neurophilosophy ashwin (01d05012) shishir (01005014) sumit (01005017) under the guidance of prof. p....
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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
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 Agraphia
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. 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
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” “Boggled Skeptics”
Emergent Generalizations Dualism
Substance 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
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.