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Methodology in Behavioral Neuroscience

Methodology in Behavioral Neuroscience. Jeremy L. Loebach NIH Postdoctoral Fellow Indiana University. Goals of Behavioral Neuroscience. Examine link between brain and behavior Brain Behavior How?. Single Unit Recordings. Microelectrode Glass micropipette Conductive wire

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Methodology in Behavioral Neuroscience

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  1. Methodology in Behavioral Neuroscience Jeremy L. Loebach NIH Postdoctoral Fellow Indiana University

  2. Goals of Behavioral Neuroscience • Examine link between brain and behavior • Brain • Behavior • How?

  3. Single Unit Recordings • Microelectrode • Glass micropipette • Conductive wire • Neutral solution • Place in or near neuron and record the electrical activity • Precise enough to isolate individual neurons

  4. Extracellular Recording • Microelectrode • Very small tip (3-10 micron ~ 1/1,000,000 m) • Small enough to isolate a single neuron • Place near cell and record changes in electrical activity • Dendrites • EPSP • IPSP • Place near a node of Ranvier • Action potential

  5. Review: Saltatory Conduction

  6. Receptive Fields of Simple Cells Hubel & Wiesel movie

  7. Intracellular Recording • Microelectrode • Glass micropipette • Much smaller tip (<1 micron) • Small enough to penetrate the cell wall • Insert electrode inside of the neuron • Record changes in resting potential • Tells you about the currents entering and exiting the neuron • Change voltage of the cell and see how the cell reacts

  8. Intracellular Recording

  9. The Voltage Clamp • Control the electrical charge of the cell from the inside • Modulate resting potential to see what effect it has on the cell • Increase • Decrease • Observe what other areas are stimulated as a result

  10. The Voltage Clamp

  11. Single Unit Recording • Pro • Can record from single neurons • Can be done in vivo or in vitro • Can systematically manipulate the conditions under which the cell will respond • Con • Invasive • Anesthesia • Difficult to do while animal is awake and behaving • Requires responses from a large number of neurons to study a system

  12. Multi-Unit Recording • Macro electrode • Larger diameter electrode is used • Record the responses of a large number of neurons at the same time • Local field potentials • Changes in the resting potential of the neurons at the dendrites • Dipole

  13. Local Field Potentials

  14. Multi Unit Recording • Pro • Can record many neurons at a time • Not as invasive • Can utilize awake behaving preparations • Con • Not as precise as single unit recording • Traces can include artifacts not related to the behavior

  15. Electro Encephalography (EEG) • Recording of Local Field Potentials from the surface of the scalp • LFPs spread out and can be measured from the surface of the skin • Record electrical activity • Electrode array (1-300 channels) • Reference electrodes on neutral areas where there are no neurons • Nose • Reference for eye movements and blinks • Eye

  16. EEG in action

  17. EEG Preparation

  18. EEG can Assess Arousal/attention

  19. Event Related Potential (ERP) • Recording of Local Field Potentials from the surface of the scalp • EEG • Synchronized to the onset of a stimulus • Change in electrical activity in response to an event

  20. ERP Components

  21. ERP Components • P1/N1 dipole • Initial positive peak followed by a negative peak • Sensory processing • P200 • Attention • P300 • Rarity • Oddball paradigm • N400 • Semantic processing

  22. EEG/ERP • Pro • Noninvasive • Inexpensive • Subject does not have to be performing a task • Great timing information • Con • Spatially poor • Imprecise

  23. Positron Emission Tomography (PET) • Measures metabolic needs of the brain • Cells require energy to function • ATP is the primary source of energy in the brain • Glucose is changed into ATP and used for energy • Follow the glucose to see which areas are active during a task

  24. PET • How? • Attach a radioactive isotope to the glucose • Cyclotron generates the isotope • Short half life (1 hour or less) • When decays it emits a positron • Positron collides with an electron and explodes, releasing photons at collision site • Photosensitive ring detects the photons • Triangulate the source • Register to the brain

  25. PET

  26. PET • Are not limited to glucose alone • Can attach tracer to any molecule • Neurotransmitter • See where a neurotransmitter is being used • Parkinson’s • Dopamine • DOPA is a precursor for Dopamine • Converted to Dopamine in substantia nigra • Substantia nigra is destroyed, Dopamine production decreases • Trace DOPA

  27. PET

  28. PET • Pro • Any molecule can be tagged • Con • Expensive • Injecting the body with radioactive substance • Poor resolution

  29. Functional Magnetic Resonance Imaging • Blood Oxygen Level Dependent Signal (BOLD) • Track oxygen in the blood using magnets • Oxygenated blood is high in iron • Iron is magnetic • Oxygen is also used by cells • When Oxygen is stripped from the blood by the cells, the blood becomes less magnetic • Flows back to the heart and lungs for re-oxygenation

  30. fMRI

  31. fMRI • Pro • Great spatial resolution • Relatively inexpensive • Con • Poor temporal resolution • 1-5 seconds • Indirect measure of neural activity • Not sure what governs the hemodynamic response in the first place

  32. Event Related Optical Signal (EROS) • Uses light to assess function • Skull is transparent to light • Shine light through skull at an angle, it will arc and exit elsewhere • Depending on what gets in the way, the light will be differentially deflected • Measure the amount of light that returns to assess neural function • Swelling of neuron due to ions entering and leaving causes light to be deflected

  33. EROS

  34. EROS

  35. EROS

  36. EROS • Pro • Great temporal resolution • Milliseconds • Fast • Inexpensive • Con • Requires registration to MRI • Surface --- can only reach a few centimeters below cortical surface

  37. Summary • Depending on what you are looking for, some methods may be more appropriate than others • Know the strengths of a technique • Know the limitations of a technique • Modern neuroimaging allows extension of techniques used in animals to humans • Ask the right questions • Use the right methodology

  38. Thank you for your attention!

  39. How do we observe this experimentally? • Record the activity of individual neurons during a task to see what they do • Extracellular • Intracellular • Sample the extracellular fluid from the synapse • What neurotransmitters are being used • Block the receptor and see how behavior is affected • Record from multiple neurons to see what a given brain region is responsible for

  40. Review: Anatomy of the Neuron • Dendrites • Soma • Axon • Nodes of Ranvier • Terminal Boutons

  41. Review: Action Potential

  42. Review: Neurotransmitters • Neurotransmitter • Chemical substances used in neural communication • Made in soma • Packaged in vesicles • Transported down the axon to the terminal boutons

  43. Review: Neurotransmission • Arrival of AP stimulates release • Crosses synaptic cleft to stimulate post-synaptic neuron

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