TMS and Perception (1) Flashcards
What did Donders (1818-1889) do?
- he developed mental chronometry
- he also created the reaction-time experiment
What is a reaction-time experiment?
- measures interval between stimulus presentation and person’s response to stimulus
What is mental chronometry?
- a measure of how long a cognitive process takes
What is the simple RT task?
- participant pushes a button quickly after a light appears
- steps: perceive the light, generate the response
What is the choice RT task?
- participant pushes one button if light is on the right side and another if the light is on the left side
- steps: perceive the light, select a button to push, generate the response
What is the subtraction method?
- Choice RT - Simple RT = Time to make a decision
How much longer does choice RT take compared to simple RT?
- 0.1 s or 100 ms
What are the assumptions of the subtraction method?
- assumption of serial stages: that processes are non-overlapping or parallel
- assumption of pure insertion: that the addition of a choice does not affect length of other processes
According to Donders, how can mental processes be measured?
- cannot be measured directly but can be inferred from a participants behaviour
What did Ebbinghaus do?
- he created the savings curve method for studying forgetting
- aimed to look at the contents of the mind including what’s unconsciously there
What is the task involved with the savings curve method?
- view a series of nonsense syllables (ex. DAX or LUH)
- repeat and predict what the next syllables will be until you can do it correctly
- after a period of time, see if you remember
What do people experience when doing the savings curve method?
- they have to repeat a fewer amount of times to ‘relearn’
- even if they have no conscious memory, at 31 days they have 20% savings
How is ‘savings’ calculated in the savings method?
savings = (initial reps - relearning reps) / initial reps
What happened during the cognitive revolution?
- birth of the digital computer
- theory of computation
- information theory
- computer science
- artificial intelligence
What did Alan Turing do?
- computability: anything that can be computed is computable by a simple “universal machine”, i.e. a Turing machine
- to the extent that what the mind does is compute, it can be specified as a computer program
What did George Miller say?
- I date the moment of conception of cognitive science as 11 September, 1956…”
What is cognitivism?
- mental functions can be explained by the use of experiments following the scientific method
- cognition consists of internal mental states whose manipulation can be described in terms of algorithms
What is cognitive psychology?
- the scientific study of how people perceive, learn, remember and think about information
- rejects introspection as a primary tool
- accepts the existence of internal mental states
What are some famous phrenologists?
- Franz Joseph Gall
- Johann Spurzheim
What is phrenology?
- interested in how the brain relates to the mind
- brain is the organ of the mind (not heart)
- parts of the brain represent different faculties with the size of the part indicating the “strength”
- studied from the outside of the brain using bumps and depressions
How many traits were identified in phrenology?
- 27 traits
- 19 common to human and animals (reproduction, courage)
- 8 unique to humans (Wisdom, vanity, satire, religion)
Which groups opposed phrenology?
- anti-localizationists: argued brain functions are an indivisible unit (brain not in sections)
- anti-materialists: argued mental/spiritual faculties are not of organic matter (mind not tied to physical part of body)
- both were wrong
What two psychologists provided evidence for localization in the 19th century?
- Paul Broca’s Tan
- Carl Wernicke
- found specific functions to be associated with specific locations
What did Paul Broca observe?
- speech loss not due to paralysis
- “loss of memory of movements needed to pronounce words”
- Broca’s area in left frontal lobe
What did Carl Wernicke observe?
- cases of lost speech comprehension
- Wernicke’s area in left temporal lobe
What were the implications of Broca’s and Wernicke’s discoveries?
- shift towards physiologically real functions (motor and sensory)
- localization of higher mental functions
How did cognitive neuropsychology start out?
- identifies the mechanisms that underlie cognition by studying the effects of brain damage
- localizes these mechanisms to particular neural structures or processes
- identifies the functions of brain regions
What does cognitive neuropsychology look like today?
- invention of non-invasive techniques to image the human brain
- the most influential technique being fMRI
How did cognitive neuroscience start?
- merging of two streams
- cognitive psychology and cognitive neuropsychology
- measure brain function and behaviour
Who coined the term cognitive neuroscience?
- George Miller and Michael Gazzaniga
What are the basic goals of cognitive neuroscience?
- determine how the brain mediates cognition and behaviour
- relate neural structures to mental functions
Why is measurement and manipulation a methodological issue?
- Is the method measuring brain activity or manipulating it?
- What specifically is it measuring or manipulating?
What are some safety concerns?
- Is it invasive?
- What are the risks?
- What are the contraindications
What is spatial resolution?
