Week 5 - topic 2 Flashcards
Methods of recording action potentials and post-synaptic potentials
These electrical events can be recorded:
- Recording with Microelectrodes
- Recording with Macroelectrodes (EEG)
- Magnetoencephalography (MEG)
Recording with microelectrodes
- Single Unit Recording: Recording of the electrical activity of a single neuron
- Microelectrodes are made of very thin wires and have a very fine tip that can be used for single unit recording.
Recording with macroelectrodes
- record the summed electrical activity of many neurons.
- EEG: an electrical brain potential recorded by placing electrodes on the scalp
Why use EEG’s?
- Non-invasive, “on-line” recording of neural activity in real time
- Clinically valuable - can be used to diagnose epilepsy and seizure disorder, detect abnormal brain states and classify sleep stages
Advantage = Excellent temporal resolution Disadvantage = Poor spatial resolution
Magnetoencephalography (MEG)
A procedure that detects groups of synchronously activated neurons by means of the magnetic field induced by their electrical activity
- > action potentials travelling down axons etc. produce magnetic fields
- > MEG is performed with devices that contain an array of several SQUIDS that are placed in a particular way, such that a computer can determine the source of specific brain signals.
Clinical applications of magnetoencephalography (MEG)
Clinical applications = finding the source of seizures so that they can be removed surgically
Record neural activity from various cognitive tasks
Funcional imaging
- When the neural activity in one part of the brain increases, so does metabolic activity in that region
- The metabolic activity of specific brain regions can be measured non-invasively in living animals (and humans) via functional imaging.
- Functional imaging = computerised method of detecting metabolic or chemical changes within the brain,
- > Positron Emission Tomography (PET)
- > functional MRI (fMRI)
Positron emission tomography
Positron emission tomography (PET) uses a radioactive tracer to localise activity in the brain. Thus, PET studies the function of the human brain
- poor spatial and temporal resolution
Steps of a positron emission tomography
- The person is injected with radioactive tracer that is specifically created in a lab fit for purpose (e.g. 2-DG - a sugar). The tracer dose is harmless.
- The person is then placed into a machine that is similar to a CT scanner.
- When the radioactive molecules of 2-DG decay, they emit subatomic particles called positrons.
- The positrons meet nearby electrons and they destroy each other. This leads to the emission of gamma rays, which travel in opposite directions.
- Sensors around the head pick up the gamma rays.
- This information is used to produce images of slices of the brain that show variations in activity
functional Magnetic Resonance Imaging
fMRI is a functional imaging method that permits the measurement of regional metabolisim in the brain by detecting changes in blood oxygen level
fMRI has excellent spatial resolution - we know exactly where activity in the brain is occuring. However, one limitation of fMRI is that it has poor temporal resolution. It takes a while for blood to travel to different parts of the brain, so you aren’t able to tell exactly when changes in neural activity are occurring
How functional Magnetic Resonance Imaging works
- Modifications are made to MRI machines to measure neural activity, by looking at blood flow and oxygen levels in the brain.
- > Blood flows to the brain.
- > Cells in the brain get oxygen via red blood cells.
- > More energy needed by the brain = more oxygen use.
- For fMRI, a large, very strong magnet is placed around participants head that measures changes in magnetic field strength with different concentrations of oxygenated and deoxygenated blood.
- Measured differences in concentration are called the BOLD Response (Blood Oxygen Level Dependent Response)
Stimulating neural activity
- Electrical stimulation
- Chemical stimulation
- Transcranial magnetic stimulation (TMS)
- Optogenetic Methods
Electrical stimulation
- passes electrical current through wire inserted into brain. Activates neurons near the electrode (cell bodies and axons).
Advantage: relatively simple
Disadvantage: not very localised
Chemical stimulation
injects small amount of excitatory amino acid into brain
Advantage: more localised
Disadvantage: relatively complex
Transcranial Magnetic Stimulation (TMS)
- stimulation of cerebral cortex by magnetic fields produced by passing pulses of electricity through a coil of wire placed next to skull.
- Interferes with functions of brain region that is stimulated.
- Treats symptoms of neurological and mental disorders.
- Can be used to create virtual lesions.
