Human Communication

verbal behaviour is a…

lateralised function; most language disturbances occur after damage to the left side of the brain

The left hemisphere is dominant for speech in…

90% of the population

The hemisphere dominant for speech can be different if people are..

left-handed or right-handed

Right hemisphere speech dominance is seen in

4% of right-handed people, in 15% of ambidextrous people and in 27% of left-handed people (Knecht et al, 2000)

When does laterality develop?

in infancy - after the age of 5

Woods, 1980

Incidence of language problems following right side damage is much greater if damage is during infancy

Vargha-Khadem, 1985 - Damage to left side results in

worse language impairment if it occurs after 5 years of age

Searlman, 1977 - Left hemispherectomy in adults

results in aphasia whereas in children almost complete recovery of langauge function

Broca’s area

region of left frontal cortex, located just at the front of the base of the left primary motor cortex, that is necessary for normal speech production

Aphasia

loss of language function

Broca’s Aphasia is characterised by

slow, laborious, and non-fluent speech. But it does not affect their ability to mostly understand conversation

Keller, 1978 - Broca’s Aphasia

Patients often mispronounce words

Broca’s Aphasia - the words Broca’s aphasia patients do say

have the correct meaning for the concept they are trying to convey

Broca (1861) suggested that this form of aphasia is produced by a

lesion of the frontal association cortex, just in front of the face region

Damage restricted to Broca's area does

not result in Broca's aphasia

To develop Broca’s Aphasia Damage must extend to the

frontal lobe and underlying subcortical white matter

Speech production is likely to be damaged because Broca's area is close

to primary motor cortex where movement of the mouth and tongue are controlled

Several functioning imaging studies have confirmed…… in the production of verbs

the importance of Broca's area and the motor cortex surrounding it in the production of verbs

Hauk et al (2004) had subjects

read verbs that related to movements of different parts of the body

Hauk et al (2004) findings

when the subjects read a verb, they saw activation in the regions of the motor cortex that controlled the relevant part of the body even though they weren't actively doing these things.

Broca's aphasia is also associated with

Agrammatism

Agrammatism

one of the unusual symptoms of Broca's aphasia; a difficulty in comprehending or properly employing grammatical devices such as verb endings and word order (Saffran, 1980)

Agrammatism (Schwartz et al, 1980) not just about..

production it is also about comprehension

Schwartz et al, 1980 procedure

Patients read a sentence - horse kicks a cow

They were asked to point to which picture represents sentence

Schwartz et al, 1980 findings

Patients performing poorly illustrating a problem with understanding word order

Boller and Dennis (1979) showed patients have difficulty..

following simple commands when word order is important eg pick up red circle and touch red  square with it

How does the Function of left frontal lobe explain getting the order wrong in BA?

function involves sequencing stimuli and events. This would explain getting the order of sounds wrong

Wernicke’s area

A region of auditory association cortex on the left temporal lobe of humans, which is important in the comprehension of words and the production of meaningful speech

Each primary sensory area of the cerebral cortex sends information to

adjacent regions, called the sensory association cortex

Circuits of neurons in the sensory association cortex…

analyse the information received from the primary sensory cortex

The primary characteristics of Wernicke's aphasia are

poor speech comprehension and production of meaningless speech

Unlike Broca's aphasia, Wernicke's aphasia is..

fluent and unlaboured; the person doesn't strain to articulate words and doesn't appear to be searching for them

The abilities that are disrupted in WA include

recognition of spoken words, comprehension of the meaning of words and ability to covert thoughts into words

Wernicke's aphasia - associated with 2 separate conditions:

Pure word deafness

Transcortical sensory Aphasia

Pure word deafness

no recognition of word but comprehension is intact

Transcortical sensory Aphasia

recognition without comprehension

Pure word deafness

• The ability to…

hear, to speak and usually to read and write without being able to comprehend the meaning of speech; caused by damage to Wernicke's area or disruption of auditory input to this region

What can pure word deafness patients understand?

meaning of non-speech sounds or emotion from the tone of a voice. Patients can usually understand written words, just not speech

Pure Word Deafness Case study (Saffran et al, 1976):

 patient had perfect hearing, could not understand spoken commands but could understand written instructions

2 types of brain injury can cause pure word deafness:

disruption of auditory input to the superior temporal cortex or damage to the superior temporal cortex (Stefanatos et al, 2005)

Transcortical sensory aphasia is due to Damage to the

posterior language area alone, which isolates Wernicke's are from the rest of the posterior language area

Transcortical sensory aphasia a person has…

difficulty comprehending speech and producing meaningful spontaneous speech but can repeat speech

Transcortical sensory aphasia - Failure to comprehend the meaning of words and the inability to express thoughts in meaningful speech - appear to be produced by

damage that extends beyond Wernicke's area into the region that surrounds the posterior part of the lateral fissure, near the junction of the temporal, occipital and parietal lobes (posterior language area)

Transcortical sensory aphasia - Case study: Geschwind et al (1968)

patient could learn songs from radio or repeat anything she heard but couldn't comprehend meaning or say anything not initiated by someone else.

