Single-unit Recording and Action (2) Flashcards
What “times” are analyses locked to?
- stimulus-locked: to see stimulus related activity
- response-locked: to see response related activity
- otherwise, difficult to see peaks
How is a singular goal obtained?
- through a specific series of motor movements
- motor control is a hierarchy
- ex. write name -> first name and last name -> individual letters -> individual lines -> specific fingers moving -> specific muscles moving
What is motor equivalence?
- movement is consistent with abstract motor plans
- upper part of motor plan is being preserved but getting translated to different motor areas
- ex. writing name with different hands, teeth or feet
What is the general motor system?
- premotor and supplementary regions
- (cerebellum and basal ganglia)
- motor cortex
- brainstem
- spinal cord
- output to muscles
What does the topography of motor and somatosensory areas look like?
- homunculus
- body mapped on brain upside down and flipped
What is cortical magnification?
- large representations for “important” areas
Where does the motor pathway decussate?
- at the medulla
What do connections from the cortex to motor neurons look like?
- cortex neurons synapse on many motor neurons and may affect many muscles
- one given cell is not responsible for one specific muscle
What was seen when recording from monkeys moving joy sticks?
- animal cued to move joy stick in particular direction
- neurons fires more depending on direction
- directional sensitivity
What is a directional tuning curve?
- graph made from direction of movement and response rate
- peak shows preferred direction
How are tuning curves used to produce population vectors?
- two cells preferred directions are plotted
- the arrows for each cell are produced in the preferred direction with magnitude indicated by length
- the population vector is produced from these two
What are the two pieces of information acquired from population vectors?
- direction: preferred direction
- length: firing rate
How is a population vector made up of?
- add up vectors for all neurons
What does a population vector represent?
- accurately represents actual movement direction
- population vector in red
- individual neuron vectors and actual direction in black
Why does data for one neuron not give us important information?
- you have nothing to compare it to
- the context is important and we don’t have it
- cannot produce population vector
How is 3D directional sensitivity measured?
- set-up: 3D space and reach towards targets
- depicted as a cube
- tuning volume is depicted as a sphere with a dip in it (this is where no activity is taking place)
- 3D individual vectors pictured on xyz graph
What does the cone represent on the 3D population vector?
- 95% directional variability cone
- 95% confident that movement direction is within this cone
How many neurons does it take to have an accurate representation of the movement direction?
- as you record from more and more neurons, the confidence cone gets narrower
- good at 150 neurons and doesn’t substantially improve from there
- will never reach no cone because there will always be noise (other stuff going on)
What is the problem with a localist representation?
- localist: each neuron has specific representation (fires strongly only for specific location)
- if we lose a neuron, we would lose the specific function of that neuron
- can no longer move in that direction
What neural representation do we see?
- distributed and spatially organized
- neuron fire most for particular direction
- surrounding neurons fire smaller amounts
What are the types of neural representations?
- distributed and arbitrary
- distributed and spatial!!
- sparse (high firing for random cells)
- localist
