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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