The difference between and Wernicke's aphasia is that patients with pure word deafness

cannot recognise spoken words, but they can understand the words if they are written down

The difference between TSA and Wernicke's aphasia is that patients

with TSA can repeat what other people say to them; therefore, they can recognise words. However, they can't comprehend the meaning of what they hear and repeat; not can they produce meaningful speech of their own

Wernicke's aphasia =

pure word deafness + TSA

• Cause by damage to both Wernicke's are and posterior language area

conduction aphasia characterised by

inability to repeat words that are heard but the ability to speak normally and comprehend the speech of others

CA patients can…

recognise words and understand them but are unable to repeat precisely

What is responsible for CA? MRI scans show the

subcortical damage - This lesion damaged the arcuate fasciculus, a fiber bundle connecting W and B area

CA Symptoms suggest 2 pathways connecting the speech mechanisms

• Direct connection conveys speech sounds

• Indirect though the posterior language conveys meaning

Damage to the indirect pathway would be expected to…

spare the ability to repeat speech but would impair comprehension

Brain Structures associated with reading

• Primary visual cortex in the occipital lobe

• Visual association cortex in the temporal lobe

• Visual word form area VWFA on bottom of temporal lobe

• Broca's area in frontal lobe

Pure Alexia/pure word blindness

loss of the ability to read without loss of the ability to write

Who described the pure Alexia syndrome?

Dejerine (1982)

Where was the brain damage in pure Alexia?

• Patient had lesion in visual cortex of the left occipital lobe and the posterior end of the corpus callosum

Where else is there brain damage in pure Alexia?

damage to Wernicke area or disruption of auditory input to this region

The flow of visual information for a person with damage to the left visual field…

enables that person to read words aloud

Process to read words aloud - stage 1

• Information from the left side of the visual field is transmitted to the right striate cortex (primary visual cortex) and then to regions of right visual association cortex

Process to read words aloud - stage 2

 the information crosses the posterior corpus callosum and is transmitted to a region of the left visual association cortex known as the visual word-form area VWFA where it is analysed further

Process to read words aloud - stage 3

transmitted to speech mechanisms located in the left frontal lobe

As pure Alexia patients have damage to..

corpus callosum so right side of brain cannot communicate with left so wont reach VWFA

Mao-Draayer and Panitch (2004) reported the case of a man with

multiple sclerosis who displayed the symptoms of pure alexia after sustaining a lesion

Mao-Draayer and Panitch (2004) reported the case of a man with what lesion did he have?

lesion that damaged both the subcortical white matter of the left occipital lobe and the posterior corpus callosum

These Lesions from Mao-Draayer and Panitch (2004) are in precisely the locations that..

Dejerine (1892) predicted would cause this syndrome

Reading involves at least 2 different processes:

direct recognition of the word as a whole and sounding it out letter by letter

Whole-word reading

reading by recognising a word as a whole

Phonetic reading

reading by decoding the phonetic significance of letter strings

Surface dyslexia

 a reading disorder in which a person can read words phonetically but has difficulty reading irregularly spelled words by the whole-word method

What can a person with surface dyslexia read?

Can read hand, can read non-words, can't read words with irregular spelling

Gurd and Marhall (1993) showed if a surface dyslexic

read the word pair they would not know if it was two of a kind or a fruit

Phonological dyslexia

a reading disorder in which a person can read familiar words even ones that have irregular spelling but has difficulty reading unfamiliar words or pronounceable non-words

Evidence from lesion and functional imaging studies with readers of Japanese suggest that

the process of whole-word reading follows the ventral stream of the visual system to a region of the fusiform gyrus, located at the base of the temporal lobe

Thuy et al (2004) and Liu et al (2008) found that the reading of

kanji words or chinese characters activated the left fusiform gyrus

Sakura et al, 2000 - phonetic reading

The region of the parietal cortex that is involved in phonetic reading is the temporoparietal cortex

the temporoparietal cortex processes the sounds associated with each letter or symbol. Patients with damage to this are unable to

process Kana symbols which like letters make a word but are able to read Kanji symbols which represent whole words