what is a decision, and what’s going on in the brain? elisabeth rounis and louise whiteley the...

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