Tony Cog Neuro Part 1 Flashcards
Temporal resolution
When the time between frames is short we have high temporal resolution
Use hertz or the time between measurements in milliseconds
Causes of Brain lesions
vascular: brain uses 20% o2 and loss causes neurone death (inclusion e.g. stroke/cerebral vascular accidents or hemorrhagic stroke e.g. bleed due to blocked blood flow from fat embolism, drop in blood psi stops reaching brain so aneurysm), trauma (mostly impact frontal lobes, sports, army, causes swelling and psi), disease (AD,hiv) and surgery. Tumours can damage tissue or add pressure on cortex, cutting off blood supply in white matter
Single and double dissociation
Ppl with damaged temporal lobe do worse in familiarity memory tasks compared to controls (single)People with frontal lobe damage do worse in recency memory task but not familiarity
Tells us about localisation (double dissociation). Single is when lesion impairs brain area x and ability on one task A. Double is damage to area x impairs task A but not b, y impairs b
Case studies
Brain and behaviour relationships, localisation. Limits generalisability, to solve use alongside lesion overlap and behavioural deficits. Phineas gage-personality diff due to frontal lobe, lesions reconstructed from skull and used mri to see location. HM had amnesia due to epilepsy surgery (hippo)-post-mortem using 3D reconstruction
Examples of lesions and deficits
Prosopagnosia, cerebral achromatopsia-colour blindness due to lesions in temp lobe, region impacts face processing but don’t have both. Neglect: ps ignore L half of visual field but can detect targets if alone (attentional deficit)
Limitations of lesions
Don’t respect functional boundaries. Presentation bias (only interesting cases). Lesions in one area can affect connections to others (can’t overcome/see). Don’t have before and after comparison
Visual fields
Contra lateral. Homonymous hemianopia is one side of visual field lost in both eyes due to lesion on primary visual cortex. GY had lesion contracoup and vision lost in R visual field. Blindsight is ability to tell diff between visual stim not consciously acknowledged. Showed primary visual cortex not only part that gets input from brain but pfc is visual consciousness. Can tell direction of motion as v5 region outside pvc responds but not to stainary. Regions outside pvc responsive to motion
TMS
Pass current through coil to create magnetic field to affect brain functioning. Done before or after seeing a letter and asked to id. Done to replicate GY and helps understand spec events like overcome issue of lesions not respecting brain boundaries
Evaluation of induced lesions
S: precise, post mortem, before and after (more spec). W: animal use, can’t generalise to humans, plasticity and reorganisation. Chemical lesions are precise and can generalise but carbon monoxide leads to specific damage naturally, uses animals
Receptive field
Neurone only fires when stim is in a certain area. Hubel and weisel got Nobel prize as understanding of the way we see by recording aps of neurones to determine receptor field
Colour and motion and face selectivity
Semir zeki: functional specialisation of the visual cortex. Diff regions are specialised for diff visual properties v4: colour, v5: motion.
Within v1 blobs and interblobs are diff specialised and project to diff areas. In the STS - selective neurones to faces
Brain measurements
From human studies, usually w intractable epilepsy who need surgery
In hippocampus found neurons specific to certain celebrities showing cells respond to identity not image
Single unit electrophysiology
Use micro electrodes to record APs to define the receptive field
Neurons have variety of responses and lie together fire together to become specialised
Approach is invasive so not done in humans mostly
EEG- electroencephalography
Measures brain waves, represent diff states. Signals driven by large electric dipoles W voltage diffs. Only for groups of neurones. When pyramidal neurones have presynaptic inputs, membrane potential change, forming dipole. Layer 4 neocortex, neurones have axons deep but dendrites closer to scalp. Signal mirrors extra cellular local field potentials.
W of EEG
doesn’t show whether excit/inhib. Neural activation doesn’t always show at the nearest electrode, depends on orientation of dipole
Eeg signals are a reflection of local field potentials, not especially APs and signals dont map onto ex/in and origin in the brain
Event related potentials
W of eef is there’s resting brainwaves that are bigger than waves from a stim so have to do repeats. Time response can relate to a pathway. Auditory evoked and visual evoked potential. Solution is when you average many trials the background can be taken out
Sensitivity to objects
Faces and cars evoke similar p1 responses (early on) but become diff at n170 (later visual processing). Semantic violations impact processing at n400 and syntactic violations at p600 stage (both later on) but semantic proceeds syntactic
Localising effects
ERP analysis restricted to electrodes of interest but can be done for all sensors. Pattern across scalp electrodes can be caused by underlying dipoles (diff signals can produce same patterns), also effected by volume conduction (blur signal). Algorithms can calc location. In MEG combined W structure, good spatial estimate
MEG
Magnetic fields, makes it easier to localise neural function. Changes in electric fields have mag fields perpendicular to them. Mag fields induce currents in coils but changes are v small so need superconductive coils by cooling W helium which is £££ but now there’s room temp ones. System needs to be in mag/electo shielded room, p under sensory that measures fields
Comparison between eeg and Meg
EEG is cheap, available, less prone to movement, diff in volume so not precise and unreliable in high signal freqs. Meg is £££, not widely available , ps can move, more precise and more reliable
Alpha oscillations
Resting waves, around 10htz when eyes closed. Performing memory task interferes with the,
History and how mri works
Started W broadmans areas of the brain, from post mortem or cortex and suggested localisation. Atoms are mag charged and align W magnetic field and diffs provide basis for signals-diff tissues give diff signals as take diff times to align to normal. High strength scanners get info from ex vivo brain compared W microscopes (scanners now at same level)
Diffusion tensor imaging and S
White matter connects brain regions and can be measured with mri in DTI.
Captures diffusion of water which is more in the axon than outside to measure direction of wiring in the brain.
S and examples of dti
Better at categorising lesions and degenerative disorders. Compare groups or conditions (ageing, neurodevelopmental blindness). Maguire taxi drivers, congenital prosopagnosia had reduced integrity of white matter in visual pathways (ventral)
Pet scans
Positron emission tomographic. Nucleus emits positron which collides w electron and produces energy (photons) can measured where they came from. Used to tag beta amyloid plaques and cancer diagnosis. W: need radioactive isotope by injection so research on healthy pjs rarely done, spatial resolution worse than mri
Fmri
Helmet to pick up small radio frequency signals from protons, frost in 52 by kwong. Neurones use o2, leads to reduction in blood o2 and then provides more 9po2 at rest. Blood o2 changes local mag properties of the tissue which change signal- called blood oxygen level dependent (bold). Dip due to reduction but smaller than flood of o2 that follows activity. Single is slow so use block designs (one condition for 10-30s then switch and measure diff). Primary visual cortex responds to static and moving stim. Kanwisher used to find fusiform face area. Good link between lesion overlap and those of achromatipsia and proso in mri
Diff ways to use mri
Can use brief events not block but have to wait 15s in between means long and £c so not many trials and timing between events and their order to optimise stats power. Multivariate analysis: compare voxel patterns. Resting:measure at rest then during condition. Owen: ps on life support asked to imagine motor or spatial, brain activity in same areas as controls-can tell whether to pull the plug (not actually in real life tho). Less animal use
