Lec 3: Methods

Question 1

single-cell recordings (neurophysiology)

Answer 1

• used to understand what individual neurons are responding to
• used on non-human animals
• measures neural activity
• primary goal to determine which experimental manipulations produce a consistent change in the response rate of an isolated cell
• this method on its own is not sufficient for understanding brain dynamics

Question 2

lesion studies (neurophysiology)

Answer 2

• experimentally induce a lesion (site of damage) that is very specific
• gives us a better understanding of what that particular area is

Question 3

medical uses of cognitive neuroimaging

Answer 3

• identifying problematic medical impairments
• localizing anatomical and/or functional disruption(s)

Question 4

experimental uses of cognitive neuroimaging

Answer 4

• examining healthy (and impaired) brain topography (structural analysis)
• examining healthy (and impaired) brain functioning (functional analysis)

Question 5

computerized axial tomography (CT scan)

Answer 5

• provides birds eye view and slice of brain
• uses 3D x-ray and makes use of diff. tissues in our bodies taking up diff. amounts of radiation
  limitations:
• not super sharp imaging
• exposing someone to radiation

Question 6

structural magnetic resonance imaging (sMRI)

Answer 6

• uses magnetic properties
• person enters strong magnetic field, and their protons become oriented parallel to magnetic field
• introduce radio waves to magnetic field and protons absorb energy and their orientation is altered
• radio waves turn off and protons rebound toward orientation of magnetic field, produces energy signals
• signal given off when this occurs is called resonance
• different tissues in the body have different resonance properties
• high resolution, safe, efficient

Question 7

voxels

Answer 7

• have to do with sMRI
• way to quantify brain space
• can specify the size of brain lesions

Question 8

lesion overlap method

Answer 8

• can overlay mri photos on top of each other and create a heat map on where common injury is
• can identify areas of the brain that are consistently damaged in a particular syndrome

Question 9

diffusion tensor imaging (DTI)

Answer 9

• uses an MRI machine
• offers info on anatomical connectivity between brain regions
• in brain, anisotropy (directional dependent movement of water molecules) is greatest in axons bc. myelin sheath creates pure li[id boundary
• boundary limits directional flow of water molecules in greater degree in white matter and water is more likely to move in direction parallel to axons
• introducing 2 large pulses to magnetic filed makes MRI signals sensitive to diffusion of water
• 1st pulse determines initial position of protons carried by water
• 2nd pulse (after short delay) provides 2nd image, each proton has moved during the delay and DTI estimates diffusion of protons
• bc. flow of water is constrained by axons, resulting images reveal major white matter tracts
• can track neurodevelopment and brain injury

Question 10

electroencephalography (EEG)

Answer 10

• electrodes placed on multiple areas of the scalp and each electrode creates a recording channel
• important for epilepsy and seizure research
• good temporal resolution, weak spatial resolution bc. measuring through the skull

Question 11

temporal resolution

Answer 11

can tell you what is happening in brain at a millisecond level (time)

Question 12

spatial resolution

Answer 12

can tell exactly where brain activity is coming from

Question 13

electrocorticography (ECoG)

Answer 13

• EEG directly on the brain
• increases spatial resolution bc skull is not in the way
• can only measure small part of the brain, can’t put a grid on the whole brain bc. you have to remove part of the skull
• ECoG electrodes are quite large, method is always based on measurement of the activity of populations of neurons
• good for seizure research

Question 14

functional magnetic resonance imaging (fMRI)

Answer 14

• uses same brain scanner as sMRI
• most commonly used
• looks at changes in blood flow
• deoxygenated hemoglobin is paramagnetic (weakly magnetic in presence of magnetic field) and oxygenated hemoglobin is not
• detectors measure the ratio of oxygenated to deoxygenated hemoglobin; value referred to as blood oxygen level dependent (BOLD) effect
• where oxygen-rich and oxygen-poor blood goes in the brain
• more oxygen blood flow = more neural activity
• uses the BOLD signal
• good spatial resolution but weak temporal solution bc it can only take full image of the brain ever 1 second

Question 15

BOLD signal

Answer 15

• used in fMRI
• Blood Oxygenation Level Dependent
• higher bold signal = more neural activity

Question 16

transcranial magnetic stimulation (TMS)

Answer 16

• temporary induction of brain dysfunction by generating a magnetic field that alters electrical activity in neurons
• repeatable
• allows us to have knowledge of pre-injured state which helps us determine how big the effect of the brain injury actually was
  limitations:
• can only activate relatively superficial areas
• can be secondary effects on connected cortical areas, limiting the spatial resolution

Question 17

spatial resolution

Answer 17

refers to the ability of a technique or method to distinguish between different brain structures or regions

Question 18

temporal resolution

Answer 18

• refers to the ability of a technique or method to capture the timing of neural activity
• describes how precisely and frequently changes in brain activity can be detected over time.

