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Foundations of Language, Brain and Cognition - Lectures
Lecture 1 (Week 1) - Brain and language. Information encoding
- Psycholinguistics: cognitive science that is concerned with how a physical signal is transformed
into a neural signal. Meaning, how do we go from electro-chemical stimuli to cognition?
- Computational Theory of Mind: we should analyze the relationship between the brain (an
information encoding design) and knowledge as an analogy between hardware and software
o linguists try to uncover the software
o we (as psycholinguists) are interested in the relationship
- The Nervous System
o central nervous system – brain
o brainstem
o spinal cord
o neurons
cell body
axons
the terminal sends electrical signals
covered by myelin, that isolates and makes the signal go through faster
dendrites
receives information / electrical impulses from other neurons
neurons are the smallest component in the big computer that is the brain
they transport one type of energy
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There are different neurons in the brain, but they have more or less the same
structure. In fact, they have the same purpose: receiving and transmitting energy.
The form of the neural substance seems to correspond to the neural function.
Neurons differ in:
Dendrite density (more density → faster processing information + more
connections)
Cell body (motor neurons → larger cell bodies due to extensive energy
and resources required to manage signals for muscle coordination,
sensory neurons → specialized structures to process information)
they are fully covered by myelin by the age of 6 =>before this,
power/energy (and thereby memory) is lost
they don’t communicate through physical touch, there is a gap between the axon
terminals and the dendrites - the synaptic gap
we can manipulate it, the neural transmission can be sped up or slowed
down (by filling it through medication, drugs, coffee etc.)
we are born with more neurons than we have now, the ones we don’t use atrophy
but the number of neurons is not important, it’s the relationship between
them that counts --> the neural networks become organized with age:
the brain is born in chaos and is pre-programmed to become structured
we impose organization on chaos: as the child grows, structure will
replace the chaos/disorder. The human brain fights chaos and redundancy
(we’re biologically programmed to organize)
the brain becomes organized not only following a genetic blueprint, but
also in response to the environment
o the frontal lobe develops after birth, responding to its
environment. The neural networks will organize according to the
environment, e.g. when we learn a specific language.
Where does meaning come from?
action potential = each neuron is under a voltage (~70 mV) (= firing of
neuron)
o the rest state: polarization
o excitatory signal: depolarization
o inhibitory signals: hyperpolarization
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polarization effects accumulate, and when the threshold is surpassed,
action potential takes place
Spike: if the neuron receives a stimulus (physical energy), the energy
will trigger a chemical reaction in the cell body
o triggers an electrical signal (spike)
o this spike is all or none, the neuron can’t fire a little bit of its
power (it’s 1 or 0)
o refractory period: the amount of time it takes for an excitable
membrane to be ready for a second stimulus once it returns to its
resting state following an excitation
Problems associated with ion channel dysfunction:
epilepsy - an avalanche of firings/uncontrolled firing of neurons
dyslexia - related to malfunctions of ion channels
- the main question for cognitive neuroscience:
how does the brain go from these electrochemical operations to cognition?
In other words,
how does the brain encode and represent information?
o the brain receives stimulation (physical energy) and translates it (into something
interpretable), and subsequently interprets it.
> interpretation is a pattern of brain activity;
> cognition is complex patterns of brain activation.
we can consider the neuron as an ASCII-type device: encodes the information in
1s and 0s.
- something gradual may result in something categorical
o if there is not enough signal from other neurons, the activation does not reach the
threshold, so it will be 0. It will be nothing more than a failed initiation and is ignored.
o we can think of categorical perception in phonetics
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- fasciculus = a bundle of neurons with a common destination
o a neural pathway
- other than neurons, the brain also has glial cells
o have resting potential, but no action potential
o they provide myelin (which is important for retaining information in neurons)
o they organize growth
o they absorb dead neurons (i.e. neurons that don’t fire > not active > die, e.g. with aphasia)
o this is very important for the critical period of language acquisition: with exposure, neural
networks are organized/structured. Without exposure, neurons don’t receive enough
physical energy, they will not fire, and eventually die.
o neurons that don’t fire have to be truncated
- The structure of the brain
o the brain needs oxygen to start chemical reactions in the cell bodies of the neurons
it gets it from the blood vessels
o the convoluted shape of the brain occurs because of the density of the brain is higher than
that of the skull. There is more convolution in the left hemisphere.
o Cerebellum
is involved in the coordination of voluntary motor movement, balance and
equilibrium, and muscle tone
responsible for learning sequential actions and procedural actions (=actions we
just know how to do, we don’t break them into parts)
