Single-Unit Recording and Action (1) Flashcards
What is single-unit recording?
- recording from single neurons using one or more microelectrodes
What are the safety concerns with using single-unit recording on humans?
- highly invasive: requires direct access to brain (trauma to scalp and skull, infection risk, and brain tissue damage)
When would single-unit recording be used on humans?
- if already entering brain for medical reasons
- if there is potential to address severe disability
What is the argument in favor of animal experiments?
- it is acceptable if:
1. suffering is minimized in all experiments
2. human benefits are gained which could not be obtained otherwise
What is the argument against animal experiments?
- 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
How is single-unit recording used to benefit quadriplegics?
- 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
What types of recordings are there?
- intracellular: voltage clamp, patch clamp
- extracellular: single-unit recording, multi-electrode recording, field potentials
- in vivo (or in vitro)
- awake (or anaesthetized)
How is the spatial and temporal resolution?
- very good!
- individual action potentials in individual neurons
- can’t get better than this
What are the challenges of single-unit recording?
- 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?
What type of electrodes and set up is possible?
- 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
What happens to data after it enters the electrode?
- amplify/filter
- analogue-to-digital conversion
- data storage
- visualized as spike clustering
What are electrode tips made of?
- platinum/tungsten
- quartz glass (longer)
What does an implanted tetrode actually record?
- 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
What can the layout of multi-electrode recording look like?
- array of 8 electrodes in a row at different depths
- spread out horizontally and vertically
What is used to identify “units”? Why is this needed?
- 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
What is depicted on a raster plot w/ histogram?
- 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
What experiment was conducted to examine working memory and DLPFC?
- 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
What was found while examining working memory and DLPFC?
- 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
What did responses of a single neuron reveal (for working memory and DLPFC experiment)?
- 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
What is a spatial tuning curve?
- representation of when a neuron fires by examining all directions and firing rates
What happens if you affect a neuron with a spatial tuning curve by lesion?
- the monkey will no longer be able to remember when the cue is at the bottom
What is cognitive map theory? What cells are needed for this?
- memory for spatial relationships in environment
- map for a specific neuron
- place cells: fire when animal is in a particular location
How was cognitive map theory studied?
- camera facing down to keep track of where animal is
- match up neuron firing and actual location of animal
How was single-unit recording used to examine dopamine?
- record from neuron that releases dopamine
When did dopamine neurons fire?
- 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
What does this tell us about dopamine neurons?
- 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)
