The methods and limitations of Neuroscience Flashcards
week 6
what are the 4 famous brain leison studies?
- Phineas Gage
- Louis Victor Leborgne “Tan”
○ Broca’s patient- after brain injury could only say the word tan - Auguste Deter
○ Neurons developed- what we know today as Alzheimer’s. - HM
explain Phineas Gage’s significance in neuroscience:
- Railroad foreman
- Iron rod driven through his head
- Much of left frontal lobe of brain destroyed
○ ‘the balance between his intellectual faculties and animal propensities seems to have been destroyed’
○ Stated his personality changed after the accident- aggressive, unruly. - A good example of where the facts have become fictionalised
○ Story often exaggerated
○ He was not aggressive, sexually deviant or a drifter
○ ‘conceived a great fondness for pets, and souvenirs, especially for children, horses and dogs’
explain Auguste Deter’s significance to neuroscience:
- 51-year-old woman from Frankfurt
- progressive cognitive impairment, hallucinations, disorientation, paranoia and psychosocial impairment
- Autopsy revealed arteriosclerotic changes, plaques, neurofibrillary tangles
○ Fibres of her neurons became tangled- formed knot like structures in the brain - Her condition was named after her Dr, Alois Alzheimer.
- What we know as Alzheimer’s today
what are the disciplines concerned with the brain?
Neuropsychology= development of behavioural principles
Medicine= treatments, e.g. brain tumours, epilepsy, schizophrenia
^ in the 20th century
explain “mass action” and Karl Lashley:
- Biological psychologist; found that rats trained to obtain food rewards in mazes retained memories even after progressive brain lesions. (experimental)
- Concluded that memories were not localised, but distributed throughout the brain
○ Could still remember the maze even after progressive brain lesions - Developed the principle of “mass action’
○ amount of memory loss proportionate to the amount of brain tissue loss
○ Thinking about quantity
○ Impairment comes from reduced brain mass not to a specific area. - Lesions made in cerebral cortex.
explain “motreal procedure” and wilder penfield (1954):
- Pioneering neurosurgeon: used electrical brain stimulation in awake patients
- Produced “vivid memories”, smell, auditory and déjà vu experiences
○ Depending on the area, certain responses were activated for the individual - Results consistent with localisation of brain function
○ If we tamper/ stimulate a specific brain region we get activation of certain memories. - Illustrates that as technology advances, our understanding of the brain also does.
what is histology?
- visualize particular brain region
○ fixation, sectioning and staining of the brain + microscopy
○ Observing under a microscope
§ Old and simple method
§ Developed in 1800s
○ identify, quantify and localize cells (e.g. using a particular neurotransmitter or receptor) - E.g.: HM’s brain was sectioned and preserved for scientific research.
- tracing neural connections
○ efferent neurons via anterograde (moving forwards) labelling
§ Where are neural pathways going to
○ afferent neurons via retrograde (moving backwards) labelling
§ Where have neural pathways come from - establish the wiring diagram of the brain
what is experimental ablation?
- The oldest method used in neuroscience, still in common use
- In modern science, typically animal studies
- Achieved via Stereotaxic surgery
- Brain tissue is destroyed, and alterations in behaviour observed (lesion studies)
○ Alterations in brain function are inferred - Allows identification of neural circuits and localisation of behaviour
- Skull is fixated (stereotaxic surgery)
○ Electrode is within the brain- destroys the brain tissue
○ Alterations in the brain are observed. - Due to manipulation (and destroyed brain tissue) it allows us to infer behaviour to explain how a specific brain region is involved in certain functioning.
how are lesions created?
- Electrical current using an electrode (older earlier method)
○ Electrode is passed through a very specific location
○ It creates heat which destroys the brain tissue
○ Indiscriminate- all the brain tissue in the are is destroyed by the electrode/heat. - Excitotoxic lesions created using injection of excitatory amino acid (newer method)
○ Destroys cell bodies
○ Neural circuitry is still in tact
○ Kills the neurons through over stimulation but spares the neural circulatory - invasive
how do experimenters use control groups in lesion studies?
the procedure to allow the creation of lesions (stereotaxic surgery) causes some damage itself, therefore sham lesions must be created in control group before any group comparisons are made- would need sham lesions for controls- make sure participant went through procedure without the lesion formed.
Enables meaningful comparisons from being drawn- not the surgery that resulted in the differences but the lesions itself
how do we measure electrical activity?
- acute vs. chronically implanted
- Can be in short or long-term
- Devices implanted to pick up on electrical activity over a longer period of time.
- using microelectrodes:
○ single-unit recordings based on stereotaxic coordinates - using macroelectrodes:
scalp recordings e.g. EEG/MEG
what are CT scans?
computerized Tomography
○ Measures x-rays passed through brain
○ X-ray on one side
○ Detector on the other side
○ Enables us to study the structure of the brain
what are MRI scans?
