2 The Lesioned Brain Flashcards
what is TMS
• TMS: a means of disrupting normal brain activity by introducing neural
noise – ‘virtual lesion’
• Michael Faraday (1791-1867)
not a lesion as not producing brain damage but a virtual lesion
stimulating the brain
what is faradays coil used in
TMS
What does TMS use
principles of electromagnetic induction
Coil - connected the wire to the electrical source and the battery and the wire to the volt meter best when switched on and off the battery could see the electrical current in the part of the wire that was not connected to the electrical source - there bc of the magnetic induction
The principle of how TMS works
the modern TMS machine
In order to stimulate the brain first we need to produce a lot of electrical energy and it’s produced in the boosters behind the blue boxes. A lot of electrical current is giving us a very high magnetic field , 2.5 Tesla it is a magnetic field also found in an MRI scanner
In order to induce electrical current in the brain this magnetic field needs to change rapidly, rate of change of magnetic field that is inducing an electrical field in the brain and then induced current tissues is flowing not only under the stimulated region but also flowing through other regions connected to that region that are active for example when people are engaged in a certain cognitive task
what is the TMS coil current
8kA
what is the Magnetic field pulse
2.5T
what is the rate of change of magnetic field
30kT
what is the induced electric field
500v/m
what is the induced tissue current
15mA/cm2
what does fMRI and PET show
fMRI and PET give us correlational evidence of brain activity so we don’t know if all these areas are absolutely necessary for the task or whether they’re just engaged in certain tasks - we then use TMS and then we can stimulate each of the nodes of this network and see if we can measure a behavioural change.
what happens when we apply tm to a critical node
If we apply a TMS pulse to any of the critical nodes and then can measure for example behaviour or how fast people are in responding to semantic categorisation we will find out if the area is critical for example inferior frontal gyrus it will take us longer to read than if the area is just supporting a certain task.
why do TMS
- Task: (i.e. reading) : a neural netw ork com prised of different brain areas is active in supporting the task.
- Apply TMS pulse at any cortical node (area) of the network, TMS will interfere with the relevant neural signal:
- efficacy of the neural signal will be degraded • observe change in behaviour (RT change – it will take us longer to read)
What are the advantages of TMS
- Interference/virtual lesion technique.
- transient and reversible
- control location of stimulation
- establishes a causal link of different brain areas and a behavioural task
where is language considered a function of
the left side of the brain
what does fMRI shoe about language lateralisation
graded continuum of language lateralization
what is Transcranial Doppler Sonography (TCD)
- functional lateralization
language lateralisation
Predict how people will recover from a stroke or aphasia as a consequence of a stroke depending on where their language lateralisation lies.
Language is function of left but most people have bilateral language mapping bc there are some aspects of language processing such as processing metaphors or jokes that are more of a right hemisphere function however articulation of language is definitely a left hemisphere function except in a small number of people where we actually have a right hemisphere articulation of language
what happened in language study
- Participants: left or right language dominant
- Picture - word verification task
- Off line TMS (600 pulses, 10 min, 110% MT)
People come to lab and do tasks without TMS and then have TMS either on left or right wernickes area and also a control stimulation on the occipital side and then test again with the same behavioural task .
Measure the behaviour behaviour before and after TMS and look at the changes
what were the findings of the language study
Language disruption correlated with degree and side of lateralization.
