Transcript The mathematical brain:

What is a decision, and what’s going on in the brain?
The mathematical brain:
Elisabeth Rounis and Louise Whiteley
What is a decision?
Choosing between different options….
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
What is involved in making decisions?
OR
?
Value
Priors
Information
gathering
Value
Short- vs.
Long-term
gain
Decision
Risk
Context
What is involved in making decisions?
OR
?
Short- vs. Long-term gain
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
What is involved in making decisions?
You have:
What would
you rather…
OR
?
Context
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
What is involved in making decisions?
OR
Risk
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Context
Risk
What is involved in making decisions?
Healthy? Or not?
Information gathering
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
What is involved in making decisions?
Vs.
Wartime
Peacetime
Prior beliefs
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
What is involved in making a decision?
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
A model that helps us understand decision making, predict behaviour, and
know kind of signals to look for in the brain…
How do we link brain, behaviour, and theory?
Prior Beliefs
Information
gathering
Value
Decision
Short- vs
Long-term
gain
Risk
Context
Do
a
behavioural
study…
Non-Dieters
Dieters
What happens in the brain?
What are the differences in
decision between dieters
and non-dieters?
Brain has specialised areas that are interconnected… but what
do these areas do?
Thinking,
planning,
moving
Feeling,
recognising
‘Higher’ Order areas
located in front…
Seeing
Understanding
… Recording directly from brain cells (‘neurons’)
dendrites
soma
axon
synapses
Average activity
Neuron 1
Neuron 2
Time
Functional Imaging of whole brain regions
What is involved in a decision?
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
Information gathering
OR
Healthy? Or not?
Information gathering
• Enigma code breakers - how much time can you
sacrifice to gather more information?
Investigating information gathering in the
brain
1. Think of a really simple decision
2. Find neurons in the brain that carry information important
for our decision
3. Find neurons in the brain that add up this information over
time
1. A really simple decision…
Which overall direction are the dots moving in?
0% coherence
(random)
50% coherence
100% coherence
(all in one direction)
The more random dots there are, the longer you need to work out the
direction of the non-random ones
i.e. the more information you need to gather…
Random dots
Random dots… Can you see a
direction?
Random dots… now they’re moving
right!
2. Neurons that care about motion…
First, we need to find an area where the brain cells (neurons) carry
information about the direction of motion…
 Area MT neurons respond more to a ‘preferred’ direction
 Stimulating neurons that prefer ‘down’ produces ‘motion hallucinations’
MT
activity of neurons
preferred direction
Britten et al. 2002, Huk and Shadlen 2005
3. Tracking information, adding it up…
LIP
MT
Gold and Shadlen 2007
Video of activity in LIP
Video of activity in LIP
Video of activity in LIP
• Note the cell is always active but more so in the presence of
the targets and as evidence accumulates
• Activity is lower if decision-maker has to choose a target that
is not in the preferred direction of the cell
Roitman and Shadlen 2002
So we’ve looked at dots, but there’s lots
of other stuff in the world too - a range
of brain areas track and gather
information
What is involved in making decisions?
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
Prior Knowledge
Healthy? Or not?
What if we now find out the patient smokes 50 a day?
Prior Knowledge
Prior
knowledge
affects
perception
What colour is a banana? YELLOW!!!
If you show people lots of bananas of different shades along the blue-yellow
spectrum and ask them which one is grey?
they pick a slightly blue one, because our expectation that they will be
yellow influences perception
judged grey
true grey
Hansen et al. 2006
So what about prior beliefs in the brain?
• This is still under
investigation!
LIP
MT
SC
• Some candidates have
been suggested,
including ‘action’ areas
of the visual system
• Understanding prior
beliefs in the brain might
help us decide between
models
Perceptual decision making…
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
Information gathering
Is Wally on the right or the left hand side of the beach?
Adding prior information
He’s definitely next to one of the boats…
Next we consider the value of different
options
Prior Beliefs
Information
gathering
Value
Short- vs
Long-term
gain
Decision
Risk
Context
Any questions…?
Let’s
‘dim’ the lights…
A candidate brain
area…
Possible
Targets
1 target
Dim
Select
Accumulation of evidence over
time is lower with more targets
to choose from (ie more
uncertainty as to probability of
target location)
4 targets
SC activity at ‘DIM’
2 targets
8 targets
Time
Basso and Wurtz 1998
A candidate brain area…
Let’s ‘dim’ the lights…
MT
SC
Accumulation of evidence over
time is lower with more targets
to choose from (ie more
uncertainty as to probability of
target location)
SC activity at ‘DIM’
LIP
Time
Basso and Wurtz 1998