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
