Lecture 2: TMS Flashcards
1
Q
What are brain perturbations?
A
They impair or influence cognitive functions
2
Q
Wht can brain perturbations arise from?
A
e.g., perturbations from brain damage in stroke patients, disease or trauma but perturbations induced experimentally using pharmacological or electrical methods
3
Q
Infromation from brain perturbations have
A
greatly advanced our understanding of the neural underpinnings of cognitive functions
4
Q
What is lesion studies?
A
When a specific brain region is purposefully or incidentally damaged, and consequentially specific cognitive functions are affected, these functions are causally connected to processing in this region.
5
Q
Lesions and TMS give advantage, over fMRI EEG being correlaiton, is that
A
causal
6
Q
Example of lesion study - (3)
A
In 1948, Phineas Gage had a workplace accident in which an iron tamping rod entered and exited his skull.
He survived but it is said that his personality changed as a result, leading to a greater understanding of the brain regions involved in personality, namely the frontal lobe
famous patient with frontal cortex lesion - accidental lesion
7
Q
There are two types of lesion studies - (2)
A
- Invasive methods
- Non-invasive methods
8
Q
Invasive methods of lesion studies - (4)
A
- Destory processing in brain region of interest –> advantage can tightly control ROI
- Can for instance be done by remving brain tissue or cooling region
- Ethically very problematic
- Done in animals
9
Q
What are non-invasive methods of lesion studies? - (2)
A
- Studying patients with incidental lesions(e.g., due to stroke/posioning) in specific parts of their brain e.g., phineas gage
- Using brain stimulation to temporarlly impair neural processing (TMS)
10
Q
What does lesion mapping in patients require?
A
use of structural imaging (e.g., structural MRI)
11
Q
What is involved in lesion mapping? - (2)
A
Carefully mapping the damaged cortical regions allows for establishing spatially specific and causal relationships between brain activations and cognitive functions
mapping where the lesions is happening
12
Q
There is database in lesion mapping across the world which - (2)
A
have structural images and where the lesion is and catalogue of functions assessed
if interested what causes arithmetic difficulties and find list of patients with this in database and overlap their lesions in MRI and find common area impaired in all of them
13
Q
Lesion Mapping in Patients
What does this diagram show? - (2)
A
MRI scans of patient D.F (on right) and healthy volunteer)
D.F had damage to visual cortex called lateral occipital and not acivated vs healthy volunteer L0 activated in task that activates it
14
Q
Whats a single dissociation in lesion studies?
A
A lesion to a specific region leads to an impairment in a specific task (but not in other tasks)
15
Q
What is the problem with single dissociations? - (2)
A
Single dissociations my be found when the two tasks are differently sensitive (e.g., different task demands or difficulty
e.g., has a patient who is deficit in factual arithemtic e.g., 2+2 = 4 but okay in comparing numbers then say task is quite difficult and different from each other
16
Q
The problem of single dissociation that they are found when 2 tasks are differently sensitive (e.g., different task demands/difficulty) is aggravated/increased by
A
fact that participants may have unspecific impairments that impair their performance in various tasks with high sensitivity
17
Q
Whats example of single dissociation? - D.F - (3)
A
Single dissociation between dorsal and ventral stream functions in the visual system
Traumatic lesion in human ventral stream (patient D.F.) leads to impaired object perception (matching card in the angle of slot), but leaves object-guided action intact (posting - card through angular slot)
healthy volunteers good at both
18
Q
What is a double dissociation? - (2)
A
A lesion to one region leads to an impairment in a specific task (but not the second task), and a lesion to another region leads to an impairment in another specific task (but not the first task)
e.g., patient who can do arithmetic 2+2 = 4 but not number comparison and patient who can do number comparison and not arithmetic and have lesions in different areas
19
Q
What does double dissociation reveal?
A
Reveals unequivocal links between lesion and putative (supposed) brain function, that are not explicable by the tasks’ sensitivity
20
Q
What is an example of double dissociation?
