In the name of God

Theoretical Bases of Apraxia

Majid Soltani

PhD student

Darley`s Model

1. Central Language Processing (CLP) (Linguistic planning)

2. Motor Speech programming (MSP)

3. Speech motor cortex (Execution)

• Origin of three-level:

-Three hierarchical stages in motor control, planning, programming and execution

• Verbal communication also entails the linguistic planning of the utterance to be made.

• Speech motor programming:

a set of processes responsible for transforming an abstract linguistic (phonological) code into spatially and temporally coordinated patterns of muscle contractions that produce speech movements.

Acquired neurogenic disorders

1. Aphasia (CLP)2. Apraxia (MSP)3. Dysarthria Apraxia: Speakers is unable to program the

musculature for its motor expression. The difficulty is not to deficits in the neuromotor execution of speech, but rather to an inability to transform phonologic plans into a code that is recognized by the speech motor system.

Van der merwe`s model

1. Linguistic-Symbolic Planning2. Motor Planning3. Motor Programming4. Execution• Basic linguistic units or phonemes are

selected…these phonemes are organized into temporospatial codes ….muscle specifice motor programs are selected and sequence….execution.

Intention in Verbal Communication

• Frontal-Limbic

• Limbic drives are transformed into motor goals or general plan through corticocortical processing

• Brooks(1986): “motivational limbic influences are needed to enact motor plans and to assemble their programs and subprograms”

Linguistic-Symbolic Planning

• Nonmotor nature

• Semantic,syntactic,lexical,morphological and phonological planning have to take place

• Linguistic-Symbolic Planning based on knowledge of the linguistic rules of the language

• Planning of utterances occurs simultaneously and not word for word.

• Semantic construction of the message, recall and selection of lexical units, and syntactic, morphological, and phonological planning occur in coherence.

• Phonological plan is invariant, and changes therein influence the meaning or intelligibility of the utterance.

• Phonological planning entails the selection and sequential combination of phonemes in accordance with the phonotactic rules of the language.

Neural structures responsible for linguistic-symbolic planning

• Temporoparietal area, particularly Wernicke`s area, and also Broca's area

• With single-word production, the prespeech cerebral potentials are more pronounced over Broca`s area than over Wernick`s area and in full sentence production vise versa.

Motor Planning

• Transformation of symbolic units (phonemes) to a code that can be handled by a motor system has to take place.

• Motor planning entails formulating the strategy of action by specifying motor goals.

• Motor planning is goal-directed.• Motor goals can be found in the spatial and

temporal specification of movements

• Each sound has own specifications, and these core features can be considered as invariant .

• Core features determine the invariant core motor plan with spatial (place and manner of articulation) and temporal specifications (voice onset time, vowel duration, vowel steady state duration, vowel formant transition, and speech rate) for each sound.

• Invariance can be found in the ultimate goals of production.

• Following recall of the core motor plan, planning of the consecutive movements necessary to fulfill the spatial and temporal goals commences.

• The different motor goals for each phoneme are to be identified, and the movements that necessary to produce the different sounds in the planned unit are then sequentially organized.

• Motor planning is articulated-specific and not muscle-specific.

• Adaptation of the core motor plan has to take place before articulation of a specifics phoneme is initiated.

• Adaptation cannot be guided by response feedback, as the movement has not yet taken place at the moment of planning.

• Internal feedback or predictive simulation guides adaptation.

• Internal feedback of an efference copy to the sensorimotor cortex is implemented to keep adaptation of the core motor plan within the limits of equivalence.

Motor Programming• The term originated from the “centralist” view

of motor control which proclaims the existence of a feedforward mechanism.

• Keele defined the motor program as a “set of muscle commands that are structured before a movement sequence to be carried out uninfluenced by peripheral feedback”.

• Marsden: the motor program is a set of muscle commands that are structured before a movement sequence begins which can be delivered without reference to external feedback.

• Gracco & Abbs : the motor program is an algorithm which sets up the system for a process whereby on-line sensory input and general motor command prespecificatins are mixed dynamically to yield appropriated intended goals.

• To indicate central planning, terms such as preprogramming, central program and generalized motor programs were used.

• Motor plans mediated by cortical association areas and motor programs prepared by the middle level of the motor hierarchy.

• Brooks: strategy and tactics

• Strategies prescribe the general nature of plans and tactics give them particular specifications in space and time.

• Specific movement parameters are computed in the motor program.

• Programs specify muscle tone, movement direction, force, rang, and rate as well as mechanical stiffness of the joints according to the requirements of the planned movement as it changes over time.

• Neural areas:

1. Basal ganglia

2. Lateral cerebellum

3. SMA

4. Motor cortex

5. Frontolimbic

• Basal ganglia and lateral cerebellum In particular are involved in programming and these parts perform complementary functions.

• Brooks:

1. Caudate circuit

2. Putamen circuit

3. Ventral striatum circuit

Execution

• The hierarchy of plans and programs is finally transformed into nonlearned automatic motor adjustment.

• Successive specifications are relayed to the lower motor centers that control joints and muscles through the “final common path”.

• Closed loop, tactile-kinesthetic feedback as a possible means of control is available.

Dysfunction on the level of Linguistic-Symbolic planning

• Inability in semantic, lexical, syntactic, morphological and phonological planning.

• Deviant phonological planning will lead to disorders in the selection and sequential combination of phonemes.

Dysfunction on the level of Motor Planning

• Inability to:

1. Recall the invariant core motor plans for specific phonemes

2. Identify the different motor goals of specific phonemes

3. Sequentially organize the movements for each phoneme and a series of movements for a sequence of phonemes

4.Adapt the core motor plan to phonetic context

5. Control interarticulatory synchronization

6.Centrally monitor the efference copy

7.Systematically relay the structure specific motor plan subroutines to the motor programming system

• Apraxia of speech represents a motor planning and programming disorder (phonetic-motoric), while deficits in phonological planning underlie phonological paraphasia speech errors (linguistically).

• Sound distortions, prolonged segment durations and prolonged intersegment durations are characteristic of AOS.

Dysfunction on the level of Motor Programming

• Impairment of :

1. The programming of muscle tone, rate, direction, and range of movements

2. Repeated initiation and feedforward of co-occurring and successive motor programs

• Sound distortion, defects in speech rate, and/or problems in the initiation of movement.

Dysfunction on the level of Execution

• Flassid paralysis is caused by damage to the nuclei, the axons or the neuromuscular junctions that make up the lower motor neuron.

• All signals to produce movement arising in the central nervous system must pass through the final common pathway

• As a result, all types of movement are impaired.

• The three-level model cannot readily accommodate other disorders than the classic neurogenic pathologies.

• A lesion in the SMA, basal ganglia, lateral cerebellum, motor cortex and frontolimbic system and its interface with the basal ganglia in particular can lead to a programming disorder, while a planning disorder is caused by a lesion in the association areas.