Neural Control of Language and Speech

communication

combination of “what” we say (sounds, words, sentences) and “how we say it (intonation/prosody, body language, facial expressions) and how these are interpreted by another

• interpretation dependent on the context (setting, intent of person)

• components are interconnected and rely on extensive networks within the brain

• components

  • speech

  • language

  • cognition

speech

motoric production of sounds

language

set of symbols to convey meaning

• finite set of arbitrary symbols combined to communicate an infinite number of concepts

• symbols express a concept of phonemes assembled in socially agreed upon manner

• not insane but learned

cognition 

executive function, attention, memory 

wericke-geshwind model “classic” model

highlights several primary language areas

1. broca’s area

2. wernicke’s area

3. arcuate fasciculus

duel path model of language processing

complex process carried out by networks 

• dorsal stream

• ventral stream 

dorsal stream

responsible for analyzing and ordering of information in time and space

dorsal stream: phonological processing

connects temporal/parietal/frontal lobes to convert voices to phonemes, retrieve words, repeat words, articulate

• arcuate fasciculus, superior longitudinal fasciculus

dorsal stream: learning new vocabulary 

converts sounds into phonemes, auditory short-term memory

• heschl gyrus, superior temporal gyrus, broca’s area, arcuate fasciculus, and superior longitudinal fasciculus 

ventral stream

concerned with semantic meaning relationship ampung phonological, morphological, syntactic and semantic elements

ventral stream: semantic processing

assigns meaning to words, word selection

• inferior fronto-occipital fasciculus, intratemporal networks, middle temporal gyrus

primarily left hemisphere

• phonology

• morphology

• syntax

left and right hemispheres

semantics

primarily right hemisphere

• pragmatics

• social cognition

common developmental disorders

• developmental language disorders

• autism spectrum disorder

• down syndrome

developmental language disorders

• multifactorial etiology

• anatomical differences in cortical and subcortical structures and white matter volumes

autism 

• rapid brain growth, large amounts of white matter, greater gray matter surface area 

• excess CSF in subarachnoid space

• reduced right/left asymmetries 

down syndrome

• trisomy 21

• small brain size

• fewer neurons, less dendritic branching

common acquired disorders

• traumatic injury

• degenerative diseases

• dementias

traumatic injury 

• contusion 

• diffuse axonal injury 

• secondary issues 

  • edema (swelling compresses brain tissue)

  • hypoxia/anoxia (lack of oxygen to brain)

degenerative diseases 

• parkinsons

• MS

• myasthenia gravis

• amyotrophic lateral sclerosis 

parkinsons

affects dopamine-producing cells

MS

affects CNS myelin

myasthenia gravis

affects neuromuscular junction

amyotrophic lateral sclerosis 

affects motor neurons

dementias

• proteinopathies

• vascular dementias

proteinopathies

proteins aggregate neurons, glial cells extracellular fluid

vascular dementias

reduction in blood vessel patency causing hemorrhages, infracts, white matter damage

• cerebral atherosclerosis

• small vessel disease

• cerebral amyloid angiopathy

aphasia

acquired language disorders, usually due to lesion in left hemisphere

• affects naming, repetition, fluency, expression and comprehension

pragmatic language disorders

• developmental disruptions- social cognition, metalizing networks

• acquired right hemisphere damage (RHD)

acquired right hemisphere damage (RHD)

strole, tumor, focal TBI

• primarily pragmatic deficits 

• difficulties with inferencing 

• inefficient communication

• disorganized discourse 

cognition: attention disorders

• stroke, tumor, TBI

• attention underlies most cognitive processes

• unilateral neglect

intervention

• knowledge of brain structures and functions improve rehab

• knowledge of brain injury needed for differential diagnosis

• brain can change in response to training if meaningful and relevant to everyday function

different models of neural control

• psycholinguistic: speech is oral manifestation of language

• motor: speech is motor act

• hierarchical state feedback control: integrates other approaches, speech production depends on linguistic content

speech sound disorder tree

• functional 

  • articulation

  • phonology

• organic

  • motor

    • execution

    • planning

  • structural

    • orofacial anomalies

  • sensory/perceptual

    • hearing

vocalization

• any complex pattern of sound production

• laughter, crying, grunting, signing, speech

speech

• most highly specialized form of vocalization

• verbal-expression of thoughts and feelings using time-varying sound patterns

  • complex, sensorimotor behavior

  • anatomical subsytems

neural control of speech

skilled motor activity consisting of integration of sensory info with motor plan before execution

• movement requires knowing where body is in space and the condition of muscles and joints

cortical structures

• primary motor cortex

• primary somatosensory cortex

• inferior frontal gyrus

• supplementary motor areas

• anterior cingulate cortex

• supramarginal gyrus

• insual

subcortical structures

• reticular formation

• periaqueductal gray matter

• thalamus

• basal ganglia

• cerebellum

efferent pathways 

anatomical subsystems 

• respiratory→ spinal nerves via medulla 

• larynx → nucleus ambiguus

• velopharyngeal → nucleus ambiguus 

• oral articulatory → facial, hypoglossal, trigeminal  

afferent pathways

• trunk → C3-T12

• head and vocal tract → via trigeminal sensory

• acoustic → auditory nerve

motor control and reflexes

• reflexes are controlled at other levels

  • brainstem, spinal cord

  • central pattern generator

• voluntary motor control is under cortical control

skilled motor activity requires

• motor plan

• integrated sensory feedback

• activation of muscles

element of motor control

• feedback

• correction

motor learning (skilled acquisition)

use closed loop system

• requires slow movement

• set reference or target

• correction from comparing accuracy to standard

• feedback and correction

motor control (skilled execution) 

• can occur at much faster pace and use accomplish tasks rapidly

• relies on previously accurate performance

• does not operate on sensory feedback or correction

• feed forward

motor learning and control steps

1. use sensory input to check for accuracy in execution

2. differentiates learning (feedback) from ongoing production (feedforward)

3. auditory model for phoneme is generated and sent to auditory cortex and somatosenory cortex

apraxia

• impaired capacity to plan or prgram sensorimotor commands necessary for directing movements

• inability to create and sequence motor plans for speech

dysarthria 

• group speech disorders resulting from disturbances in muscular control from damage to central or peripheral nervous system 

• impacting control of respiratory, phonatory, articulatory and prosodic scpet of speech and production