- how detailed an image is
- a low resolution image will be very pixelated
What is temporal resolution?
- frames/second
- a low resolution image will look ‘jumpy’ whereas a high resolution will be smooth
Why is fMRI so revolutionary?
- in general imaging methods that are more invasive have better temporal and spatial resolution
- fMRI has good spatial and temporal resolution despite being non-invasive
Why are parameters a methodological issue?
- need to consider what the options or settings are
- ex. ERPs: number of electrodes
Why are experimental limitations a methodological issue?
- need to consider the complications/limitations of the experimental design
- ex. fMRI: noisy, can’t move
Why is experimental design a methodological issue?
- need to consider the typical experimental design for a certain type of measurement
Why is data preprocessing and data analysis a methodological issue?
- Need to consider what has to be done to the data before it can be analyzed
- need to consider how data is typically analyzed
Why is interpreting results a methodological issue?
- need to consider what we can and can’t conclude
How did transcranial magnetic stimulation (TMS) begin?
- wanted to manipulate brain without invasion
- early attempts struggled to generate necessary field strength (Thompson)
When was the first successful TMS on humans?
- 1985
- Barker et al
- they used a smaller coil and stronger magnetic fields
How does TMS work?
- run a strong current through a coil to produce a magnetic field
What are the types of TMS coils?
- round coil
- figure eight coil
- double coil
- H coil
How does TMS stimulate the brain?
- the magnetic field induces current in the brain
- in other words causes neural activity or changes in resting potentials
Where do the strongest voltage effects occur?
- for the round coil: in a circular shape that mirrors the coil
- for the figure eight coil: between the two coils giving a more precise reading
- the activity is localized but non-specific!!
What is important for inducing the current?
- rapid change in magnetic field, not the strength of the magnetic field
What technology uses the same principle as TMS?
- wireless (inductive) charging
- induce current in phone using coils to charge
What are the two types of effects TMS can have?
- activation/facilitation: muscle movements, phosphenes
- inhibition/disruption: impaired movement, scotomas
What are the (physical) safety risks of TMS?
- seizure induction: caused by spread of excitation
- Hearing loss: because of loud click in the most sensitive frequency range
- local neck pain and headaches: caused by stimulation of local muscles and nerves (particularly over fronto-temporal regions)
When is seizure induction most risky?
- for single-pulse TMS, only seizures in patients have been induced
- with rTMS seizures can be induced in patients and normal volunteers
What are the (psychological) safety risks of TMS?
- effect on cognition: improved verbal memory, delayed recall and better motor rt
- effect on mood in normals: dependent on site and frequency, can worsen or improve
- long-term effects: if multiple sessions of rTMS
What must be considered to make rTMS safe?
- limit on duration based on frequency
- ex. at 1 Hz, duration can be 1800+ s and at 25 Hz, duration can be .84 s
- guidelines are not perfect however
What is a motor threshold?
- calibrated for each participant
What are some contraindictions (reasons not to be a participant) for TMS?
- metallic hardware
- history of seizures
- pregnancy
- history of head trauma or substance abuse
- stroke
- brain surgery
- other medical conditions or medications associated with seizures
What are some guidelines to follow when administering TMS?
- safety screening
- informed consent
- potential benefit must outweigh risk
- equal distribution of risk (vulnerable patient populations should be avoided)
How is TMS spatial resolution?
- depends on coil shape and size
- as good as a few millimeter for peak effect
- peripheral areas also effected
How is TMS temporal resolution?
- single pulse TMS: about 1 millisecond!
- rTMS: depends on duration of pulse train (less than one second to greater than a minute)
What are the parameters of TMS?
- pulse sequence, frequency and duration
- location and orientation
- intensity (motor threshold used as a reference point)
What are the experimental limitations of TMS?
- limited stimulation depth (can’t reach medial and sub-cortical areas)
- difficulty to localization
- spread of activation (connected effects and paradoxical effects)
- noise (distracting)
- risks
What are connected effects?
- when regions are affected due to a connection to the region being stimulated
What are paradoxical effects?
- when the region that you are applying TMS to normally inhibits another region, but the TMS causes a release of the inhibition
What are the experimental designs used with TMS?
- mapping in space (virtual lesion): where things are being processed
- mapping in time (chronometry): when things are being processed
- may use multiple coils
- may combine with EEG, PET, fMRI..
How are the results f TMS interpreted?
- virtual lesion: infer role by resulting deficit
- chronometry: infer timing of neural processing
- functional connectivity: infer connectivity between brain areas by effects of spreading activation
