Lecture 15 - linking senses and behaviour to memory

Question 1

the drift-diffusion model

Answer 1

• as you get evidence going one way or another way, imaginary marker goes up/ down
• then execute the motor output

Question 2

distribution of reaction times in non-Gaussain (skewed right)

Answer 2

• how long it takes for a human to react to dots and move gaze one way to another
• Gaussian distribution is recovered if you scale the x-axis according to reciprocal (1/X) of reaction time

Question 3

what is the Gaussian distribution a rate of?

Answer 3

evidence accumulation

Question 4

reaction times in Drosophila (easy task vs hard task)

Answer 4

• easy task is odour vs low conc odour - they chose it quickly
• hard task is odour vs 0.9 concentration (simialr concentrations) - take longer to decide
• has same right-hand skew

Question 5

speed-accuracy trade off (time for mouse to sniff odour)

Answer 5

• put mouse in time pressure to choose odour for reward
• longer the mouse has to sniff the odour, the more accurate the decision it makes
• less accurate with less time

Question 6

what does drift-diffusion explain?

Answer 6

• explains why being forced to decided too early would make decisions less accurate
• not enough time to accumulate input and choose correct decision bound

Question 7

moving the decision bound

Answer 7

• can move decision bound to make trade off yourself e.g. choosing speed over accuracy
• lowering decision bound - only some evidence used but faster decicison
• can modify over course of task, decision bounds can be flexible

Question 8

why record from the monkey visual cortex for evidence accumulation?

Answer 8

because it is thought to be where decision is made

Question 9

what is LIP?

Answer 9

-lateral intraparietal area
- increases when shown moving dots on screen

Question 10

what does strongest sensory input result in?

Answer 10

LIP activity changes faster

Question 11

what model does evidence accumulation match with?

Answer 11

drift-diffusion model

Question 12

where does evidence accumulation appear in for drosophila?

Answer 12

appears in dendritic integration in drosophila kenyon cells

Question 13

what i different for drosophila in spike rate?

Answer 13

fruit fly accumulator not spike rate but sub-threshold membrane depolarisation for key neuron

Question 14

what is the mutation in drosophila for them to take longer in deciding?

Answer 14

transcription factor FoxP (conserved in human for motor patterning and language)

Question 15

FoxP mutant Kenyon cells

Answer 15

• have excess K+ channel expression, making them ‘leaky’. This slows down evidence accumulation (depoalrisation up to spike threshold)