Lecture 7 Flashcards
Manipulating brain-behaviour interactions
DBS, TMS
Measuring the brain’s electrical activity
EEG, MEG
Anatomical imaging techniques
CT, MRI
Functional brain imaging
fMRI, fNRI, PET
Postmortem examination in humans with brain lesions
- Focus on the substantia nigra
- Healthy SN will show cell bodies of dopamine neurons
- Weakened SN will show degenerated dopamine neurons - contributing to symptoms of Parkinson’s disease
Neuropsychological testing of humans with brain lesions
- Examiner taps out a sequence of blocks. The block numbers are visible in the examiner’s side of the board but not the participants side.
- Participants’ task is the trace between the two outlines of the star like looking at their hand in a mirror. Crossing a line constitutes an error.
- Participants’ task is to identify which picture they saw most recently.
Brain research techniques (5)
- Spatial resolution
- Temporal resolution
- Invasiveness
- Anatomical (static)
- Functional (dynamic)
Sterotaxic appartus
Allows targeting of a specific part of the brain.
- Psychosurgery (ablation, lesions, gamma “knife” radiation)
- Deep brain stimulation
Psychosurgery
- Irreversible lesion techniques
- Reversible lesion techniques
Irreversible lesion techniques
- Electrolytic
- Neurotoxic
- High-intensity focused ultrasound (HIFU)
- Permanent lesions lead to compensation (neuroplasticity)
Reversible lesion techniques
- Regional cooling
- Local administration of a GABA agonist
Electrolytic
Burning by passing current through electrode
Neurotoxic
Intoxication through infusion of neuron-killing chemical
High intensity focused ultrasound
Heating with focused ultrasonic beams
Deep-brain stimulation (DBS)
Electrodes implanted in the brain stimulate a target area with continuous pulses of low-voltage electrical current to facilitate behaviour
Four major techniques for measuring the brains electrical activity
- Single cell recording (action potentials)
- EEGs (graded potentials)
- ERPs
- MEGs
Single cell recording
- Extracellular: record electrical activity of multiple neurons at once (clusters)
- Intracellular: allows study and recording of electrical activity of a single neuron
Main disadvantage is that it works well for dish grown neurons but requires surgery when recording brain cells in living organisms
EEG
Measures graded potentials (EPSP & IPSP) of similarly orientated neurons that are simultaneously active
- High temporal resolution
- Poor spatial resolution
Why can EEG not record action potentials?
Potentials can only be recorded at the scalp if they occur at approximately the same time across thousands or millions of neurons.
- Action potentials have very short duration (1ms)
- Neurons rarely fire at exactly the same time
Axons are relatively randomly orientated
EEG recording postsynaptic potentials
- EPSPs and IPSPs typically last longer (10s-100s ms)
- EPSPs and IPSPs occur instantaneously
- EPSPs and IPSPs occur at dendrites and cell bodies, which are typically orientated perpendicular to the surface of the cortex
NB: graded potentials recorded at the scalp reflect summed EPSPs and IPSPs
MEGs
Magnetic counterpart of EEG and ERP.
Main disadvantage: more expensive than EEG, ERP
- High temporal resolution
- High spatial resolution
Why does MEG have a higher spatial resolution than EEG?
Magnetic waves undergo less distortion through brain tissue and scalp compared to EEG or ERP
Source localisation in EEG and MEG
Record data first, the ntry to infer what sources ‘caused’ data.
Inverse problem: no unique solution - multiple sources might yield the same data
Possible solutions can be derived using models involving prior knowledge of brain functioning
CT scan
- Low temporal resolution
- High spatial resolution
Appropriate for localising bone fractures, brain tumours and lesions. - Grey and white matter cannot be distinguished on CT scan.
- Main advantage: relatively inexpensive
- Main disadvantage: uses X-ray radiation.
MRI
Magnetic counterpart of CT
More expensive, slower compared to CT.
Based on the principle that hydrogen atoms behave like spinning bar magnets in the presence of a magnetic field.
- Low temporal resolution
- High spatial resolution
- Disadvantage: subjects must lie motionless in a noisy tube for a long time
- NB: grey and white matter can be distinguished
DTI
MRI method that detects directional movements of water molecules
- Water can move relatively free along the axon but less freely across cell membranes
- Used to create visual images of nerve fibre tracts in the brain and identify changes in axon myelination
MRA
MRI focused on blood vessels
fMRI
Functional MRI
When the brain region is active, the amount of blood, oxygen and glucose flowing to the region increases.
NB: oxygen-rich blood is less magnetic than oxygen poor blood.
- Low temporal resolution
- High spatial resolution
fNIRS
Functional near-infrared spectroscopy
- Good temporal resolution
- Fairly high spatial resolution
- Main advantage: inexpensive, noninvasive
Main disadvantage: max dept of 2cm so only superficial layers.
PET
Positron emission tomography
Used to study metabolic activity of the brain cells by injecting a small amount of water labeled with radioactive molecules into the blood stream.
- Low temporal resolution
- Fairly high spatial resolution
- Often combined with CT, MRI or EEG.
- NB: biggest disadvantage: required preparation of radiochemicals = very expensive.
