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Physiological basis of fluency disorders

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Neuro-physiological correlates of speech in stuttering

Published in: Health & Medicine
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Physiological basis of fluency disorders

  1. 1. Presenter V Amith Kishore 2 Msc(SLP) Physiological basis of fluency and its disorders
  2. 2. The physiological basis of the fluency: Coordination and timing  Coordination of speech movements may be thought of in two different ways, according to the kinds of errors a failure of coordination can produce.  The first kind of coordination has to do with spatial precision of movements. Discoordination of this type results in movements that are imprecise with regard to placement.
  3. 3.  This kind of discoordination by itself result in articulation errors and seems of lesser interest in a study of fluency than do other discoordinations.  Although spatial precision does not seem to be an aspect of fluency itself, a number of facts suggest a relation between articulation errors, at least the functional kind, and stuttering.
  4. 4.  Furthermore, the child’s developing capacity for spatially precise speech movements may affect the development of speech fluency.  The other kind of discoordination has to do with precision of timing.  To be temporally coordinated, the different movements that comprise a speech gesture have to be accurate not only in placement but also in timing.
  5. 5.  Timing coordination refers to the ability to produce different movements and have all of them occur at the right time in relation to each other or to a starting point.  Temporal precision is just as important as spatial precision.  It will be helpful, in discussing coordination, to understand the term coordinative structure (Fowler and Turvey. 1980).
  6. 6.  A coordinative structure is a set of body parts, muscles for moving them, and associated neural mechanism that participate in the same act.  It seems that the capacity to relax antagonistic muscles has more to do with fluency than the capacity to contract agonistic muscles.  A coordinative structure is often said to operate like a mass-spring system. Muscle tissue may be stiff or springy depending on its current tonus, and the body parts that muscle move around differ in massiveness.
  7. 7.  These variations mean that a given coordinative structure may be characterized according to its springiness-its tendency to return to its original length when stretched- as well as according to its mass-which governs its tendency to continue moving in a given direction.  These two properties will have an important influence on the way a specific speech movement is performed.  The more massive a coordinative is, the more difficult it will be for the speaker to get it moving and, once moving, to stop it or change the direction of its movement.
  8. 8.  Thus movements of the jaw are slower to start and stop than movements of the tongue tip because the jaw is more massive.  Stiffness in the coordinative structure will reduce the peak velocity of the structure.  In addition every mass-spring system has a characteristic resonant frequency.  Resonant frequency of a speech coordinative structure is not fixed.
  9. 9.  Of course, the timing of movements does not depend on massiveness and stiffness of the peripheral mechanism.  Certain neural mechanisms, both peripheral and central, have an important influence in the timing of movements.  Different neurons transmit impulses at different speeds, according to size of neuron, although neural transmission is so rapid that it is unlikely to influence the speed of structural movement.
  10. 10.  A coordinative structure may contain a number of synapses, and each synapse requires additional time.  A coordinative structure involving more synaptic junctures will be slower than one containing less.  Although the time taken by signal to cross the synaptic space may be a factor in speed of neural mechanism.
  11. 11. Findings Reaction time  The reaction times of normal subjects vary with structure, the subjects’ focus of attention, the hemisphere stimulated, the age and sex of the subjects, and a number of other variables (Shadden, 1979).  Although probably related to coordination and motor control, the relation of reaction time measures to speech in normal subjects is not known.
  12. 12. Feedback  DAF disrupts speech production (Black, 1951; Lee, 1951, Wingate 1970)  Auditory masking increases loudness, raises fundamental frequency, and slows rate (Wingate, 1970) Gestural synchrony. Interference  Stuttering, and other discontinuities are both likely to occur at syntactic locations where language is being formulated (Starkweather and Godor., 1983)
  13. 13. The relation of coordination to rhythm  The rhythm depends on the speaker’s central capacity to generate a temporal structure and allocate peripheral speech movements to it.  The speaker ability to use his or her sense of rhythm, to adapt it to rhythmic needs of speech, which may change from moment to moment, is probably a more important capacity for fluency than simple presence of a central rhythmic “clock.”
  14. 14. Physiological characteristics of persons who stutter
  15. 15. Physiological characteristics of persons who stutter  There has been a considerable research during the past hundred years on the physiological functioning of persons who stutter.  Some findings that pertain to the following questions are summarized here.
  16. 16.  What physiological process are investigated??  How do persons who stutter, as a group, differ from normal-speaking peers with regard to physiological functioning???  Are there subgroups of stutterers who function in physiologically abnormal ways that may contribute to the onset or maintenance of their stuttering????
