Tools to study to brain Flashcards
What are mental representations of stimuli?
The way that properties of objects are interpreted by cognition.
What are neural representations of stimuli?
The way that properties of objects manifest themselves in neural signals.
What are grandmother cells?
Refers to the idea that specific neurons fire in response to specific stimuli. e.g a ‘grandmother’ neuron that fires every time you see your grandmother.
Define rate coding.
The rate of a neuron’s firing can code for information such as stimulus strength.
Define temporal coding.
The synchrony of firing between several different neurons. (neurons that fire together bind together information. e.g a blue circular object moving from left to right)
What are single cell recordings?
The use of very small electrodes to measure activity from individual neurons.
What are the two types of single cell recordings?
Intracellular - neural activity from within the axon
Extracellular - neural activity from outside the axon.
What does EEG stand for?
Electroencephalography.
What do EEGs do?
Record electrical activity of neurons in real-time.
When and who conducted the first EEG in humans?
Hans Berger in 1924
What exactly does EEG measure?
Changes in voltage on the scalp which represent the summed activity of millions of neurons underneath each electrode.
What are two strengths of using EEGs to measure brain activity?
+ Very good temporal resolution
+ Transportable and cheap.
What is one limitation of using EEGs to measure brain activity?
- Poor spatial resolution
What does ERP stand for?
Event-related potential.
What are ERPs?
The average waveform that is generated when EEG responses to the same stimulus are measured several times over.
What are the names of the different frequencies that brain oscillations occur at?
- Delta
- Theta
- Alpha
- Beta
- Gamma
Which frequencies do delta waves operate at?
0.5Hz - 4Hz
Which frequencies do theta waves operate at?
4Hz - 8Hz
Which frequencies do alpha waves operate at?
8Hz - 12Hz
Which frequencies do beta waves operate at?
13Hz-30Hz
Which frequencies do gamma waves operate at?
30Hz-100Hz
True or false: Different patterns of oscillations can reveal the state that the participant is in (asleep, awake, relaxed, aroused, etc)
True.
What does MRI stand for?
Magnetic Resonance Imaging
How does MRI work? (6 steps)
- Initially, H+ protons in the brain all face different directions.
- A magnetic field is applied, which causes almost all of the protons to align.
- A radio wave is then sent across the brain which flips the protons into the opposite direction.
- The protons immediately return to the direction they were facing before the radio wave was applied.
- Protons in grey matter, white matter or in CSF take different amounts of time to revert to their original orientation.
- The different structures can be seen on the MRI scan.
What is fMRI?
Functional magnetic resonance imaging.
What does fMRI measure?
BOLD signal.
What is the BOLD signal?
Blood oxygenation Level Dependent signal. Active brain regions require oxygen, so are supplied with oxygenated blood. However, an overshoot of oxygenated blood occurs, meaning the blood in active brain regions is oxygenated, even after it has absorbed the oxygen it needs.
Oxygenated blood causes less magnetic field disturbance than deoxygenated blood, so active brain regions will have a higher signal. (and will show up lighter on the scanner)
What does HRF stand for?
Hemodynamic response function
What is an HRF?
The typical change in BOLD signal in response to a stimulus.
Describe the HRF.
The BOLD signal initially dips as deoxygenated blood disturbs the signal. However, as oxygenated blood is sent to the active regions, the BOLD signal increases up to it’s peak (after 5/6 seconds). It then decreases and undershoots, before returning to it’s original level.
What are the main two differences between MRI and fMRI?
MRI has higher spatial resolution.
fMRI can observe changes in activity over time.
What is fMRI Subtraction Logic?
The difference in activity between a baseline task and an active task. Found by taking one away (subtracting) from another.
What are block designs?
fMRI experiments in which similar stimuli are grouped together.
What are event related designs?
fMRI recordings are taken following a certain event. Can be random, unexpected or chosen by participants.
What are three limitations of using fMRI?
- Many tasks require the activation of several different brain areas. (some areas are even active during rest)
- Only correlational, not causational.
- The HRF is very slow (seconds) while many cognitive processes are vey quick (milliseconds)
What does TMS stand for?
Transcranial magnetic stimulation.
What does TMS do?
It uses short magnetic pulses that temporarily affect electrical activity. It is usually applied before or during a cognitive task and can boost or inhibit performance.
What does tDCS stand for?
Transcranial direct current stimulation.
What does tACS stand for?
Transcranial alternating current stimulation.
What does tDCS/tACS do?
They can perform the same job as TMS, but uses a small current that flows from a cathode to an anode on the scalp.
Which areas are thought to be excited and inhibited when tDCS/tACS is used?
Areas under the anode are thought to be excited and inhibited under the cathode.
What are two strengths of using brain stimulation techniques?
+ Can be beneficial for patients with depression.
+ Can provide causal evidence that a specific region is linked to a specific function.
What are two weaknesses of using brain stimulation techniques?
- Brain stimulation is relatively mild. Thinking itself can stimulate the brain more.
- It cannot be used on epileptic patients - could be dangerous for them.
