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The Linguistic brain Summary
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Summary of all the lectures of the Linguistic brain (language and communication) course of the Brain and Cognition minor
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THE LINGUISTIC BRAIN SUMMARYLECTURES 1-2: LINGUISTICS IN THE BABY BRAIN
Genie: was isolated from 18 months onwards, for years and she was unable to learn grammatical rules. She
was able to learn vocabulary but never learned how to put words together. Vocabulary showed rapid
development whereas grammar showed slow to no development. She showed rapid cognitive development in
non-language dependent tests but her linguistic development was independent from that and showed limited
development. Our language system is independent from other cognitive abilities. When Genie did a dichotic
listening test, she showed left ear dominance for linguistic stimuli which means that her right hemisphere was
processing language predominantly, unlike healthy people (left hemisphere is responsible for language, right
ear dominance for linguistic stimuli). Thus, Genie’s language system did not show healthy development.
- Critical period hypothesis: left hemisphere lateralization can only happen during a specific critical
period. In this case, the right hemisphere will be processing language, but it is not the most optimal
and not designed for this task. Genie’s language use and comprehension resembles the one of split-
brain patients and patients of left hemispherectomy.
Home-sign: another form of language deprivation in deaf children born in hearing-speaking communities
where no sign language is available. These children develop their own communication system. Home-sign
contains some language components such as fixed order of units and systematic ways to express negation and
questions. But it does not contain syntax or phonology. It is expressive but not receptive thus, making the
topics address limited. If home-sign is used, there are deficits in learning a sign language later in life.
Non-human primates: no abilities to learn or use complex syntax, just like infants or deprived children. They
can learn vocabulary but cannot understand or construct complex sentences. The brain areas responsible for
syntactically complex sentence processing are BA44 and STG (dorsal pathway). Non-human primates lack
connectivity in the dorsal pathway. In new-born humans this connection of the dorsal pathway is not yet
develop but it does through time.
LANGUAGE COMPREHENSION
Bottom-up processing: hearing something (phonological word detection).
Top-down processing: identify semantic relationships between the units that were perceived and integration
of meaning and grammar (syntax).
,ONTOGENY
Pathways in the healthy developing brain: in the young groups there is no to little syntactic processing and
this can be seen due to the non-existent dorsal pathway. The BA44 is not active thus it is not assisting language
comprehension. The younger groups thus use the ventral pathway more and base the language they process
on the world knowledge, instead of the syntactic knowledge they have (the mouse that killed the cat).
Fractional anisotropy (FA): reflects structural connectivity
(in the dorsal and ventral routes). There is an interaction
between the accuracy of responses to non-canonical
sentences and amount of connectivity in the dorsal
pathway.
There are two dorsal pathways: one is connecting the
posterior temporal cortex to the premotor cortex,
supporting integration of sensory and motor
representations that is used for establishing phoneme
representations and non-adjacent dependencies.
Home-sign patients late language learners: Research shows
that home-signers that started learning their first sign
language have very deviant scores on connectivity in the
dorsal pathway of the left hemisphere. It could be that home-
signers did not lateralize language efficiently. This shows a
clear effect of early deprivation of language input.
LATERALIZATION
Language is left-hemisphere dominant in most adults. Is the lateralization of language processing already
present at birth or does it appear gradually?
- Experiment (2-day old infants vs 3-month-olds): strong connectivity between the two hemispheres and
weak left-intra-hemispheric connections in 2-day olds. In 3-month-olds there are connections within the
left-hemisphere, between the posterior STG and IF regions.
,- Experiment (many age groups): Forward speech vs backward speech, Activity in the right hemisphere
dissipates over development.
- Lesions in 18 to 24-month-olds: left and right hemisphere injury equally resulted in delayed or absent
language development
- Hemispherectomy before the age of 13 resulted in permanent aphasia only in a small percentage of
children, irrespective of the hemisphere, whereas in adults, left hemispherectomy always led to
permanent aphasia and right hemispherectomy did not cause any language deficits.
However, there is contradicting evidence as some studies found no difference in lateralization between
children and adults.