  17. 17.  Many physiological processes have been investigated in an attempt to identify the organic cause for stuttering.  Those to which the most attention has been directed during the past 100 years are discussed as follows.
  18. 18. The processes which we are going to discuss are interrelated and have several implications. 1) when an investigator studies one process, he or she is likely to be indirectly study others. 2) Investigator has to be cautious when interpreting the results of his or her studies.
  19. 19.  Respiration  Cardiovascular functioning  Biochemical functioning  Central nervous system functioning  Autonomous nervous system functioning  Sensori-perceptual functioning
  20. 20. Biochemical functioning Three approaches have been used in research. 1) There have been studies in which the levels of specific biochemicals in there bodies were compared to those in stutterers (Hill, 1944a; Rastatter & Harr 1988) 2) There have been studies in which biochemicals abnormalities were inferred by observing the effect of certain drugs (such as Haloperidol) on their speech fluency 3) There have been studies on the incidence of stuttering among persons who have particular disturbance in biochemical functioning, such as diabetes (van Riper, 1982)
  21. 21. Central nervous system functioning  Among the investigated phenomena mediated by this system are the following…  Action potentials from the bilaterally paired musculature of speech mechanism.  Motor control  Brain waves  Hemispheric asymmetries for language processing
  22. 22.  Involuntary movements including tremors  Manual motor performance  Performance on neuropsychological tests Autonomic nervous system functioning.  It is well established that there is positive relationship between the level of activity of the sympathetic division and anxiety.
  23. 23.  It is also well established that there is a negative relationship between its level of activity and relaxation  In addition it is generally accepted that anxiety level can affect motor performance, including respiration, phonation and articulation.
  24. 24. Sensori-perceptual functioning:  Whether stutterers are different from their normal speaking with regard to the functioning of their auditory, tactile-kinesthetic, and visual systems  Why study Sensori-perceptual functioning?
  25. 25.  Lets have a look how do they differ in functioning Respiration  Systematic research on the breathing movements of persons who stutter started at the beginning of last century (Beech & Fransella, 1968)  The findings of most of this research support the following conclusions:  Various kinds of abnormalities in breathing movements may occur during moments of stuttering.
  26. 26.  The same type of breathing abnormalities tend to occur during both moments of stuttering and expectancy of stuttering (van Riper 1936).  Pattern of chest wall posturing for phonation are qualitatively same.  Abnormalities observed in the breathing movements during moments of stuttering usually are not present during silence (Bloodstein, 1987)
  27. 27. Cardiovascular functioning  Systematic research on this topic has been ongoing more than 90-years.  Results show that pulse rate increases before and during moments of stuttering (Fletcher, 1914)  The following phenomenon are investigated…  Heart rate, sinus arrhythmia, blood pressure, and basal metabolic rate.
  28. 28. Biochemical functioning:  The research on chemical make-up has been going for more than 75 years.  Among the biochemical phenomena that have been studied indirectly or directly are alveolar Co2 level.  Chemical composition of the blood, plasma levels of adrenergic neurotransmitters and primary amino acids.  Some of the studies show indifferences.
  29. 29. Central nervous system functioning:  Much of the recent physiological research is dealt with CNS functioning.  During 1930 s the studies suggest that stutterer are less likely than normal speakers to have established unilateral cerebral dominance.  The studies have suggested that there is no difference of brain waves during silence, auditory and visual representation of the word anticipation of speaking, and speaking.  The prevalence of stuttering among persons with known brain damage has been reported to be higher than the general population.
  30. 30.  In this particular aspect the cerebral lateralization of function has been more subjected to research.  Aspects of sensory, motor and language functioning have been studied that they are thought to be mediated by either right or left side of their structure.  One of the first strategies to investigate cerebral lateralization of function and other manifestations of cerebral sidedness, such as eyedness and footedness (spanido, 1941) is handedness.
  31. 31.  Many studies have been carried by authors and they hypothesized many things.  Intrest on research of sidedness was lessened after 1940 s.  The renewed interest in this topic was cerebral lateralization of speech and language.
  32. 32.  The Wada test was one of the first methodologies used during1960 s.  Jones, 1966 reported that lack of lateralization  Rosenfield & liljestrand, 1981 did not detect any lack of lateralization.
