Cogneuro wk 1 Flashcards
1
Q
Single unit recording
A
Electrodes, consisting of thin wires,
are implanted into specific areas of
the brain. Recordings of brain cell
activities are made by measuring
the electrical potential of nearby
neurons that are in close proximity
to the electrode.
2
Q
single cell recording
A
Very small electrode implanted into axon
(intracellular) or outside axon membrane
(extracellular)
Records neural activity from population of
neurons
3
Q
machine used to conduct single cell recording
A
Oscilloscope
4
Q
intracellular recording
vs extracellular recording
single cell
A
either into the neuron itself (intracellular recording) or outside the membrane (extracellular recording)
5
Q
what is he normal type of single cell recording in the mammalian brain
A
Extracellular recordings are the norm in the mammalian brain because of the small size of neurons
6
Q
what is the dependant measure of single cell recording
A
The number of times that an action potential is produced in response to a given stimulus (e.g., a face) is counted, and the dependent measure is often referred to as “spikes” per second, firing rate or spiking rate.
7
Q
where does the physiological basis of EEG current originate
A
at the postsynaptic site of the dendritic currents = passive currents (rather than axonal = active current (as is related to action potential))
8
Q
what are the requirements for an electrical signal to be detected at the scalp?
A
- whole population of neurons must be active in synchrony to generate a large enough electrical field
- This population of neurons must be orientated in parallel orientation so that they summate rather than cancel out.
(this is the case in the cerebral cortex, but not in the thalamus)
9
Q
ERP measures
A
ammount of electrical activity (in terms of voltage change at scalp) as a result of a stimulus or other event
10
Q
how to measure How synchronous the EEG signal is
A
the extend to which it exhibits undulating wave like properties as opposed to random structure
11
Q
neurons are considered to be communicating when
A
when they are responding in synch
12
Q
To gain an EEG measure, what do we do with the sites
A
Compare the voltage between two or more different sites.
A good reference site is usually one that isn’t influenced by the variable under question.
e.g. the average of all sites, or point at mastoid point behind ears, or nasal reference.
13
Q
How are the electrodes on an EEG labelled?
A
according to location (P = parietal, O = occipital … C = Central).
and their hemisphere (odd numbers are left, even numbers are right)
14
Q
How good is EEG for detecting location of neural activity?
why?
A
Poor.
Electrical activity in one location can be detected in other locations.
(and thus electrical activity in one location can not necessarily be attributed to electrical activity in that region)
15
Q
The signal to noise ratio of EEG is very ____
why?
A
low.
EEG waveform reflects activity from all parts of the brain.
Some of this activity may be related to the current task, But most will relate to spontaneous activity of neurones.
16
Q
How can the signal to noise ratio of EEG be increased ?
A
averaging the EEG signal over many presentations of the stimulus at the onset of the stimulus.
17
Q
How are EEG waveforms represented graphically and labelled
A
time (milliseconds) on x axis, electrode potential (microvolts) on y axis.
asymptote at 0 mV.
Done for every electrode (each with diff plot).
Labels.
Positive peaks = P
Negative peaks = N
P1, P2 refer to first and second negative peaks.
OR labelled with P, N and time
e.g. P 300 would be negative peak at 300ms
18
Q
What is a Dipole
A
a pair of negative and positive electrical charges separated by a small distance
19
Q
what does polarity reflect in cognitive terms
what does polarity depend on
A
does not reflect any real cognitive significance.
positive peak does not reflect excitation and negative peak does not reflect inhibition.
Polarity depends on the spatial arangements of the neurons that are giving rise to the signal in that particular moment in time
20
Q
on an ionic level, what gives rise to the peaks and dips of EEG
A
Positive ions flow into dendrites when excitatory NT is released, leaving a net Negative in extracellular space.
This creates a dipole. (negative compared to positive net at axon)
Dipoles from diff regions and neurons summate and conduct at the skull, give rise to characteristic peaks and troughs of the ERP waveform
21
Q
what is of interest to the ERP waveform in linking it to cognition?