When stimulated the right wernickes area - left dominant people were faster in word picture verification task
Opposite is true for right dominant people
Right dominant language - stimulated right wernickes area - slower by 18 milliseconds
Left wernickes area- caused 15ms faster in right dominant people
Occipital people did not cause any changes
what is TES
transcranial electric stimulation
is TES modulation
not a stimulation technique bc it is a modulation technique - called stimulation but amount of electrical stimulation that is applied is really low -therefore we know that we cannot properly stimulate the brain but we can definitely modulate the brain response
what currents does TES use
TES uses low level (1-2 mA) currents applied via scalp electrodes to specific brain regions
what are the 3 different protocols for TES
- Transcranial direct current stim ulation - tDCS
- Transcranial alternating current stim ulation -tACS
- Transcranial random noise stim ulation - tRNS
what is the current generator
Current generator: battery delivers constant current of up to 2mA, with 2 sponge electrodes in saline solution (20-35cm2). The stimulation is less focal, and very safe
what happens when tDCS is applied in sessions of repeated stimulation
When applied in sessions of repeated stimulation, tDCS can lead to changes in neuronal excitability that outlast the stimulation itself. Such aftereffects are at the heart of the tDCS protocols for clinical application (Nitsche et al., 2011)
what does TES have promisin results in
Promising results in therapy: migraines, dementia, stroke, Parkinson’s disease, neglect, depression, schizophrenia, OCD, eating disorders….
what is tDCS
transcranial direct current stimulation
what is tACS
transcranial alternating current stimulation
what is tRNS
transcranial random noise stimulation
what is the tCDS protocol
- Anodal : facilitation effects
- Cathodal:– inhibition effects
- Sham (CONTROL) - 30sec stimulation
positive electrode
anode
negative electrode
cathode
what happenns in tDCS
Direct current stimulation- flows from the anode to the cathode
In the alternating current stimulation - current flows from anode to cathode and back at a certain frequency that we preset
Usually in tDCS the anodal stimulation has facilitatory effects
Cathodal - inhibitory effect
Control - sham - 30s - people cannot judge the difference
what does anodal stimulation inhibit
GABA
what does cathodal stimulation inhibit
glutamate
what is GABA
Inhibitory neurotransmitter - GABA
If you inhibit the inhibitory neurotransmitter you will get excitation
what is glutamate
In the modern nervous system
Inhibits glutamate
Glutamate is an excitatory neurotransmitter
Will usually produce inhibition
what current does tACS use
Transcranial alternating current stim ulation (tACS) uses low level (0.5-2 mA) alternating currents applied via scalp electrodes to specific brain regions.
what happens in tACS
The rationale behind tACS is the entrainment (synchronization) of internal brain rhythms with externally applied oscillating electric fields. The oscillatory fields cause phase-locking of a large pool of neurons, leading to increases of neural synchronization at the corresponding frequency
Low level current
Current alternates from anode to cathode at certain frequencies
Applied to the brain rhythms already in the brain
brain has its own oscillations that can be picked up by EEG
Apply 2 electrodes and alternating currents at certain brain areas- alternating current can then cause entrainment - it can enhance certain brain frequencies at the frequency it is applied - produces a modulation of a certain brain oscillation that are for example important for certain tasks
what is a lucid dream
Inducing and lucid dreaming
A lucid dream can be thought of as an overlap between two states of consciousness — the one that exists in normal dreaming, and the one during wakefulness, which involves higher levels of awareness and control
In lucid dreaming, we transfer elements of waking consciousness into the dream
Such overlap is reflected in the brain waves (EEG). When people have lucid dreams, they show gamma waves in the frontal cortex, an activity pattern that is linked to consciousness but is nearly absent during sleep and normal dreaming
what happens in the frontal cortex in lucid dreaming
increased gamma activity
linked to conscious but nearly absent in normal dreaming
what happened in the lucid dreaming study
EEG was measured in 27 participants who were not lucid dreamers, while tACS was applied 2min
2 minutes after participants entered REM phase, tACS was applied for 30sec in the range of 2Hz-100Hz. The participants were then immediately woken up to report their dreams (LuCID scale)
The LuCiD scale consists of 28 statements, each followed by a 6-point rating scale (0 strongly disagree - 5 strongly agree).