: Double dissociation between dorsal and ventral stream functions in the primate visual system - (3)
A
- Trained macaque monkeys in two tasks: 1) object discrimination of always picking up Toblerone shape object wherever it is, 2) landmark discrimination of monkeys always pick up the piece closer to cylinder
- Artificial lesions in macaque animals’ ventral stream (temporal lobe) leads to an impairment in object discrimination but not in landmark discrimination
- Artifical lesions in macaque animal’s dorsal steam (parietal cortex) leads to impairment in landmark discrimination but not object discrimination
21
Q
What does this graph show in terms of single vs double dissociation? - (2)
A
- single dissociation, region A is reduced in function X but not in function Y
- In double dissociation , region A is reduced in function X but not in function Y, region B is reduced in function Y and not X
22
Q
What are the 2 advantages of lesion studies? - (2)
A
- Reveals causal links between brain regions and functions esp in double dissociation in patients
- High spatial precision (when done invasively - in animals artifical lesions)
23
Q
What are the weaknesses of lesion studies? - (4)
A
- Low temporal precision
- Low spatial precision (when studying incidental lesions)
- Confounding impairments are not unlikely –> e.g., patients have number of processing deficits but may also have speech problems - lesions may not just impair one function so lesion mapping is useful
- Experimentation can be difficult, costly, and unethical (animals in lab)
24
Q
What is brain stimulation?
A
Driving neural activation to understand brain function
25
What is the idea of brain stimulation - (2)
When neurons communicate, they change their membrane potentials and eventually fire action potentials.
By inducing electrical currents into neurons, we can either push neurons to fire more (or to be more excitable) or induce chaotic activations that prevent coordinated firing.
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What are the two methods of methods in brain stimulation - (2)
* Invasive
* Non-invasive
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What are inasive methods of brian timulation - (2)?
* Electric stimulation of neurons in particular brain regions
* In humans: Rarely possible for patients with implanted electrodes (e.g., for informing epilepsy treatment)
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Disrupting the neural processing using direct electrical stimulation of specific brain region (i.e., perturbation by intracranial brain stimulation)
the technique in humans is limited to
patients with serious medical problems
29
Direct cortical stimulation is an important technique for
estbalishing the necessity of brain region for cognitive construct
30
How does direct cortical stimulation work? - (2)
electrical current is introduced using electrodes that are placed on the surface or the brain or directly into deeper brain tissue
The current is delivered via a relatively large electrodes that stimulate a large region or via a small electrodes that stimulate a few neurons
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32
What are the modern uses of direct cortical stimulation - (3)
- Today, direct cortical stimulation is most frequently used to map areas of critical functions (e.g., language, motor abilities) in patients awaiting undergoing neurosuregrey
- Based on function of brain regions located near the surgical target, neurosurgeons may change the path taken through the brain surface to leave critical area s intact while removing a deep tumour
o It reduces the change the patient will suffer from motor, language or other deficits
33
Modern methods of direct stimulation - (5):
- In modern practice of direct cortical stimulation, a pair of stimulating electrodes are placed on the surface of the cortex (Figure 13.1A):
- One electrode (anode) provides the source of electrical current
- The second electrode (Cathode) provides the sink to which current will flow
- Stimulation consist of weak current pulses that are rapidly presented
- Surgeon moves electrode to different locations on exposed cortical surface and tests effect of stimulation on regions of interest
34
Modern methods of direct cortical stimulation - grids - (3)
- Some epilepsy patients have grids of electrodes implanted subdural for over a period of days or weeks as shown on the right:
