Motor Speech Disorders - PowerPoint Presentation

Slide1

Motor Speech Disorders

Apraxia of Speech and the DysarthriasSlide2

Introduction

No human movement patterns are as intricate, complex, or intertwined with all the human activities of learning, loving, and living as is speech.

Far more area of the brain is devoted to the control of the tiny muscular adjustments of the tongue, lips, vocal folds, and other speech articulators than to those muscle groups needed for walking upright.

Far more coordination and synchrony are needed for speech than for riding a unicycle, threading a needle, rolling a log, or removing a thorn from the foot.Slide3

Introduction

The amazing think is that the act of speech becomes so automatic that we hardly think about it—until something goes wrong.

Damage that disturbs the delicate sequence of sensory-muscular-integrative events can affect the function of the respiratory mechanism, the tone-producing mechanism, resonance system, and the articulatory system that shapes and molds the sound stream into recognizable words.

Motor speech disturbances, such as apraxia of speech (AOS) or the various

dysarthrias

, depend on the level of motor control that experiences damage.Slide4

Speech Production

As a fine motor skill, speech production is performed with accuracy and speed; it involves motor flexibility in achieving goals; and it improves with practice.

Speakers are capable of reaching highly precise successions of vocal tract shapes at critical points in time, with spatial-temporal goals being reached rapidly, interactively, and automatically.

Velocity and directional changes in articulatory movements are accomplished automatically in the upper airway while constant subglottic air pressure is maintained.

Speech is also goal-directed: the goal is to produce the appropriate acoustic patterns via motor actions. Slide5

Speech Production

Motor actions are

afferently

-guided by the speaker’s internal referent of how it feels and sounds to produce certain speech movements and acoustics.

Therefore, motor actions are not fixed movement routines or stored patterns of muscle contractions.

Speakers are capable of generating functionally equivalent motor sequences when needed.

Because speech requires adaptive control, it is one of the most advanced examples of selective access to muscle pattern generators for the purpose of spontaneously creating novel motor acts. Slide6

Motor Control Processes

Individuals who study the neurophysiology of speech movement recognize several levels in the speech motor control process.

The levels most commonly identified are planning, programming, and execution.

Motor control process levels are thought to be distinct operations occurring prior to or during the generation of speech motor output.

While definitions of these contracts are often

operationalized

, the terms are not always used uniformly.Slide7

Motor Planning

Motor planning is considered an early process in speech motor control, preceding programming.

Motor planning is seen primarily as a cognitive process involving ideation and intention related to the formulation of the spoken message.

The intended goals of speech production can be thought of as linguistic units of phonemes, words, or phrases.

In the planning of speech utterances, such units are represented or coded in terms of spatial, aerodynamic, or acoustic targets. Slide8

Motor Planning

The motor plan, then, represents an open-ended package of motor actions for generating higher order linguistic and phonological rules.

It involves selection of an appropriate movement strategy in light of intended goals and prevailing physical conditions (e.g., the “an” versus “a” for nouns; lip rounding of /s/ in “soup” versus lip retraction in “see.”

It involves processes that cannot be easily automatized because they involve the manipulation of unpredictable or infrequent processing variables depending upon the speaker’s discourse, selection of lexical items, and syntactic/morphological decisions.Slide9

Motor Programming

Motor programming entails provisional specification of precisely how the motor plan is to be achieved: which muscles are to contract, how much, and when.

Programming involves

pretuning

the excitability of various sensory and motor pathways to be involved in the ensuing movement process so as to provide for optimal use of sensory information during execution.

The motor program is responsive to time constraints which limits it to

automatizeable

processes operating on predictable, highly repetitive, not-too-varied relationships.Slide10

Motor Programming

Motor programming processes might include translation of the action plan into a chain of executable and coordinated articulatory movements, and adjustment of the output to actual speaking conditions.

By making optimal use of sensory information, the motor programmer organizes and assembles a set of muscle command subroutines into an appropriate movement configuration for action.

It does not detail movements and specific muscle contractions; instead is assembles predictable movement sequence templates, such as those needed to produce stridency, or

retroflexion

, etc. Slide11

Motor Execution

At the level of motoric execution, neural activation of synergistic speech muscle groups for a given movement sequence is initiated based on motor action programs.

Through the course of the execution process, the discharge of motor neurons may be influenced to varying degrees by numerous brain centers and sensory pathways.

It is at this final level of execution that speech motor control, or the neuromotor-sensory mechanisms that direct and regulate muscle contractions for speech production, come into play. Slide12

Motor Control Summary

The “plan” is the cognitive strategy for achieving spoken message formulation.