The EEG data showed that the brain’s gamma activity increased during stimulation with 40 Hz, and to a lesser degree during stimulation with 25 Hz
what are the 3 components measured in lucid dreaming
Insight is the awareness that one is currently dreaming
Dissociation is taking a third-person perspective
Control is control over the dream plot
conclusions of lucid dream study
if applied tACS at gamma frequency it induced lucid dreaming
does non-invasive brain stimulation have a prominent effect on cognitive processes
yes
can TMS and tES cause after-effects on excitability of neurons and networks that outlast the stimulation by minutes, even hours
yes
can TMS and tES combined with behavioural training offer promising alternatives to pharmacological interventions and can enhance cognitive performance
yes
why do we study brain damaged patients
Studying brain damaged patients – by studying abnormal, it is possible to gain insight into normal function
what are the 2 traditions of patient-based neuropsychology
Patient based neuropsychology has two traditions:
- Classical neuropsychology
- Cognitive neuropsychology
what is classical neuropsychology?
Classical neuropsychology: What functions are disrupted by damage to region X?
Addresses questions of functional specialization, converging evidence to functional imaging
Tends to use group study methods
Intuitive
Damage - what can these people do
Combined with fMRI studies to inform cognitive theories
what is cognitive neuropsychology?
Cognitive neuropsychology: Can a particular function be spared/impaired relative to other
cognitive functions?
Addresses questions of what the building blocks of cognition are (irrespective of where they are)
Tends to use single case methodology
single patient with damage
brain damage
- Cerebrovascular accident (CVA or stroke)
- Neurosurgery (split brain)
- Viral infections (HSE - herpes, HIV)
- Tumour (glioma)
- Head injury (traffic accidents, rugby)
- Neurodegenerative disease (Dementias: Alzheimer type)
what is a stroke
A stroke - loss of brain function after disturbance of blood supply
what is ischemia (ischemic stroke)
lack of glucose and oxygen supply
blood clot stops the flow of blood to an area of the brain
ischemic stroke - lack of glucose and oxygen supply and it is usually a clot that isn’t allowing the blood to reach all areas of the brain - brain areas die off
what is a hemmorrhagic stroke
bleeding into brain tissue
weakened/diseased blood vessels rupture
blood leaks into brain tissue
Haemorrhage- blood vessel or capillary can burst and blood can blood brain tissue and then our neurons drown in the blood - death of brain cells
what does neuropsychology testing test
• Intelligence • Memory • Visuospatial • Executive functions • Sensation
what neuropsychological test is for semantic memory
pyramids and palm trees
which is more similar in meaning to probe
camel and cactus
what neuropsychological testtests visuospatial testing
figure of ray
copu picture or draw figure of ray from memory
what happens when people recover from accute stage of stroke
When patients recover from this acute phase of the stroke cognitive neuropsychologists come in and give them loads of neuropsychological tests
See what functions are spared or impaired
what is a single dissociation
If a patient is impaired on a particular task (Task A), but relatively spared on another task (Task B), this is known as a single dissociation
what is a classical single dissociation
If patient performs within the normal range on the Task B, this has been termed as classical single dissociation
what is a strong single dissociation
If patient is impaired on both tasks, but is significantly more impaired on one task, this is referred to as a strong single dissociation (Shallice, 1988)
what is an example of a classical single dissociation
patient CF
patient CF
Patient CF – 43 year old right handed engineer, suffered an ischemic stroke to the left parietal area (angular gyrus - AG); Examined 2 weeks post the stroke. At the time of examination he was completely speechless, but could communicate through gestures. Wrote with his left hand (right hemiplegia).