  33. 33.  A second methodology that was used during this period to study was dichotic listening  Studies done by Curry and Gregory, 1969 are consistent with this hypothesis.  While Quinn, 1972; Cerf and Perkins, 1974 are not
  34. 34.  The third methodology that has been used to study cerebral lateralization of speech and language is Electroencephalography.  Change in the brain waves that (usually alpha ones) that usually occur in the right hemisphere are compared to those that occur in the left while tasks are being performed that involves linguistic processing  Normal speakers tend to evidence a larger change in the left than in right hemisphere while performing such tasks
  35. 35.  Some persons who stutters, on the other hand, have reported to evidence large changes in right hemisphere than in left hemispheres while doing so (Moore, 1986).  There are several other methodologies that have been used to study cerebral lateralization for speech and language include  Auditory tracking  Tachistoscopic viewing  Finger tapping with right and left hands while performing speech tasks  The findings of studies which use this methodologies are mixed
  36. 36.  Some findings of studies done by Johannsen and victor, 1986; Rasatter and Dell, 1986b; Sussman and MacNeilage, 1975) suggested that atleast some persons who stutter use their right hemisphere more than normal speakers do to process speech and language.  How ever these authors Brutten and Trotter, 1985; Neilson, Quinn and Neilson 1976, did not indicate any difference
  37. 37. Autonomic nervous system functioning.  Seeman 1934, was the one of the first to look into the possibility that abnormality in the functioning of the autonomic nervous system could contribute the etiology of stuttering.  He hypothesized that stuttering may be due to hyperactivity of sympathetic divison.
  38. 38.  His hypothesis received some support from the findings of several studies of stutterers –sympathetic reactivity during silence (Sedlacek 1947-48); Sovak 1935).  However the presence of the abnormality is not a necessary condition for the development of stuttering.
  39. 39. Auditory functioning  The prevalence of stuttering in hearing impaired population appears to be lower than in the general population (Andrews et al., 1983; Montgomery & Fitch, 1988).  The following aspects of the auditory functioning have been investigated:  Threshold for pure tones (St Louis & Hinzman, 1988)
  40. 40.  Relative phase angle of air- and bone conducted sounds (Stromsta, 1957, 1972).  Right ear versus left ear presentation of stimuls- as in dichotic listening (Curry and Gregory, 1969; Libertrau and Daly, 1981)  Effect on delayed auditory feedback on oral cavity not involving speech (Stark and Peirce 1970)
  41. 41.  The results of these studies were mixed  Central auditory functioning at the level of the brainstem (Anderson, Hood and Sellers, 1988; Bonin, Ramig, & Prescott, 1985, Kent,1983; Stager, 1990)  Horovitz et al., 1978 speculated, the reported differences in auditory functioning resulted, in part, from differences between them in anxiety level.
  42. 42. Tactile-kinesthetic functioning  A disturbance in tactile-kinesthetic feedback can have detrimental effect on performance of motor acts.  While such acts are occuring, information is continuously being sent to the brain from receptors in the muscles and the skin about the state of contraction of the various muscles and the location in space of the various structures involved in performing the acts.
  43. 43.  Could a disturbance in tactile-kinesthetic feedback disrupt the movement of articulators and vocalfolds in a way that would cause a breakdown in fluency.  The aspects they studied included threshold for vibratory sensation (Fucci et al., 1985), intra-oral two point discrimination (Jenson et al., 1975), and oral recognition of forms (Jenson et al., 1975; Martin et al., 1981; Stewart, Evans, & Fitch, 1985).  The results of these studies were mixed
  44. 44.  The central component or experiential nature of stuttering has for years been accepted to play a large role in the pathology (Sheehan 1970, Van Riper 1982).  However, the origin of stuttering is thoight to be a central involuntary block, though its true origin and physiological nature remains unknown (Kalinowski et al. 2000).
  45. 45.  Numerous neuroimaging studies have found stuttering to be associated with increased activity in motor regions such as the supplementary motor area and superior lateral premotor cortex with right lateralization (Fox et al., 1996)  Right frontal operculum (Preibisch et al. 2003)  Fronto-motor areas, parietal, temporal, limbic and insular areas of the right hemisphere (Neumann et al, 2003)
  46. 46.  Further, suppression or deactivation relative to normal speakers has been found in the primary auditory association areas, left inferior frontal cortex (Fox et al. 1996, Ingham et al, 2000).  Posterior regions of the brain (Braun et al. 1997).  Precentral gyrus (Preibisch et al. 2003).
  47. 47.  Though these data have been interpreted by some to suggest factors causal to stuttering, they are more likely to reflect a compensation or neural effect of stuttering (Preibisch et al. 2003, Neumann et al. 2003),especially since these aberrant neural activity disappear under choral speech conditions.  Therefore these aberrant neural activities probably reflect the highest level of compensation or the neural effects of all covert and overt stuttering behaviours.
  48. 48. Thank you…

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