Neuroscience Flashcards
What is cytoarchitectonics?
A method of segmenting the brain into areas based on the microscopic appearance of cell types and layers.
What are Brodmann areas?
Numbered brain areas defined by Brodmann based on cytoarchitectonics and comparative neuroanatomy.
How does Transcranial Magnetic Stimulation (TMS) work?
A magnetic field generated by a coil induces an electric field in the brain, exciting neurons.
What are the main applications of TMS?
EEG records ongoing brain electrical activity, while ERPs are EEG signals averaged and time-locked to specific events.
Distinguish between exogenous and endogenous ERPs.
Exogenous ERPs are automatic responses driven by physical stimulus properties, while endogenous ERPs reflect cognitive processes like attention and expectation.
What is the purpose of cytoarchitectonics?
To segment the brain into areas based on the microscopic appearance of cell types and layers (cytoarchitecture).
Who pioneered the cytoarchitectonic mapping of the brain?
Korbinian Brodmann in the early 1900s, defining numbered Brodmann areas.
What does a wide layer V indicate about a cortical area?
A wide layer V suggests the area is involved in output processing, sending signals from the brain to the periphery.
What does a wide layer IV indicate?
A wide layer IV suggests the area is involved in input processing, receiving signals from the periphery.
What is the basic principle behind TMS?
Creating temporary virtual lesions, studying chronometry of brain activation, and assessing functional connectivity.
What are the main applications of TMS?
Creating temporary virtual lesions, studying chronometry of brain activation, and assessing functional connectivity.
How are TMS effects measured for motor cortex stimulation?
By observing muscle twitches corresponding to the somatotopic map of the motor cortex.
What is a key advantage of TMS over patient lesion studies?
TMS allows studying virtual lesions in healthy participants with better experimental control.
What is the EEG measuring?
The electrical activity generated by neurons in the brain, recorded from electrodes on the scalp.
How are ERPs derived from the EEG?
By averaging EEG segments time-locked to specific events of interest to extract the event-related signal.
What are exogenous ERPs?
ERPs directly driven by physical properties of the stimulus, like the auditory N1 response.
Give an example of an endogenous ERP component.
The P300 or P3 component, elicited in response to infrequent or unexpected events.
What is the contingent negative variation (CNV)?
A negative ERP reflecting anticipation and preparation between a warning stimulus and an imperative stimulus.
List the following in order of temporal resolution – EEG, fMRI, MEG ERP, and MRI
MEG, ERP, EEG, fMRI, MRI
Which has better spatial resolution? EEG or fMRI? fMRI
fMRI
What is an advantage of EEG compared with fMRI?
What is an advantage of EEG compared with fMRI? Better temporal resolution – well-suited to transient events such as the onset of stimuli. Whereas with fMRI there is a time lapse between brain activity and the movement of blood which limits the speed at which you can perform experiments
Is MRI structural or functional? Why?
Structural – compares the behaviour of charged Hydrogen ions in relation to fat and water content in different brain areas.
Which are Brodmann’s areas 7, 4, 1,2,3 and 41?
7 = Primary Visual Cortex, 4 = Primary motor cortex, 1,2,3 = Primary Somatosensory Cortex, 41 = Primary Auditory Cortex
What assumption did Brodmann make?
6 cortical layers – 4 = input, 5&6 = output
In the PMC, which cortical layer is notably wide?
4 (input)
In the PSC, which cortical layer is notably wide?
5 (output)
How does transcranial magnetic stimulation work?
Device placed against head => brief pulse => magnetic coil forms a magnetic field with perpendicular flux lines => activates cortical cells trans-synaptically.
What is the temporal resolution of TMS? Ms
Ms
What are some key weaknesses of TMS?
- Can only measure 1 point at once
- Auditory stimuli hard to measure due to loud coil click
How many mm lateral from the vortex should you place the TMS coil in order to trigger a response to the thumb?
5mm
How long does it take for a contracted vs relaxed muscle to respond to TMS?
150 vs 20ms
What are motor neuroelectrical signals measured in (TMS)
Motor EP’s
What are visual neuroelectrical signals measured in? (TMS)
Phosphemes
What has TMS shown re. early blind individuals, describe 2 study designs
Cross-modal plasticity – use the visual cortex to read braille, as shown in an ISI design (20ms for occipital cortex response vs 50-80ms for a SSC response) and a virtual lesion design (blind participants struggled to read braille when lesion was to the occipital cortex whereas control struggled more when lesion was to the somatosensory cortex).
What are some key advantages of TMS?
- Ms temporal resolution
- Can repeat studies
- Group studies can be standardised
- Can study double dissociations
- Virtual lesions may be better defined than real lesions
True or false? fMRI induces interference whereas EEG and TMS show correlation between activation and cognitive event
False, TMS induces interference, the others show correlation
What is the term for the simplest synchronous activation in EEG?