A
timing and amplitude of the peaks,
22
Q
What are the frequency ranges for alpha, beta, and gamma waves in EEG?
A
Alpha: 7–14 Hz
Beta: 15–30 Hz
Gamma: 30 Hz and above
23
Q
What is the relationship between EEG oscillations and neuronal activity?
A
EEG oscillations reflect synchronised neuronal firing (action potentials) and slower dendritic potentials, which form the basis of the EEG signal.
24
Q
How has EEG oscillatory power been linked to cognitive function?
A
- Alpha increases have been linked to attention and filtering out irrelevant information.
- Gamma increases have been linked to perceptual integration and object recognition.
25
Why is it unlikely that frequency bands map directly to specific cognitive functions or brain regions?
Frequency bands (e.g., alpha, gamma) are linked to a wide range of cognitive functions, and each brain region can produce different kinds of oscillations.
26
What behavioural measures should be obtained in ERP experiments?
Participants usually perform a task requiring an overt behavioural response (e.g., button press), analysed for reaction times and/or error rates
27
Why can’t vocal responses be recorded in EEG experiments?
Jaw movements disrupt the EEG signal, making vocal responses (e.g., picture naming) unsuitable
28
Why should hypotheses in ERP experiments constrain the ERP component of interest?
Constraining hypotheses (e.g., predicting changes in P300 latency) reduces the risk of finding unjustified or non-replicable "significant" results.
29
What is a major source of interference in EEG experiments?
Eye movements and eyelid activity, which occur at the same frequencies as important EEG components, can interfere with the signal.
30
How can interference from eye movements in EEG experiments be reduced?
Instruct participants not to blink or to blink only at specific times (e.g., after their response).
Discard or filter trials with eye movements (Luck, 2014), ensuring a large number of trials for sufficient "clean" data.
31
What is mental chronometry?
The study of the time-course of information processing in the human nervous system (Posner, 1978).
32
What does mental chronometry aim to study?
How changes in the nature or efficiency of information processing manifest in task completion times.
33
How does mental chronometry explain reaction time differences in mathematical tasks?
- Verifying "4 + 2 = 6" is faster than "4 + 3 = 7", which is faster than "5 + 3 = 8".
- This suggests sums are not stored as simple facts. Instead, a processing stage encodes numerical size, and larger sums reduce processing efficiency.
34
What is the additive factors method?
A general method for dividing reaction times into different stages.
35
What is the significance of reaction time differences in mental chronometry?
They provide insights into the nature and efficiency of cognitive processes.
36
What stages did Sternberg (1969) propose in his working memory task?
Encoding the probe digit.
Comparing the probe digit with items in memory.
Deciding which response to make.
Executing the button press.
37
what is the additive factors method, and how does it work?
The additive factors method, developed by Sternberg (1969), divides reaction times into separate processing stages (e.g., encoding, comparison, decision, response). It identifies whether factors influencing a task have additive effects (affecting different stages) or interactive effects (affecting the same stage). For example:
Encoding stage: Influenced by perceptibility (e.g., probe digit on a patterned background).
Comparison stage: Influenced by memory load (e.g., slower with more items to compare).
This method allows researchers to analyse how unknown factors (e.g., sleep deprivation) affect specific stages of processing.
38
What do additive and interactive effects in the additive factors method imply?
- Additive effects: When factors have independent effects on reaction time, it implies they influence separate stages of processing. For example, stimulus perceptibility might affect the encoding stage, while memory load affects the comparison stage.
- Interactive effects: When factors interact and jointly influence reaction time, it implies they affect the same processing stage. For example, a factor like sleep deprivation might interact with memory load, suggesting it specifically impacts the comparison stage.
39
What is a key limitation of the additive factors approach?
It assumes that processing stages are strictly sequential (later stages do not occur until earlier ones are complete), but this assumption is not always valid.
40
How does mental chronometry relate to ERP data?
ERP waveforms consist of a series of peaks and troughs that vary over time. These peaks and troughs may correspond to different cognitive stages of processing, such as:
Earlier peaks reflecting perceptual encoding.
Later peaks reflecting stages like comparison.
