Optogenetics (Disruptive) Technologies applied to systems neuroscience research

Question 1

What is an important aspect of systems neuroscience?

Answer 1

That it requires us to think of things at different spatial and temporal scales

Question 2

What are the different levels of description to consider in systems neuroscience?

Answer 2

Psychological level
Systems level
Microcircuit level
Neuronal level
Intracellular level
Molecular level

Question 3

What is the issue with different levels of description?

Answer 3

A single method will usually only provide information at one level of description when to understand an entire disease or drug treament we must consider many different levels

Question 4

What can behavioural scientists do?

Answer 4

Combine different methodologies

Question 5

What is a downside of Ca2+ imaging?

Answer 5

Invasive- may be best for preclinical studies

Question 6

What are the constraints that must be considered?

Answer 6

Expertise
Facilities
Time
Money
Ethics

Different methods are affected in different ways by these constraints. e.g. consider blood pressure measurement in human vs. functional MRI in an animal model.

Question 7

The extent to which constraints are insurmountable depends on what?

Answer 7

The importance of the question
(and your ability as a scientist to make your case)

It is possible to get grants and ethical approval so long as you justify the work - these are the appropriate methods to answer the question

Question 8

To do good science with ethical approval what should we aim to do?

Answer 8

Minimise cost and maximise benenfit

Question 9

What do we also need to consider to test a hypothesis?

Answer 9

What type of data we need to easily test the hypothesis

Question 10

What does the best type of research bring together?

Answer 10

In modern neuroscience, it is often the case that the best research brings multiple techniques together in a single study

Multiple approaches and techniques together

Question 11

What do we need to consider in visualising and stimulating the brain?

Answer 11

What methods are available?

What are their relative strengths / weaknesses?

How can these both affect the results and the conclusions drawn from the research

Question 12

What is MRI?

Answer 12

MRI scanners use magnetism to ‘see’ the position of hydrogen atoms in water molecules inside the body

This allows it to build up an image of the internal structures.

So MRI allows you to build up a detailed picture of brain structure that is sensitive to the differing tissue types (can differentiate between white and grey matter)

Very high spatial resolution, but this is just brain ‘structure’ not function

Question 13

How can we assess function?

Answer 13

fMRI

Question 14

What is fMRI?

Answer 14

The principle is same as MRI, but you ‘tune’ your scanner to be sensitive to something that disturbs the way the energy is absorbed and the emitted

This is blood, because blood contains haemoglobin, which contains iron and iron is paramagnetic

The scanner can be made very sensitive to the effect of the iron in the blood on the way the energy given to tissue by the radiofrequency pulse is re-emitted

When haemoglobin is carrying oxygen, it ‘hides’ the iron, so actually fMRI is really picking up on the oxygenation of blood in the tissue

Question 15

What is BOLD fMRI

Answer 15

picks up signal from blood flow in the tissue so not directly measuring neural activity

Activated brain cells can call up more (fresh, oxygenated) blood, so fMRI tells us about brain activity

Question 16

What is the contrast agent in fMRI?

Answer 16

Blood is the contrast agent

Question 17

What is PET imaging?

Answer 17

We make a contrast agent that is specifically targeted to the biological process we want to image

Get a chemical that binds to the target (e.g. oxygen, glucose, specific receptors)
Attach a radioisotope (radiation emitting molecule) to that chemical (specifically a positron emitter)

Inject this tracer (contrast agent) into the subject
Detect the emitted radiation and use a computer to work our where it is coming from (tomography)

Question 18

What is PET excellent for?

Answer 18

Look at where the tracer goes to and where it collects so it is excellent for informing on specific biological processes (fMRI very limited in this respect)

Question 19

What are two limitations of PET?

Answer 19

Spatial and temporal resolution poor compared to fMRI- limited in terms of what we can track in terms of processes

Uses radiation, so much more limited in research applications- means we muight have to avoid repeat measurement and means it cannot really be used in children

Question 20

How can we overcome the limitations of PET?

Answer 20

Use PET-fMRI
-Combine advantages of PET and MRI/fMRI

Question 21

What if we want to do molre direct recording of neurons in humans?

Answer 21

Use EEG and MEG instead

Question 22

What is EEG?

Answer 22

EEG gives indication of regional brain activity underlying electrodes

Question 23

What are strengths of EEG?

Answer 23

good temporal resolution

Signals are often separated into different frequency bands (slow waves or fast waves) - Different frequency bands appear to relate to distinct neurophysiological processes- greater insight

Question 24

What are three limitations of EEG?

Answer 24

Poor spatial resolution- detecting signal but through the scalp, the skull and even the hair

Analysis is complex and takes a lot of time!

Needs to have subject in an electrically shielded environment to minimise electrical noise- otherwise can convolute the signal

Question 25

What do we get from EEG?

Answer 25

As well as monitoring ongoing activity, EEG (like any of the techniques described) can be used to look at brain responses to a specific stimulus – and Event Related Potential (ERP)

Question 26

What is MEG?

Answer 26

Magnetoencephalography

The electrical current of large numbers of cells and white matter tracts (bundles of axons, think wires) induces a magnetic field that can be detected with a very large machine

Question 27

What is a limitation of MEG?

Answer 27

MEG signals are very small and hard to detect

Question 28

What is a strength of MEG?

