoreceptors, may underlie proprioception in the face. The results suggested that strains associated with lower-lip movements were of sufficient magnitude to elicit cutaneous mechanoreceptor discharge, as shown in recent human microneurographic studies. Further, the magnitude of multiple strains was predictive of lower-lip movement endpoints. These results highlight the potential importance of cutaneous mechanoreceptors as putative proprioceptors.

Quantitative morphology and histochemistry of intrinsic lingual muscle fibers in Macaca fascicularis.

Histological, histochemical, and quantitative morphometric techniques were used to determine muscle fiber-type distributions and sizes in four intrinsic tongue muscles of Macaca fascicularis. Histologically, fiber interdigitation among muscles was striking with pronounced infiltration of endomysium into muscle fascicles. Endomysium and perimysium were most prominent anteriorly. Histochemically, with a sample of 20,106 fibers, type II fibers predominated (73.9%) over type I fibers (26.1%) and 99% of type II fibers were categorized as IIA. The relative density of type I and type IIA fibers varied consistently within all muscles from anterior to posterior and to a lesser degree from superficial to deep. Although the tongue apex was composed almost exclusively of type IIA fibers, the proportion of type I to type IIA fibers increased posteriorly. Most posteriorly, type I and IIA fibers were in about equal proportions. These nonuniform fiber-type concentrations may suggest that different segments of individual primate intrinsic tongue muscles may be functionally independent, supporting recent models of tongue motor system biomechanics. For example, predominantly type IIA fibers in the anterior segments of a given muscle may underlie characteristic rapid tongue tip movements while slower movements of the posterior tongue are executed via separately activated type I fibers. Mean fiber diameters were quantified in one animal (n = 7,758). The distribution was unimodal (5.61-63.03 microns) and overall type IIA fibers were larger than type I fibers. However, within all muscles studied, sizes of both fiber types were greater at posterior sites, further suggesting functional intramuscular segregation.

Dysarthria associated with focal unilateral upper motor neuron lesion.

Speech motor changes in six patients with focal unilateral upper motor neuron (UUMN) lesions were characterised using a variety of techniques including listener judgements, speech acoustic analyses, electromyographic and strength measures. Listener judgements of speech understand-ability, intelligibility and dysarthric features indicated mild dysarthria. Diadochokinesis, electromyographic and strength measures corroborated these observations. The findings of this study delineate the characteristics of the dysarthria associated with unilateral upper motor neuron lesions and have important implications for identifying potential upper motor neuron components of other neurogenic disorders of speech and language.

Kinaesthetic acuity of stutterers and non-stutterers for oral and non-oral movements.

Six adult stutterers and six normal speakers were instructed to make the smallest possible movements of the jaw, lower lip, tongue and right index finger, both with and without continuous visual feedback. In the non-visual (kinaesthetic) condition, the stutterers showed significantly larger minimal displacements (MDs) than did the non-stutterers for oral but not for finger movements. However, movements made in the presence of visual feedback were consistently smaller for all subjects than those made without, and no differences in MD were found between the stutterers and the non-stutterers when visual feedback was provided. The results suggested the presence of a sensorimotor deficit among at least some adult stutterers that is confined to oral movements. Given the importance of somatic sensory feedback during speech production, these observed orosensory deficiencies among stutterers may provide important insights into causal factors which contribute to the breakdowns in stutterers' speech.

Finger movement responses of cutaneous mechanoreceptors in the dorsal skin of the human hand.

1. The movement sensitivity of dorsal skin mechanoreceptors in the human hand was studied by the use of single afferent recording techniques. 2. Units were classified as slowly (SA) and fast adapting (FA) and further characterized by thresholds to vertical indentation and by receptive-field sizes. Whereas SA units were evenly distributed within the supply area of the superficial branch of the radial nerve. FA units were usually situated near joints. 3. The proportion of different receptor types (32% SAI, 32% SAII, 28% FAI, 8% FAII; n = 107) compared favorably with previous electrophysiological and anatomic data, arguing for minimal sampling bias. The majority of the skin mechanoreceptive units were SA, largely due to a relative scarcity of FAII [Pacinian corpuscles (PC)] units. 4. A large majority (92%) of the afferents responded to active hand or finger movements. Responses in all unit types were consistent with observed movement-induced deformations of their receptive fields. 5. FAI units responded bidirectionally, albeit usually with somewhat higher discharge frequencies for finger flexion, which in most cases were associated with skin stretch. FAI units showed meager responses to remote stimuli, typically responding to one or, at the most, two adjacent joints. 6. SA units typically showed simple directional responses to joint movements with an increased discharge during flexion and a reduced discharge during extension. Joint movement that influenced the skin within the receptive field of SA units elicited graded responses even if the field, as assessed by perpendicular indentations, was minute. This finding suggests that definition of cutaneous receptive fields by classical perpendicular indentations may be inappropriate for the receptors in the hairy, nonglabrous skin. 7. The interpretation of the data from these recordings suggests that cutaneous mechanoreceptors in the dorsal skin can provide the CNS with detailed kinematic information, at least for movements of the hand.