41
How can ERP waveforms be used to analyse task variables?
Researchers can observe:
How the amplitude of peaks changes with variables like the number of items to be compared.
Whether a new factor (e.g., sleep deprivation) affects earlier or later peaks.
42
What are ERP components, and why is their interpretation complex in terms of determining the cognitive task they relate to
ERP components are peaks and troughs in ERP waveforms, but:
A single cognitive component may involve several neural populations affecting multiple ERP components.
Several cognitive components may occur simultaneously, summing together or cancelling out in the ERP waveform.
43
Why do some researchers prefer the term "ERP deflection" over "ERP component"?
The term "ERP deflection" is more neutral because it avoids the assumption of a one-to-one mapping between ERP components and cognitive processes.
44
What are the basic stages of face processing?
1. Perceptual coding: Identifying facial features like eyes and mouth.
2. Facial identity computation: Mapping perceptual codes onto a store of known faces, irrespective of viewing conditions.
3. Identity representation: Linking the face or name to other knowledge (e.g., occupation).
45
What is the N170 ERP component, and what does it indicate?
- The N170 is a negative peak at 170 ms, strongest over right posterior temporal electrode sites.
- It is relatively selective to face processing compared to other visual objects.
- It is unaffected by familiarity (famous vs non-famous faces) but is reduced when the face is perceptually degraded.
46
How is face processing supported by ERP and single-cell results?
Both ERP and single-cell studies indicate specialised neural mechanisms for face processing, with ERP components like N170 and N250 revealing distinct stages of facial recognition and identity retrieval
47
What is associative priming?
Reaction times are faster to a stimulus if it is preceded by a stimulus that tends to co-occur with it in the environment (e.g., Gorbachev’s face following Yeltsin’s face or name).
48
What does the interaction of associative priming with stimulus degradation and perceptual distinctiveness suggest?
The interaction suggests that associative priming begins at a perceptual stage of processing. For example, seeing Gorbachev's face may activate the perceptual representation of Yeltsin's face because they are related. This challenges the idea that associative priming only occurs at later, post-perceptual stages of processing.
49
How did Schweinberger (1996) use ERP to investigate the locus of associative priming?
Found that associative priming affects ERP waveform at late stages (after 300 ms), consistent with a post-perceptual locus.
Stimulus degradation effects were found under 150 ms, indicating early perceptual processes.
50
Why might the Sternberg method lead to invalid conclusions in associative priming studies?
The Sternberg method assumes discrete processing stages, but Schweinberger’s (1996) ERP findings suggest associative priming involves both early perceptual and late post-perceptual processes.
51
What are exogenous ERP components?
Exogenous components are ERP responses that depend on the physical properties of a stimulus (e.g., sensory modality, size, intensity) and are often called evoked potentials. They tend to occur earlier than endogenous components.
52
What are endogenous ERP components?
Endogenous components are ERP responses that depend on task-related properties (e.g., what the participant is required to do with the stimulus) and can occur even without an external stimulus (e.g., when an expected stimulus does not appear).
53
How should the exogenous–endogenous classification of ERP components be understood?
The exogenous–endogenous distinction is best viewed as a dimension, not a strict categorical separation, as components may depend on both stimulus properties and task context.
54
What does the study of N170 responses to horizontal symbols (+ +) reveal about the exogenous–endogenous distinction?
N170 is typically considered an exogenous component linked to face perception. and does not respond to horizontal symbols alone.
However, when symbols (+ +) are previously shown in a face context (e.g., as eyes), they elicit the N170.
This shows that N170 can depend on interpretive bias (a task-related property), blurring the exogenous–endogenous distinction
55
What is magnetoencephalography (MEG)?
MEG is a method for measuring magnetic fields generated by brain activity. It is similar to EEG, capable of examining rhythmic neural oscillations and stimulus-evoked changes.
56
What is the primary advantage of MEG over EEG?
MEG provides much better spatial resolution than EEG while maintaining excellent temporal resolution (Hari et al., 2010).
57
How does MEG research on face processing compare to EEG?
