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CSD 333 Oral Language Development

Week 7

Oct. 6 - 10, 2014

The brain and language

• Overview of neuroscience concepts

• Brain regions involved in speech-language processing

What is neuroscience?

1) Study of brain mechanisms that allow acquisition and regulation of higher mental functions and production of basic and skilled actions

2) Study of the nervous system, from perspectives of biology, chemistry, medicine, speech & hearing sciences, and others

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Studying the nervous system

• Biology (biochemistry): allows study of the smallest functional units of the nervous system, i.e., neurons

• Chemistry: communication in the nervous system is electrochemical

• Speech-language pathology and psychology: the nervous system can be understood in the context of function and pathology

Studying the brain and language

• In the past: lesion studies from post-mortem examination of stroke victims, TBI (traumatic brain injury) patients…

• Now: Various neuroimaging techniques such as CT, PET, MRI

• It’s possible to study not only structure (anatomy), but also how the brain works in (almost) real-time through PET, fMRI

Neuroscience and speech-language

• Work by physician Paul Broca on language impairment and the brain laid foundations for neuroscience study– Confirmed that function could be localized

to brain structure

Bear et al., 2006

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Basic functional units• What is the smallest functional unit of the

brain?– Neurons!

• Neurons are the information bearing cell of the nervous system

• Types and sub-types of neurons exist but there are basic common cellular structures

Neurons

• 15 billion + neurons with CNS that function as populations to serve all brain functions: sensation, movement, cognition …– With trillions of synapses!!!

Neurons

• Neurons communicate by means of electrochemical nerve impulses called action potentials

• Action potentials are either excitatory (increasing activation) or inhibitory (decreasing activation)

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The typical neuron

Synapse

Cell body

• Terminal structure is the synapse

• Bouton at end of neuron that releases neurotransmitters

• Synaptic cleft between 2 communicating neurons

• Neurotransmitters travel across cleft to affect receptor structures on communicating neuron

Presynaptic Postsynaptic

Bhatnagar, 2002

Divisions of the Nervous System

Blumenfeld, 2002

• Central nervous system (CNS): The brain and spinal cord

• Peripheral nervous system (PNS): cranial and spinal nerves– 12 pairs of cranial nerves

provide sensory, motor function to head and neck

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Afferent vs. efferent

• Afferent means toward the brain– Afferent neurons carry nerve impulses from

receptors (sense organs) to the brain

• Efferent means away from the brain– Efferent neurons carry commands from the

brain to e.g., muscles

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Gray / White Matter• Typically, cell bodies and

dendrites are distinctively gray in dissections

• Axons are white due to myelin– Myelin insulates axon

allowing for rapid conduction

Blumenfeld, 2002

Gray / White Matter• White matter affects how

the brain learns and functions, relaying action potentials among brain regions

• Gray matter is associated with processing and cognition

Blumenfeld, 2002

Gray-White matter in the cerebrum

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White matter fibers in the brain shown with diffusion tensor imaging

Bhatnagar, 2002

Rostral

Caudal

Rostral

Caudal

Spinal Cord

Cortex

Rostral / Caudal Orientation

“toward the head”

“toward the tail”

Bhatnagar, 2002

Proximal

Distal

Proximal: Relatively closer to the anatomical site of reference in the nervous system

Distal: Relatively further from the anatomical site of reference in the nervous system

Proximal / Distal

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Anatomical Orientation

(Adj: “cerebral”)

Major brain divisions

Major brain divisions

• Cerebrum serves higher mental functions

• Cerebellum: helps coordinate movements and regulates balance

• Brainstem: contains the cranial nerve cell bodies (nuclei); regulates respiration, phonation, and heart beat

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Gross anatomy of the CNS

Cortex: outer layer of the cerebrum• Composed of folded gray

matter• Plays an important role in

consciousness

Brain hemispheres

• The cerebrum is divided into two hemispheres, left and right

• Two key language regions, Broca’s area and Wernicke’s area, are located in the left hemisphere in most people– Wada test is used to establish which

hemisphere is used for language

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Some functions of lobes

• Frontal lobe: reasoning, planning, problem solving; pragmatics

• Parietal lobe: integrating sensory information

• Temporal lobe: sense of sound

• Occipital lobe: sense of sight– All four lobes are involved in processing

language!