- By recording the frequency and locations of seizures within this grid, the patient’s physicians can determine whether a particular surgical excision would reduce or eliminate seizures
- Since patients are conscious, alert and comfortable during direct stimulation studies much useful info is obtained about their higher cognitive functions from these procedures
35
Limitation of direct cortical stimulation - (3)
* Invasive and bring on seizure on patients who suffer epilsepy
* High electrical currents sufficient to depolarise neurons and may spread from stimulating electrodes to excite brain regions distant away --> thus cathode and anode kept in close proximity
* Positive or negative effects does not ncessairly indicate surgical removal of stimulated region cause corresponding deficits
36
Whats non invasive methods of brain stimulation - (2)
* Using fast changing magnetic fields (Transcranial Magnetic Stimulations) to stimulate neurons
* [Using transcranial direct (tDCS) or alternating (tACS) current stimulation across the head to modulate activity outside of the brain]
37
How does tDCS work? - (2)
- tDCS protocol involves 2 small electrodes placed on different parts of the scalp – often with one over target site and another at distant reference location
-
- Weak direct current is delivered over extended periof of time
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TMS is less invasive method than
tDCS (transcranial direct stimulation)
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A far less invasive approach as compared to perturbation by intracranial brain stimulation is to
disrupt cognitive processing in normal subjects is transcranial magnetic stimulation (TMS)
40
For studies in humans electrical activity in brain influenced by
by either directly by applying an electrical current (tDCS) or a focal magnetic field (TMS) to surface of the scalp
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What is the difference between TMS or tDCS/tACS?
One uses magnetic fields (TMS) and another uses electrical currents (tDCS/tACS)
42
Diagram of history of TMS
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History of TMS - (13)
* In 1832 Farady discovers electromagnetic induction
* Took a while to produce machines for high enough magnetic fields to go through the skull
* 1848 Du Bois-Reymond shows link between electric current and nerve-cell activity
* In 1875, Ferrier uses electrical currents to stimulate the cortex and map cortical responses in dogs and monkeys
* In 1In 1896 “d’Arsonval presents the first report of magnetically induced phosphenes in human subjects by stimulation of the retina, not the cortex”. - painless stimulation of nervous system by electromagnetic induction
* In 1910 “Silvanus P. Thompson experiments on himself. Again, the phosphenes were due to retinal, not cortical, stimulation. - First successful generation of magnetically induced phosphenes by d'Arsonval (1896), 1902 Beer, 1910 Thompson
* Mangussen and Stevenson - arrangment of coils to provide a magnetic field of sufficient strength to induce phosphenes
* In 1974, Baker begins using brief magnetic pulses to stimulate peripheral nerves and report msucule contractions and skin sensations
* In 1985 “Barker and colleagues report the first successful magnetic stimulation of the human motor cortex”. - current era of TMS machines begins
* In 1989, Amassian et al and Day et al publish first studies on TMS as virtual lesion technique in visual and motor cortex
* In 19991, Pascual-Leone et al report TMS induced speech arrest in population of epiletic subjects
* In 1994, Pasucul Leone et al produce visual extinction using repetitve pulse TMS
* In 1996, George et al report TMS related improvements in mood and concomitant changes in blood flow of prefrontal cortex in depression
* TMS lab at YNiC with TMS at Nov 2008
44
TMS operates on Faraday's principle of electromagnetic induction - (2)
- Faraday showed that an electrical current passed through one coil could induce a current in a nearby coil. The current in the first coil produces a magnetic field that in turn causes current to flow in the second coil
-
- In TMS, that second coil is replaced by brain tissue and the induced electric field elicits neuronal activity
45
What is phosphenes? - (2)
a sensation of a ring or spot of light produced by pressure on the eyeball or direct stimulation of the visual system other than by light.