Question 19

transcranial direct current stimulation (tDCS)

Answer 19

• delivers constant, low current to brain via electrodes on scalp
• current is sent between 2 electrodes: anode and cathode
• neurons under anode become depolarized, more likely to initiate A.P., leads to improvement in performance
• neurons under cathode become hyperpolarized, less likely to fire, leads to hinderd performance
• can selectively excite or inhibit targeted neural areas
  limitation: poor spatial resolution

Question 20

transcranial alternating current stimulation (tACS)

Answer 20

• uses oscillating electrical current
• diff. frequencies of brain oscillations are associated with diff. cog functions

Question 21

transcranial static magnetic stimulation (tSMS)

Answer 21

• uses strong magnets to create magnetic field that disrupts electrical activity and temporarily alters cortical function
  pros:
• inexpensive and does not require skilled operator
• does not produce side effects of other techniques

Question 22

transcranial focused ultrasound (tFUS)

Answer 22

• emerging method promising improved spatial resolution and ability to target deeper structures
• generation of low-intensity, low-frequency ultrasound signal that increases activity of voltage-gated Na+ and Ca+ channels, triggering A.P.s

Question 23

single dissociation

Answer 23

• Occurs when a lesion or damage to a specific brain area affects one cognitive function but not another.
• suggests that the affected brain region may be important for the impaired function but does not definitively demonstrate whether the two functions are independent or rely on different brain systems

Question 24

double dissociation

Answer 24

• Occurs when two patients with damage to different brain regions show opposite patterns of cognitive impairment
• damage to one brain area affects Function A but not Function B, while damage to another area affects Function B but not Function A
• provides stronger evidence that the two cognitive functions rely on separate and independent brain systems, rather than one function being a byproduct of the other

Question 25

event-related potential (ERP)

Answer 25

• tiny signal embedded in ongoing EEG triggered by stimulus or movement
• by averaging traces, can extract this signal, which reflects neural activity specifically related to the sensory, motor, or cognitive event that evoked it

Question 26

Magnetoencephalography (MEG)

Answer 26

• measures the magnetic signals generated by the brain
• Sensitive magnetic detectors placed along the scalp measure the small magnetic fields produced by the electrical activity of neurons
• record and average MEG traces over a series of trials to obtain event-related signals, called event-related fields (ERFs)
• ERFs have the same temporal resolution as ERPs, but they have the advantage that we can estimate the source of the signal more accurately
  limitation: system is expensive because the magnetic fields generated by the brain are extremely weak.

Question 27

hemodynamic response

Answer 27

• change in blood flow to neural tissues
• can be detected by PET and fMRI

Question 28

Positron emission tomography

Answer 28

• use radioactive-labeled compounds to measure local variations in cerebral blood flow that correlate with mental activity
• inject radioactive substance (tracer) into the bloodstream, the more active neural areas have higher metabolic demand and therefore receive more tracer
• the PET scanner monitors the radiation emitted by the tracer
• common isotope used is oxygen-15
• poor temporal resolution
• constrained by decay rate of the radioactive agent

Question 29

block-design experiment

Answer 29

• used in PET studies and less commonly in fMRI
• block consists of multiple trials of the same type
• activity across the block is averaged and can be compared to activity in another block of a different trial type
• Because of the extended time requirement, the specificity of correlating activation patterns with a specific cognitive process suffers

Question 30

event-related design

Answer 30

• used in fMRI studies
• different types of trials may occur randomly
• BOLD response to particular stimuli or responses can be extracted from signal data
• BOLD response links to specific events, such as the presentation of a stimulus or the onset of a movement
• because the researcher presents the experimental and control trials randomly, helps ensure that the participants are in a similar attentional state during both types of trials
• increases likelihood that observed diffs. reflect hypothesized processing demands and not more generic factors

Question 31

multivoxel pattern analysis (MVPA)

Answer 31

• pattern classification algorithm in which researcher identified distributed patterns of neural activity consistently present for a particular task, stimulus etc
• activation patterns can provide info about functional role of brain areas and networks

Question 32

magnetic resonance spectroscopy (MRS)

Answer 32

• uses MRI machine
• obtain info about chemical composition of tissues
• molecules have unique proton compositions that behave differently in a magnetic field
• from the data, can estimate concentration of different neurochemicals in one brain area or the same neurotransmitter in multiple areas
• can also ask how concentrations change during or after a person performs a task

Question 33

connectivity maps (connectomes)

Answer 33

• visualization of structural or functional connections within the brain
• offer new methods for examining variation between individuals or groups

Question 34

4 steps in constructing a brain network

Answer 34

1. define network nodes (can use data from structural imaging methods)
2. measure correlation between possible pairs of nodes using dependent variable of interest (ie. BOLD response for fMRI or fractional anisotropy for DTI)
3. generate association matrix by compiling pairwise associations between nodes
4. visualize correlations in connectivity map

Question 35

conceptual definiton

Answer 35

• general, abstract explanation or understanding of a concept
• refers to what a concept means in a theoretical sense
  ex. intelligence might be defined as “the ability to learn from experience, solve problems, and adapt to new situations

Question 36

operational definition

Answer 36

• specifies how a concept will be measured or manipulated in a specific study
  ex. intelligence might be defined by a score on an IQ test or performance on specific cognitive tasks

Question 37

functional anisotropy

Answer 37

• measures how directionally restricted water diffusion is within tissues
• 0 indicates that diffusion occurs equally in all directions, suggesting homogeneous tissue, such as in cerebrospinal fluid
• 1 indicates that diffusion is highly directionally restricted, such as in aligned fiber tracts like white matter in the brain
• way to calculate how much the water is moving in one direction versus other directions
• higher # means stronger pathway