Task-dependent variations in parkinsonian motor impairments.

Studies of visually-guided arm movements in patients with Parkinson's disease (PD) have suggested a relationship between slowness of movement and a reduction in the ratio of movement amplitude and peak velocity. Recent studies indicate, however, that PD impairments may be different for well-learned, natural movements performed without visual guidance, or movements associated with sequential motor behaviours such as speech. To address this issue, PD subjects and age/sex-matched controls were compared on the performance of three tasks, all of which required lowering the jaw: (1) single, rapid, visually-guided movements; (2) equivalent movements associated with a single speech syllable (inherently without visual guidance), and (3) well-learned speech movements produced in a natural sequence. PD subjects manifested similar deficits for visually-guided jaw lowering as those previously reported for arm movements, namely reduced velocity/amplitude ratios and increased movement durations. By contrast, analogous jaw movements during the sequential speech tasks were unimpaired on these measures. These results suggest that PD motor impairments are influenced by a variety of factors, including the degree to which tasks are familiar and natural, and the availability of visual information.

Influence of speaking rate on the upper lip, lower lip, and jaw peak velocity sequencing during bilabial closing movements.

Upper lip, lower lip, and jaw movements were recorded in five adult speakers for repeated sequences of the utterance [bae] at different speech rates. The results failed to confirm several earlier reports of an invariant upper lip, lower lip, jaw peak velocity sequencing pattern for bilabial closures. While the earlier reported sequence was the most frequent, a wide variety of different sequences was also commonly observed. In addition, significant intersubject differences in sequencing were found. The present results thus do not support the earlier hypothesis that oral closure gestures reflect aspects of a centrally generated pattern of motor output during speech.

Influences of object weight and instruction on grip force adjustments.

This study investigated the influence of object weight and instructions on grip force responses in humans. Using a precision grip, subjects lifted a small instrumented test object to a predetermined height. Prior to each set of 40 trials, subjects were verbally instructed to either "hold" or "let go" of the object in response to any change in weight. Unpredictably on some trials (less than 20%), a sudden sustained increase (load) or decrease (unload) in vertical load was applied to the object. Grip responses to these induced weight changes were evaluated by measuring grip force, object position, and associated electromyographic (EMG) activity. Grip force changes for a load were over three times greater than those for an unload. Such asymmetry may reflect everyday grasp and manipulation in a gravity-influenced world. Grip force adjustments to loads following "hold" instructions were on the average somewhat larger than those following "let go" instructions, but there was no influence of instructions on responses to unloads. These findings contrast with more robust influences of verbal instruction on automatic postural and proximal upper limb responses and also may suggest that grip force adjustments are influenced to a greater extent by intrinsic task variables than by extrinsic volitional intent. Such organization appears tailored to functional task requirements in natural environmental contexts.

Sensorimotor contributions of the basal ganglia: recent advances.

In the last decade, a great deal of research has been aimed at ascertaining the manner in which the basal ganglia (BG) contribute to the control of movement. The formation of workable hypotheses, however, has been limited by the great variety of putative roles reported in the literature. Reported functions have often been in direct conflict. Recent developments, however, provide new perspectives from which to view seemingly discordant functions. Data reviewed in this article suggest a distinct anatomical topography within the BG, allowing for highly specialized subfunctions. In parallel, BG cellular activity has been found primarily in association with specific sensory and task-related dimensions relevant to particular movements. The multiple sensorimotor contributions of the BG therefore are not contradictory, but represent BG contributions within different functional contexts. These multiple roles of the BG offer particular clinical insights.

Musculotopic organization of the facial motor nucleus in Macaca fascicularis: a morphometric and retrograde tracing study with cholera toxin B-HRP.

