what is a decision, and what’s going on in the brain? elisabeth rounis and louise whiteley the...
TRANSCRIPT
What is a decision, and what’s going on in the brain?
Elisabeth Rounis and Louise Whiteley
The mathematical brain:
What is a decision?
DecisionShort- vs
Long-termgain
ContextRisk
Information gathering
Prior Beliefs
Value
Choosing between different options….
What is involved in making decisions?
OR ?
Value
DecisionShort- vs. Long-term
gain
Context
Risk
Information gathering
Priors
Value
What is involved in making decisions?
OR
?
Short- vs. Long-term gain
DecisionShort- vs Long-term
gain
Context
Risk
Information gathering
Prior Beliefs
Value
What is involved in making decisions?You have:
What would you rather… OR ?
Context
DecisionShort- vs
Long-termgain
Context
Risk
Information gathering
Prior Beliefs
Value
What is involved in making decisions?
OR
Risk
DecisionShort- vs
Long-termgain
ContextRisk
Information gathering
Prior Beliefs
Value
What is involved in making decisions?
Healthy? Or not?
Information gathering
DecisionShort- vs
Long-termgain
Context
Risk
Information gathering
Prior Beliefs
Value
What is involved in making decisions?
Vs.
Wartime Peacetime
Prior beliefs
DecisionShort- vs
Long-termgain
Context
Risk
Information gathering
Prior Beliefs
Value
What is involved in making a decision?
A model that helps us understand decision making, predict behaviour, and know kind of signals to look for in the brain…
DecisionShort- vs
Long-termgain
ContextRisk
Information gathering
Prior Beliefs
Value
How do we link brain, behaviour, and theory?
DecisionShort- vs
Long-termgain
Context
Risk
Information gathering
Prior Beliefs
Value
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
Seeing
Understanding
‘Higher’ Order areas located in front…
… Recording directly from brain cells (‘neurons’)
Neuron 1
Neuron 2
Aver
age
activ
ity
Time
dendrites
soma
axon
synapses
Functional Imaging of whole brain regions
What is involved in a decision?
DecisionShort- vs
Long-termgain
ContextRisk
Information gathering
Prior Beliefs
Value
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)
100% coherence(all in one direction)50% coherence
The more random dots there are, the longer you need to work out the direction of the non-random onesi.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’
MTac
tivity
of n
euro
ns
preferred direction
Britten et al. 2002, Huk and Shadlen 2005
3. Tracking information, adding it up…
MT
LIP
Gold and Shadlen 2007
Video of activity in LIP
Video of activity in LIP
Video of activity in LIP
Roitman and Shadlen 2002
• 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
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?
DecisionShort- vs
Long-termgain
ContextRisk
Information gathering
Prior Beliefs
Value
Prior Knowledge
Healthy? Or not?
What if we now find out the patient smokes 50 a day?
Prior Knowledge
Prior knowledge affects perceptionWhat 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
true greyjudged grey Hansen et al. 2006
So what about prior beliefs in the brain?
MT
LIP• This is still under investigation!
• Some candidates have been suggested, including ‘action’ areas of the visual system
• Understanding prior beliefs in the brain might help us decide between models
SC
Perceptual decision making…
DecisionShort- vs
Long-termgain
Context
Risk
Information gathering
Prior Beliefs
Value
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
DecisionShort- vs
Long-termgain
Context
Risk
Information gathering
Prior Beliefs
Value
Any questions…?
A candidate brain area…
1 target
2 targets
4 targets
DimPossible Targets Select
8 targets
Accumulation of evidence over time is lower with more targets to choose from (ie more uncertainty as to probability of target location)
SC a
ctivi
ty a
t ‘D
IM’
TimeBasso and Wurtz 1998
Let’s ‘dim’ the lights…
A candidate brain area…
Accumulation of evidence over time is lower with more targets to choose from (ie more uncertainty as to probability of target location)
SC a
ctivi
ty a
t ‘D
IM’
TimeBasso and Wurtz 1998
Let’s ‘dim’ the lights…
MT
LIP
SC