-
What is MRI
- Magnetic Resonance Imaging
- Uses magnetic fields, and thew reflection of radio waves to produce a picture of internal workings
- Maps out the diffusion of molecules, mainly water
-
What is VBM?
- Voxel-based morphometry
- The brain is scanned and its volume is mapped
- This is then compared to a template which 'smooths out differences'
- This is then used to create an image using voxels, which represent the average volume of that cell and its neighbours
- Used by Woollett & Maguire (2011) who found that the back part of the posterior hippocampus was on average larger in the taxi drivers compared to control subjects while the anterior hippocampus was smaller
-
What is DTI?
- Diffusion tensor imaging
- Like MRI but measures the restricted movement of molecules in tissues
- Use multiple scans to create voxels that differ on movement, speed and how much stuff moves
-
What are the pros and cons of VBM and DTI?
- Automated means of revealing the relationship between variations in regional brain size /white matter pathways and cognition/behaviour
- BUT doesn't shed any light into the link between brain and behaviour, or why any increases that are observed are happening (e.g, are there more neural connections now?)
-
What is tract tracing?
- Inject a solution (depending on what type of tracing you're doing) into an axon, or area around
- Follow the solution, to see how the diffusion and connectivity in that area use
- For instance, in autoradiographic tract tracing you follow the radioactive signature
-
What is Immunohistochemistry?
- Antibodies are extracted by infecting rabbits, or by culturing cells extracted from the immune system of mice
- These are specific to neurochemicals being produced in the brain
- Bath slices of the brain these antibodies are specific to, and see where they bind
- Use fluorescent markers to tell where the binding has occurred, and thus where the neurochemicals are being produced
- Mostly used on animals, but some donors now donate to a 'brain bank' allowing human testing
-
Why is it harder to see white matter than grey matter?
- It is surrounded by myelin fat, which is opaque
- Up until recently we had to cut this away to see structures
-
Why do we no longer have to slice brains up to see them?
- We can now make myelin transparent!
- A mesh of monomers is created to replace the opaque phospholipid bilayer
- A positive electrical field is generated around the cells, pulling negatively charged tissue molecules out, through active transport
- Chung et al, 2013
-
What is the Allen brain atlas?
Project aimed at creating gene expression maps for the brain of mice and humans
-
What are the advantages of tract tracing and immunohistochemistry?
- Tract tracing allows specification of which cells which connect brain regions
- Immunohistochemistry allows different types of nerve cells to be distinguished, even if they look the same
- Combined tract tracing and immunohistochemistry allows circuit descriptions of the brain
- Immunohistochemistry can also be used to identify whether cells are healthy, or not
-
What are the disadvantages of tract tracing and immunohistochemistry?
- Both tract tracing and immunohistochemistry require fixation of the brain, so cannot be done in live animals or humans
- Not all neurochemicals can be studied – it depends if you can raise antibodies
- Allows only a single snapshot of the brain, so it is difficult to study dynamical processes such as memory or perception
-
How does human neuropsychology usually work?
- Compare a patient with brain damage (case study), or group of patients (group study), to healthy or control brain damaged patients, on psychological tests
- Use the results to determine if damage to a particular region is needed for a that task
- Make inferences about the role of structures or pathways
-
What are the advantages of neuropsychology?
- Helps identify which brain regions are necessary
- Allows insight into the human brain – functions like language and be studied
- Helps understand what might be the pathology in diseases processes such as Alzhiemers or mental health problems
- Not constrained by the lab or apparatus used–(e.g. you can study whole body motion)
-
What are the types of genetic modification?
- Deletions: lead to large scale neural changes and sometimes compensation, often fatal
- Knock-downs: gene expression is reduced
- Knock-outs: gene only silenced by particular chemicals, so only certain circuits are affected
- Knock-ins: new genes introduced
-
What are the disadvantages of neuropsychology?
- Lesions are never selective
- Compensation can occur over time. The dynamics of recovery can be complex.
- You cannot study Brain dynamics, Global brain involvement, Interactions between regions (not easily at least) or processes such as memory encoding
-
What is optogenetics?
- Control of nervous activity with light.
- Rhodopsin is light-sensitive, so uses this to trigger action potentials and cellular activity.
-
What are animal lesions, and what are there advantages?
- Precisely cut out parts of the brain thought to be associated with specific functioning. Watch what happens and make inferences from behaviour and activation
- Use of animals allows repeatable controlled experiments
- Allows precise lesions of particular areas, even particular types of nerve cells,
- Allows reversible lesions, at specified time points
- Helps identify which brain regions are necessary
-
What are the disadvantages of animal lesions?
- Compensation may occur, even for transient lesions
- It is difficult to determine whether nerve cells contribute directly to perceptions, or are instead connected to those that do
- You cannot ask an animal what is seeing, feeling or thinking
-
What does tCDS do?
- Low current delivered to area by small electrodes on skull.
- Alleged to improve normal cognitive ability, though meta-analyses find no net effect in any direction.
- SEE TCDS LAB REPORT
-
What does fMRI do, and what are its benefits?
- MRI that measures concentration of deoxyhaemoglobin; so can see regions of brain that are active during certain tasks (using a lot of oxygen)
- Radiowaves are transmitted into the person in a magnetic field, and the re-emissions are measured
- No radiation, and non-invasive.
- Good spatial resolution which remains consistent
-
What is Magnetoencephalography?
Detects the net electromagnetic activity (caused by ion currents) of neurons to can see which brain areas become excited.
-
What is Electroencephalography?
Measures electrical activity through the scalp (conduction of Action potentials)
-
What are the advantages and disadvantages of brain imaging methods?
- Brain imaging allows you to examine the dynamics of the whole brain – not just small regions
- Understand how many different brain regions interact
- Examine processes impossible with lesion approach – e.g. memory encoding
- Understand the brain regions and networks involved in processes such as language
- BUT Can not tell you if a region is necessary
- Limited in the ability to understand how individual cells, or small networks of cells contribute to cognition/behaviour
- Limited by the immobility of the equipment–e.g. can’t examine brain activity in running
-
What is calcium imaging?
- Fluorescent recorder picks up Ca2+ as it moves around neurons
- Links structure to function - can deduce synaptic pathways.
-
What is single unit recording?
- Looks at firing rates of single neurons, using electrodes to see what neuron is firing in response to stimuli.
- E.g. useful in epilepsy as can insert electrodes to find foci of the epilepsy/seizures.
-
What are Multiple-unit recordings?
- Uses spiky electrode plate.
- Can look at 50-100 neurons at a time. Then analyses them individually or together.
-
What is Microdialysis?
- First, drill a small hole in skull.
- Insert probe. Pump fluid into brain. Substances in ECF diffuse through tubing. Fluid is collected and analysed.
- Allows assessment of neurotransmitter concentration, for example, or changes in neurotransmitter concentration during certain tasks/stimuli.
|
|