When writing words he systematically omitted vowel only
BOLOGNA – BLGN
TAVOLINO - TVLN
Cubelli, 1991
By contrast Kay and Hanley (1994) reported another patient who made spelling errors selectively on consonants (e.g. “record” is spelled as recorg)
what do single dissociations show
The basic logic behind these single dissociations is that a difficulty in one domain, relative to an absence in difficulty in another domain can be used to infer the independence of these domains - cognitive neuropsychology
Comparing these two cases, we could conclude that the brain has separate neural resources for processing of written vowels relative to consonants
This difference could be relative, neuropsychologist test for a whole range of stimuli in order to make conclusions about the exclusivity of function
RFTD - a case study - strong single dissociation
Behavioural variant of frontotemporal dementia / right hemispheric variant of semantic dementia
• Now on sick leave (60y old)
• kisses, sings and humms to customers for the past 3-5 years
• also sings happy birthday to her dead relatives on the cemetery
misunderstanding the meaning social behaviour and sensory social cues
SD - a case study
strong single dissociation
Single case study of semantic dementia - atrophy or neurodegeneration in the temporal areas
This patient has neurodegenration in the left anterior temporal lobe
what is social concept discrimination task
social judgement. vs animal function judgement
Behavioural task
Respond as accurately as possible whether the proverb matches one of the two distractor
what did the social concept discrimination task show
Both patients were significantly impaired on both social and non social tasks
Left ATL- SD - equally impaired on both social and non social tasks
Right ATL - RFTD - was significantly more impaired on the social tasks - example of a strong single dissociation
RFTD case - an example of strong single dissociation (processing of social concepts in particular)
what is a double dissociation
Most of the neuropsychological work aims at showing that 2 or more tasks have different cognitive and neural resources
Double dissociation is derived from 2 (or more) single cases with complementary profiles
Brain has separate neural resources for processing written vowels relative to consonants
two patients form a double dissociation
cubelli and kay and hanleys findings form a
double dissociation
vowels and consonans
example of a double dissociation
language
brocas aphasia and wernickes aphasia
what happens in brocas aphasia
Brocas aphasia - conditions known as production aphasia - patients that have damage in the green areas have difficulty with language production but usually they understand language quite well
what happens in wernickes aphasia
Wernickes aphasia - patients have more difficulty with meanings of the language and they can usually have a relatively fluent speech
issues with single case studies
- Lesion needs to be assessed for each patient, and no guarantee that same anatomical lesions have same cognitive effect in different patients
- Therefore the cognitive profile of each patient needs to be assessed separately from other patients
- Argument is not against testing more than one patient, but this becomes a series of single case studies and not necessarily a group study (in that the data from patients are combined to a group average)
can you form an average observation from single studies
no
one can not average observations from single studies because each patient may have a different cognitive lesion that we can not know a priori- before we administer the experiment
why do we present group data as a series of single cases
bc different lesions - different observations
their performance varies even though all classed as semantic dementia patients
what are groups studies
There is a reason to group patients - can group by syndrome, behavioural symptoms or by lesion location
group by syndrome
(1 ) Group by syndrome: useful for investigating neural correlates of a disease
pathology (e.g. Alzheimer’s) but not for dissecting cognitive theory
Syndrome - useful way of grouping e.g. when interested in neural correlates of the disease for example Alzheimer’s disease but not for cognitive theory
group by behavioural symptom
(2) Group by behavioural symptom: Can potentially identify multiple regions
that are implicated in a behaviour
Symptoms - important for cognitive theory but there can be different areas of brain that are implicated for different behaviours
grouped by lesion location
(3) Group by lesion location: Useful for testing predictions derived from functional imaging
Lesion location - important for predicting where our activations from functional imaging can occur
what is the independent variable
grouping
what is the dependent measure
data
group study
behavioural syndrome - lesion location
behavioural symptom - lesion location
lesion location - behavioural symptoms
methods for studying the brain
Transcranial Magnetic Stimulation (TMS) Transcranial Direct Current Stimulation (tDCS) Neuropsychology
what is cognitive subtraction
In functional neuroimaging studies, cognitive subtraction refers to an aspect of experimental design involving the comparison of two conditions or brain states that are presumed to differ in only one discrete feature (the independent variable). Cognitive subtraction designs rely on the assumption of “pure insertion” – the notion that a single cognitive process can be inserted into a task without affecting the remaining processes, or that there are no interactions among the cognitive components of a task.
brain imaging on the exam
TMS
tDCS
neuropsychology
lesion brain
