Tutorial 2 (No 1): Brain Research Techniques Flashcards
What is electrophysiology?
Refers to the electrical potentials generated in nerve cells (including brain cells, neurons, and muscles)
What are the four techniques in which brain activity is recorded?
Micro-electrode Recordings
Electroencephalography (EEG) - recording brain activity
Magnetoencephalography (MEG) - recording brain activity
Electromyography (EMG) - recording from muscles
Micro-Electrode Recordings:
- What is it
- Invasiveness
- Strength
(AKA SINGLE CELL RECORDINGS)
Neurons generate two kinds of electrical activity
–> Action Potentials (Spikes)
–> Post-Synaptic Potentials
Both kinds of potentials can be measured from brain tissue using very thin electrodes (micro-electrodes) inserted into the brain precisely at the desired locations
INVASIVENESS: requires surgery
–> can only be done on individuals who undergo brain surgery
–> therefore use in humans is very limited
STRENGTH: it is very direct measure of neuronal activity (temporally and spatially highly precise)
Electroencephalography (EEG)
- How does it work
Performs measurmenets from THE SCALP
–> The signal is the summation of multiple Local Field Potentials recorded on the scalp
Key Concept: Field Potentials
–> The communication between brain cells (neurons) leads to large amounts of ions entering/exiting the neurons –> results in POST-SYNAPTIC POTENTIALS inside neurons
–> As a consequence - the areas from which these neurons leave/enter have temporary surplus/deficits in charge (referred to as local field potentials)
On an EEG reading - each row represented ELECTRODES (not specific brain areas) - it is very difficult to attribute electrode signals to specific areas of the brain
Event-Related Potentials
- What are they
- How are they used in experiments
Used to examine stimulus-induced changes in an EEG signal (done by extracting from the continuous EEG segments ‘time-locked’ to a particular type of stimulus)
–> To perform comparisons between stimuli - you need to average multiple segments of EEG corresponding to each stimulus type separately
The ERP signal contains a number of departures and returns from its baseline (the average signal over 100-200ms prior to stimulus onset)
COMPONENTS: these changes in the signal (negative/positive peaks)
–> Their timing, amplitude, and polarity depend on the process that elicited the ERP
Components are labelled by their polarity and order/polarity and timing
–> EG: N1 - the first negative polarity peak in the ERP (order)
–> EG: P300 - positive polarity maximal at about 300ms after stimulus (timing)
A component also has a characteristic SCALP DISTRIBUTION - the map of the magnitude of the component over all the scalp sensors (indicates where on the SCALP the component is largest in its magnitude)
–> Therefore ERPs have timing/polarity/scalp distribution, so often serve as a ‘spatio-temporal’ signature of a process
*In experiments: lots of ERP samples and cancelled/averaged - so background noise cancels out, and the only consistent within the measure (stimulus) remains
Common Example: during semantic incongruencies (answer that makes the least sense) - N400 gets LARGER
Neuroimaging: Structural and Functional Magnetic Resonance Imaging (MRI)
- What is it
- What does MRI not show
- What is fMRI
Structural MRI (MRI)
Functional MRI (fMRI)
MRI measures the MAGNETIC SIGNAL COMING FROM HYDROGEN IONS (essentially they act as very small magnets)
–> By applying a magnetic field that oscillates at the frequency of radio waves - these atoms respond (resonant) emitting a magnetic signal and the same frequency
–> Body is put in a VERY strong magnetic field (MRI scanner) - makes sure that the orientation of the hydrogen atoms is similar (to produce a high-resolution structural image)
Structural MRI ONLY produces an image - does NOT measure brain function
fMRI:
–> Haemoglobin reduces the MRI signal wen it is de-oxygenated
–> Increase in blood flow (oxygenated blood) to more active regions = stronger MRI signal (surplus of oxyhaemoglobin)
–> This is referred to as BOLD contrast (Blood Oxygen Level Dependent) between more vs less metabolically active regions
–> fMRI is safe and superior to PET in terms of spatial and temporal resolution
–> BUT: its temporal resolution (speed) is still MUCH LOWER THAN EEG, ALSO: limits for people with metal implants/claustrophobia/loud noises
Neuropsychology
- What is neuropsychology and why is it used
- What are the key drawbacks of the method
Study of the consequences of anatomically-selective brain damage
–> Solves the problem of CAUSALITY (both PET, fMRI, + other activity measures) cannot determine whether a brain region is NECESSARY, or that the measured activity CAUSES the behaviour
A neuropsychologists attempts to establish whether there is a systematic relationship between a psychological process and brain structure, AND can determine whether different stimuli rely on different processes by investigating anatomical substrates
ISSUE: Dissociations
–> Single dissociations (damage to brain region impairs performance in Condition A compared to Condition B) may not be sufficient enough
–> MUST demonstrate that damage to ANOTHER brain region leads to a greater impairment in Condition B than Condition A (a double dissociation)
ISSUES of the METHOD:
1 Patient availability is dictated by extraneous factors such as brain damage frequency
2. Extent of brain damage (very selective lesions are rare)
3. Secondary medical and psychological conditions of brain damage (eg. anxiety) can confound effects of specific behaviours/processes
4. AGE BIAS - brain damage (eg. stroke, degeneration) much more prevalent in older age
Transcranial Magnetic Stimulation (TMS)
- What is it
- How does it work
- What are the challenges
The application to the surface of the head of a strong magnetic field (electric current in a coil) in very brief (>10ms) pulses
–> Magnetic field reaches the SURFACE (cortex) of the brain, inducing electrical potentials in the neurons under the coil
Depending on the intensity/frequency/number of pulses, the effect of TMS can be excitatory or inhibitory
–> it tends to impair performance of cognitive tasks
Has been used extensively for clinical purposes, as well as in research to safely disrupt signals
–> LOW DOSE in research is very brief - provides precise temporal information concerning the time of disrupted psychological process (it has high temporal resolution)
–> Because the stimulation is relatively focal, the spatial resolution is also high
ISSUE: high connectivity between cortical areas
–> stimulating one may cause changes in another area
–> Also - ruling out the significant effects of the pulse ‘click’ noise and associated sensations (eg. muscle twitches)
(controlled for by stimulating another region of the brain as a control - producing similar effects but not the neuro-disruptive effects of stimulating the target)
–> Confined to the CORTEX (cannot stimulate deeper brain structures as the signal decays with distance - eg. can’t stimulate the hippocampus, amygdala etc.)
