Karteikarten
04. Modern Techniques to Study Brain Function
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- 1Name modern techniques to study brain function• Measuring electromagnetic activity
• Functional brain imaging techniques
• Brain stimulation - 2What is a neurone?Neurons are cells that receive, process and transmit information from one neuron to another through electrical and chemical signals. These signals between neurons occur via specialized connections called synapses.
- 3Neurones and action potentialsA signal / information is passed on in the form of an action potential. During an action potential, membrane channels open up and sodium is moved into the cell, causing depolarization (negative charge changes to positive charge) and potassium is moved out of the cell (repolarization.
- 4Glial cells and their properties• Glial cells support and enhance neural activity by removing debris from dead / injured cells, maintaining synapses and myelination. It is also an astrocyte.
- Myelin is an outgrowth of a type of glial cell. It is a fatty white substance that surrounds the axon of some nerve cells, and cause a faster transmission of signals by increasing the speed at which impulses propagate across the axon, since myelin increases electrical resistance across the cell membrane.
- Astrocytes receive synapses directly from neurons, and surround and monitor activity of nearby neuronal synapses. They are involved in the formation of new synapses, and regulate local blood flow to provide more supplies to neurons when they are active. - 5How signals are passed between neurones• Signals are passed on between neurons using neurotransmitters, which are action potentials converted into chemical signals. These signals are passed on from synapses. Multiple neurons can be linked to the same neuron.
- The electrical signal is converted to a chemical signal, which will produce electrical changes in the postsynaptic neuron.
- Neurotransmitters can be depolarising or hyperpolarising - 6The energy consumption of the brainThe brain accounts for 2% of the body weight and for 20% of the oxygen consumed by the body. Ongoing metabolic activity consists largely of the oxidation of glucose, which produces energy (ATP) required for action potential and needed for active signalling processes (e.g. glutamate cycling, synapse activity) and astrocytes.
- 7How are blood flow, oxygen and glucose consumption related?• Increased neuronal activity is associated with increased blood flow in that brain area.
• Blood oxygen and glucose utilisation increase in proportion to the change in blood flow. - 8Summary of methods which measure electromagnetic activity
- 9List invasive and less invasive methods of measuring electromagnetic activity• Invasive: Intracellular (single cells), extracellular (single or many cells)
• Non-invasive: Extracellular current (averaged activity of many cells), magnetic field (averaged activity of many cells) - 10Explain single unit recordingSingle unit recording is invasive, although it can record from a single cell (intracellular) or a group of cells (extracellular). These are usually animal or patient studies.
• Hubel and Wiesel (1959) placed electrodes in a cat’s brain, recording activity from neurons.
• One example of how single unit recording is used in patients, is that people with seizures can have electrodes placed in their brain to control the seizures. - 11Explain the electroencephalogram (EEG)Electroencephalogram (EEG) involves placing electrodes on the scalp surface in order to measure electrical activity generated by the brain. Usually, 128 or 256 channels are used.
• An EEG can show on-going electrical brain activity, i.e. monitor cognitive engagement, such as for example in learning mode or when asleep. An on-going EEG measures how / if brainwaves are changing over time. - 12Explain event-related potentials (ERP)Event Related Potentials (ERP) record if electrical brain activity is related to certain tasks. It is the same set-up as an EEG although this time, participants engage in a task.
• An ERP measures significant voltage fluctuations resulting from evoked neural activity (external or internal stimuli). We can’t measure the absolute activity, but we can compute the difference between a signal (active) electrode and a reference electrode. This is because things are going on at the same time, e.g. breathing. So, the reference electrode helps subtract “regular activation” from the activity, showing only the activity that comes from the particular task. This removes the “background noise”. Sometimes many trials / exposure to stimulus are required to see results / trends. - 13Example of an ERP study• Rossion and Jacques (2011) studied face perception: In this study, participants see a lot of faces and are asked to indicate whether the faces are positive, sad, etc. The study found that actual reaction time lies at 500 ms. However, much happens before the participant reacts! There was an early change in activity at 170 ms, before the actual response to the task. Using an ERP we can see approximately where the activity comes from; in this case, areas which are associated by other studies to be facial recognition areas. Other studies show that the same peak occurs for meaningful objects, suggesting that this area responds to meaningful objects (including faces). There is a peak at N100 for any object; the timing of activity can therefore be very important in distinguishing activities from one another.
- 14The downside of ERPERP needs a lot of data and the location of the activity can only be approximated and not known for certain.
