Transcript Seminar Slides

Neurophilosophy
Ashwin (01d05012)
Shishir (01005014)
Sumit (01005017)
Under the guidance of
Prof. P. Bhattacharya
Starters
 “Neuroscience is science and in
pushing back the bounds of darkness
it is … teaching us … ourselves ... In a
straight forward sense we are
discovering what we are and how to
make sense of ourselves. This is as
much a part of anyone’s philosophical
aspirations as any quest there is.”
- P.C.
Churchland
Motivation
 What is consciousness ?
 Is anything special about the
subjective point of view ?
 What are mental states ?
 How does the mind-brain work ?
 Are we the only ones who can think ?
 What is enlightenment ?
 Do the above
questions have
answers in terms of
physiological
processes in the
brain?
 Bridging the gap
 Cognitive studies
 Psychological
experiments
 Functioning of neuron
assemblies
Philosophical questions
Psychological studies
Neurological explanation
Scope
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Evidence for the “mind-brain”
Overview of neurological theory
Arguments for a unified theory
Possibility of a unified theory
Reductive approach
Think for yourself!
Evidence
 Higher functions :
 What functions does the brain perform
 Which parts perform what functions
 Trying to connect neuropsychology,
neural mapping hypotheses and
neurophysiology
Early work
 Phrenology : Gall (1758-1828)
 That the brain is made up of distinct
faculties with different physical locations.
 Died off as a science and became more
of a party exhibit.
 Lesion studies:
 Interesting case of Phineas Gage, 1848,
Vermont
 “If A is the lesioned area and the patient
can no longer do Y, is A the centre for
Y?”
 Dejerine’s patient: Alexia without
Split brain studies
 Disconnection effect : the confused cat
 Implications for unity of self and control
 “What would happen to me if my brain were
dissected?”
 What do commisurotomized patients have “two”
of?
 How much connectedness and integration
are required for unity of self?
 Appearances are deceptive : What then do
we take as given/ certain ?
 Objective: Create an edifice of basic
knowledge based solely on the observed
 Can the mind contain a faithful picture of
reality? Work of Kant
 Hence the need for psychological
investigation as an appropriate means.
 Logical empiricism  Reduction 
Implications for a theory of the mind.
How Does Brain Work
 Understanding fundamental elements of
nervous system : Neurons.
 Limitations of neurons.
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Number of neurons
Number of connections
Time course of neuronal events
Silicon at 10-9 vs. neurons at 10-3
 Neurons are similar in all nervous systems.
 Evolution is the reason for it.
 What differs is their connections and
orchestration.
The Biological Neuron
Human brain is made of nerve cells called
neurons
 Sensory neurons
 Motor neurons
 Interneurons
Neurons differ from other cells in body
 Dendrites and Axons.
 Communication via electrochemical
process
 Contains specialized structures (eg.
Synapses) and chemicals (eg.
neurotransmitters)
Synapses and Neurotransmitters
 Synapse - point where the axon of one
neuron connects to a dendrite of another
 Electrical synapse - two cells touch and are
connected by tiny holes, which lets the nerve
impulse pass directly from one neuron to the
other
 Chemical synapse - two cells do not touch and
the nerve impulse needs particular molecules to
bridge the gap between them
 Neurotransmitters are chemical molecules
that “ferry” nerve impulses across the
synapse from one neuron to the next
A Pictorial Representation
Message Propagation in
neurons
 The Resting Potential
 An electrical charge across the plasma
membrane, with the interior of the cell
negative with respect to the exterior.
 -70mv in neuron
 The sodium/potassium ATPase : K+ in /
Na+ out
 Loss of +ve charge of cell
 Some potassium channels in the plasma
membrane are "leaky" allowing a slow
facilitated diffusion of K+ out of the cell
(red arrow).
Action Potential
 Depolarization (due to mechanical stimuli
eg.sound waves , stretching) reaches
threshold
 Voltage-gated sodium channels open
 7000 Na+ rush into the cell
 sudden depolarization opens up more of
sodium channels in adjacent portion of
membrane.
 This is action potential or nerve impulse
The refractory period
 Once the neuron is depolarized it is in
refractory period
 Impulse is retriggered only when
neuron comes back to resting potential
 Repolarization is first established by
the facilitated diffusion of potassium
ions out of the cell
 The action potential is all-or-none
 strong stimuli produce no stronger action
potentials than weak ones
 the strength of the stimulus is encoded in
the frequency of the action potentials that it
generates
Integration of signals figure
Role of Axon Hillock
 Region where the axon emerges from
the cell body.