Magnetic Resonance Imaging
○ Measures magnetic field passed through brain
○ Different molecules within the brain have different frequencies
§ More or less dense (grey v white matter)
○ Brain tissue varies in terms of density so when measured through MRI scans the frequencies will be picked up.
More details- more expensive.
how do we measure etabolic activity?
- Neuroimaging techniques measure metabolic activity as an indirect measure of brain activity
○ If energy is being used up, indirect assumption that there is brain activity taking palace - Use of energy
- 3 methods of measuring it (PET, SPECT, fMRI)
What are PET scans?
Positron Emission Tomography
§ radioactive markers combined with sugar
§ Up taken by the brain cells (not metabolised)
§ When molecules decay, they emit particles that are travelling in directly opposite directions
§ Sensors around head, enables us to locate positrons (trace) the emission through a computer.
§ Better image to use
What are SPECT scans?
Single Positron Emission Computerised Tomography
§ Different radioactive markers
Cheaper method that PET scans- do the same thing
what are fMRI scans?
functional Magnetic Resonance imaging
§ oxygen in blood vessels of brain
* Areas that require more energy will have more oxygen.
* Using fMRI to examine brain activity during psychological tests
* Identify the brain area which “lights up” showing greater blood flow
* Conclude that THAT area is associated with THAT cognitive activity
* Which has the greater blood flow is associated with that specific cognitive activity in the task.
what is optic dynamic laser/ electron microscopy?
- Precision images of cellular processes and metabolism
○ Uses lights from lasers - Real Time dynamic images
- In-vivo
- 3 dimensional images
- Weaknesses:
○ Limited to animal studies
○ Extremely time consuming
what is psychology of the brain?
- Brain understood as physical location of psychological phenomena since the late 16th century
- All of psychology (learning, memory, personality, psychomotor performance, motivation, emotion, mental health) is mediated by the brain
○ Brain is involved in all psychological processes
how do we measure neural activity using EEG scans?
- Brain activity can also be detected by measuring voltage fluctuations within neurons using the electroencephalogram (EEG)
- EEG, combined with eye‐movement (electro‐oculogram EOG ) and muscle tension (electromyogram EMG) measures can be combined to measure sleep – polysomnography (PSG)
- REM sleep= dream stage
- Gained popularity in the 1960s.
- e.g.: measuring sleep
what are the stages of EEG stage sleep?
- Stage N1: drowsiness not quite fully awake.
- Stage N2: ‘true’ sleep, but light (spindles)
○ Spikes in activity - Stages N3: ‘deep sleep’.
○ Delta waves formed- spaced out electrical activity - REM: Rapid Eye
○ Hight decrease in electrical activity
○ Movement Sleep - Sleep is characterised by wave forms which demonstrate the different stage so sleep
what are PSG measures of sleep (selected)?
- Sleep Latency: the time taken to get to sleep (from ‘lights out’ to stage N1)
○ Can tell the wave form changes - Total Sleep: total (N1+N2+N3+R)
○ Using wave forms we can identify how much sleep an individual gets - Is PSG “better than” subjective experience?
○ More scientific
○ Perhaps more accurate
○ Fails to account for individual and how they may perceive their sleep - Wave form= is it better to have these wave forms to know more about sleep or would it be better to ask the individual about their sleep
PSG v Subjective Experience (adam, tomeny and Oswalk, 1986)- what are the differences?
- In general, people over‐estimate Sleep Latency (we think it takes longer to get to sleep than it really does)
- In general, people underestimate Total Sleep Time (we think our sleep is shorter than it really is)
- So, are the machines “better”?
○ May be more accurate in telling us the time spent asleep and sleep latency.
Sleep is experiential.
what did Borkovec et al (1981) study on perceptions of sleep?
- Compared the sleep of 25 insomniacs and 10 good sleepers
- Each woken up in the 5th minute of first episode of Stage 2 (N2)
- Asked “were you awake or asleep?”
- Most good sleepers said “asleep”; most insomniacs said “awake”
○ Sleep may be due to our perception
○ Mismatch in what is experienced versus what is told by the objective methods for insomniacs (were actually asleep even though they believed they were awake) - Subjective experience is important for individuals.
- Despite identical electrophysiology, people “experience” their sleep differently
- Sleep onset is an experiential, as well as an electrophysiological phenomenon
- The way we experience things is different.
what are the gaps in neuroscience?
Intelligence
Inter-personal relationships
Mental illness
Consciousness
what is the problem of the brain and mind?
even in the context of neuroscience
If the mind is purely in the brain, we cant understand conscious experience because there is nothing to suggest we have it.
* What, then, are the limitations of neuroscience?
○ Doesn’t help us explain what it means to be conscious
○ Need to look at other disciplines (psychology, philosophy)
* David Chalmers= conscious experience may represent a limit of science
what are the problems with objective measurement?
- Neuroscience is founded on objective measurement
- Much of psychology is concerned with people’s experience (subjective):
○ Mental illness
○ Motivation - Objective measures of experiential factors are not possible.
