HC9 Causal methods Flashcards
What are causal methods in neuroscience?
Methods that induce changes in brain activity, either directly (e.g., stimulation) or indirectly (e.g., medication, neurofeedback).
What is the difference between correlational and causal methods?
Correlational methods show associations, whereas causal methods actively influence brain regions.
Can causal methods establish absolute causality?
No, they provide stronger evidence for causality but cannot confirm it with absolute certainty.
What is invasive electrophysiology?
A causal method where electrodes are implanted into neural tissue to stimulate specific brain regions, often used for epilepsy patients.
What is electrocorticography (ECoG)?
A technique where electrodes are placed directly on the brain’s exposed surface to record cortical electrical activity.
What is stereo-electroencephalography (SEEG), and how does it differ from EEG?
SEEG records electroencephalographic signals using depth electrodes and has much better temporal and spatial resolution than EEG.
What are the advantages and disadvantages of ECoG and SEEG?
Advantages: High temporal and spatial resolution, better signal-to-noise ratio.
Disadvantages: Invasive, limited subject availability, no control group.
What is microstimulation?
A technique where a small electrical current is applied inside neural tissue to influence neuron activity.
What are the risks of microstimulation?
Too strong a current can cause brain damage
What is deep brain stimulation (DBS)?
Implanted electrodes in deep brain structures, used for Parkinson’s disease and obsessive-compulsive disorder (OCD).
What is the effect of DBS on tremors and verbal fluency?
Higher current reduces tremors but decreases verbal fluency, while lower current increases verbal fluency but worsens tremors.
What is FUS?
Focused Ultrasound Stimulation.
A technique that uses focused ultrasound waves to modulate brain activity at a specific location.
How does FUS compare to fNIRS?
FUS is less affected by bone structures than fNIRS. Because bones reduce the amplitude dramatically and don’t scatter sound waves.
What is a high-intensity application of FUS?
It can create brain lesions by heating and damaging tissue.
What is the mechanism of TMS?
A magnetic field induces an electric current in the brain, which stimulates or depolarizes neurons.
TMS and Faraday’s principle
- There is an electric current in the coil (the thin black arrow in the grey coil).
- This generates a transient magnetic field perpendicular to the coil (the red lines).
- This magnetic field induces a second current in the brain which flows parallel but in the opposite direction (the thick black arrow). This leads to the stimulation or depolarisation of neurons.
How does the shape of the coil affect stimulation?
An 8-shaped coil has a strong magnetic field where both coils come together. This way, neural activation can be better localised than with just 1 single coil.
What factors influence the effectiveness of TMS?
- The distance to the coil: a longer distance between the brain and the coil gives a smaller effect.
- Conductivity of the tissue and the orientation of the axons.
TMS, limitations of the temporal resolution
TMS has a very good temporal resolution and has a spatial resolution of 1 cm. But the temporal resolution is limited by the duration of the pulse and the number of time-points tested:
- Single or double pulse TMS gives a higher temporal resolution.
- The longer the pulse, the lower the temporal resolution.
- The more time point, the better the temporal resolution.
What is repetitive TMS (rTMS)?
Multiple pulses that have a stronger and longer-lasting effect, used for depression treatment.
What is the difference between single-pulse and double-pulse TMS?
They provide higher temporal resolution and are used for migraine treatment.
Why are control conditions important in TMS?
To rule out placebo effects, such as in the sham condition (coil rotated 90°).
Why would you use TMS?
- To diagnose the connectivity between the motor cortex and the peripheral muscles.
- Clinical treatment for many disorders.
- For major depression.
- For migrain
What is transcranial current stimulation (TCS)?
A technique similar to TMS but it uses an electric current instead of magnetic stimulation.
What is the difference between the anode and cathode in TCS?
The anode induces depolarization (excitatory), and the cathode induces hyperpolarization (inhibitory).
What are the disadvantages of TCS?
It has a poor spatial and temporal resolution. You need to stimulate long enough to get an effect and when you stop stimulating, you don’t know when the effect is gone so you have to wait very long.
What are the variants of TCS?
tDCS: Direct current in one direction.
tACS: Alternating current at a fixed frequency.
tRNS: Alternating current with a random frequency spectrum.
What is Transcranial Direct Current Stimulation (tDCS)?
Direct current in one direction, the location of electrodes determines the flow of the current. This is the method which is the most used.
What is Transcranial Alternating Current Stimulation (tACS)?
An alternating current at fixed frequency to test whether particular frequency ranges are involved.
What is Transcranial Random Noise Stimulation (tRNS)?
An alternating current based on random frequency spectrum.
What is the rationale behind lesion studies?
If damage to a brain region causes a specific behavioral deficit, that region plays a crucial role in the function.
What is double dissociation?
When lesions in different brain regions have opposite effects on two cognitive functions.
What is voxel-based lesion-symptom mapping (VBLSM)?
Comparing behavioral scores between patients with and without a lesion in a specific voxel.
What are the advantages of VBLSM?
High resolution, no need for predefined regions, can control for covariates like age.
What is a limitation of VBLSM?
Brain damage may extend beyond the visible lesion, affecting white matter connections.
What is an alternative to VBLSM?
Network-based lesion-symptom mapping, which considers both necrosis and disconnection effects.
What is the difference between on- and off-medication conditions?
On-medication: Testing while taking medication.
Off-medication: Testing without medication to isolate drug effects.
Why are dopamine-related studies common?
Dopamine has a relatively clear effect, whereas other medications have broader, more complex effects.
What is an example of a dopamine intervention study?
Kim et al. (2018) found that dopamine normalizes underactivation of the putamen and overactivation of the insula in Parkinson’s patients.