i.e., stimulate visual cortex in dark room getting phosphenes
46
How does TMS work? - (2)
* Figure 8 TMS head coil over participants' head
* In the coil, current which induces magnetic field that goes through the skull and induces electric field in opposite direciton in underlying brain tissue
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48
Why do we use Figure 8 coil in TMS? - (2)
* graph of electric field
* The problem with using circular coil is that field is not specific as compared to Figure of 8 which targets specific region maximally and peak
49
What does this graph show in terms of principles of TMS? - (4)
* Important for TMS is the quick rise time of magnetic field pulse in milliseconds --> reason why it took long for TMS machines to develop
* Coil goes from 0 to 2.5 T in magnetic field pulse graph less than 0.2 milliseconds --> quick rise time
* The rate of change in magnetic field is what induces the electric field
* So stimulating coil current current goes have to go quickly and down as well as magnetic field pulse
50
Diagram of cortical effects of TMS how TMS affects brain processing- Baker's model - (5)
* How TMS affects brain processing depends on the orientation of the magnetic field to the axons
* Some regiosn axons are more organised and some regions are not
* In A, if we have magnetic field going along the axon then there is no change/effect on brain
* In B, if we have magnetic field crossing the axons perpendicular then see hyerpolarisation/depolarisation and if its strong enough then lead to action potential and see change in brain
* Same for if axon is bent across magnetic field in C and get differential which may induce change in AP
51
There is two modes of cortical effect of TMS
1. Disruptive mode is inducing neural noise to area of brains
2. Productive mode : stimulating areas of producing phosphenes (visual cortex; colour phosphenes if stimulating areas for colour) or hand movements (motor cortex)
52
Example of disruptive mode in TMS - (2)
e.g., adding noise to normal processing in area leading to slower performance in task that activates the region)
adding noise to speech production areas over making participant slower to speak - speech arrest but also confounds as eye blinking
53
TMS is a ... technique
interference
54
TMS is an interference technique meaning - (2)
* Infering with processing of the brain
* Either priducing something that is independent of external input or adding noise to normal processing
55
TMS can be designed to have in terms of pulses - (2)
single or trains of pulses (repetitive TMS- rTMS)
56
How does single TMS pulse work and its benefits - (3)
* o Apply a single TMS pulse to a brain area at specific times during the course of task trial (pulse delivered just before a stimulus for example or at a specific delay after a stimulus)
* Then researchers study its influence on task performance on that trial
* A benefit of this approach is that it has greater temporal resolution in measuring the role of brain area of interest in a cognitive task
57
fMRI and MEG measure
correlations
58
Example of single pulse of TMS - (2)
* Study looking at someone's motor threshold and seeing whats the minimal stimulation I have to give to participant to evoke a muscle evoked potential
* Give one pulse and see whether they move or not
59
How does repetitive TMS work generally?
* Apply a series of TMS pulses (e.g., one per second) over several minutes – repetitive TMS (rTMS)
* o The influence of rTMS on cognitive function can be examined by behavioural tests that can be done during or after TMS
o Research studies have demonstrated , using this approach, that depending on strength of stimulation the TMS can impair or improve performance on tasks involving the stimulated area which allows to produce inferences about the role of the area in performing that task
60
Trains of pulses repetitive TMS - rTMS can involve - (3)
* High frequency – typically online while participant is doing a task (E.g. 5 pulses at 10 Hz - quite fast), every 100 milliseconds get a pulse,
* Low frequency – typically offline meaning do this before someone does a task and changing state of an area (E.g. 1 Hz rTMS for 10 minutes)
* Theta burst (Huang et al., 2005) 50 Hz - 50 pulses in a second - high and short
61
Useful to use trains of pulse rTMS when:
not sure what time point an area is important
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low frequency rTMS is used for treatment
of depression
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Stimulation of human primary motor cortex (M1) using TMS has shown - (2)
* TMS can depolarize corticospinal tract neurons
* evokes contralateral (other side) hand muscle movements (measured in MEP - muscule evoked potential)
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In other brain regions, TMS simulation studies have shown - (2)
* TMS effect not constrained to stimulation site - esp low freuency pulse repetition
* propagates into connected and functionally coupled areas, including subcortical areas
65
In Allen et al., (2007) investigated other physiological effects in TMS
