Causal Methods Flashcards
(38 cards)
Causal methods
Induce changes in brain activity
- directily, by influencing physical properties of neural tissue
- there are also indirect method such as mediaction etc.
–> even causal methods cannot infer causality with certainty!
Stimulation methods
= what is being applied at physical level
=/= effect on neural processing
Intracranial recordings and stimulation
- Invasive electrophysciology
Choice of electrode depends on clinical need and anatomical objective
- especially in epilepsy patients not responding to medical treatment
- mostly limbic and frontal regions
- electrodes removed prior to surgery
Electrocorticography ECoG
Use of electrodes placed directly on the exposed surface of the brain to record electrical activity from the cortex
Stereo-electroencephalography SEEG
Recording electroencephalographic signals via depth electrodes
- very similar to EEG, but with much much better signal to noise ratio and very hihg temporal and spatial resolution
- but depends on available subjects, limited time available, invasive and lack of control set
Microstimulation
Electrode inside neural tissue: only performed when electrodes are crucial for clinical purposes
–> mall electrical current:
- influences activity of neurons near the tip
- the larger the current, the wider the affected area
- too strong = damage (burn)
- strong = action potentials
- weak = membrane potential change
Deep brain stimulation DBS
Like microstimulation –> electrodes in deep structure of the brain
- parkinson’s disease
- severe depression and OCD
- neural pacemaker
- as a treatment through various mechanisms (enhancing, inhibiting or synchronizing activity)
Focused ultrasound stimulation FUS
Ultrasound
- focused volume of space in which waves propagate
- applied transcranially (bone reduced amplitude, but does not scatter the sound wave)
Ultrasound
Frequencies of a few hundred kHz (far beyond hearing range)
FUS stimulated region
Stimulated region looks like rugby ball
- loong axis: orthogonal to scalp surface, so can penetrate at least a cm
- spatial resolution = few mm
- higer than other non-invasive stimulation methodes in lateral directions
- typically guided by anatomical MRI
Can be used to lesion brain structures (high intensiy heats up and can burn)
Low-intensity FUS
Leads to neural stimulation
- non-thermal mechanical energy
- small displacements of cell
- hypothesized effects on properties of receptors
Transcranial magnetic stimulation TMS
Electromagnetic induction (Faraday’s principle; left hand rule magnet)
- electric current in coil
- generates transient magnetic field haaks op de coil
- induces second current in brain that flows parallel but in opposite direction
–> stimulates/depolarizes neurons
Shape of coil
Determines shape of magnetic field and induced current
- figure of 8 coil design
- more docused magnetic field
- more precise location of altered neural activity
Determinants properties and effect electrical current
- physical factors (distance to coil)
- biological factors
- physical parameters easier to characterize than biological parameters
- predicting effect on neural activity is difficult
Spatial resolution of TMS
- 1 cm
- TMS of occipital face area OFA only affects face processing
- TMS of extrastriate body area EBA only affects body processing
- these rgions are less than 2 cm apart
- but functional differentiation between adjacent subregions is not possible for all cortical areas
Temporal resolution in TMS
Very good temporal resolution
- if only a single or double pulse is applied
- limited by duration of puls (s) and number of time-points tested
Variants of TMS
Repetitive TMS
- multiple pulses (frequency; duration)
- influences temporal resolution
- stronger effect (also higher risks)
Single/double pulse TMS
Sometimes combined: rTMS first to establish causal link, fllowed by single/double pulse TMS for better temporal resolution
Control conditions TMS
Sham: turn coil by 90 degrees
- magnetic field does not influence neural activity
- difference easy to detect by participant
Stimulation of vertex = highest point of skull
- assumption: no/little effect on behavior
Where to stimulate with TMS
- international 10-20 EEG system: locates electrodes on scalp using standard cranial landmarks
- standardized function-guided procedure: rely upon functional criteria such as motor responses or phosphenes
- neuronavigation: using structural/anatomical MRI scan of participant
- fMRI-guided TMS: using an fMRI localiser task + neuronavigation
Potentials of TMS
- diagnostic value for testing connectivity between motor cortex and peripheral muscles (motor related disorders and adter a stroke)
- as part of clinical treatment
- major depression (alternative or electroconvulsive therapy)
- migraine (single pulse over visual cortex)
Transcranial current stimulation TCS
- principle similar to TMS but uses electrical stimualtion
- current flows from anode (depolarization of neuron, +, excitatory) to cathode (hyperpolarization of neuron, -, inhibitory
TCS
- typical current strength(effect size at neural level and sideeffects)
- control condition, often sham TCS
- poort spatial resolution: 5 cm (contact area 25 cm^2, uniform delivery of current)
- very poor temporal resolution (extended duration of stimulation and duration of effect)
Variants of TCS
- transcranial direct current stimulation tDCS
- transcranial alternating current stimulation tACS
- transcranial random noise stimulation tRNS
tDCS
Direct current in one direction; location of electrodes determines flow current