- 15Explain the magnetoencephalogram (MEG) + its downsideMagnetoencephalography (MEG) is a more accurate measure than EEG, measuring the magnetic field that is generated by neural activity. The magnetic field is measured by detectors, and 306 independent measurement channels are used.
• MEGs measure a lot of activity, of which the human brain’s is only a small part.
• For example, in a task of distinguishing between a word or a pseudoword, we can approximately see where the activity happens in the brain, aka where in the brain it comes from.
• However, magnetic fields decay rapidly. - 16What are functional brain imaging techniques?In contrast to functional techniques, MRI (Magnetic Resonance Imaging) is a structural method, during which a magnet aligns protons in the brain tissue. The alignment is disrupted via a brief audio frequency wave pulse. Protons in different tissues take different times to re-align, depending on their densities.
- 17Summary of functional brain imaging techniques
- 18Explain functional magnetic resonance imaging (fMRI)Active brain tissue used more blood (i.e. glucose, oxygen). Therefore, oxygen level in blood translates how active a brain area is, causing a hemodynamic response. A hemodynamic response allows the rapid delivery of blood to active neuronal tissues, which can be measured.
• Deoxygenated and oxygenated haemoglobin have different magnetic properties. Changes in deoxygenated and oxygenated blood are detected by fMRI. Astrocytes function as a link between synapses and blood vessels during the hemodynamic response.
• The temporal resolution (i.e. precision of measurement with respect to time) of fMRI is sufficient for longer trials.
• Activity is measured in the following manner: Activation – Rest = Difference Task activation - 19Examples of fMRI studies• Geschwind et al. (2012) showed 22 participants a block of faces, a block of places and a block of scrambled images. He found activation in certain areas associated with facial responsiveness, including for example the amygdala and the fusiform face area.
• Kanwisher, McDermott and Chun (1997) supported Geschwind’s (2012) study in their aim to explore activity in the fusiform gyrus. - 20Explain Position Emission Tomography (PET)Active areas show increased blood flow. Radioactive positrons are injected in the blood and travel to the areas that are most active. The positrons set off detectors that measure their position.
• PET shows poor temporal resolution. - 21Example of a study using PETHaense et al. (2012) aimed to investigate the link between neurotransmitter and mild cognitive impairment (MCI). They used 21 healthy control subjects and 17 MCI patients, the latter of which showed memory decline without significant impact on activities of daily living. This study showed that activity is reduced in MCI patients and changes can be seen at very early stages.
- 22Name brain stimulation techniquesTranscranial Magnetic Stimulation (TMS)
Single Pulse TMS
Repetitive TMS (rTMS) - 23Explain Transcranial Magnetic Stimulation (TMS)Transcranial Magnetic Stimulation (TMS) is a non-invasive and pain-free method of stimulating the human cortex to study the link between brain and behaviour. TSM detects behavioural and perceptual changes (positive or disruptive, e.g. muscle twitches) and neurophysiological and metabolical changes (e.g. blood flow, oxygenation changes).
- 24Explain Single Pulse TMSSingle Pulse TMS is applied at a certain time, e.g. time-locked with the target presentation. For example, 100 / 200 / 250 ms after the target presentation, in order to find when the stimulation impairs or enhances performance.
- 25Explain Repetitive TMSRepetitive TMS (rTMS) is capable of changing the activity in a certain brain area even beyond the duration of the rTMS application itself. For example, it can lower detection threshold but instead give e.g. neglect-like behaviour for 30 minutes.
• Pitcher et a. (2007) studied what face areas we can investigate with TMS using a facial discrimination task, where some selective impairment actually had an effect at some TMS timings. - 26Advantages of brain stimulation techniquesPrecise timing (single pulse) and good / okay localisation
Can create ‘lesion-like’ behaviour without interference of other lesioned areas - 27Disadvantages of brain stimulation techniquesImpossible to stimulate deep brain structures directly
Magnetic field decays quickly, and coil position needs to be monitored - 28Other things to consider regarding brain stimulation techniquesCoil position: Guided by prior evidences (location and timing)
Precise timing: Choose correct time window
How much to stimulate (motor threshold)?
Control location and time, control trials / task without TMS - 29Depending on the research question, how would you choose which research question to use?• What does the technique measure?
• What would you need to consider when designing your experiment?
• What are the advantages / disadvantages of these techniques (e.g. spatial / temporal resolution)
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- Psychology 2A (Psychobiology) Karteikarten am 04. Modern Techniques to Study Brain Function, erstellt von Nina Olsson am 26/07/2018.
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