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Biological Research Methods, Knife cuts: nerve or tract cut - Coggle…
Biological Research Methods
Brain Anatomy
Roots in phrenology - idea that you could tell a lot about someone's behaviour by the shape of their skull
Phrenologists would make maps of skulls and decide whether someone could be classed as intelligent, trustworthy, devious, etc.
inspired modern psychologist view that you can link certain parts of the brain to different functions
Early x-ray that allows you to look inside the body, created problem where only area you couldn't look at was the head due to different tissues and skull protecting brain (cannot see features)
Computerised axial tomography (CAT) or computerised tomography (CT)
- first way to look at brain
Instead of taking one x-ray, takes lots of x-rays from every angle, until; its got a 360 degree angle. Picks up subtle differences and contrasts between different tissues in the brain - builds image of brain
to improve contrast, CAT scans involves injection of dye into bloodstream that is taken up by the blood vessels into the brain ad improves contrast
disadvantage of exposure to radiation
Method:
Patient placed in centre of large cylinder
One side of cylinder X-ray source, other side X-ray detector
Cylinder rotates around the had to take many individual pictures at one level of the brain, which are then combined into one photograph of that particular horizontal brain section
X-ray source and x-ray detector then moved horizontally to next level
Magnetic Resonance Imagine (MRI)
Powerful magnetic field (1.5 - 3 Tesla) - makes use of the magnetic probabilities of the hydrogen in the body
Method:
Head placed in magnet
Hydrogen atoms align along the magnetic field
Radiofrequency pulse flips the hydrogen atoms
Hydrogen atoms return to original state and thereby emit a signal that is measured and used to form an image of the brain
Different tissues/substances (water, brain matter, bone) emit energy with different speed image
Disadvantage: Person must lie as motionless as possible (makes it difficult but not impossible to use with children and anyone who fears enclosed spaces
Recording brain activity
Electroencephalogram (EEG)
Method:
Records electrical activity of neurons
Electrical activity recorded by electrodes placed on the scalp
Recording of spontaneous activity
Does not record activity from a single neuron but from a large number of neuron
Event-related potential (ERP)
- recording of responses to stimuli or events
Follows information processing on the millisecond-scale and can reveal information that self-reports or overt responses do not
Disadvantage: spatial resolution rather poor
Magnetoencephalogram (MEG)
Similar to EEG - records magnetic fields generated by electrical activity of neuron. Recorded by extremely sensitive devices mounted in a helmet
Spatial resolution better than EEG because magnetic fields are not distorted by scalp, skull, and meninges as is EEG signal. Temporal resolution excellent
Disadvantage: more expensive than EEG, sensitive to movement, small signal that needs to be shielded from other magnetic sources (even frim the earths magnetic necessary, and other potential sources e.g. cars, trains, etc.)
Positron-Emission Tomography (PET)
Records the emission of radioactivity from injected chemicals (e.g. 2-deoxyglucose)
Chemical accumulates in certain brain regions (regional cerebral blood flow, rCBF)
Detectors surrounding the head measure radioactivity emitted from each brain area
Images show e.g. which brain areas are active
Disadvantage: radioactive substances, low temporal resolution, expensive
Functional Magnetic Resonance Imaging (fMRI)
Same basic principles as MRI: magnetic field and radiofrequency pulses used to generate a signal. Very powerful method evolved during the last 10 years
Method:
Based on haemoglobin (protein in the red cells of blood that carries oxygen)
Amount of haemoglobin with oxygen increases in active brain regions a couple of seconds after the neurons have increased their activity (rCBF)
Stronger signals emitted from the hydrogen atoms in brain areas with relatively more haemoglobin with oxygen (BOLD response)
By comparing different conditions relative levels of brain activity can be measured and related to cognitive functions or behaviour
Microelectrode Recordings
Thin electrode inserted into the brain
If only for research, restricted to animals
In humans in the context of neurological surgeries
Can be used to study the electrical activity within one neuron (intracellular unit recording), the electrical activity outside one neuron (extracellular unit recording) or the activity of many nearby neurons (multiple unit recording)
Very good temporal and spatial resolution
Disadvantage: Invasive
Examine effects of brain damage
Study of victims of stroke or other brain injuries
Relates brain damage to behavioural impairments e.g. Broca's area
Recognise Faces
Attend to one hemisphere
Disadvantage: lack of control (other areas may also be damaged)
Double Dissociation
Link between brain area and function suggestive of localisation of function, but not proof
Find 2 patients with mirror deficits, then those functions must be independent systems
Lesion methods
Intentional damage of a selected area
Only in laboratory animals
Lesion – damage to a brain area
Ablation – removal of a brain area
Stereotaxic instrument used to locate precise brain areas
In contrast to the neuropsychological approach where behaviour is studied following accidental brain damage, in lesion methods some part of the nervous system is intentionally damaged
Aspiration lesion: cortical tissue drawn of by suction through a pipette
RF lesion: high-frequency current passed through the tissue
Brain stimulation
Transcranial Magnetic Stimulation (TMS) - another way to study effects of brain damage without permanently damaging brain
Intense magnetic field applied to the scalp which temporarily inactivates the neurons below the magnet
Cognition and behaviour can be studied with certain brain regions active and inactive
New method, fundamental questions about depth of effect, mechanism of neural disruption and safety not yet fully answered
Recording of psychophysiological activity
Muscle Tension
Measured using the electromyogram (EMG)
Electrodes taped to the surface of the skin over the muscle of interest
Indicator for physiological arousal, in emotion research (facial muscles)
Eye Movement
Measured using the electrooculogram (EOG)
Electrodes taped above, below, and beside the eyes
Skin Conductance
Measures the ability of the skin to conduct electricity
Indices: skin conductance level (SCL) and skin conductance response (SCR)
Application: Study of emotional thought and experiences
Cardiovascular activity
Heart Rate: Electrocardiogram (ECG or EKG)
ECG measures the electrical signal associated with each heartbeat
Blood Pressure (sphygmomanometer)
Blood Volume (plethysmography)
Behavioural Research methods
Traditional Conditioning Paradigms
Pavlovian Conditioning
Initially neutral Conditional Stimulus paired with an Unconditional Stimulus, a stimulus that elicits an Unconditional Response
After many repetitions of such pairings, the Conditional Stimulus alone will evoke the response, which is now called Conditional Response
Operant conditioning
The rate a particular behaviour is emitted is either increased by reinforcement or decreased by punishment
Semi natural Animal Learning paradigms
Conditioned taste aversion
Paradigm to study ability of rats to learn the relationship between a particular taste and subsequent illness
Radical arm maze, Morris Water maze
Both paradigms to study the spatial abilities of rodents
Behavioural responses to biological stimuli
Techniques so far have measured biological responses to stimuli (e.g. perceptual or social). We can also measure responses to biological stimuli
e.g. hormones
Hormones and faces
Oxytocin is a hormone important in social bonding in many species
Can be administered via intranasal spray
Administering oxytocin increased ratings of attractiveness and trustworthiness relative to control group (Theodoridou et al. 2009)
Men and women have different levels of hormones, especially sex hormones
Law-Smith et al. (2005) assayed women for estrogen and photographed faces
Faces with high estrogen were more feminine and more attractive
Comparison across species
Does a large brain mean high intelligence?
Whales and elephants have much larger brain than humans…
Early studies found no relation, some new MRI studies do
Consider brain size relative to body size (encephalization quotient)
Knife cuts: nerve or tract cut
Cryogenic blockade: tissue temporarily inactivated by cooling it down just above freezing level