MEG detects the M170, equivalent to the N170 in EEG, linked to structural encoding of faces. The M170 is sensitive to:
Facial expressions (e.g., angry, happy, neutral).
Head posture (e.g., aloof or downcast), influenced by different brain regions.
58
Why is MEG more challenging and costly than EEG?
The development of SQUIDs (Superconducting Quantum Interference Devices) enabled MEG to measure the brain's tiny magnetic fields.
59
How is the MEG signal different from the EEG signal in terms of interference?
MEG: Signal is unaffected by the skull, meninges, etc.
EEG: Signal is affected by the skull, meninges, etc
60
How do MEG and EEG differ in detecting deep dipoles?
MEG: Poor at detecting deep dipoles.
EEG: Detects both deep and shallow dipoles.
61
How do MEG and EEG differ in sensitivity to brain activity?
MEG: More sensitive to activity in sulci.
EEG: Sensitive to activity in both gyri and sulci.
62
How do MEG and EEG compare in temporal resolution?
Both MEG and EEG have millisecond temporal resolution.
63
How do MEG and EEG compare in spatial resolution?
MEG: Potentially good spatial resolution (2–3 mm).
EEG: Poor spatial resolution
64
How do MEG and EEG compare in cost and availability?
MEG: Expensive and limited availability.
EEG: Cheaper and widely available.
65
What is structural imaging?
Measures the spatial configuration of different types of tissue in the brain (e.g., skull, grey matter, white matter, cerebrospinal fluid), primarily using CT and MRI.
66
What is functional imaging?
easures temporary changes in brain physiology associated with cognitive processing. The most common method is fMRI, based on a hemodynamic measure
67
What is a CT scan, and how does it work?
CT scans use X-rays to measure the amount of absorption in different tissues, which reflects their density:
Bone: Absorbs the most (appears white).
Cerebrospinal fluid: Absorbs the least (appears black).
Brain matter: Intermediate absorption (appears grey).
68
What are the clinical uses of CT scans?
CT scans are used to diagnose tumors, identify haemorrhaging, and detect gross brain anomalies.
69
What are the limitations of CT scans compared to MRI?
CT cannot distinguish between grey matter and white matter as MRI can.
CT cannot be adapted for functional imaging purposes.
70
does a CT scan expose the patient to radiation?
Yes, CT scans use X-rays, so the patient is exposed to a small amount of radiation.
71
What are the advantages of MRI over CT scanning?
No ionizing radiation: Safe for repeated use.
Better spatial resolution: Can discern the folds of individual gyri.
Improved tissue discrimination: Can distinguish grey matter and white matter better, aiding in early diagnosis and studying brain structure.
Adaptable for functional imaging: Used for detecting blood oxygenation changes in functional MRI (fMRI).
72
How does MRI support the study of cognitive abilities?
MRI's ability to distinguish grey and white matter helps explore how variations in brain structure are linked to cognitive differences.
73
What is functional MRI (fMRI)?
basic compared to mri
An adaptation of MRI that detects changes in blood oxygenation associated with neural activity, enabling dynamic mapping of brain function.
74
What are the steps involved in acquiring an MRI scan?
1. Magnetic field applied: Protons in hydrogen nuclei align with the field (1.5–7 T in strength).
2. Radio frequency pulse: Aligns protons at 90° to the magnetic field.
3. Proton precession: Produces a detectable change in the magnetic field.
4. Relaxation: Protons return to their original alignment with the field.
75
What are the two key components of the MR signal?
T1 relaxation time: Measures how protons return to alignment with the magnetic field; used for structural imaging (T1-weighted images).
T2 signal decay: Measures signal loss due to local molecular interactions; distortions caused by deoxyhaemoglobin form the basis of functional MRI (T2* images).
76
What is a T1-weighted image used for?
T1-weighted images are used for structural imaging of the brain, where grey matter appears grey and white matter appears white.
77
What is a T2* image in fMRI?
A T2* image reflects signal distortions caused by deoxyhaemoglobin, which are used to map neural activity during functional imaging experiments.
78
How fast can a whole brain be scanned with modern MRI techniques?
