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4. BIOL257 > Neurophysiological techniques > Flashcards

Neurophysiological techniques Flashcards

1
Q

name types of electrophysical neurophysiological techniques:

A
  • direct measurement of neuronal activity

- direct manipulation of neuronal activity

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2
Q

electrophysiological: direct measurement eg.

A
  • ERG (retina)
  • EMG (muscle contractions)
  • ECG/ EKG (heart)
  • EEG
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3
Q

electrophysiological: direct manipulation eg.

A
  • deep brain electrical stimulation
  • transcranial magnetic stimulation - (induced electrical activation of neurons)
  • optogenetics
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4
Q

functional imaging: features

A
  • measures changes in neural activity indirectly
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5
Q

functional imaging: eg.

A
  • functional MRI (fMRI) whole brain
  • f Near-infrared spectroscopy (fNIRS) limited to cortex
  • positron emission spectroscopy (PET)
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6
Q

electrocenphalography (EEG): features

A
  • traditional method of recording brain activity
  • diagnostic and research uses
  • increasingly replaced by imaging techniques (MRI, CT esp for locating physical damage, tumours)
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7
Q

electrocenphalography (EEG): still useful for diagnosis of

A
  • sleep disorders
  • epilepsy
  • multiple sclerosis
  • optic neuropathy (trauma, diabetes)
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8
Q

electrocenphalography (EEG): types of activity

A
  • spontaneuous

- event-related activity

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9
Q

electrocenphalography (EEG): spontaneous activity

A
  • electrical activity that occurs in absence of obvious stimulus or behavioural manifestation
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10
Q

electrocenphalography (EEG): event-related activity

A
  • evoked potentials: electrical activity triggered by specific stimuli (images, sounds)
  • induced potentials: electrical activity related to stimulus processing but w variable timing following event
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11
Q

electrocenphalography (EEG): mechanisms

A
  • measures extracellular electrical currents generated by postsynaptic activity
  • sum fo synchronous activity (excitation + inhibition) by neurons w similar spatial orientation
  • cortical pyramidal neurons -> aligned in radial columns and fire together
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12
Q

electrocenphalography (EEG): volume conduction -> red arrows

A
  • intracellular primary currents generated by synaptic activity
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13
Q

electrocenphalography (EEG): yellow lines

A
  • extracellular secondary currents generated in surrounding tissues
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14
Q

electrocenphalography (EEG): volume conduction features

A
  • summed w secondary currents generated by other neurons nearby
  • charge spreads to surface of cortex beneath skull (volume conduction)
  • voltage (potential difference) btw areas detected by scalp electrodes (V)
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15
Q

electrocenphalography (EEG): recording set up

A
  • standardised scalp electrode positions to allow comparison
  • 10-20 system
  • spacing allows each electrode to preferentially a 6cm area of cortex
  • other types of recording often performed simultaneously eg. ECG, EKG to remove artefacts or correlate w behaviours
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16
Q

electrocenphalography (EEG): recording compared by

A
  • bipolar recordings = dif btw pairs of electrodes (A)

- referential recordings = dif of each electrode compared to auricle reference (B)

17
Q

electrocenphalography (EEG): analysis - oscillation frequency of EEG signal indicates

A
  • indicates normal brain state
18
Q

electrocenphalography (EEG): types of brainwaves

A
  • gamma
  • beta
  • alpha
  • theta
  • delta
19
Q

electrocenphalography (EEG): recording compared by

A
  • bipolar recordings = dif btw pairs of electrodes (A)

- referential recordings = dif of each electrode compared to auricle reference (B)

20
Q

electrocenphalography (EEG): analysis - oscillation frequency of EEG signal indicates

A
  • indicates normal brain state
21
Q

electrocenphalography (EEG): types of brainwaves

A
  • gamma
  • beta
  • alpha
  • theta
  • delta
22
Q

magnetic resonance imaging (MRI): technique initial

A
  • relies on quantum properties of H atoms in body, mostly present as water
  • nucleus of H atom spins around axis
  • orientation is random
  • in MRI machine, magnetic fields generated by electromagnets surrounding patient cause all nuclei to line up in one direction
23
Q

electrocenphalography (EEG): generalised tonic-clonic ‘grand mal’ seizure

A

A. normal activity before
B. generalised seizure pattern (no obvious focal origin) across all electroe positions
C. waveforms obscured by muscle spasms (motor activity)
D. immediate postictal period - slow waves
E. normal activity resumed

