What is a decision, and what’s going on in the brain? Elisabeth Rounis and Louise Whiteley The mathematical brain:

What is a decision? Decision Short- vs Long-term gain Context Risk Information gathering Prior Beliefs Value Choosing between different options….

What is involved in making decisions? OR?

Value Decision Short- vs. Long-term gain Context Risk Information gathering Priors Value

What is involved in making decisions? OR ?

Short- vs. Long-term gain Decision Short- 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 Decision Short- vs Long-term gain Context Risk Information gathering Prior Beliefs Value

What is involved in making decisions? OR

Risk Decision Short- vs Long-term gain Context Risk Information gathering Prior Beliefs Value

What is involved in making decisions? Healthy? Or not?

Information gathering Decision Short- vs Long-term gain Context Risk Information gathering Prior Beliefs Value

What is involved in making decisions? Vs. WartimePeacetime

Prior beliefs Decision Short- vs Long-term gain 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… Decision Short- vs Long-term gain Context Risk Information gathering Prior Beliefs Value

How do we link brain, behaviour, and theory? Decision Short- vs Long-term gain 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 Average activity Time dendrites soma axon synapses

Functional Imaging of whole brain regions

What is involved in a decision? Decision Short- vs Long-term gain Context Risk 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 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… MT LIP Gold and Shadlen 2007

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? Decision Short- vs Long-term gain Context Risk 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 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 true grey judged 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… Decision Short- vs Long-term gain 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 Decision Short- vs Long-term gain Context Risk Information gathering Prior Beliefs Value

Any questions…?

A candidate brain area… 1 target 2 targets 4 targets Dim Possible 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 activity at ‘DIM’ Time Basso 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 activity at ‘DIM’ Time Basso and Wurtz 1998 Let’s ‘dim’ the lights… MT LIP SC