research methods in biopsych - week 4 Flashcards
how do neuroimaging methods work?
visualising the brain
What are the 2 types of scans?
structural scans (CT, MRI), focus on anatomy
functional scans (fMRI, PET), explore function
what is the aim of neuroimaging methods?
To identify normal and abnormal brain structure and function and relate this to behaviour and experience
They use healthy and clinical populations
What is computerised topography?
X-ray detectors move around the head passing radioactive beams through the brain. They measure how much radioactivity gets through - compute how much is absorbed as tissue with different densities absorb x-rays to different extents. Ct software translates the absorption info from multiple scans into an image showing areas of tissues with varying densities (CT scan)
what is a CT scan?
Scans of horizontal brain sections combine to create a 3D brain. Brain structure e.g damage can be linked to behaviour.
CT scans suffer from relatively poor spatial resolution, e.g. no distinction between grey and white matter
what is Magnetic Resonance imaging?
Measure varying water content in different areas of the brain with hydrogen atoms.
Strong magnetic field passed through patients head - hydrogen atoms align with magnetic force.
Radio waves then passed through the brain, the atoms wobble and realign which releases energy.
The energy released varies with hydrogen concentration of tissue scanned.
Computer creates an image that maps areas of the brain that differ on this variable.
Why can MRI be better than CT scan?
higher spatial resolution - more detailed structural information can be related to behaviour
Major fibre bundles (white matter) can be distinguished
Functional Magnetic Resonance Imaging (fMRI)
An active brain needs more oxygen so blood flow to that region increases
Changes in oxygen content of blood alters magnetic field
fMRI detects magnetism changes and maps them to specific brain locations
Signal recorded is called BOLD signal (blood level oxygen level dependent signal)
Changes in activity during experimental tasks is inferred from these BOLD signals
Positron emission tomography (PET)
Active brain areas require increased glucose supply (by increased blood flow)
Radioactive tracer similar to glucose (2-DG) is injected into the carotid artery (feeds ipsilateral cerebral hemisphere)
Cells in a more active areas pick up more tracer and emit more radioactivity
PET scan like a coloured map which represents in radioactivity across the brain
fMRI vs PET - advantages and disadvantages
fMRI
Research and clinical applications / healthy and clinical populations
Good spatial resolution (vs PET)
Non-invasive (vs PET)
Good temporal resolution (vs PET) – but still poor so misses some neural activity (blood oxygen changes and image creation slow but neural activity very fast).
Less expensive (vs PET) but still costly
Confined space and needs to be still limit its application
Indirect: relationship between BOLD signal and neural activity is complex
PET
Research and clinical applications / healthy and clinical populations
Both spatial and temporal resolution are poor relative to fMRI
Very expensive
Mildly invasive
Indirect
Measuring psychophysiology
Records physiological activity from the surface of the body
Non-invasive technique
Common physiological measures :
Muscle tension (EMG) and eye movement (EOG): measure somantic NS activity
Skin conductance (GSR) and cardiovascular responses (e.g. HR via ECG) measure autonomic NS activity
EEG: electrical brain activity from scalp
Electroencephalography
EEG measured via electrodes attached to the scalp
EEG signal reflects net activity of many thousands of firing neurons
Different EEG waveforms associated with different states of consciousness
E.g. Alpha waves associated with relaxed wakefulness, beta waves with mental concentration, and theta and delta associated with light and deep sleep, respectively).
Event related potentials (EPR)
EEG waves that accompany a discreet psychological event referred to as ERP’s
Signal (response to the stimulus) minus noise (background EEG activity)
Background noise cancelled out by signal averaging
Good temporal resolution, but poor (yet improving) spatial resolution
Invasive physiological methods
Direct measure (animals only)
Often performed using stereotaxic surgery
Methods of precisely positioning experimental devises deep in the brain
Hold the head using stereotaxic apparatus
Locate brain structure using stereotaxic atlas
Drill hole and insert electrode with precision
Experimental lesions
Part of the brain is removed, damaged or destroyed and the impact on behaviour observed
Various methods including:
Aspiration lesions
Radio-frequency lesions
Knife cuts
Cryogenic blockade – reversible lesion
Chemical lesions (neurotoxins)
Invasive electrical methods
Electrical stimulation
Electrical current sent down bipolar electrode to increase firing of nearby neurons –> observe behavioural effect
Accidental discovery of ‘pleasure centres’ in the brain – Olds and Milner, 1953
Electrical signal of septum lead to rewarding effects
Rats forgeo food, water and sex to continue to stimulate this area of the brain
Rewards system important in furthering our understanding of:
Psychiatric illness
Drug abuse
Motivation and learning
Psychopharmacology
Investigation of the effect of drugs on NS and behaviour
Administer psychoactive drugs that increase or decrease neurotransmitter effects and observe behavioural consequences.
Interested in which structures of the brain drugs stimulate
Majority of the research utilises animal subjects e.g. administer a drug in a particular area of the brain and observe the effect on levels of exploratory behaviour.
The therapeutic value can only however be established by examining the drug’s effects in humans.
Genetic engineering
Used to clarify the neural mechanisms of behaviour.
Gene knockout techniques – create genetically modified organism by inactivating a particular gene under investigation
Provides valuable clues about what that gene normally does
E.g. role of melanopsin in control of circadian rhythms by light (Ruby et al 2002)
Gene replacement techniques – inserting pathological genes from human cells into other animals
E.g. suspected defective gene coding for schizophrenia inserted into mice. They subsequently displayed cerebral abnormalities and abnormal behaviours consistent with human schizophrenic symptoms confirming the causal role of the gene in this psychiatric illness (Shen et al. 2008)
Neuropsychology
Study of behavioural effects of brain damage in humans
Locate the neural mechanisms underlying behaviour
Damage caused by disease, accident, or neurosurgery
Damage to the brain is naturally occurring so cannot be controlled
Accidental damage – case study Phineas Gage
Conclusion – frontal lobe plays important role in personality, decision making and processing of emotional information
Neuropsychological testing
Typically used to explore the extent and nature of the damage in brain injured patients
E.g. cognition/ memory, motivation, emotion, perception
Also used in healthy populations in psychological research
Assessment can be singular or repeated over a given period
A collection of tests is referred to as a ‘test battery’
Behavioural paradigms (animals)
Open field test – used to access fearfulness
Elevated plus maze – used to test anxiolytic effects of drugs
Morris water maze – used to study the spatial abilities of rats
