Language and the Brain

Question 1

what is language?

Answer 1

• A System by which sounds, symbols, and gestures are used for communication
• Sensory Process: Auditory (speech), Visual (sign, reading), tactile (tadoma)
• Motor Processes: Produces speech, writing, signs, gestures
• Subsystems of Language: Lexicon, semantics, phonology, morphology, syntax, pragmatics

Question 2

language vs. speech/sign

Answer 2

• Language is the abstract representation of the form-meaning mapping through which symbols are converted into meaningful constructions and messages
  
  • Abstract rules for putting together symbols to convey complex meanings about states and events in the world
  • The rules must be understood and acquired by all speakers of the language
• Speech or sign is the use of a physical medium to transmit and receive the symbols of language
• Brain areas might be identified for perception or production of speech, or for the abstract representation of grammar

Question 3

Broca’s and Wernicke’s areas

Answer 3

• Broca’s: BA 44, 45, 46
  
  • Subcortical structures: basal ganglia, thalamus and medial subcallosal fasciculus (nerve bundle under the callosum connecting SMA to anterior cingulate)
• Wernicke’s: BA 22, 41, 42
  
  • Middle temporal, angular gyrus and subcortical structures (basal ganglia & thalamus)

Question 4

__________ areas are adjacent to Broca’s area

Answer 4

motor

Question 5

example of Broca’s aphasia speech

Answer 5

“Yes … ah … Monday … er … Dad and Peter (his name) and Dad … er …. Hospital … and ah …. Wednesday … Wednesday, 9 o’clock … and oh … Thursday … 10 o’clock … ah Doctors … two … an doctors … and er … teeth … yah!”

Question 6

characteristics of Broca’s aphasia speech

Answer 6

• Effortful articulation: Slowness in planning, execution & sequencing of speech
• Anomia (inability to access words) & paraphasias (sound or meaning substitutions)
  
  • Semantic: table for bed
  • Phonological: school for stool
• “Telegraphic” speech: Dominated by high content nouns, verbs & adjectives, absence of functors (articles, aux verbs, prepositions, morphological affixes)
• Agrammatism– sometimes evident: comprehension deficit related to failure to access syntactic organization of utterances or sentences

Question 7

Broca’s aphasia - production and comprehension deficit

Answer 7

• Agrammatism:
  
  • The dog was licked by the cat. Who did was licking?
  • The cow that chased the donkey was bitten by the dog. Who bit whom?
• Broca’s aphasia often associated with inability to answer these questions accurately
• Comprehension is not fully represented
• Suggests this is not just a production deficit

Question 8

Broca’s aphasia - idiomatic language

Answer 8

Idiomatic Language:

• Broca’s aphasics often use overlearned idiomatic phrases (“that’s the way the cookie crumbles”) in substitution for productive language
• Such aspects of language are thought to be strongly represented in Right hemisphere analogue of Broca’s area

Question 9

impairments associated with Broca’s aphasia

Answer 9

• Dysarthria (neuromuscular speech impairment)
• Verbal apraxia (inability to articulate w/o motor impairment)
• Buccofacial/Oral apraxia (Inability to move oral features in the absence of paresis
• Right hemiparesis or hemiplegia (motor impairment on right half of body), right hemisensory defect (inability to perceive stimulation on right side)

Question 10

characteristics of Wernike’s aphasia speech

Answer 10

• Speech is fluent (or rapid at least) but often meaningless
  
  • Word salad, jargon, paraphasias
  • Contains many functors, but often used inappropriately in long strings with few content words
• Characterized by:
  
  • Limited comprehension of spoken or written language
  • “Empty” but fluent speech, depth of meaning is absent
  • Poor repetition
  • Paraphasias
  • Neologisms and jargon (“word-salad”)
• Associated signs: Right hemisensory deficits, right hemianopia (cortical blindness)

Question 11

example of Wernicke’s aphasia speech

Answer 11

“I feel very well. My hearing, writing been doing well. Things that I couldn’t hear from. In other words, I used to be able to work cigarettes I didn’t know how to be any able to.”

Question 12

Wernicke-Geschwind Model of Aphasia

Answer 12

Proposed circuit involving:

• Striate (Visual) Cortex
• Broca’s area
• Wernicke’s area
• Arcuate Fasciculus (tract connecting Wernicke’s and Broca’s Areas)
• Angular gyrus

Question 13

Wernicke-Geschwind Model of Auditory Processsing

Answer 13

Simple repetition task:

• Speech input - auditory cortex
• Meaning of utterance is processed in Wernicke’s area
• Sent to Broca’s area via the arcuate fasciculus
• Processed in Broca’s area for speech production
• Sent to Motor cortex for speech production

Question 14

Wernicke-Geschwind Model of Reading and Written Language

Answer 14

• Written input - visual cortex
• Converted into sound representation in Angular Gyrus
• Meaning of utterance is processed in Wernicke’s area
• Sent to Broca’s area via the arcuate fasciculus
• Processed in Broca’s area for speech production
• Sent to Motor cortex for speech production

Question 15

Wernicke-Geshwind model
Role of Arcuate Fasciculus

Answer 15

• Conduction Aphasia
• Lesion of fibers composing arcuate fasciculus
• Comparison with Broca’s aphasia, Wernicke’s aphasia: Comprehension good, speech fluent
• Difficulty repeating words
• Symptoms:
  
  • Repetition task: Substitutes/omits words, paraphasic errors,
  • cannot reproduce: functions, nonsense words, polysyllabic words
• Generally taken to support W-G model, since Broca’s and Wernicke’s areas are intact

Question 16

problems with Wernicke-Geshwind model

Answer 16

• Too simplistic: Circuits are clearly more interconnected than proposed
• Not all written text is converted into phonological representations
• Several thalamic and basal ganglia areas involved in language
• Comprehension vs. Production does not characterize the full complexity of deficits such as agrammatism etc.