Morphometric and retrograde tracing methods were used to determine the location and number of motoneurons innervating individual facial muscles in Macaca fascicularis. Intramuscular injections of the cholera toxin B subunit-horseradish peroxidase conjugate produced discrete labeling patterns in the ipsilateral facial motor nucleus with good definition of somata and their processes. The facial nucleus extended rostrocaudally in the pons for about 2 mm, varying in shape and cross-sectional area along this axis. Motoneurons were clustered in subnuclei, but their boundaries were not sharp and they were not segregated by fiber bundles. The length, number, and area of subnuclei varied with rostrocaudal location. Retrograde labeling patterns revealed that individual muscles were innervated by longitudinal columns of motoneurons with each muscle region represented at all rostrocaudal levels of its column. The columns began at different rostrocaudal levels and varied in length. Columns for closely related muscles, such as the orbicularis oris and mentalis of the lower lip, tended to overlap, whereas columns for disparate muscles, such as the perioral and orbital, did not overlap. The dendritic processes of most motoneurons branched extensively among several different columns or subnuclei. Some dendrites extended outside of the nucleus into the surrounding tegmentum. Mean soma diameter (10.4-42.2 microns) was distributed unimodally, reflecting the absence of gamma motoneurons and lack of muscle spindles in the facial muscles. Large and small motoneurons were found in all regions of the nucleus, but the largest ones were located caudally and innervated muscles of the upper and lower lip. The perioral muscles also had more neurons, longer columns, and a lower cell density than the other muscle groups examined. These features may reflect the functions of the perioral muscles in facial expression and vocalization.

Uniform frequency of parkinsonian resting tremor in the lips, jaw, tongue, and index finger.

Parkinsonian resting tremor was examined in the lips, jaw, tongue, and index finger using electromyography (EMG) and displacement transduction. Long-term spectral averaging of tremor movement and EMG signals revealed that resting tremor frequencies were remarkably uniform across these orofacial and hand structures within the same parkinsonian subjects. However, marked variability in tremor spectral amplitude across structures and subtle moment-to-moment variations in tremor period, amplitude, and waveform shape were also observed. Although these observations argue for a central source of tremor, it appears that interactive central and/or peripheral neural circuitry may yield variations in tremor characteristics.

Neuronal RNA in nucleus ambiguus and nucleus hypoglossus of patients with amyotrophic lateral sclerosis.

To establish objectively the involvement of neurons in the medulla oblongata in patients with amyotrophic lateral sclerosis (ALS), ribonucleic acid (RNA) content was determined in neurons of the hypoglossal nucleus and the nucleus ambiguus. Neurons from those two nuclei showed a significant loss of RNA content in patients with ALS; only 57% and 38% of the normal RNA content was found in hypoglossal and ambiguus neurons, respectively. This marked loss of neuronal RNA suggests changes in functional states of neurons, which may contribute to fasciculations in the tongue and difficulties in swallowing often associated with ALS.

Parkinsonian deficits in serial multiarticulate movements for speech.

Unlike the single joint arm movements so commonly the focus of Parkinson's disease (PD) studies, orofacial movements for speech are well-learned, complex motor sequences generated without visual guidance. The present study of upper lip, lower lip, and jaw movements during speech in PD was thus aimed at determining whether (1) PD speech kinematic deficits are comparable to those often observed in simpler limb movements; (2) coordination for multimovement actions such as speech is aberrant in PD, as recently claimed; and (3) the component muscle groups involved in this behaviour manifest uniform deficits. Results indicated that despite reduced amplitudes of jaw and upper lip displacement in PD subjects, all three of these oral movements were of normal duration. Secondly, PD lower lip movements manifested no deficits and bradykinesia (reduced velocity) was only found in movements of the jaw. Finally, there was an indication of movement coordination aberrations in these parkinsonian subjects. Overall, these results not only suggest a difference between orofacial and limb movement impairments in PD, but also document the need to broaden our perspectives on this movement disorder by examining a wider range of functional motor tasks.

Sensorimotor characteristics of speech motor sequences.