Dipoles
Biophysical basis of EEG
Cortical neurons generate dipoles under the influence of post-synaptic potentials (i.e. mini electric currents produced by NT release => change in electric field).
Describe the Berger effect:
Biophysical basis of EEG Cortical neurons generate dipoles under the influence of post-synaptic potentials (i.e. mini electric currents produced by NT release => change in electric field).
What is the difference between spontaneous and continuous oscillations?
Spontaneous = ongoing, intrinsic activity. Continuous oscillations tend to occur in response to external inputs/specific cognitive processes.
Which oscillations are 3-7 Hz?
Theta
What are the two types of electrophysiological signals produced in EEG? + what do they measure?
EROs (frequency) and ERPs (voltage)
Complete the blank? ERP’s are defined in _____ to an _____
Latency, event
Thut et al. 2016
Visualspatial attention task – had to pay attention to stimuli on one side of a screen. Found decreased alpha activity when ppts had been given a cue and were waiting for a target. Strongest for R motion @ L electrodes and vice versa.
What are the 2 prerequisites of ERP?
1) Neurons are active in synchrony
2) Electric fields are oriented so they cumulate spatially
Exogenous vs endogenous ERP’s?
Exogenous = auto responses controlled by physical properties of a stimulus e.g. auditory.
Endogenous = interaction between subject and event e.g. attention, task relevance & expectations
What are key weaknesses of ERP’s?
- Source localisation i.e. lateral areas harder to pinpoint than front/central areas
- scalp smears the readings
- topography depends on reference electrode placement
Describe Mismatch Negativity and how it is different in schizophrenic / dyslexic individuals
MMN = ERP component elicited by ‘deviant tone’ in passive auditory oddball paradigm. Larger deviance = larger MMN. Sz = reduced MMN, stronger for duration than freq. Dyslexia = reduced amp correlated with dyslexia severity.
What is the basis of MRI?
- Hydrogen ions are charged
- Body is 70% water
- Can align the magnetic fields of H ions with big magnet
- Then use 3 RF coils to manipulate the magnetic field
- Time how long it takes to return to the equilibrium state
T1 vs T2
T1 = spin lattice. Resolution along Z axis. Good for fat vs water.
T2 = spin spin. Relaxation due to transverse magnetisation decays i.e. component of magnetisation perpendicular to main magnetic field. T2 measured as time for 63% of transverse magnetisation to be lost. Faster for water tissues.
What does the fMRI BOLD signal measure?
Blood oxygen
How does fMRI work?
- Blood oxygen has weak negative magnetic susceptibility
- Activity => oxygenation => increased homogenous magnetic field => longer T2 relaxation time
Oxygenated vs deoxygenated magnetic properties
Oxygenated = diamagnetic
Deoxygenated = paramagnetic
THE key weakness of fMRI
Time delay between stimulus & BOLD signal is huge relative to the speed of sensory and cognitive processes
2 types of fMRI experiments?
- Block designs (overlapping trials, stimuli must be the same) – more robust/statistically reliable but less flexible
- Rapid event-related design (baso random firing of different types of stimuli. We’ll sort it out later approach) – avoids habituation but less sensitive to neural events
What 3 steps need to be carried out post-signal collection?
- Motion correction (realign images)
- Coregistration between functional and anatomical scans (superimpose functional onto spatial maps to improve spatial resolution)
- Normalisation to allow for intra-individual comparisons (multiple ppts can be aligned)
Example of a brain atlas/co-ord system?
Talairach-Touronoux – not v precise but well standardised
How to quantify MR signals?
- Compare predicted and observed timecourses of activation
- How closely they align = correlation
- Run a GLM to establish correlation
Which neuroimaging method has a high chance of type 1 error?
fMRI
3 examples of hemi-spatial neglect tasks?
- Albert task (cross out lines below dots)
- Line bisection task
- Drawing/copying task
Which brain area is associated with hemispatial neglect?
Temporo-parietal junction
Do lesions necessarily equate to brain damage in the identified region? Why?
No – could also affect relay stations, instead of the functional region itself
Association vs dissociation
Association = damage to a single region => multiple deficits
Dissociation = task A impaired but task B remains the same
Example association lesion – symptoms and affected brain region
Balint’s syndrome – associated with the parieto-occipital cortex
1. Simultanagnosia - 1 object at a time
2. Oculomotor apraxia – irregular eye movements
3. Ocular ataxia – difficulty reaching for objects
Example dissociation lesion – symptoms and affected area
Visual form agnosia - Ventro-lateral lesion
- Letterbox task fine
- Couldn’t describe whether horizontal or vertical
Suggests recognition impaired but movement fine
Double dissociations example (visual)
Extrasiate visual areas have 2 pathways – occipital-temporal and occipital parietal. Mirrored by M cells => parietal cortex and P cells => temporal
Double dissociations example (Frontal lobe lesion)
FL lesion on right side implicated memory for designs whereas on left side implicated memory for words – suggests hemifield specialisation
