5. Research Methods Flashcards
golgi stain
golgi stain is taken up by few neurons
Shows outside neuronal structure in great detail
Nissl stain
provides gross indication of brain structure by selectively staining groups of neural cell (low magnification)
individual neural cell bodies can be distinguished a high resolution
what are the comparisons between the nissl and golgi stain?
- Golgi stain shows shape and reach of neurons.
* Nissle stain shows number of neurons in each layer.
what different layers of the neicortex do nissl and golgi stains reveal?
- molecular layer
- External granular layer
- external pyramidal layer
- internal granular layer
- internal pyramid layer
- multiform layer
electron microscope
- Preparation of tissue slices with electron-absorbing substance
- Neuronal structure captured in great detail.
what are contrast x eays?
used for visualising the living brain. they are an adaptation of standard X-ray technique
how do contrast x-rays work?
- Inject radiopaque substance into structure of interest
- Radiopaque substance absorbs X-rays
- Result: increased contrast with neighbouring tissue
- Specific technique: Angiography
what do Computed (axial) Tomography do?
- CT scan provides 3D view of brain structure
* Image not sharp
how do CAT work?
- X-ray gun & X-ray detector rotate appositionally at about 8 different levels of the brain
- Image constructed from combined scans
- Figure shows CT scan of one level
- Each pixel (picture element) results from complex mathematical computation of associated brain region viewed from different angles
- Spatial resolution high enough to observe even small changes (e.g., shrinkage of a gyrus)
Where are CATs used?
Used in a number of disorders (e.g. Alzheimer’s, dyslexia)
Magnetic Resonance Imaging
MRI has greater contrast resolution than CT; no exposure to X-rays
• Provides 2D and 3D images
• Resolution superior: neural structures vary in hydrogen atom density
• Reveals very small changes, such as loss of myelin around groups of axons
How do MIRs work?
Measures waves emitted by hydrogen atoms when placed in magnetic field
Provides 2D and 3D images
What do Positron Emission tomographys do?
Highlights active brain regions (rather than showing all)
• Brain can be mapped during different states (attention, movement, tasks)
• Can identify also abnormally functioning regions
how do the Positron Emission tomographys work?
- Injection of radioisotopes (e.g. , 2-deoxyglucose): differential uptake
- 2-DG (type of radioactive glucose) taken up but cannot be metabolised
- Increased metabolic activity revealed through accumulated radio-activity
What do Functional MRI (fMRI) do?
Can detect oxygen consumption in active brain regions
• BOLD signal (blood-oxygen-level-dependent signal)
how do fMRIs work?
- Improvement on MRI in terms of speed (temporal resolution)
* Uses rapidly oscillating magnetic field gradients & more powerful computational techniques
What is the benefits between fMRI and PET?
- No substances injected
- One image provides structural and functional information
- Better spatial resolution
- Real time measurements; can measure many times from same person
what are the difficulties with the fMRI and PET
- Noise
* Disentangling various cognitive processes
What does Transcranial Magnetic Stimulation do?
Stimulates the living brain
• NOT a measure of neural activity
• Provides an experimental probe to alter neural activity
how do Transcranial Magnetic Stimulations work?
TMS applies a brief, strong magnetic field that alters neural activity
• Can either activate or “deactivate” brain structures
• Observe changes in behavior in consequence to manipulation
what does Electroencephalography do?
records physiological signals.
• EEG represents sum of all electrical activity: does not reveal underlying
neural activity
• EEG wave forms associated with different states of consciousness
EEG signal
difference as a function of time in electrical potential between two scalp electrodes
what is seen in epileptic seizures according to the EEG?
synchronised depolarisation of neurons.
What does Event-related potentials (EPRs) record?
physiological signals.
They reveal characteristic peaks (with differing latencies and amplitudes)