Methods - (3)
short rTMS trains (1-4 s) at various frequencies (1-8 Hz) in cat visual cortex
Had cats that either saw nothing or saw gratings on the screen. At same time applying short rTMS trains and chagning its length to 1-4 s and manipulate frequencies
Using measures of single unit activity, (electrodes in visual cortex and measured their firing) local field potential tissue oxygenation (looking at local field potentials outside the cell) and haemodynamic recordings (akin to BOLD in MRI)
66
What were Allen's et al., (2007) three key findings? - (3)
1. Effects more prounouced with longer trains and higher frequency
2. TMS perturbs phase relationship among neural responses
3. Tight coupling between TMS evoked neural responses and changes in cerebral hemodynamics
67
What did Allen's effects more pronounced with longer trains and higher frequency show - (3)
2. Enhacenement of spontaneous activity (if cat was not looking at something and stimulated) of up to 200% lasting up to 1 min after TMS
3. Activity in the visual cortex evoked by cats looking at sinusodial gratings suppressed up to 60% after TMS and gradually recovered after 10 minute or longer
4. Effects depend on stimulation frequency and duration
68
Allen's et al (2007) finding that TMS perturbs phase relationship among neural responses means - (2)
* This is when they looked at neural spikes and osciliations across frequency bands
* Phase relationship disturbed and disrupting normal neural processing
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What did Allen et al (2007) finding that tight coupling between TMS-evoked neural responses and changes in hemodynamics?
If stimulate in TMS changes in hemodynamic as TMS led to an initial increase and longer lasting decrease in tissue oxygenation and haemoglobin concentration
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Why is the spatial resolution of TMS confusing?
- The magnetic field produced by TMS is not spatially focal (centre)
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Experiments showing spatial resolution of TMS - (2)
* Paus et al (1997)
* Illmoniemi et al., (1997)
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Paus et al (1997) study of spatial resolution of PET - (4)
* Used TMS and PET (injection of radioactive tracer)
* Positive correlation between cerebral blood flow and number of trains at stimulation site
* Changes are small so in 1-2 cm in diamaeter of stimulation site
* Observed also distal CBF changes - at distant regions -stimulating at parietal cortex and see some changes in areas known are connected in pre frontal cortex
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PET measures
vivo measurements of CBF in humans.
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Illmoniemi et al (1997) study of spatial resolution of TMS using EEG and TMS (tricky switching EEG/TMS on and off alternating) -->
* EEG responses when stimulated in right hemisphere can spread to other hemisphere (left) within 20-30 ms
* There is a difference between physiological TMS effect ad functional TMS effect on behaviour e.g., might see some difference in simulation in activity of neurons whethr it is enough to produce change in behaviour/experience is another question --> exp design are important for this
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Studies investigating temporal resolution of TMS: deciding what timepoint important for brain region - (3)
* Critical time for TMS delivery coincides with time at which single unit responses can be recorded (earlier than ERPs)
* Effects of a single TMS pulse may last up to 70ms (but not all physiologically active)
* In behavioural studies: at least 10ms (Ashbridge et al. 1997)
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The temporal resolution of TMS depends on
using single or trains of pulse - single better than trains for temporal
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In order to show the
specificity
of a given TMS effect:
- (2)
* Control tasks --> baseline comparison and minimise confounds variables
* Control sites --> ideally quite close to ROI - offer baseline comparisons
78
The different approaches of localisation of TMS sites - (5)
1. fMRI-guided TMS Neuronavigation
2. MRI-guided Neuronavigation
3. TMS Neuronavigation based on group coordinates
4. TMS based on the 10-20 EEG System (anatomical landmark approach)
5. functional TMS localiser
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The different approaches of localisation of TMS sites ask
here do I know where am I stimulating in TMS
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What do we use in YNIC lab for registering MRI scan wtih TMS - (3)
Brainsight2 --> used for neurosuregrey
Participant come in lab with MRI scan done and already ahve their structural image and what you do is participant come in and coregisters the participants' structural MRI scan with participant in space of lab
Then put TMS coil and shows trajectory where magnetic field going in and target to area you want to target
81
What happens in fMRI-guided TMS neuronavigation?
