Linking Senses+Behaviour to Memory

Question 1

What is the Drift Diffusion Model?

Answer 1

• Framework used to describe the decision making process regarding neuroscience in noisy/ambiguous environments

Question 2

What are the components of the drift diffusion model?

Answer 2

1. Drift rate: Rate at which evidence accumulates in favour of one decision over another
2. Threshold: How much evidence is needed to make a decision?
3. Noise : Random fluctuations in accumulation of evidence
4. reaction time: The gap in time from when the evidence starts accumulating to when the decision is made

Question 3

What is the other title for ‘Normal distribution’?

Answer 3

Gaussian distribution

Question 4

How does reaction time plot on a graph?

Answer 4

1/reaction time gives a normal distribution which implies the varying factor is rate of evidence accumulation

Question 5

What experiments can be used to test reaction time in drosophila and what were the results?

Answer 5

• Odours in two chambers one is attractive one is repellent - quick reaction time
• When the odours are more complex and more ambiguous then the decision making takes longer
• Rightward skew in reaction time

Question 6

Explain reaction time experiments in mice

Answer 6

• Mouse pokes its nose in the odour port – when it hears a buzz, it has to stop sniffing and choose a water port based on which odour it smelled.
• Reward only for going to the correct water port.
• If mouse’s odour sampling time is cut short by the buzzer it makes less accurate decisions

Question 7

How can the mouse reaction time experiments be explained by the drift diffusion model?

Answer 7

• Accumulating lots of evidence when the buzzer allows a long time , you make the right decision
• If you don’t allow enough time to reach the full decision threshold you are likely to make a mistake (not gathering enough evidence)

Question 8

When is the threshold for evidence accumulation set lower?

Answer 8

Under certain conditions where there is a priority on speed not accuracy e.g. in danger

Question 9

What is the physical implication of drift diffusion?

Answer 9

Ramping up neural activity

Question 10

Explain the physical implications of the drift diffusion model including motor command neurons in monkeys brain

Answer 10

• Motor command neurons exhibit increased activity when monkey is ab to move its eyes to the right (opposite for the left)
• Before the monkey makes a decision about which direction to move its eyes, neuron activity gradually increases (evidence accumulation)
• The rate of this ‘ramping’ depends on the strength of evidence accumulation (higher/lower drift rate)
• Neuron reaches peak activity around 70ms before decision, suggests consistent timing despite stimulus strength
• Once threshold is reached, decision is made implying evidence for the neuron ‘causing’ the decision

Question 11

How are Kenyon cells related to decision making?

Answer 11

• Kenyon cells store olfactory memories
• Fly mutant, FoxP takes abnormally long to decide between two odours
• Due to Kenyon cells being ‘leaky due to excess K+ channel expression
• This slows down their rate of evidence accumulation