1. Intro to Brain and Language

Examples of lateralised abilities

• alot in the media about left and right brain

• left - logic, language, rationality

• right - creativity, attention, face processing

How does brain lateralisation manifest?

sensory input & motor control of one side of the body are linked to contralateral hemisphere

What are the features of brain lateralisation in the left hemisphere? (motor and touch)

• controls right side of body

• gets touch input from the right side

What are the features of brain lateralisation in the right hemisphere? (motor and touch)

• controls left side of the body

• gets touch input from the left side

How is brain lateralisation seen for vision?

• the left hemisphere gets direct visual input from the right visual field

• the right hemisphere gets direct visual input from the left visual field

How are differences in handedness seen regarding language in the brain?

• for most right-handed people, the left hemisphere is responsible for most language functions

• right-hemisphere dominance observed only in 30% of left handers

What is involved in the explanation of why there is hemisphere asymmetry in humans that it is due to precedents in the animal kingdom?

• behavioural asymmetries in many vertebrates (e.g., visual, manipulation)

• mammalian brain shows left lateralised preference for vocal communication (e.g., mice)

What is involved in the explanation of why there is hemisphere asymmetry in humans regarding possible mechanisms in evolution?

• fitness benefits, especially in bipedal man

• parallel processing of complementary information (e.g., global vs. local processing)

Why is naming objects is faster if the object is presented to the RVF?

• Because RVF projects directly to the Left Hemisphere (LH).

• The LVF in contrast projects directly to the RH, so naming is slower when the information has to be shared across the hemispheres via the corpus callosum, as represented in the image.

Why can split brain patients not name objects presented in the LVF?

• Because the visual information is projected to the RH and would need to be shared with the LH to find the name stored in it.

• Since the corpus callosum is severed, this information cannot be shared with the LH.

Why does the right visual field have an advantage for word recognition?

• for reading, anything presented in right visual field will get to left hemisphere faster then words presented to left hemisphere

• an even greater effect for longer words, shorter words can be globally perceived

How is the processing of auditory information lateralised?

• tested using dichotic listening

• speech sounds are more left lateralised (right ear) and music is right lateralised (left ear)

• intonation also right lateralised - therefore also associated with emotion

The Bantu Language

• more activity in the LH than RH

• uses clicks - but activating LH more because they are connected to meaning

What are the main brain structures implicated in language?

• traditional view developed using post-mortem methods

• in the sylvanian fissure - the auditory cortex receives the input

• brocas area = inferior frontal gyrus

• superior and middle temporal gyrus = to do with words and representations of info about the world

What are the important language-related white matter fibres?

• the ventral route: meaning

• the dorsal route: audition to motor cortex and output

What might a lesion in the auditory cortex and Wernicke’s area cause?

• auditory cortex is in the STG, extracts sound identity (phonemes)

• wernicke’s area, STG: fluent aphasia, nonsensical speech, impaired understanding

• because they can’t hear others, they cannot hear themselves; cannot monitor what they are saying

What have imaging studies shown up about understanding spoken words?

• presenting intelligible vs unintelligible speech

temporal lobe involved in processing intelligible speech

What have imaging studies shown up about understanding spoken words?

• complex sentences vs baseline

• all the regions active

• all of ventral route activated with more than one word

What is activated when familiar words are understood?

ventral route

When is the dorsal route engaged?

• sound repetition (involved in first and second language learning) engages the dorsal route

• does not necessarily activate meaning

Which routes are involved in spontaneous production? e.g. I need some water

• ventral route; saying something meaningful

• and dorsal for production

What damage does this patient have?

• dorsal damage

• substitution of sounds - phonological problems

• and semantics preserved

What is involved in Disfluent aphasia?

• left inferior frontal gyrus damage (Broca’s area)

• affects the ability to convert thoughts into sentences

• particularly affects the ability to construct a sentence around the action or verb

• comprehension unimpaired

• tested using procedures such as the cookie theft task

How is sentence comprehension tested in disfluent aphasia? And what is found

• most of the time, Broca’s aphasics have little problems in comprehension

• more subtle comprehension impairments are observed when small relational words are required for understanding

• semantic knowledge may help interpretation, so the most difficult cases are those where interpretation cannot be inferred from word order or general world knowledge (reversible sentences)

In terms of sentence comprehension, disfluent aphasia causes problems with…

• relationships between words and verb retrieval

• small words like is, by, the, of

• inflectual endings like -ed, -ing, -s

In terms of sentence comprehension, disfluent aphasia patients base understanding on…

• the meaning of individual words

• general knowledge

• simple word order assumptions

Which of the following would be the hardest for a patient with disfluent aphasia?

the cat that the dog is biting is black

What function of the LIFG relates to disfluent aphasia?

contributes to the combination of words in comprehension and production