Week 1 Flashcards
What are the orientations in the vertebrate NS?
Dorsal - the top Anterior - the front Ventral - the bottom Posterior - to the back Medial - to the middle (central line) Lateral - to the outside Superior - above Inferior - below Rostral - towards the head Caudal - towards the tail Contralateral - the other side Ipsilateral - the same side Bilateral - both sides Unilateral - same side Proximal - close to the main body mass Distal - far form the main body mass
Synonyms for below
Inferior
Sub
Hypo
Infra
Synonyms for fibre bundles or neural pathways
Tract
Fasciculus
Funiculus
Lemniscus
Reference planes
Sagittal plane - the plane between the hemispheres (mid-sagittal - down the middle vs para-sagittal - off centre)
Horizontal plane - also transverse
Frontal plane - also coronal, splits the front and the back
Cross section - straight cut through
Oblique plane - in any odd direction
Structure
tells about the morphology or form of things
• CT scan may show brain structure and indicate a
tumour that may be causing some observable
behaviour
Function
tells us about activity
• an EEG may show abnormal brain activity that is
indicative of a seizure
Invasive
Invasive - “Puncture or incision of the skin and denoting
procedures or tests that require an insertion of an
instrument or material that is foreign into the body.”
(psychologydictionary.org)
• Single cell recordings require electrodes to be implanted
into the brain – highly invasive
• PET scans require the injection of radioactive isotopes –
somewhat invasive
Non-invasive
• EEG requires the placement of electrodes on the external
scalp – non-invasive
Spatial resolution
To how small a region in space can you resolve 2
locations – smaller the region, higher the SR
• EEG can provide information about brain activity
localised to several centimetres – low SR
• fMRI can provide information at the mm level – high SR
• Single cell recordings provide information at the micro
level – super high SR
Temporal resolution
To how small an interval of time can you resolve 2
events – smaller the interval, higher the TR
• fMRI can tell you when something occurred within
seconds – low TR
• EEG can tell you when something occurred within ms – high TR
• Single cell recordings can tell you when something
occurred within microseconds (or faster) – super high
TR
Correlation
A reliable relationship between 2 things
Correlative – fMRI BUT just because activity in a
region is correlated with a behaviour does not
mean that the activity caused the behaviour
Causation
Does X cause Y ????
1. There is a reliable relationship between X and Y – e.g. when X occurs, Y occurs (1a - X must happen before Y)
2. If you take away X then Y stops happening
Causative - stimulation that interferes with the
behaviour indicates that the affected brain region is
necessary to perform the behaviour normally
Physiological response - startle response
startle response - brainstem reflex for protection eg. loud noise causes blinking The fear-potentiated startle - amplitude of is increased when presented with a cue that has been previously paired with an aversive stimulus • Measure fear conditioning
Physiological response - Electrodermal activity (EDA)
Skin conductance response (SCR) or galvanic skin response or electrodermal response (EDR) or psychogalvanic reflex (PGR) or sympathetic skin response (SSR) • Fight or flight response • Index of autonomic activity – measure of emotional arousal • Skin momentarily becomes a better conductor
Acquired brain injury
Anytime brain damage after birth eg stroke, alcohol/drugs, TBIPierre Paul Broca – Patient Tan • Could only say ‘tan’ (initially at least, no other problems) • Autopsy revealed a large legion in the posterior inferior frontal gyrus • Broca’s area
Lesion studies - Stimulating/disrupting activity
• Removing or disabling a portion of the brain and observing the resulting behaviour. • Aspiration lesion • Radio frequency lesion • Knife cuts Rarely administered with 100% accuracy. • Some neighbouring tissue is lesioned. • Functions are inadvertently attributed to the target structure that are actually carried out by the neighbouring tissue. • Sometimes a portion remains - as well as some function.