TMS stimulation site is determined for each individual based on their personal activation peak for a specific fMRI contrast
82
Example of fMRI-guided TMS neuronavigation - (4)
* Using same participants for TMS in fMRI study doing task you are interested in
* Getting into fMRI scanner doing number processing task and control task
* For each pp do fMRI analysis and find region most active in number task vs control task
* Use that peak coordinates a marker in person's MRI scan which is then targeted using TMS coil
83
MRI-guided neuronavigation used
when don't hae money to use MRI experiment on 20 pps or many existing literature showing its TMS location site is near anterior IPS
84
In MRI -guided neuronavigation
TMS stimulaiton based on individual MRI data (e.g., anteiror IPS)
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TMS neuronavigation based on group coordinates is where
Stimulation site is
based on group
peak activation
of an fMRI
experiment - could be own research or another paper
86
TMS based on 10-20 EEG system in which - (2)
its anatomical landmark approach of where to put electrodes on cap uses inion and naisan of the participant
International 10-20 system for EEG placement is used (e.g. TMS stimulation site would be P4 for example)
87
The functional TMS localiser method is where
For each participant the site at which TMS provides maximal
disruption in a different task is determined
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2 examples of functional TMS localiser - (2)
1. want to find motor cortex by finding itroughly by using participants' hand jerking response
2. can find area known as forsal angular gyrus is important for visual searching by having participants do visual search task and hover coil and find area when participants have impairments in the taks in finding red line which was present in some trials (picture)
89
Sack et al., (2008) compared methods 1-4 which is - (4)
1. fMRI-guided TMS Neuronavigation
2. MRI-guided Neuronavigation
3. TMS Neuronavigation based on group coordinates
4. TMS based on the 10-20 EEG System (anatomical landmark approach)
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Sack et al., (2008) compared number of participants required to reach signifiance for methods 1-4 and found
Need less participants for methods 1 (5) than methods 4 (~43) to reach sig
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What are 2 examples of TMS experiments - (2)
Making the blindsighted see - silvanto et al ., (2007)
Combining TMS & fMRI
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What is blindslight? - (3)
Destruction of the primary visual cortex (V1) --> blind
Above chance ability to detect and localize stimuli in the blind field when they are forced --> showing which direction in which lights moving in
Some info in visual processing they are not aware of it
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Example of blindsight patient
Patient GY (no left V1 so blind in right visual field)
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Example TMS experiment of making blindsighted see in Silvanio rt al. waned to see
* Patient GY was tested on phosphenes so unaware on right visual field wanted to produce the experience on phopsohenes on right visual field he is blind in
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Metthodology of Silvanto et al., (2007) TMS experiment of making the blindsighted see - (4)
Uni/bilateral TMS stimulation:
Over V5/MT (since GY did not have V1)
As determined by individual MRI/fMRI for GY
Defined functionally for control participants
96
In Silvanto et al., (2007) TMS experiment subjective report of control participants --> where perceive phosphenes
A. unilateral
B. Bilateral TMS
A participants see phopshenes in left visual field when stimulating right in A
In B when stimulating both sides seeing phopshenes across both visual field
97
In Silvanto et al., (2007) TMS experiment subjective report of control participants -> where perceive phosphenes
A. unilaterla
B. Bilateral TMS - (2)
in A stimulating the right in which has right V1 seeing percepts of phosphenes in left visual field hes not blind in like in control pps
In B, however, stimulated both motion areas for very first time in time he reported seeing flasshes in his blind right visual field
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What does Silvanto et al., (2007) study show - (2)
GY experiences TMS induced visual qualia in his blind field for bilateral TMS stimulation
V1 necessary for conscious awareness
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In experiment combining TMS and fMRI they saw that there is changes seen in braina ctivation in stroke and wanted to see - (2)
Is this due to altered brain structure? = differences in connectivity
Or related to reorganisation of brain function? = or right hemisphere taking over functions of the left
100
In combining TMS and fMRI they did 2 tasks of select and execute in which - (2)
In the execute task the participants had to press a button index finger when they saw a circle or a square.