Speech, language, hearing

• Primary auditory cortex

• Primary motor cortex

• Primary somatosensory cortex

• Broca’s area

• Wernicke’s area

Structures in the brain

• Sulcus (plural: sulci): Depression or groove in cerebral cortex

• Gyrus (plural: gyri): Ridge on the cerebral cortex

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Important gyri and sulci

• Sulci– Lateral sulcus

– Central sulcus

• Gyri– Precentral gyrus

– Postcentral gyrus

– Inferior frontal gyrus

– Superior temporal gyrus

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Primary auditory cortex

• Responsible for perception of sound

• Important for phonology

• Located in the lateral sulcus and on superior temporal gyrus

• Shows a tonotopic organization– Frequency sensitive regions are arranged

from lower to higher, anterior to posterior

Primary auditory cortex

Primary motor cortex

• Responsible for planning and executing movement along with supplementary motor area (SMA), premotor area (PMA)

• Located in precentral gyrus (posterior frontal lobe just anterior to central sulcus)

• Organized according to a homunculus (“little man”), reflecting arrangement of motor neurons controlling body parts

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Frontal lobe• Primary motor cortex is housed within the precentral gyrus

• Premotor motor area (PMA) and supplementary motor areas (SMA) is anterior to the primary motor cortex

Primary motor cortex

Primary somatosensory cortex

• Main sensory receptive area for sense of touch

• Located in postcentral gyrus

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41

Somatotopic mapping in human somatosensory and motor cortex

Blumenfeld, 2002

Broca’s area

• Characterized by Paul Broca

• Important for language production

• Important for syntactic comprehension

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Broca’s area

• Broca’s area is in the inferior frontal gyrus (generally in left hemisphere)– Pars opercularis and pars triangularis parts

of the inferior frontal gyrus

• Damage to Broca’s area leads to Broca’s aphasia (or expressive aphasia)– Characterized by loss of ability to produce

language; speech is nonfluent and halting, and language is disjointed

Broca’s area

Broca’s aphasia(Gardner, 1975)

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Wernicke’s area

• Involved in the understanding of spoken and written language

• Located in posterior section of superior temporal gyrus

Wernicke’s area

Wernicke’s aphasia• In Wernicke’s aphasia, speech sounds

normal but meaning and language are impaired

Examiner: Tell me the names of each of these. Patient:

[cigarette] This is a cigarette.[comb] a wongt.[fork] a fillt.[key] a wote.[knife] a mergiss…

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Brodmann areas

• Scientist Korbinian Brodmann used Nissl staining technique to map groups of similar neurons

• A Brodmann area is a region of cerebral cortex defined based on cell organization

Korbinian Brodmann(1868-1918)

Franz Nissl(1860-1919)

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Types of neurons

Brodmann’s maps

Brodmann’s areas

• Primary auditory cortex: Brodmann area 41 & 42 and part of 22

• Primary motor cortex: Brodmann area 4

• Primary somatosensory cortex: Brodmann areas 3, 1, and 2

• Broca’s area: Brodmann area 44 & 45

• Wernicke’s area: Brodmann area 22

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Contralateral Control

• Anatomical terminology:– Contralateral: opposite side– Ipsilateral: same side

• In general, the left side of the brain controls the right side of the body (“contralateral control”)– Also vice versa– A few exceptions

Bhatnagar, 2002

The developing brain

• New synaptic connections are forged among neurons during development

• Synaptogenesis refers to formation of synaptic connections– Driven by sensory and motor experiences

• Infants’ brains at 1 year contain about 2x as many synapses as adults– Synaptic pruning: elimination of synapses

Neuroplasticity

• Neuroplasticity means changing of neurons, the organization of their networks, and their function via new experiences

• Infants (but not adults) with left hemisphere damage can achieve typical or near-typical language function

• Plasticity is possible at any age to some degree– Significant implications for assessment, therapy,

rehabilitation