The “program” is the actual neural code of motor processing instructions needed to perform a sequence of motor actions.

Motor execution involves the direct activation of motor neurons, muscle contraction, and movement.Slide13

Neurology of Speech Motor Behavior

Production of speech requires the complex interaction of cortical, subcortical, and peripheral levels of the nervous system.

The cerebral cortex contains motor and sensory areas that are important in skilled voluntary movement.

The cortical motor areas in the frontal lobe plan and sequence the organization of motor activities.

They continually transmit and receive updated information on motor and sensory activity from various other cortical and subcortical areas.Slide14

Neurology of Speech Motor

Behavior

The neurons in the lower portion of the primary motor cortex control the execution of motor commands to the structures used in articulation, phonation, and resonation

.

Just in front of this motor strip, the premotor area supplements the functioning of the motor strip by integrating and refining oral motor output and also participating in planning.Slide15

Neurology of Speech Motor Behavior

The supplemental motor cortex, lying beneath the premotor cortex, receives input from the occipital, parietal, and temporal lobes and passes this information on to the primary motor cortex

.

The direct motor pathways from the primary motor cortex, the corticobulbar tracts, descend through the

subcortex

and brainstem to connect with the cranial nerves that control the oral mechanism.Slide16

Neurology of Speech Motor Behavior

An indirect motor system loops through various subcortical structures and the cerebellum to regulate and coordinate the neural impulses of the motor and premotor cortex

.

Specifically, the cerebellum functions as an error control device by comparing motor output from the motor cortex with sensory signals from joints and muscles.Slide17

Neurology of Speech Motor Behavior

Because

it is furnished with information about all levels of motor activity, it is an integrating center for coordinated movement, muscle tone and strength, and posture and position of the body.

The cranial and spinal nerves make up the peripheral nervous system (PNS).

The cranial nerves originate in the brainstem and receive motor execution signals from both the right and left motor cortices to activate the muscles for speech production.

They also provide sensory feedback by way of the indirect motor system to the premotor cortex for movement modification.Slide18

Motor Speech Disorders

As a neuromotor-sensory process, speech requires

complex neural integration and rapid coordination of several physiological systems: respiration, phonation, resonation, and articulation.

When any of the underlying structural or physiological components of speech processing are disrupted through neurological injury or disease, there are certain predictable consequences

.

Neurologically based disturbances in the selection, sequencing, and coordinated production of speech sounds have been labeled oral apraxia, verbal apraxia, phonemic

paraphasia

, literal

paraphasia

, oral-verbal apraxia,

anarthria

, dysarthria,

apraxic

-dysarthria, cortical dysarthria, and phonetic disintegration.Slide19

Apraxia of Speech, Dysarthria, Aphasia

The differential classification of dysarthria from apraxia is less problematic, as such differentiation is currently syndrome based (

Croot

, 2002).

However, there is still quite a bit of controversy when it comes to the labels of speech apraxia and phonemic

paraphasia

.

Because the jury is still out on the correct label for these entities, for the purposes of our discussion, we will define speech apraxia as primarily a phonetic-motoric disorder and phonemic

paraphasia

as primarily a linguistic- phonemic disorder.Slide20

Apraxia of Speech, Dysarthria, Aphasia

Remember, that

motor planning

is the process in which movement goals for speech articulators are specified and synchronized whereas

motor programming

involves commands for particular muscle groups to realize motor plans.

Disruption to linguistic processes prior to the computation of motor plans and programs is defined as

aphasia

.

Disruption subsequent to the computation of motor plans and programs is defined as

dysarthria

.

It is likely that AOS represents a disruption in both the computation of the motor plan and the motor

program, resulting from

cortical

and white matter lesions of the dominant hemisphere.Slide21

Apraxia of Speech

The most popular cognitive model for distinguishing AOS from aphasia and dysarthria proposes that AOS is the appropriate diagnosis when a person is able to complete the linguistic processing required for speech production but is hindered in his ability to produce the articulatory sequences of retrieved phonological representations.

In other words, someone with ASO has the conceptual, semantic, and grammatical formulation of the message to be communicated and can retrieve the abstract phonological representation for the intended words, but he is not able to transform retrieved phonological representations in specifications for articulation (Code, 1998; Miller, 1991; and

Itoh

&

Sasnuma

, 1984) .