In the select task the participants had to press buttons with two different fingers, depending on which forms they saw - task where premotor task is involved in
101
Incombining TMS and fMRI experiment they - (4)
* Used TMS to stimulate a lesion in healthy pps
* Used TMS and fMRI to inspect brain changes
* If reorganisation is the reason then see with TMS
* If its due to altered brain connectivity it should be seen in MRI and not brief TMS
102
Diagram of brain activation in healthy participants in combining fMRI and TMS experiment:
Healthy participants had higher activation in select task than execute task in right and left pre motor cortex
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What we are interested in combining TMS and fMRI is that:
After a unilateral stroke affecting the dorsal premotor cortex in one hemisphere the dorsal premotor cortex in the intact hemisphere is often more active
is this... - (2)
Is this due to altered brain structure/connectivity?
Or is it related to reorganisation of brain function?
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In combining TMS and fMRI
How to answer the question
After a unilateral stroke affecting the dorsal premotor cortex in one hemisphere the dorsal premotor cortex in the intact hemisphere is often more active
Is this due to altered brain structure/connectivity?
Or is it related to reorganisation of brain function?
- (2)
* did fMRI tasks of select and execute pre TMS then TMS then fMRI tasks post TMS
* in TMS, applied TMS to pps left premotor cortex
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Results of combining TMS and fMRI - (2)
* They found in healthy participants, after 1 Hz TMS over left pre motor cortex in high activity in right premotor cortex in select task than execute task
* After 1 Hz TMS over left sensory motor area (control site) found no increase in BOLD response in right pre motor cortex in two tasks
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What conclusion did experiment of combining MRI and TMS did
Changes in stroke patients in right dorsal premotor cortex are due to reorganisation of function and not only due to changes in brain structure
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What are strengths of TMS - (6)
Reveals causal links between brain regions and function
High temporal precision, reasonable spatial precision (depends on using single/trains of pulse/localisation methods)
Experimentation is relatively easy and cheap
Higher spatial resolution than EEG, ERP or MEG
Higher temporal resolution than fMRI or PET
Based on interference and not correlation
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What is weakness of TMS? - (5)
Underlying neural mechanisms not yet well understood
Widespread, remote effects possible
Cannot specifically target all part of the brain --> TMS tends to affect a large area limiting anatomical resolution and TMS only delivered effectively to superifical exterior brain regions
Technique can result in concurrent (simultaneous) stimulation of scalp and head muscles , especially attempting to stimulate specific regions of frontal and temporal lobes, which can cause uncomfortable and even painful twitching
Although TMS is non-invasive, stimulation entails some risk (e.g., strongly stimulating brain may trigger a seizure in a person with physiological predisposition towards epilepsy)
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Double dissociation can also be called
cross-over dissociations
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The first person to use electromagnetic induction to stimulate the nervous system was
A. Duchene
B. Thompson
C. Faraday
D. d'Arsonval
D
111
Which of these frequencies is NOT typically used when rTMS is applied to human subjects ?
A. 1
B. 10
C. 15
D. 50
C
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Which of the following physiological effects of TMS was NOT found in the study by Allen et al. (2001) ?
A. enhacment of spotaneous neural activity after TMS
B. visual cortex activity evoked by gratings is increaed by TMS
C. Perturbed phase relationship between neural responses
D. tight coupling between TMS evoked neural responses and changes in cerebral haemodynamics
B
113
Which of the following best describes the situation in which performance of a cognitive task A but not task B is impaired by damage to a particular neural structure, while damage to a different neural structure impairs task B but not task A?
A.single dissociation
B.double dissociation
C.cognitive disassociation
D.an interaction effect
B
