Lecture 8 - neurophysiology

Question 1

What are tracers and what do they allows us to look at?

Answer 1

injectable substances that can be tagged to see what the distribution is.
they allow us to look at the wiring of the brain of either long distance circuits or local circuits

Question 2

What are the 2 types of tracers used?

Answer 2

1. anterograde tracer
2. retrograde tracer

Question 3

What does an anterograde tracer do?

Answer 3

picked up by cell bodies and look for synapse sin a target area.

Question 4

What does a retrograde tracer do?

Answer 4

the opposite to anterograde tracers.
they are picked up by synaptic terminals and transported back to the cell bodies in the target area.

Question 5

What is the purpose of clarity?

Answer 5

• allows us to remove opaque elements from neuronal tissue but leaves the neurons in tact.
• end up with a transparent bit of brain.
• can get more info on neurons and their structure.

Question 6

Name the 7 ways there is for measuring neural activity?

Answer 6

1. EGG
2. MRI
3. EMG
4. ECoG
5. LFP
6. Optical imaging
7. Neuronal recordings

Question 7

Briefly describe an EEG.

Answer 7

• electroencephalography
• putting electrodes against the surface of the head and measuring the results.

Question 8

What can an EEG be used to measure?

Answer 8

• oscillatory brain waves at various frequencies
• measurement of evoked potentials to stimulation.

Question 9

Briefly describe an ECoG.

Answer 9

• electrocorticography
• uses electrodes placed directly onto the exposed surface of the brain so more invasive but more localised than EEG.
• records electrical activity from the cerebral cortex

Question 10

What patient is an ECoG used in.

Answer 10

epilepsy patients

Question 11

Briefly describe LFP.

Answer 11

• local field potential
• electrode placed into brain
• measures the summed activity of the synapses and neurons in a specific area.
• laminar profile (surface of the brain) to see how many different layers respond to one stimulus.

Question 12

What are transients when referring to LFP?

Answer 12

the APs in the neurons around the electrode.

Question 13

What can transients when referring to LFP tell us?

Answer 13

• can use the size and shape to extract activity information on more neurons.
• can look at how they differ with different behaviour/stimuli.

Question 14

What do neuronal recordings show us?

Answer 14

• allows the recording from 10s to 100s of neurons at the same time.
• can study interactions between neurons and areas.

Question 15

What are the 3 sensory modalities for perturbing the CNS?

Answer 15

1. visual and auditory
2. somatosensory
3. mechanical somatosensory

Question 16

Describe visual and auditory sensory modality.

Answer 16

• stimulus could be flash of light/loud bang
• record the activity from the parts of the brain involved in vision/hearing via EEG
• visual/auditory evoked potential produced
• amplitude and latency measured
• integrity of pathway seen

Question 17

Describe somatosensory modality.

Answer 17

• electrical activation of axons in the nerve
• electrodes placed on the skin
• EEG recorded
• deviations recorded that are positive and negative allows to measure the amplitude and latency.
• integrity of pathway tested.

Question 18

What is cortical mapping?

Answer 18

• used to see pathways directly in the brain.
• non-invasive transcranial magnetic stimulation
• not very localised but localised enough to activate different groups of muscle

Question 19

Describe optogenetics.

Answer 19

• neurons in the brain don’t respond to light.
• viral vector (coupled with a gene-encoding opsin) used to transfect neurons inside the brain to express a light sensitive ion channel.
• light shining can then hyperpolarise/depolarise a cell.