Using echo planar imaging, a whole brain can be scanned in about 2 seconds, with slices of approximately 3 mm.
79
What does functional imaging measure?
Functional imaging measures the moment-to-moment variable characteristics of the brain associated with changes in cognitive processing.
80
What physiological process underpins functional imaging?
The brain consumes 20% of the body's oxygen uptake and depends on the local blood supply for oxygen and glucose. When neuronal activity increases, blood flow to that region increases to meet the metabolic demand.
81
What are hemodynamic methods in functional imaging?
echniques that measure changes in blood flow or oxygen concentration in the blood. These include:
PET (positron emission tomography): Measures blood flow using a radioactive tracer.
fMRI: Sensitive to blood oxygen concentration.
fNIRS: Measures blood oxygenation using near-infrared light.
82
How do PET and fMRI differ in their methodology?
PET: Requires a radioactive tracer to measure blood flow.
fMRI: Uses a naturally occurring signal in the blood (the BOLD response) to measure oxygen concentration.
83
Why has fMRI largely replaced PET in cognitive neuroscience?
fMRI does not require radioactive tracers and provides a safer, non-invasive way to measure brain activity. PET is still used for targeting specific neurotransmitter pathways with specialist tracers.
84
How can small-scale differences in brain structure be analysed using MRI?
Small-scale differences in white and grey matter organisation can be analysed using two methods:
Voxel-based morphometry (VBM): Measures grey and white matter density.
Diffusion tensor imaging (DTI): Measures white matter connectivity.
85
What is voxel-based morphometry (VBM)?
VBM divides the brain into tens of thousands of small regions (voxels) and estimates the concentration of grey and white matter in each voxel. It compares individual differences in brain structure and their relation to cognition.
86
What kinds of questions can VBM address?
How does learning a new skill (e.g., a second language) affect grey matter density?
How do genetic variants influence brain development?
Which brain regions differ in size for people with strong vs weak social skills?
87
What is diffusion tensor imaging (DTI)?
DTI measures white matter connectivity by tracking how water diffuses in axons. Water moves freely along axons but is restricted by the fatty membrane, enabling quantification of fibre organisation using fractional anisotropy.
88
how is DTI used to study cognition
DTI reveals how white matter connectivity develops with learning. For example, learning piano affects different white matter fibres depending on whether it is learned in childhood, adolescence, or adulthood (Bengtsson et al., 2005).
89
How does DTI differ from VBM?
VBM: Measures the amount of white and grey matter without assessing connectivity.
DTI: Measures the connectivity of white matter tracts by analysing water diffusion in axons
90
Why is it meaningless to observe only blood and oxygen flow in functional imaging experiments?
Blood and oxygen flow are essential for all neurons at all times. Functional imaging must compare physiological responses during one task relative to a baseline condition to identify specific activity related to cognition.
91
What is required for functional imaging experiments to interpret neural activity?
Physiological responses must be compared between tasks and baseline conditions.
Baseline tasks must be appropriately matched to experimental tasks to avoid misinterpretation.
92
How do hemodynamic methods differ from EEG and MEG?
Hemodynamic methods (e.g., fMRI, PET): Measure downstream consequences of neural activity (e.g., blood flow/oxygenation).
EEG and MEG: Directly measure electrical and magnetic fields generated by neuronal activity.
93
What is fractional anisotropy (FA)?
A measure of the extent to which water diffusion occurs more in some directions than others, used in diffusion tensor imaging (DTI) to map white matter connectivity.
94
What is a voxel in brain imaging?
A voxel is a 3D volume-based unit (similar to a 2D pixel) used to divide the brain into thousands of small regions for analysis.
95
What is voxel-based morphometry (VBM)?
A technique that measures differences in grey and white matter concentration across voxels in the brain.
96
What is diffusion tensor imaging (DTI)?
A method that uses MRI to measure white matter connectivity between brain regions by analysing water diffusion in axons.
97
MRI stands for
magnetic resonance imaging
98
What component of the MR signal is used in fMRI?
