L5: Research Methods

Methods of visualising the brain

contrast xrays, ct scan, mri, functional mri, diffusion tensor mri, positron emission tomography

method to stimulate the brain

TMS - Transcranial Magnetic Stimulation

Recording physiological signals

Scalp electroencegraphy (EEG), event related potentials (ERP)

2 methods of animal studies

invasive methods and lesion methods

Contrast x rays

patient injected with radiopaque substance which absorbs x-rays differently, useful for angiography

computed tomography (CT scan)

X ray gun compiling 8-9 images to make 3d view of brain structure, not so clear

MRI

waves emitted by hydrogen atom when in magnetic field, provides 2d/3d images, very detailed structure of brain

MRI pros

more resolution than CT scan and no X ray exposure

functional MRI

detects oxygen consumption of active brain regions (BOLD signal), can see brain activity while someone performs task, shows brain structure

fMRI pros

provides structural and functional information, can see full image of brain from all planes

fMRI cons

correlational information, poor temporal resolution (Dead salmon study)

diffusion tensor MRI

identifying pathways that water molecules diffuse through (tracts), can see connections in brain and find injuries

positron emmission tomography

injection of radioisotopes which accumulate in active neurons and reveals brain activity, shows brain in different states and identify abnormal regions

PET cons

provides maps of radioactivity, not images of the brain, requires substance injection

TMS

brief, strong magnetic field which alters neural energy, can see cause+effect on behaviour

TMS cons

not a measure of neural activity, not specific with spatial location

Electroencegraphy EEG

measures sum of all electrical activity = EEG signal, different waveforms show different consciousness

Event related potentials ERP

derived of average signals from EEG, can see responses to specific events

Stereotaxic surgery

invasive animal study, drill hole in specific location in skull, insert electrode to measure specific brain areas

requires bregma (reference point) + stereotaxic instruments

Lesion methods for animal studies include

aspiration methods, radio-frequency lesions, sectioning, reversible lesions

aspiration method

sucking visible cortical region tissues into tube

radio-frequency lesion method

destroying target regions through currents of radiofrequency with stereotaxic instrument

sectioning method

using subcortical knife cuts to eliminate nerve tracts with high precision

reversible lesion method

region temporarily switched off with cyrogenic blockade or anaesthetic

Electrical stimulation

done prior to lesioning, usually opposite effects, can trigger behavioural changes

recording methods include

intracellular methods, extracellular unit recording, multiple unit recording, invasive EEG recording

intracellular recording

intracellular microelectrode records membrane potential from 1 neuron as it fires

extracellular single unit recording

extracellular microelectrode records electrical disturbance created every time adjacent neuron fires

multiple unit recording

small electrode records activity of many neurons simultaneously

invasive eeg recording

large implanted electrode picks up changes in electrical brain activity

pharmacological methods refer to

drug administration to focus on the effect of NTs, different adminisration routes

genetic engineering methods include

gene knockout techniques, gene replacement technology

Gene knock out techniques

removing specific genes

gene replacement techniques

replacing 1 gene with another, can insert modified genes which switch on/switch off

Methods to measure neurotransmitters in animals include

Western blotting, flow cytometry, mass spectrometry, immunoaffinity based methods

Measuring neurotransmitters in humans can be done through

mass spectometry, immunoaffinity based methods ELISA

Mass spectometry

identifies particular biomarkers based on mass/fragmentation patterns, very sensitive and specific

immunoaffinity based methods ELISA

antibody (enzyme) with affinity added to sample - attaches and fluoresces

selective chemical lesions

inject neurotoxins to damage neurons releasing specific NTs

measuring chemical activity in behavioural studies can be done through

2-deoxyglucose technique, in vivo cerebral dialysis

2-deoxyglucose technique

subject is killed, level of NT in brain structures measured

in vivo cerebral dialysis

brain implantation of tube

neuropsychological testing strategies include

clock drawing test, single test vs battery approaches

clock drawing test

tests for presence of planning and conceptual deficits, mostly used with alzheimer’s and huntington disease patients

behavioural paradigms in lab include

species common behaviours, conditioning paradigms, learning

behavioural learning tests

taste aversion, radial arm maze, morris water maze, defensive burying