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.