The fMRI signal is sensitive to the amount of deoxyhaemoglobin in the blood, which distorts the local magnetic field due to its paramagnetic properties.
99
What is the BOLD signal in fMRI?
The blood oxygen-level-dependent (BOLD) signal reflects changes in the concentration of deoxyhaemoglobin in the blood, providing an indirect measure of neural activity.
100
: What is the hemodynamic response function (HRF)?
The HRF describes how the BOLD signal evolves over time in response to neural activity. It consists of three phases:
Initial dip: A temporary increase in deoxyhaemoglobin, reducing the BOLD signal.
Overcompensation: Increased blood flow exceeds oxygen consumption, causing a significant BOLD signal increase.
Undershoot: Blood flow and oxygen consumption dip before returning to baseline, briefly increasing deoxyhaemoglobin.
101
What does the overcompensation phase of the HRF indicate?
It represents the largest BOLD signal increase, reflecting a blood flow response that exceeds oxygen consumption, and is used to infer regional activity during a task.
102
What is the role of deoxyhaemoglobin in fMRI?
Deoxyhaemoglobin's paramagnetic properties create distortions in the magnetic field, allowing fMRI to measure its concentration and track neural activity indirectly.
103
How large are hemodynamic signal changes in fMRI?
Hemodynamic signal changes are small, approximately 1–3% with moderately sized magnets (1.5 T).
104
How consistent is the HRF?
The HRF is stable across sessions for the same participant and region but varies across brain regions within an individual and between individuals.
105
What is the spatial resolution of fMRI?
fMRI has a spatial resolution of up to 1 mm, depending on the size of the voxel.
106
What is the temporal resolution of fMRI, and why is it limited?
The temporal resolution of fMRI is several seconds due to the sluggish hemodynamic response, which peaks and returns to baseline slowly.
107
How does fMRI handle stimuli presentation despite the slow HRF?
- Stimuli can be presented without waiting for the BOLD signal to return to baseline, as different HRFs can be superimposed (Dale & Buckner, 1997).
- fMRI experiments often have fewer, spaced-out trials and include null events to provide variability in the signal.
108
How does the amount of data in fMRI experiments differ from standard cognitive psychology experiments?
In fMRI, the data corresponds to the number of brain volumes acquired, whereas in standard experiments it corresponds to the number of trials and responses.
109
What does fNIRS measure?
fNIRS measures the BOLD signal, like fMRI, but uses near-infrared light (~800 nm) instead of magnetic fields.
110
How does fNIRS compute the BOLD response?
Near-infrared light passes through bone and skin but is strongly scattered by oxy- and deoxyhaemoglobin.
The scattering differences at specific wavelengths are used to calculate the BOLD response.
111
How is a larger BOLD response in fNIRS interpreted?
A larger BOLD response is taken to reflect greater cognitive and neural activity, similar to fMRI.
112
What are the advantages of fNIRS compared to fMRI?
More portable.
More tolerant of movement.
Far cheaper.
Popular in developmental research due to these benefits.
113
: What is a key limitation of fNIRS?
fNIRS can only image shallow neural activity close to the scalp.
114
What is cognitive subtraction in functional imaging?
Cognitive subtraction involves comparing brain activity in an experimental task that uses a specific cognitive component (e.g., visual word recognition) to a baseline task that does not, to infer which brain regions are specialised for that component.
115
Why is cognitive subtraction necessary in functional imaging?
The brain is always physiologically active, so it is impossible to infer region-specific activity from a single task. A comparison between tasks or conditions is required to isolate activity related to specific cognitive processes.
116
What did Petersen et al. (1988) study using cognitive subtraction?
They identified brain regions involved in:
Recognising written words.
Producing spoken words.
Retrieving the meaning of words.
117
How did Petersen et al. isolate regions for recognising written words?
They compared passive viewing of words (e.g., CAKE) with passive viewing of a cross (+). Subtracting the baseline cancels out general visual processing, leaving activity specific to visual word recognition.
118
How did Petersen et al. isolate regions for producing spoken words?