Question 17

aphasia in bilinguals and the deaf

Answer 17

• Aphasia in bilinguals
  
  • Language affected depends on: Order of acquisition, fluency in each language, how often language is used
• Sign language aphasias
  
  • Analagous to speech aphasias - but can be produced by lesions in slightly different locations
• Case Study: Verbal and sign language aphasia in same person
  
  • Both aphasias recovered together - indicating common regions used for both media
  • Evidence suggests some universality to language processing in the brain and abstract linguistic representations independent of modality

Question 18

Asymmetrical Language Processing in the Cerebral Hemispheres

Answer 18

• Paul Broca originally postulated Left Hemisphere was responsible for language production
• Wada test (Anesthetization of one hemisphere using sodium amytal injected into carotid artery) shows loss of speech in dominant hemisphere
• 90% are right handed
• 96% of right handers are left dominant for language
• 70% of left handers are also left dominant for language
• = 96% of all people are left dominant for language

Question 19

split brain studies

Answer 19

• Roger Sperry studied split-brained monkeys in 1950s
  
  • Severed axons in the corpus callosum
  • No major deficits at first sight
  • With proper experiments, discovered that animals behaved as if they had 2 brains
• Language Processing in Split-Brain Humans
  
  • Gazzaniga: Present stimuli to one hemisphere
  • Two hemispheres initiated conflicting behaviors

Question 20

left hemisphere language dominance

Answer 20

• Words to Right visual field - Repeated easily
• Words to Left visual field à Difficulty verbalizing
• Image only in left visual field à Picks correct object w/ left hand, but unable to describe in words
• Unable to describe anything to left of visual fixation point

Question 21

language functions of the right hemisphere

Answer 21

• Functions of right hemisphere: Read and understand numbers, letters, and short words (nonverbal response)
• Baynes, Gazzaniga, and colleagues: Right hemisphere able to write, but cannot speak
• Right hemisphere: Drawing, puzzles, sound nuances
• Left hemisphere: Language
• Language impairments associated with right hemisphere damage: Prosody, Gesture, Idioms, Connected discourse

Question 22

anatomical asymmetry and language

Answer 22

• Left lateral (Sylvian) fissure longer and less steep than right
• Geschwind and Levitsky: Left planum temporale larger than right in 65% cases
• Functional human asymmetry: More than 90% humans right-handed
• Animals: Equal numbers of right-handers and left-handers
• Suggests that human handedness might be related to language asymmetry

Question 23

other asphasias and language pathologies

Answer 23

• Global Aphasias (Broca’s + Wernicke’s)
• Transcortical Aphasias (Watershed areas)
• Dyslexia (reading problems), Alexia (Word blindness)
• Dysgraphia (inability to write)

Question 24

global aphasia

Answer 24

• Combination of Broca’s and Wernicke’s
• Typically associated with occlusion of main stem of middle cerebral artery (thus, impeding flow in both anterior and posterior branches)

Question 25

transcortical aphasias

Answer 25

• Generally: Repetition intact, disruption of motor and/or sensory abilities
• Mixed: Broca’s, Wernike’s and Arcuate Fasciculus intact; Destruction of watershed areas surrounding these structures
• Motor: Isolation of Broca’s Area only
• Sensory: Isolation of Wernicke’s area alone

Question 26

list of aphasias

Answer 26

• Conduction: Fluent Speech, Poor Repetition, Good Comprehension, Poor Naming, No Right-side Hemiplegia, Some Sensory Deficits
• Global: Nonfluent Speech, Poor Repetition, Poor Comprehension, Poor Naming, Right-side Hemiplegia, Sensory Deficits
• Transcortical Motor: Nonfluent Speech, Good Repetition, Good Comprehension, Poor Naming, Some Right-side Hemiplegia, No Sensory Deficits
• Transcortical Sensory: Fluent Speech, Good Repetition, Poor Comprehension, Poor Naming, Some Right-side Hemiplegia, Sensory Deficits
• Transcortical Mixed: Nonfluent Speech, Good Repetition, Poor Comprehension, Poor Naming, Some Right-side Hemiplegia, Sensory Deficits
• Anomia: Fluent Speech, Good Repetition, Good Comprehension, Poor Naming, No Right-side Hemiplegia, No Sensory Deficits

Question 27

Reading and Writing:
Agraphia, Dysgraphia, Alexia, Dyslexia

Answer 27

• Anterior supramarginal gyrus; Posterior angular gyrus
• Alexia with agraphia (angular gyrus)