Neural Bases of Speech: Motor, Language, and Brain Structures

Motor Programming / Execution

Send parameterized commands—timing, force, ROM—to muscles

Neural Hubs -- Conceptualization (want to say & why)

• Bilateral prefrontal & parietal association cortex

• limbic system & anterior cingulate (drive/affect)

Neural Hubs -- Language Planning

• L inferior frontal gyrus (Broca)

• posterior superior

• middle temporal gyri (Wernicke/STG)

• angular & supramarginal gyri

• basal temporal word-form area

Neural Hubs -- Motor Planning

• L premotor cortex

• supplementary motor area (SMA)

• anterior insula

• precentral gyrus "mouth/face" strip

• basal ganglia

• & cerebellar loops prepping the plan

Neural Hubs -- Motor Programming/Execution

• Primary motor cortex ↔ brainstem/SC via

corticobulbar/spinal tracts

• basal ganglia direct/indirect/hyper-direct loops (gating &

sequencing)

• cerebellum & dentate nucleus

Cognitive-linguistic disorders

Disorders affecting the cognitive aspects of language processing

- breakdown of conceptualization (what do i want to say & why)

Aprosodia

A condition characterized by the inability to convey or interpret emotional tone in speech

- breakdown of conceptualization (what do i want to say & why)

Classic aphasias

Language disorders resulting from brain damage, affecting speech production and comprehension

- - breakdown of language planning

Apraxia of Speech (AOS)

A speech disorder where the brain has difficulty coordinating the movements needed for speech

- breakdown in motor planning (movement chunks)

Dysarthria

A motor speech disorder resulting in slurred, weak, or uncoordinated speech

- breakdown in motor programming (timing, force, ROM to muscles)

Primary motor cortex

The brain region responsible for sending the final signal to execute movement

Basal ganglia

A group of nuclei in the brain involved in the control of movement and coordination

Cerebellum

A brain structure that checks for mistakes and corrects them during movement

Brainstem

The part of the brain that connects the cerebrum with the spinal cord and controls vital functions

Spinal cord

The cylindrical structure of nervous tissue that runs through the vertebral column and transmits signals to and from the brain

Sensory Feedback

The process of using sensory information to monitor and adjust speech

Ears (STG)

The auditory system that hears one's own speech and catches sound errors

Touch/proprioception

The sense that allows awareness of body position and movement

Default-mode network

A network of brain regions active during rest and involved in self-referential thought

Sylvian fissure

A deep groove in the brain that separates the frontal and temporal lobes

Inferior frontal gyrus (Broca's area)

The brain region responsible for building grammar and sentence structure

STG/MTG

Regions of the brain that pick the right words and sounds

Angular & supramarginal gyri

Brain areas that help with word meaning and sound memory

Movement templates

Reusable plans stored in the brain for common speech sounds

Indirect Activation Pathway

A neural pathway that varies in origin (cortex & brainstem) and destination (cranial and spinal nerve nuclei)

Rubrospinal tract

Assists in controlling voluntary limb movements (especially flexor muscles); works in tandem with pyramidal system.

Reticulospinal tract

Maintaining upright body posture and positioning body towards external stimuli.

Vestibulospinal tract

Helps with balance and posture, especially in response to head movement.

Tectospinal tract

Aligns head and eyes toward external stimuli.

Hypertonia

Increased muscle tone.

Spasticity

Velocity-dependent resistance to passive movement.

Abnormal postures

Postures that deviate from normal positioning.

Involuntary movements

Movements such as tremors and dystonia that occur without voluntary control.

Poor coordination of automatic movements

Difficulty in coordinating movements that support voluntary speech.

Direct Activation Pathway

Also known as the pyramidal tract; responsible for voluntary movement of skeletal muscles.

Corticobulbar tract

Controls head and face muscles (especially those for speech and swallowing).

Corticospinal tract

Controls limb and trunk movements.

Pyramidal tract/Direct Activation Pathway Hallmark signs

• weakness/paralysis (contralateral if lesion is above the brainstem decussation)

• loss of fine, skilled voluntary movement

• hypotonia initially

• absent/diminished reflexes initially —> possible hyperreflexia due to UMN disinhibition

• no major impact on posture or automatic movements

Loss of fine, skilled voluntary movement

Inability to perform precise movements due to lesions.

Hypotonia

Reduced muscle tone initially observed in lesions.

Absent or diminished reflexes

Initial loss of reflexes that may later show hyperreflexia due to UMN disinhibition.

Lower Motor Neurons (LMN)

Neurons that execute voluntary movement commands sent from UMNs.

Origin of LMN

Located in the brainstem (for cranial nerves) and spinal cord (for spinal nerves).

Destination of LMN

Skeletal muscles (voluntary muscles for speech and movement).

Key functions of LMN

Directly innervate muscles responsible for speech, swallowing, and body movement.

LMN hallmark characteristic signs of lesion

• Flaccid paralysis or weakness (ipsilateral) in muscles

• muscle atropy and fasciculations

• hypotonia

• hyporeflexia

Muscle atrophy

Shrinkage or wasting away of muscles.

Fasciculations

Small, visible twitches or ripples in muscles.

Hyporeflexia

Weak or absent reflexes.

Cranial Nerve V

Trigeminal; responsible for jaw movement and facial sensation.

Cranial Nerve VII

Facial; upper face innervated bilaterally, lower face contralaterally; responsible for facial expression.

Cranial Nerve IX

Glossopharyngeal; responsible for swallowing and taste.

