Single-Unit Recording and Action (1)

Question 1

What is single-unit recording?

Answer 1

• recording from single neurons using one or more microelectrodes

Question 2

What are the safety concerns with using single-unit recording on humans?

Answer 2

• highly invasive: requires direct access to brain (trauma to scalp and skull, infection risk, and brain tissue damage)

Question 3

When would single-unit recording be used on humans?

Answer 3

• if already entering brain for medical reasons

- if there is potential to address severe disability

Question 4

What is the argument in favor of animal experiments?

Answer 4

• it is acceptable if:
  1. suffering is minimized in all experiments
  2. human benefits are gained which could not be obtained otherwise

Question 5

What is the argument against animal experiments?

Answer 5

• it is always unacceptable because:
  1. it causes suffering
  2. benefits to humans are not proven
  3. human benefits could be produced in other ways

Question 6

How is single-unit recording used to benefit quadriplegics?

Answer 6

• insert microelectrode arrays to left motor cortex (these detect neuron signals)
• neuron signals pass to connectors attached to the skull
• amplified signals are fed to a brain-machine interface which interprets them and passes on to arm
• interface operates robotic arm

Question 7

What types of recordings are there?

Answer 7

• intracellular: voltage clamp, patch clamp
• extracellular: single-unit recording, multi-electrode recording, field potentials
• in vivo (or in vitro)
• awake (or anaesthetized)

Question 8

How is the spatial and temporal resolution?

Answer 8

• very good!
• individual action potentials in individual neurons
• can’t get better than this

Question 9

What are the challenges of single-unit recording?

Answer 9

• How to find the “right” neurons
• How does this neuron relate to the other 100 billion (what is the rest of the brain doing)
• Do unexpected results mean that you are wrong or recording from the wrong neurons?

Question 10

What type of electrodes and set up is possible?

Answer 10

• single electrode, 4 electrodes (tetrode) or multiple, or array
• electrode can be connected to animal, feed up through a commutator that rotates
• this allows animal to walk around

Question 11

What happens to data after it enters the electrode?

Answer 11

• amplify/filter
• analogue-to-digital conversion
• data storage
• visualized as spike clustering

Question 12

What are electrode tips made of?

Answer 12

• platinum/tungsten

- quartz glass (longer)

Question 13

What does an implanted tetrode actually record?

Answer 13

• tetrode will record from multiple neurons that are physically near to it
• similarly, the signal of one neuron is likely detected by more than one electrode

Question 14

What can the layout of multi-electrode recording look like?

Answer 14

• array of 8 electrodes in a row at different depths

- spread out horizontally and vertically

Question 15

What is used to identify “units”? Why is this needed?

Answer 15

• methods such as clustering are using to identify distinct units (hopefully individual neurons)
• because multiple neurons recorded by electrode and single neuron may be recorded by multiple electrodes

Question 16

What is depicted on a raster plot w/ histogram?

Answer 16

• data from a single unit over many trials
• indicates when conditioned stimulus is presented and when response occurred
• trials are lined up on some time point

Question 17

What experiment was conducted to examine working memory and DLPFC?

Answer 17

• oculomotor delayed response task with monkeys
• monkey stares at fixation point
• a cue appears
• the cue disappears, the fixation point disappears and then the monkey must move it’s eyes to the cue

Question 18

What was found while examining working memory and DLPFC?

Answer 18

• firing of some neurons at cue
• firing of some neurons during delay
• firing of some neurons during action
• indicates the DLPFC maintains information and working memory

Question 19

What did responses of a single neuron reveal (for working memory and DLPFC experiment)?

Answer 19

• individual rastors with three lines each that indicate: cue, cue leaves and response
• this neuron fires during the delay period but only when the cue is at the bottom position

Question 20

What is a spatial tuning curve?

Answer 20

• representation of when a neuron fires by examining all directions and firing rates

Question 21

What happens if you affect a neuron with a spatial tuning curve by lesion?

Answer 21

• the monkey will no longer be able to remember when the cue is at the bottom

Question 22

What is cognitive map theory? What cells are needed for this?

Answer 22

• memory for spatial relationships in environment
• map for a specific neuron
• place cells: fire when animal is in a particular location

Question 23

How was cognitive map theory studied?

Answer 23

• camera facing down to keep track of where animal is

- match up neuron firing and actual location of animal

Question 24

How was single-unit recording used to examine dopamine?

Answer 24

• record from neuron that releases dopamine

Question 25

When did dopamine neurons fire?

Answer 25

• if animal learns something new and you give it a reward: neurons fire
• if sound a beep and give reward, then sound a beep: neurons fire
• ## if sound a beep and no reward: neurons fire below threshold

Question 26

What does this tell us about dopamine neurons?

Answer 26

• they signal to tell the animal when expectations are violated (good or bad)
• record reward prediction error, not reward itself
• often called reinforcement learning (used with AI)