They compared reading aloud words (e.g., see CAKE, say “cake”) with passive viewing of words (e.g., see CAKE). Subtracting the baseline cancels out visual processing and word recognition, leaving activity related to spoken output.
119
How did Petersen et al. isolate regions for retrieving word meaning?
they compared verb generation (e.g., see CAKE, say “eat”) with reading aloud words (e.g., see CAKE, say “cake”). Subtracting the baseline cancels out visual processing, word recognition, and spoken output, leaving activity specific to generating semantic associates.
120
What were the key findings of Petersen et al. (1988) in cognitive subtraction?
Recognising written words: Activated bilateral visual cortex and the left occipitotemporal junction.
Producing spoken words: Activated the sensorimotor cortex bilaterally.
Generating word meanings: Activated the left inferior frontal gyrus.
121
Why was the activation of the left inferior frontal gyrus during verb generation controversial?
It appeared inconsistent with lesion data, sparking debate about the role of this region in semantic processing.
122
What are the two broad scenarios of disagreement between functional imaging and lesion data?
Imaging suggests a region is used in a task, but lesion data suggest it is not essential (imaging +, lesion −).
Imaging suggests a region is not used, but lesion data suggest it is critical (imaging −, lesion +).
123
Why might imaging data suggest a brain region is used in a task, but lesion data suggest it is not essential (imaging +, lesion −)?
The activated region reflects a strategy adopted by participants that is not essential for the task.
The region reflects the recruitment of a general cognitive resource (e.g., attention or arousal) rather than task-specific activity.
The region is being inhibited rather than activated.
Lesion studies may lack power (e.g., too few patients, incorrect lesion location, mismatched tasks).
124
Why might imaging data suggest a brain region is not used, but lesion data suggest it is critical (imaging −, lesion +)?
The experimental and baseline tasks both depend critically on the same region, causing a null result.
Activity in the region is hard to detect due to:
The region's small size.
Variability in its location across individuals.
Genuine activity producing a small signal change.
Impaired performance after lesion reflects damage to tracts passing through the region rather than its synaptic activity.
125
How should disagreements between imaging and lesion data be viewed?
Disagreements should be seen as theoretically interesting rather than as failures of either method, requiring rigorous experimentation to resolve them (Henson, 2005).
126
What does PET measure, and how does it work?
PET measures regional blood flow using a radioactive tracer. The tracer peaks in ~30 seconds, and areas of high radioactivity indicate increased brain activity.
127
What are the limitations of PET?
PET has poor temporal resolution due to the slow peak time of the tracer and involves exposure to radioactive substances.
128
What is the temporal resolution of fMRI, and why is it limited?
MRI has a temporal resolution of several seconds because the hemodynamic response function (HRF) peaks at 6–8 seconds and returns to baseline slowly.
129
What does fMRI correlate in brain studies?
fMRI correlates brain activity (via the BOLD signal) with stimulus timings during tasks.
130
Why is choosing an appropriate baseline task crucial in cognitive subtraction?
Choosing a poorly matched baseline can lead to meaningless results, as the baseline task must cancel out irrelevant brain activity while isolating the cognitive component of interest.
131
What does MEG measure, and what are its advantages?
MEG measures magnetic fields generated by brain activity. It has excellent temporal resolution (millisecond scale) and good spatial resolution.
132
How does EEG produce event-related potentials (ERPs)?
EEG measures the electrical activity of populations of neurons. By averaging EEG signals from multiple trials, ERPs are extracted and time-locked to specific events or stimuli.
133
What do the N170 and P300 ERP components indicate?
N170: Linked to face processing, particularly the structural encoding of faces.
P300: Linked to the recognition of famous or familiar faces.
134
What are the limitations of fNIRS?
fNIRS cannot image deep brain structures, as it only measures activity close to the scalp.
135
what does fNIRS stand for
fNIRS (Functional Near-Infrared Spectroscopy)
136
What is iEEG/ECoG, and what are its advantages?
iEEG/ECoG measures brain activity directly from the cortical surface during neurosurgery. It provides high spatial and temporal resolution and is used to locate seizures and map brain functions.