24
Q

magnetic resonance imaging (MRI): features

A
  • uses strong magnetic fields (3 Teslas)
  • non-invasive tomographic techniques
  • 3D reconstruction of internal anatomy from virtual sections
  • no radiation
25
Q

magnetic resonance imaging (MRI): technique

A
  • relies on quantum properties of H atoms in body, mostly present as water
    A. nucleus of H atom spins around axis
    B. orientation is random
    C. in MRI machine, magnetic firelds generated by electromagnets surrounding patient cause all nuclei to line up in one direction
26
Q

magnetic resonance imaging (MRI): technique contd.

A
  • axes now aligned but still wobble (precession)
  • separate (resonant) radio-frequency magnetic pulse at 90º
  • cause nuclei line up at 90º but wobble more
  • when pulse off, precession first becomes dephased = T2 signal
  • nuclei revert to og orientation in magnetic field (H) = T1 signal
27
Q

magnetic resonance imaging (MRI): technique detected by

A

changes in phase and orientation detected by sensitive coils in MRI machine

28
Q

magnetic resonance imaging (MRI): eg. frontotemporal dementia (FTD)

A
  • loss of grey matter (spindle neurons)
  • extreme changes in personality
  • speech/ language problems
  • movement disorders
29
Q

magnetic resonance imaging (MRI): eg. brain tumour (glioblastoma)

A
  • patient suffers headaches

- compression of brain tissue and ventricles

30
Q

functional magnetic resonance imaging (fMRI): features

A
  • shows anatomical structures but not functional changes in activity
  • sequential images in quick succession to show changes in brain activity
31
Q

functional magnetic resonance imaging (fMRI): most common fMRI technique

A
  • relies on blood oxygenation level dependent (BOLD) contrast imaging
  • detects changes in blood flow triggered by localised changes in brain activity
32
Q

functional magnetic resonance imaging (fMRI): neurovascular coupling

A
  • stimulus causes increase neural activity
  • triggers local increase in cortical blood flow (CBF) = haemodynamic response
  • delivers more oxygenated blood to active brain region
  • and more glucose (not stored in brain) for generation of ATP to drive activity of ion pumps -> maintain ionic conc. gradients
33
Q

functional magnetic resonance imaging (fMRI): haemodynamic response

A
  • inflow of oxygenated blood displaces deoxygenated blood
  • arterial oxygenation usually high anyway
  • dramatically increases oxygenated blood in venous vasculature
34
Q

functional magnetic resonance imaging (fMRI): haemoglobin

A
  • de/oxygenated blood have different magnetic properties related to haemoglobin protein that binds/ carries oxygen
  • oxyhaemoglobin (Hb) = repelled by magnetic fields (diamagnetic)
  • deoxyhaemoglobin (dHb) = attracted (paramagnetic)
35
Q

functional magnetic resonance imaging (fMRI): BOLD signal

A
  • dHb interferes w MRI signal, Hb doesn’t
  • dHb decreases strength if alot
  • fMRI signal depends on ratio of Hb:dHb in venous microvasculature
36
Q

functional magnetic resonance imaging (fMRI): voxels

A
  • fMRI records images of brain as stack of slices

- each slice comprises of array of cubes or voxels (3D pixel)

37
Q

functional magnetic resonance imaging (fMRI): data time series

A
  • each slice is scanned repeatedly w set interval = repetition time (TR)
  • BOLD signal in each voxel recorded over time
38
Q

functional magnetic resonance imaging (fMRI): analysis

A
  • images/ slices taken before/ during stimulus presentation
  • averaged BOLD signal in each voxel compared btw image sets
  • 3D voxel intensity -> 2D pixel brightness -> contrast map show activity level
  • projected on to high res MRI image
39
Q

functional magnetic resonance imaging (fMRI): pitfalls

A
  • single fMRI volume (3D image) contains as many as 130 000 voxels
  • multiple comparisons of before/ after
  • false positives inevitable unless proper statistical corrections are applied
  • 25-40% prior to 2010 didn’t use proper correction methods

4. BIOL257 (18 decks)

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