Cranial Nerve X

Vagus; responsible for voice and swallowing.

Cranial Nerve XI

Accessory; responsible for head and shoulder movement.

Cranial Nerve XII

Hypoglossal; responsible for tongue movement.

UMN Dysfunction

• Weakness or loss of skilled speech movements

• unilateral damage causes opposite side weakness.

• If damage is on one side (unilateral), weakness happens on the opposite side of the body

• Some muscles get signals from both sides of the brain (bilateral), so effects may be less severe if only one side is damaged

• If both sides are damaged (bilateral), weakness can be mild to severe

• Muscle tone changes — muscles become stiff or tight (spasticity)

• Loss of fine motor control for speech

LMN Dysfunction

• Problems depend on the affected cranial nerve

• Weakness in all types of movement (both voluntary and automatic)

• Fasciculations: small, visible twitches or ripples in muscles that look like worms moving under

the skin

• Muscles shrink or waste away (atrophy)

• Reflexes become weak or disappear

• Muscle tone drops (muscles feel floppy)

• Can affect breathing, voice, resonance, and clarity of speech

Basal Ganglia Problems

Movements become either too slow or too fast; may have dyskinesias (involuntary movement)

Cerebellum Problems

• Trouble with balance and posture (can’t sit or stand still without falling or swaying) — called truncal ataxia

• Problems walking normally (gait disturbances)

• Eyes make uncontrolled movements (nystagmus)

• Shaking when trying to make intentional movements (intention tremors)

• Movements become clumsy or uncoordinated

• Trouble judging the range of motion (dysmetria)

• Difficulty with quick alternating movements (dysdiadochokinesia)

Dysmetria

Difficulty judging the range of motion.

Dysdiadochokinesia

Difficulty with quick alternating movements.

Motor Speech Assessment

Evaluation of speech problems and their neurological causes.

Respiration

Breathing support for speech.

Phonation

Voice production via vocal cords.

Resonance

Vibration of sound in mouth/nose/throat.

Articulation

Making speech sounds clearly.

Prosody

Rhythm, stress, and intonation of speech.

Features of Neuromuscular Function to Assess

• Muscle strength

• Speed, range, accuracy of movement

• Motor steadiness

• Muscle tone

Speed of movement

How fast can muscles move?

Accuracy of movement

How precise are the movements?

Medical Records

Provide clinical history, imaging, diagnosis, and treatment history.

Case History Interview to help make differential diagnosis

• Learn about onset (sudden vs gradual), progression, and associated symptoms.

• Understanding patient’s medical background, family history, lifestyle

Whole side facial paralysis (upper and lower face) usually means..

a lower motor neuron (LMN) lesion on that side (e.g., Bell's palsy).

Flaccid Dysarthria common causes

LMN damage, e.g., Bell's palsy, myasthenia gravis.

Flaccid means

Weak, breathy voice, muscle atrophy, fasciculations.

Speech Production Components to Evaluate

• Respiration — breathing support for speech

• Phonation — voice production (vocal cords)

• Resonance — how sound vibrates in mouth/nose/throat

• Articulation — making speech sounds clearly

• Prosody — rhythm, stress, and intonation of speech

Co-existing Motor Signs in Dysarthrias

• Flaccid: Muscle weakness, atrophy, fasciculations.

• Spastic: Spasticity, hyperreflexia

• Ataxic: Incoordination, tremor

• Hypokinetic: Rigidity, resting tremor, reduced movement

• Hyperkinetic: Involuntary movements, chorea, dystonia

What to Look for in Differential Diagnosis

• Onset and progression of symptoms.

• Specific speech characteristics and motor signs

• Neurological exam findings

• Imaging and lab results from medical records

• Patient history and symptom context

Evidence-Based Treatment Approaches

Know treatments tailored to dysarthria type (e.g., Lee Silverman Voice Treatment for hypokinetic dysarthria).

ICF Framework Levels & Motor Speech Intervention

Body Functions & Structures: Focus on the anatomical and physiological aspects of the speech mechanism.

LSVT LOUD®

An intervention for phonation in hypokinetic dysarthria.

EMST

An intervention for breath support in flaccid dysarthria.

Articulation drills

Exercises aimed at improving imprecise consonants.

Relaxation or stretching

Techniques used to address spasticity.

Motor Speech Goals

Objectives aimed at improving speech intelligibility, speaking rate, and conversational ability.

Pacing boards or metronomes

Tools used to control speaking rate.

Contrastive stress tasks

Activities designed to improve prosody.

Role-play/practice

Engagement in common communicative activities to enhance skills.

Use of scripts

Structured conversation practice using predefined dialogues.

Group therapy

A form of intervention that involves multiple participants to enhance communication.

Counseling

Support aimed at reducing communication anxiety.

Environmental modifications

Changes made to surroundings to facilitate communication.

AAC

Augmentative and Alternative Communication used for participation in larger groups.

Personal Factors

Elements like motivation, emotions, and attitudes that affect communication.

Collaborative goal setting

A process where clients are involved in defining their therapy objectives.

Motivational interviewing

A technique used to enhance client motivation.

Informed Consent

The process of explaining the nature, purpose, risks, and benefits of assessment and treatment.

Scope of Competence

The principle of providing only services one is qualified to offer.

Autonomy & Client-Centered Care

Respecting clients' rights to make decisions about their care.

Cultural Competence

Understanding how cultural backgrounds influence communication styles and treatment preferences.