The present experiment focused on the characteristics of sequential speech movements. Subjects generated two successive lip and jaw closing movements associated with the two 'p's' in 'sapapple'. By selectively manipulating the lower lip perturbation it was possible to discern the role of somatic sensory interactions with the presumed sequential movement programming. Lower lip perturbation duration was manipulated to yield two different load conditions. In the Load On (LN) condition, the perturbation remained on for both closing movements. In the Load On/Off (LNF) condition, the perturbation was removed at variable times prior to the second closing movement. Analyses focused on comparing the EMG and resulting kinematic changes for the second "p" closure across the two load conditions relative to the normal control (no load) condition. The second "p" closure was differentially affected by the load conditions resulting in changes in the upper and lower lip compensations. Upper lip changes reflected consistent load duration differences; however, the magnitude of the lower lip EMG and kinematic adjustments did not mirror those of the upper lip. In contrast to the differential upper lip/lower lip changes observed for the magnitude adjustments, timing adjustments were similar for both upper lip and lower lip suggesting a separation between the specification of magnitude and timing of speech movements. Differential load effects were also observed for the timing of the second closing movements. For the LN condition, the onset of muscle activity and subsequent movement occurred earlier (re: control); for the LNF condition, load removal delayed the onset of muscle activity and the subsequent movement (re: control). Further, the opening movement preceding the second closing movement was modified for both load conditions suggesting that all movements in the sequence, not just closing movements, can be modified. The present results suggest that the programming of speech movement sequences is a dynamic process involving scaling and timing of motor commands relying on various degrees of sensory interaction. The apparent separation in the magnitude and timing specification of the movement sequences suggests the parallel influences of different neural systems. The consequence of this control scheme is that specification of movement parameters for sequential motor acts is a flexible real-time sensorimotor process interacting with less-flexible well-established central motor relations. Further, motor program for speech may reflect certain generalized movement actions (e.g., oral opening, oral closing) rather than individual words, syllables, or other linguistic categories programmed on a movement-to-movement basis.

Deficits in the production of grip forces in Down syndrome.

Down syndrome (DS) and control individuals were examined as to their ability to adapt grip forces to changes in the properties of lifted objects. The DS group generated substantially greater grip forces than the controls in all tests and failed to adapt normally to changes in the frictional properties of the objects. Their greater grip forces were not due to greater slipperiness of the skin of their fingers. These results are consistent with other findings of subtle deficits in DS individuals' use of somatosensory information for controlling movement and posture.

Grip force adjustments evoked by load force perturbations of a grasped object.

1. Brief increases or decreases in vertical load force were applied to an object held between the thumb and finger. Grip force increases occurred consistently from 60 to 90 ms after onset of the load force increase. These responses did not adapt and were typically from 100 to 200 ms in duration. Reductions in object load force yielded rapid reductions in grip force at latencies comparable to those for load increases. 2. Response magnitude was proportional to the size or velocity of the load force increment, but did not vary with the level of the preexisting grip force. Thus these responses did not maintain the grip force at a specified level above the object's slip point. 3. Grip force responses were abolished or substantially reduced when loads were delivered directly to the hand rather than to the object. In contrast, force responses were not always abolished upon anesthetization of the thumb and finger. These results are discussed in relation to the role of cutaneous mechano-receptors of the digital pulps and proprioceptors of the arm and hand for providing necessary afferent information utilized in load-related grip force modulation. 4. Rapid and automatic grip force adjustments to load force variations may contribute importantly to grasp tasks in which the load forces vary dynamically and without complete predictability, such as in the manipulation of tools or objects that contact the environment.

Clinical investigations of adductor spastic dysphonia.

Spastic (spasmodic) dysphonia (SD) may coexist with or reflect certain neurologic or psychogenic illnesses. The present study of four patients with adductor SD (ASD) revealed several consistent clinical findings and characteristics that could be differentiated, while other findings were not distinguishable. Oscillographic and spectral analyses suggested voice tremor as a component of the dysphonia in all ASD patients studied. Clinical neurologic and otolaryngologic findings were nonconfirmatory regarding a disease process or state.

Kinematic analysis of multiple movement coordination during speech in stutterers.

This study addresses the long-standing claim that stuttering reflects an impairment in the neuromotor coordination of multiple speech movements. Upper lip (UL), lower lip (LL), and jaw (J) kinematics for nonstuttered speech behaviours in stutterers and normal speakers were examined using quantitative indices of normal multiple movement coordination reported in recent studies of gait, reaching, grasping, and speech. While two measures of coordination--dynamic movement composition and intermovement motor equivalence--did not distinguish between stutterers and normals, stutterers manifested striking differences from normal on a third measure, the sequencing of UL, LL, and J movement onsets and velocity peaks. These findings suggest that, contrary to previous hypotheses, stutterers do not manifest general problems of coordination of speech movement. Instead, stuttering appears to be associated with a specific impairment in multiple movement coordination associated with sequencing of those movements.