These articulatory specifications seem to overlap the motor plans and motor programs.Slide22

Apraxia

of Speech

Because

the discipline’s

cognitive model

of articulatory planning and programming

is still

“

under construction,” it is not yet clear to what extent motor plans and programs are retrieved from a precompiled store or computed online, take account of feedback, or apply to phoneme-sized segments or larger units such as syllables, words, or phrases.

Presently, the recommendation is to continuing diagnosing a disorder as AOS when the hypothesized cognitive disruption occurs in the translation of phonological representation into specifications for articulation.

Behaviors that are symptomatic of AOS, whether as a relatively pure presentation, or in association with aphasia or dysarthria, or both include:Slide23

Apraxia

of Speech

Errors in the production of speech segments, including distortions, perceived phoneme omissions, substitutions, additions, and exchanges;

Poor

transitionalization

between segments of syllables of speech (reduced coarticulation);

Reduced speech rate;

Equal syllable stress altering normal prosody; and

A range of other behaviors or qualities of speech production including articulatory groping, struggle or search,

effortfulness

, and difficulty initiating speech

.

In contrast with the phonological errors in aphasia,

apraxic

sound errors are more consistent in both location and type than phonological errors.Slide24

Apraxia of Speech

Moreover

, successive attempts at the target and greater target accuracy occur less often in AOS than they do in phonological disruption

.

AOS

is highly likely to co-occur with aphasia, or dysarthria, or both

.

Many

aphasic,

apraxic

, and dysarthric disorders occur as the result of extensive lesions that impair multiple cognitive systems, resulting in “aphasia with AOS” or “AOS with dysarthria.”Slide25

Dysarthria

Dysarthria is primarily a problem with motor

execution

.

Depending upon the location of damage to the CNS or PNS, multiple system difficulties underlying speech production will be realized.

Speech characteristics, oral mechanism abnormalities, lesion site, and etiology all help to distinguish the six major kinds of dysarthria from AOS.

The six types of dysarthria are described by the predominant impairment to motor execution.

The descriptor

flaccid

is applied to movements which reflect a lack of muscle tone, or evidence of muscle weakness or paralysis.Slide26

Dysarthria

The descriptor

spastic

is applied to movements which reflect reduced range and speed of motion, and increased muscle tone.

Ataxia

refers to impaired movement coordination and control.

The descriptor

hyperkinetic

is applied to a pattern of excess movement due to lack of motor inhibition.

In contrast, the descriptor

hypokinetic

is applied to lack of appropriate movement and muscle tone, control, and posture.

Combinations of two or more of these movement abnormalities results in a

mixed

designation.Slide27

Dysarthria

Lesion Sites

Dysarthrias are also classified by their site of lesion.

If

the lesion occurs in the cortex and pyramidal tracts—the upper motor

neurons (UMNs)--

the errors seen will primarily be ones of programming

function.

If

the lesion occurs in the extrapyramidal system, including the cerebellum, coordination of laryngeal function may be affected, especially control of pitch and loudness

.

If lesions occur in the brainstem or the cranial nerve itself—lower motor

neuron

(

LMN) disorders--

the result may be a specific kind of

movement

paralysis, or a change in

muscle

tone

.Slide28

Dysarthria

Classification

Type

Site of Lesion

Cause

Speech

Flaccid

Cranial Nerve(s)

Belly's Palsy

MG

shallow breathing, breathy voice, hoarseness, reduced pitch/ loudness, hypernasality, imprecise articulation

Spastic

Motor Pathway

Stroke, TBI

drooling, chewing, swallowing difficulties; observable facial or articulatory weakness, slow, jerky consonant production, harsh vocal quality, emotional lability

Slide29

Dysarthria

Classification

Type

Site of Lesion

Cause

Speech

Ataxic

Cerebellum

Cerebellar damage

articulatory inaccuracy, inappropriate loudness modulation, and poor pitch control

Hyperkinetic

Basal Nuclei

Huntington’s

sudden forced inspiration or expiration, voice stoppages, periods of breathiness, harsh voice quality, excessive loudness variations, intermittent hypernasality, distortion of speech sounds

Slide30

Dysarthria

Classification

Type

Site of Lesion

Cause

Speech

Hypokinetic

Basal Nuclei

Parkinson’s

reduced loudness and pitch variability, imprecisely formed consonants, short rushes of speech, hoarse and breathy voice

Mixed

Multiple Areas

ALS; MS

ALS: labored and slow rate, short phrasing with lengthy silences, severely impaired articulation; hypernasality (flaccid/spastic)

MS: impaired loudness, harshness, defective articulation, impaired stress (spastic/ataxic).