Answer 28

Less interference by scalp & skull than electrical signals so can offer better spatial resolution than EEG - this can compensate for the small signals being hard to detect

Question 29

What can we use to stimulate the brain ?

Answer 29

TMS or TDCS

Question 30

What is TMS?

Answer 30

Transcranial Magnetic Stimulation

arguably less physiological which is something to consider for the aims of research

Induces electrical current in brain tissue which disrupts the ongoing activity

Used in research to ‘turn off’ parts of the brain so that their role in a cognitive function can be assessed

Question 31

What is a limitation of TMS?

Answer 31

Hard to target precisely

Question 32

What is a strength of TMS?

Answer 32

Some evidence of clinical potential (e.g. in treating depression)

Question 33

What is TDCS?

Answer 33

Transcranial Direct Current Stimulation

Pass (mild) current through the brain, between the positively charged anode and the negatively charged cathode
Can excite or inhibit underlying brain tissue, which may be useful experimentally

Question 34

What are some limitations of TDCS?

Answer 34

Arguably low cost and accessible but its true effects arent fully known yet

Early evidence for cognitive enhancement effects and possible clinical benefits, but simplicity of device may risk mis/over-use

Question 35

What are other psychophysiological measures?

Answer 35

External or internal stimuli that are of survival significance will act through the brain to trigger the sympathetic nervous system

It is probably a uniquely human phenomenon that ‘thoughts’ can also achieve these responses

Through this, it means that aspects of brain function can be inferred by measuring systemic (non-CNS) factors

Question 36

What are some non-CNS factors?

Answer 36

Skin conductance (sweating)
Heart Rate
Blood Pressure
Pupil Dilation
Muscle Tension
Body Language?

Question 37

When choosing a method, other than spatial and temporal resolution, what do we need to consider?

Answer 37

Invasive vs non-invasive method

Question 38

In research what is there a tradeoff between?

Answer 38

Trade-offs between spatial resolution, temporal resolution, invasiveness and cost.

Question 39

What are invasive methods typically be used for?

Answer 39

Animal models

These are Strictly regulated (by the Home Office in the UK)
Requires a careful justification of how likely benefits of the research for either other animals or humans outweigh the costs

Question 40

What are the three guiding principles for all research involving animals? (3Rs)

Answer 40

Replacement (can another method be used)

Refinement (can it be done in a better way that further maximises the cost:benefit equation)

Reduction (can it be done with a smaller number of animals)

Question 41

What animals are used in research in the UK?

Answer 41

Mice- 82.6%
Fish- 15%
Rats- 1.5%

Stats from: Animal Research Statistics for Great Britain, 2021

Question 42

What is possible if we use invasive methods that is not possible in humans?

Answer 42

Make direct measurements of the activity of brain cells.

Direct measurement of activity of human brain cells is possible, but only in rare circumstances
e.g. although EEG measures electrical activity of neurons the spatial resolution is poor.

Question 43

What are the different types of recording invasively?

Answer 43

There are several different methods of recording activity of brain cells

Some target single cells (intracellular recording, also termed unicellular recording)

Some record from larger numbers of cells (extracellular recording)

Question 44

What does intra vs extra -cellular refer to?

Answer 44

Whether the tip of the electrode is inside the cell itself (intra), where it is relatively insulated from the activity of surrounding cells

Question 45

Other than direct measurements, what else can we examine with invasive methods?

Answer 45

Determine connectivity between structures, flow of information

Stimulating electrodes can be inserted into one part of the brain (including into single cells) and recording electrodes inserted into another region (or single cell)

The effect of stimulating the first region (or cell) on the second can then be determined

Question 46

What is a retrograde tracer ?

Answer 46

Tracer travels backwards along axon towards cell body in region

Question 47

What is an anterograde tracer?

Answer 47

Tracer travels forward along axon towards next synapses

Question 48

What else can invasive methods allow us to do?
-Disruption

Answer 48

Disrupt connectivity between structures to determine effects upon circuit function
Measure effects on activity in downstream structures
Measure effects on behaviour

This gives us some understanding of causation in brain circuits (or behaviour), but results can still be difficult to interpret

Question 49

What else can invasive methods allow us to do?
-Lesions

Answer 49

Lesion specific structures to inform us about what function that structure performs

This gives us some understanding of function of specific structures but again results can be difficult to interpret

Might be able to lesion a structure but not specific cell types but does still give us an idea of functiojn

Question 50

What is psychopharmacology?

Answer 50

A field that investigates the effect of drugs on thoughts or behaviour

Psychoactive drugs such as these and other (illegal) compounds often have complex actions on many brain regions, acting on different types of receptor on different cell types

From a research perspective, is it often necessary to use specially designed compounds that have much more targeted (and known) actions

Question 51

What is pharmacological research methods?

Answer 51

Different drugs will act at different points in the process of neurotransmission, e.g.

Some will mimic the neurotransmitter to act on the receptor
Some will block the receptor
Some will prevent manufacture of the neurotransmitter
Some will block re-uptake
Others….

Question 52

How can pharmacological studies be developed?

Answer 52

Pharmacological manipulations can be combined with other methods:

Administer drug…..
Stimulate a region
Block the receptor thought to be involved along a hypothesisd pathway

…and see if the resulting effects on Region B, or behaviour are similar to effects of a lesion of structure A (or the pathway)