 Evaluates the total picture of EPSPs
and IPSPs created in the dendrites
and cell body.
 Action potential is generated here
 Net sum of depolarizing signals
exceeds the threshold  action
potential generated
Theories of Brain Function
 We know structure of nervous
system but what about how it
functions?
 Advertised theories are metaphors
in search of genuine theoretical
articulation
 Holographic theory by Van Heerden
 Theory that links brain to a computer
 Crick said – “realize what the
problem is before trying to solve it”
Tensor Network Theory
 Effort to explain how brain functions
for sensorimotor control
 Tensor : generalized mathematical
function to transform vectors from
one reference frame to other
 Models cerebellum as a tensor that
transforms input phase space to
output phase space
A Cartoon Story
 Robot with
 forearm
 back arm
 two eyes.
 It looks at an apple.
 Coordinate of apple represented as a pair of
angles
 Convert this to co-ordinates of his forearm
and back arm movement
 Tensor used as a converter between two
phase spaces
Reduction
 Relation between reduced theory TR and
another more basic theory TB
s.t.
TR can be derived logically from TB and
some
extra conditions
 Phenomena reduction : PR → PB is a
derivative of a more basic claim : TR → TB
 Meaning of “reducibility of mental states to
brain states”
Advantages of Reduction
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Explanatory unification
Co-evolution
Ontological simplification
Correctness
In search of the right approach
Mental states == Brain states ?
 No Unified Theory
 Can there ever be one?
 “ … some psychological phenomena are
forever beyond reductive research of
neuroscience …”
- P. C. Churchland
 Arguments
 Assumptions
 Spectrum
Arguments for Irreducibility
Irreducibility Arguments
“Principled Skeptics”
Emergent Generalizations
Substance
“Boggled Skeptics”
Dualism
Property
“Boggled Skeptics “
 The human brain is more complicated
than it is smart
 Provide no concrete reason
 Hard to support or counter
Substance Dualism
 Mind vs. Brain – Physical vs. Non –
Physical
 Mental States – Not states of brain
 Mind substance
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Responsible for higher functions
Independent from brain substance
Not spatially extended
Interacts with brain substance
 Inherent reducibility
 Evidence
 Erstwhile machines simple
 Unimaginable complexity
 Problems with substance dualism
 Interaction between radically different
substances
 Independence of higher functions –
effects of drugs
 Evolutionary problems – GOD ?
 Split brain studies
 Older school of thought
So is the red you see same as that
seen by everyone else?
Property Dualism
 Subjective experience
 Major standing refutation of reductionism
 Produced by brain but character and quality uniquely
and irreducibly mental
 Emergent w.r.t. physical brain
 Emergence
 If a property of one theory has powers that are not
equaled or comprehended by any property in the
second, more basic theory, then the property is
considered to be emergent w.r.t. the second theory.
 But emergence needs to be proved independent of
knowledge
Nagel’s Argument
 “Having a Point of View”
 Irreducibility - character of introspective
access
 The qualia of my sensations are knowable to me
by introspection.
 The properties of my brain states are not
knowable to me by introspection.
 The qualia of my sensations ≠ the properties of
my brain
 Loop holes
 Dependent on information about brain
 Intentional fallacies
Jackson’s Argument
 Experiment
 Mary knows everything there is to know about
brain states and their properties
 It is not the case that Mary knows everything
there is to know about sensations and their
properties
 Therefore, sensations and their properties ≠
brain states and their properties
 Loop holes
 “Knows about”
 “Knows everything”
Intentionality and Intertheoretic
Reduction
 Representational nature of thought
 Intension – aboutness
 Popper and World of Intelligibilia
 Concept of 3 worlds
 Problem – computers
 Intentional states in robotics
 Searle’s Chinese Room
Conclusion
 Strong case for cooperation between
different theories
 Neurological theory has a lot more to
explain
 Our belief : “Emergence of creativity”
remains the final frontier.
“ We can see only a short distance
ahead, but we can see that much
remains to be done”
-- Alan Turing
Bibliography
 Churchland, P.C. (1986).
Neurophilosophy. MIT Press,
Cambridge, London, England.
 Churchland, Paul M. (1984).
Reducion, qualia and the direct
inrospection of brain states. Journal
of Philosophy 82:8-28
 Russel, S. J., and Norvig P. (1995).
Artificial Intelligence. Prentice Hall,
New Jersey.