Neurostmulation I Flashcards
What is neurostimulation?
Stretch the idea of neuroimaging but go hand in hand with neuroimaging to look at brain fction can be modulated either to tell us smtg about how the brain works (cog neuroscience or psychology exps), use brain stimulation techniques to try and modulate bvr, make a prediction in the reverse direction of neuroimaging
Interfere with brain areas and see effect on bvr instead of seeinghow bvr affects brain activations
More causal techniques, create temporary interruptions in parts of the brain and see how it affects bvr
We can modulate or change our brain by applying an external stim
What we can do with neurostim at the moment is very limited (can’t remove M or implant knowledge)
What are the 2 main types of neurostimulation?
– Transcranial Magnetic Stimulation (TMS)
– Transcranial Direct Current Stimulation (tDCS)
* More generally transcranial electrical stimulation– tDCS, tACS, tRNS
What is deep brain stimulation? (DBS)
Implanted electrodes deep in the brain, provide chronic electrical stim to aleviate symptoms
of PD. Stereotactic placement of electrodes.
Used for medical treatment (DBS for PD and
other neurological disorders and treatment
resistant psych disorders like depression and
chronic pain), chronically implant electrodes to
modulate brain fction to relieve symptoms
What is electroconvulsive therapy (ECT)?
ECT = imp treatment for depression
Strong electrical stim to cause a seizure in patient
Cause generalised seizure under anesthesia
What is Electrical stimulation mapping (ESM)?
Use for investigation for certain kinds of epilepsy, implanted electrodes deep in the brain to evoke seizures = confirmatory diagnostic procedure
Stereotactic EEG, implant electrodes into brain to see where epileptic activity is coming from (when seizures are very disruptive
and meds arent working) see if can capture epileptic area to surgically ablate it later
Used to stim as well to evoke seizure activity
What is Direct cortical electrical stimulation (DCES)?
Treatment for epilepsy, implanted electrodes on the cortical surface, also for surgical intervention in the brain to understand the importance of certain areas in the brain to not remove imp parts, evoke fction during surgery
Neurosurgery (part of brain is being resected), don’t want to interfere with imp parts of brain, electrically stim around area to see what parts of cortex would cause interruptions in activities
What is Focused Ultrasound (FUS)?
Alternative treatment in neurosurgical areas for tumors, focus ultrasound in brain parts, use sound waves to ablate tumors
Used experimentally to transiently disrupt fction in part of brain or increase permeability in the BBB
Ultrasound transducer focuses sound waves, used to ablate tissue (ex. tumor) or change the permeability of the membrane around the tumor so a drug can be better uptaken into it
Can be used experimentally to map out parts of the brain ex S1 (person indicates where they’re feeling smtg when they’re being stim)
Advantage = can be focused in contrast to mag and electrical stims (better spatial res and can reach deeper), mag field can only stim cortex surface bc mag field drops off quickly
Electrical stim can reach deeper but takes the path of least resistance (less spatial res)
TfUShas higher spatial resolution (tES or TMS) and can reach deep structures
Non invasive exp technique (at low levels of intensity) but also a therapeutic technique
What is red light?
Near-infrared light stims parts of the brain, measure whats going on in the brain
What is Transcranial magnetic stimulation (TMS)?
Electromagnet non invasively stims a part of the brain through the scull
Can’t focus a mag stim but if have figure 8 coils (mag field created in 2 coils at once wound in opposite directions, will get a stronger mag field in the centre and weaker at the edges)
Pass a large current which creates a 90° mag field, if put it close to a conductor (the brain largely made of water), can induce a current via mag induction in the brain under the coil, if current is large enough, will get lots of synchronous PAs in the cells that are stim and an evoked response there
Used to map the network activity within the brain by combining it with EEG, see response in brain evoked by stim one gr of neurons, the PA will propagate outwards to the next neurons so we can map the fctional connectome, get
widespread activations in diff parts of the brain, get temporal evolution of how the activity spreads throughout the brain
However, when send a large mag field through smtg that records tiny elect signals, will have very large artifacts (huge stim artifact in the recording electrodes), stim saturates the channels
What are 4 types of Transcranial electrical stimulation?
- Transcranial direct current stimulation (tDCS) Apply a direct current to the brain transcranially, Most simply, use a bipolar montage (2 electrodes) and apply current through it, current flows from one side of the circuit to the other, in order to do that, some of the current will go through the brain and cause some kind of change in whats going on
– Anodal: +, put anodal side over part of brain want to excite
– Cathodal: -, put cathodal side over part of brain want to inhi - Transcranial alternating current stimulation (tACS): Circuit and electronics that change the poles in a sinusoidal manner
- Transcranial random noise stimulation (tRNS): Not a smooth fction, randomly swap poles fast or slow
- Sham stimulation: Apply smtg to the head, the person who has “stim” thinks they’re being stim, evokes response, makes them anxious, aroused, changes their attention to what you’re doing, like a placebo effect, ctrl gr for exps
What is the history of tDCS?
- In 1801, Giovanni Aldini showed that direct current stimulation improved the mood of melancholy patients.
Change mood of depressed patients by stim their brain - 1960s D. J. Albert discovered that positive and negative stimulation had different effects on the cortical excitability.
- Recently interest in tDCS is renewed
bc of technological advances (consumer type devices)
What are the acute effects of tDCS?
- Acute effects of tDCS due to changes in resting membrane potential
Neurons encode info by going from one state to another rapidly
Current stim shifts the resting potential, anodal stim shifts the resting potential closer to the firing threshold so that any incoming stim causes the firing threshold to be reached for less input or sooner or to reach a higher level of depola, allows us to ex do tasks faster. Opposite is true for cathodal stim (dim excitability)
What are fo.cus gaming devices?
– Affordable “gaming” devices
– Pitched to enhance cognitive function
– ~ 2% of the cost of research/clinical grade systems
Consumer based devices, idea is that could improve ability in visual search tasks
What is tDCS?
- The anodal electrode is positively charged: cathodal electrode is negatively charged.
- Current flows from the anode through the skull and brain to the cathode.
- The device that delivers the current has controls that set the current intensity as well as the duration of stimulation
How much of the stim enters the brain depends on the intensity of the current delivered, if to low, get no effect but if too high, burn the scalp
– Non-invasive brain stimulation
– Electrical currents delivered to the scalp
– Equivalent to voltages naturally produced by the brain (1 - 2 mA)
Very small currents, apply this to the scalp but this isnt what’s reaching the brain, what actually reaches the cortex is a lot smaller, controversy over how effective it could be
– The most simple form of tDCS involves 2 electrodes - 1 x ANODE: delivers positively-charged current
– Stimulates nearby cortical regions
– Increase positive charge
– Neurons more likely to reach action potential Can have big array of electrodes and apply shaped currents across the whole scalp
tDCS by itself doesn’t cause PA, it just modulates the resting memb potential - 1 x CATHODE: attracts negatively-charged current
– Inhibits nearby cortical regions
– Increases negative charge
– Neurons less likely to reach action potential
What is the polar issue with tDCS?
- tDCS is bipolar – pure anodal or cathodal stimulation is not possible
There is always the opposite stim somewhere else so it can be difficult to disambiguate what the stim is actually doing (bipolar effect)