Transcranial Direct Current Stimulation - Stimulating/disrupting activity
• Small current between anode and cathode • Transiently disrupt neural activity • Neurons under anode become depolarised – more likely to fire • Neurons under cathode become hyperpolarised – less likely to fire • Changes in behavioural performance – general – anodal improves, cathodal hinders
Drug Blocks - Stimulating/disrupting activity
• Injection of local anaesthetics
• Wada test
• Prior to ablative surgery – determine
lateralisation of vital functions (e.g. speech)
• Inject left or right internal carotid then assess
Cryogenic Block - Stimulating/disrupting activity
• Cryoprobe cools neurons near tip so they
stop firing – virtual lesion
• Invasive
Transcranial Magnetic Stimulation (TMS) - Stimulating/disrupting activity
Single magnetic pulses are applied to specific locations on the scalp at specific times during a behavioural task; or repetitively prior to task performance (rTMS). • Magnetic activity causes neurons to fire – focal stimulation - cognitive or behavioural consequences are then observed. Stimulation effects (e.g. motor or visual activation) • Disruption effects - synchronised discharge interferes with normal activity – timing important (e.g. disrupt letter recognition) • rTMS – longer effects – maybe related to LTP/LTD but unclear • Permits causal inference about the necessity of a specific brain region for performing a given task. • rTMS in clinical – depression and neuropathic pain
Magneto-encephlography (MEG) - Recording associated activity
• Electric currents generate small magnetic fields
• Measure at the scalp
• Very high temporal resolution
• Relativity direct measure of activity
• But … no good for subcortical, hard to model
sources, very expensive equipment
Electroencephalography (EEG) - Recording associated activity
• Electrical activity generates electric fields which can be measured • Scalp – measures gross electrical activity of the brain • Sum of electrical events – action potentials, postsynaptic potentials, muscle activity, etc • Measured electrical activity correlates with underlying neural activity • Idiosyncratic waveforms associated with different states of consciousness • Relaxed – alpha (8-12 Hz) • Deep sleep – delta (<4 Hz) • Focussed – beta (16-31 Hz)
Electroencephalography (EEG) - Recording associated activity
Event Related Potentials
• Name peaks based on polarity – N (negative) or P (positive)
• But note – weird convention that N is up!
Typical ERPs
• Sensory processes within less than 100ms
• 100ms modulated by attention – N100 and P100 selective attention
• N200 – mismatch negativity – stimulus physically deviates from previous
• P300 – attended stimulus appears
• P400 – unexpected stimulus (surprise)
Or compare conditions
Attended versus
unattended stimulus
EEG - Advantages
- High temporal resolution
- Measure of activity
- No drugs, tracers - non invasive
- Relatively low cost
EEG - Disadvantages
• Low spatial resolution (although source modelling possible) • Poor for activity below superficial layers (cortex – gyri) • Low signal to noise and signals easily contaminated – need lots of trials and lots of subjects – time consuming
Positron Emission Tomography (PET) - Imaging the brain
• Radioactive tracer coupled to biologically active molecule
• Inject a radioactive isotope e.g. 2-deoxyglucose (2-DG).
• Inhale C15O2
(a radioactive isotope of CO2)
• Isotope is taken up by active portions of the brain but not brokendown - accumulates
• Radioactivity is short-lived. Half life of the isotopes is less than 3 hours.
-Paired image subtraction method (finding the difference between pic A and pic B)
Magnetic Resonance Imaging (MRI) - Imaging the brain
• Hydrogen atoms line up in a strong magnetic field
• Perturb with a RF pulse and detect EM waves emitted as
they return
• Additional magnetic fields permit 3D imaging
• High spatial resolution structural imaging
Diffusion Tensor Imaging (DTI) - Imaging the brain
Variant of MRI • Measures density and motion of water molecules – restricted movement along axon fibres • Measure diffusion anisotropy
Functional Magnetic Resonance Imaging (fMRI) - Imaging the brain
Measures neural activity (indirectly)
• Active neurons – blood flow increases bringing oxyhemoglobin
• Oxyhemoglobin increase greater than oxygen consumption
increase so increased ratio oxy to deoxy in veins
• Oxy and deoxy different magnetic properties
• Less deoxy relative to oxy – MR signal increased intensity – BOLD
– blood oxygen level dependent contrast
- fMRI subtraction = stimulus image - blank stimulus image = area associated with stimulus
fMRI - Advantages
• Compared to PET - no tracers, better temporal and spatial resolution, faster acquisition. • No known health risks. • Structural and functional information in the same image. • 3-D images of activity over the whole brain.
fMRI - Disadvantages
• Low temporal resolution • Indirect measure of neuronal activity – correlated but relationship between BOLD and neural activity complex and variable • 2-3 seconds to create an image • Not causal
