Linking sense and behaviour to memory Flashcards
Why is the world like a ‘code’?
Lots of sensory information (light, chemicals, pressures) that the brain has to turn into a NEURAL ACTIVITY, DECODE and turn into a MEANINGFUL ACTION (eg. approach, avoid)
What is the ‘drift-diffusion model’ used to measure?
The subjective experience of a person or animal through their pattern of choices and response times
Describe the ‘drift-diffusion’ model
- Have evidence bounds
- Start at a middle point and go up or down, based upon the sensory information at a point in time
- Eventually reach threshold of ‘match’ or ‘miss match’ - depending on how much evidence accumulated
Why is there a distribution of reaction times between different people?
Evidence accumulation is NOISY
What is a typical experiment for behaviour of the drift-diffusion model?
Animal decides which way the dots on the screen are moving
After some time - animal flicks eyes in the direction that the dots are moving
What is the distribution of reaction times?
How is this recovered?
What does this show?
Skewed to the right (non-Gaussian)
Recovered when scale the X-axis according to the RECIPROCAL of the reaction time (1/reaction time)
What is the underlying variable of the distribution of reaction times that has a gaussian distribution?
The RATE of evidence ACCUMULATION
What does the equation t=A/r relate to? How?
Height of the decision bound: A
Width (reaction time):t
Rate (slope of the line): r
What is reaction time inversely proportional to?
The RATE of evidence ACCUMULATION
Describe the experiment where making drosophila make a decision
When is this decision easy? Hard?
- 2 chambers with 2 different odours
- Chose between bad odour and lower concentration of the bad odour
- At the interface where the two odour meet - drosophila must make a decision (decision zone) - carry on walking or turn around
Decision is easy if there is a large difference between the 2 concentrations
Decision is hard if there is a little difference between the 2 concentrations
What happens if plot the reaction of the drosophila as a frequency distribution?
Why?
Rightward skew
Easy decisions are made quicker
Hard decisions take longer to make
Describe the speed-accuracy trade-off
If have a difficult decision and want to be accurate - takes a long time
If want to make the decision quickly –> less accurate
Describe the speed-accuracy trade-off experiment in mice
- Mouse has to choose the water port based upon an odour they smelt
- Reward –> correct water port
- Depending on hoe long give the mice to choose - decide more of less accurately
What happens if plot the results of the mouse speed-accuracy trade-off experiment?
Curve that increases gradually and eventually saturates at a certain reaction time
What explains why being forced to make a decision too early would make less accurate decisions?
How?
The DRIFT-DIFFUSION model:
- Start at 0
- Can diffuse to 1 (correct decision)
- Can diffuse to -1 (incorrect decision)
- If let the mice decide on their own - almost always get it right
- But it takes time to diffuse to 1
- If cut the decision time short, curve may be below 0 as haven’t gathered enough evidence
What adjusts the trade-off between speed and accuracy?
How?
Moving the HEIGHT of the decision bounds
- If decision bounds are far away from 0 - lots of time to integrate evidence
- The closer the decision bounds are to 0, the quicker a decision will be made, however this decision may be LESS ACCURATE
When can an animal adjust their decision bound?
Based on context (eg. if a predator is coming)
- Urgency is encoded in the neurons of the brain
- Move decision bounds closer together
What happens to the decision bounds over time as the need to make a decision is more urgent?
Over time, decision bounds come closer and closer together (lines are sloped)
How does evidence accumulation appear?
In spike rate of certain neurons in the visual cortex
What is responsible to moving the eyes of a monkey left or right in a decision experiment?
What is it thought converged on this area?
The INTRAPARIETAL AREA
Sensory input from the eyes and from the visual cortex
What happens to the firing rate of the neurons when the task is easier?
What does this cause?
Firing rate increases faster
(Due to the strength of the evidence being stronger)
Spike rate increase faster –> hit the decision bound quicker
What do the recordings from the monkey intraparietal area show?
When the monkey moves its eyes to the OPPOSITE side of where the readings are taken from:
- Neuron spike rate DECREASES
- The activity of the neuron correlates with the monkey eventually decides to do (spike rate correlates with the accumulation of sensory evidence in the task)
- Peak just before the monkey makes a decision
What happens in a fly with a FoxP mutant?
Why?
Fly takes abnormally long to make a decision:
- FoxP regulates a K+ channel
- KO FoxP –> more K+ channels in the membrane of the KC
- Hyper polarisation of the membrane
- Takes longer to depolarise
- Slows down the rate of evidence accumulation