Lateralization index: compares the difference between LH and
RH activation with the total activation. LIs near 0 indicate
bilateral and equal activation in the two hemispheres, whereas
positive LIs indicate left lateralization. However, because the LI
is a difference score, potentially important information may be
lost.
Experiment (children that suffered a stroke): The children with
large perinatal strokes in the left hemisphere (frontal and
temporal lobes) showed activation for sentence processing in
the right homotopic regions. Performance on language tasks
was equally good to healthy controls in fairly natural language
production and comprehension performance, when it was not
too complex.
There is bilateral representation of language very early in life, which works as a protective factor in case of
injury of the left hemisphere. When there is injury in the language areas of the left hemisphere early in life, the
homotopic regions in the right hemisphere can take over and process language just as well (if there is
appropriate input from the environment). = as an anatomical safety measure to ensure language
development.
CRITICAL PERIODS AND PLASTICITY
Brain plasticity: ability to alter brain functioning response to experience
(facilitates learning). In the case of critical periods, brain plasticity is
driven by molecules that adjust the circuit connectivity through
neuronal activity. A critical period can open through changes in the
environment as well as the brain itself through development.
There are different critical periods for different components of
language learning and processing, that open and close during different
periods of life, with different durations. The timing of the initial opening
is largely constrained by the maturation of underlying circuit. In other
words, a circuit has to be ready and have an optimal excitatory-
inhibitory balance. This is governed by specific GABA circuits that drive
plasticity, such as Parvalbumin (PV) which is a positive subtype of GABA
neurons. The PV works to initiate a plastic state in the immature brain.
Once the critical period needs to be closed, molecular breaks stabilize
connectivity, through myelinization of perineural nets (prevent synaptic
, pruning and outgrowth) or through epigenetic modifications that silence the gene programs necessary for
synaptic rewiring. These lead to the plastic state shifting into a stable state.
A critical period in itself is plastic; it can be extended or narrowed related to the amount of experience
available. Critical periods can open earlier/later than expected or critical periods that never open or close (due
to deficits).
Language acquisition involves multiple critical periods: Perceptual narrowing (synaptic pruning): when babies
are born, they are able to distinguish a plethora of sounds, not only from their native language. There seems to
be a decline in non-native perception and improvement of the native perception; 8-10 months for consonants
and 10-12 months the consolidation period happens, with under-maturational control, losing the ability to
distinguish between non-native sounds. After the consolidation period more and more entertaining experience
is needed for language acquisition.
- At 10 months, double the exposure time was needed to get favourable results in a sound discrimination
task.
- Distinguishing Hindi sounds: English speaking babies were equally good as Indian babies from 8-10
months, but not when they were 10-12 months old.
- Distinction of English sounds: Japanese speaking go through perceptual narrowing for these non-native
sounds.
- Premature infants: their perceptual narrowing occurs later than full-term infants even though their
broadcast speech experience starts earlier. Thus, certain level of maturation is required, despite the level
of input.
- International adoptees: retain stored knowledge that helps in relearning birth-language features several
years later. Retained experience of general properties of the birth language may be available.
Pharmacological and hormonal influences in critical periods: SSRIs taken by pregnant mothers influence the
opening of critical periods. There were precocious critical periods for sound discrimination in the foetuses of
women taking SSRIs, thus, accelerated timing of perceptual attunement. But, in depressed women that did not
take SSRIs, the foetuses shoed delayed timing of perceptual attunement, at 10 months the infants were still
able to discriminate between non-native sounds (maybe due to flat intonation of depressed mother’s speech
and less input).
Early deprivation: at what age is it appropriate to introduce cochlear implants in deaf children? There might be
a limited time window for use of cochlear implants. The critical period for perceptual attunement to native
language sounds closes at 10-12 months. If the critical period opening is delayed due to lack of input that
means that there’s more time available and cochlear implants can be introduced up to the age of 3.5 years.
There’s the controversial issue of whether a deaf infant should be presented with sign language before they
receive a cochlear implant. This could interfere with the auditory system and processing spoken language, as it
would be taken over by the visual system (however this is too simplistic).
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