Methodology in Behavioral Neuroscience

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Methodology in Behavioral Neuroscience

• Jeremy L. Loebach
• NIH Postdoctoral Fellow
• Indiana University

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Goals of Behavioral Neuroscience

• Examine link between brain and behavior
• Brain
• Behavior
• How?

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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

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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

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Review Saltatory Conduction
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Receptive Fields of Simple Cells
Hubel Wiesel movie
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Intracellular Recording

• Microelectrode
• Glass micropipette
• Much smaller tip (lt1 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

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Intracellular Recording
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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

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The Voltage Clamp
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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

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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

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Local Field Potentials
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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

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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

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EEG in action
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EEG Preparation
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EEG can Assess Arousal/attention
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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

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ERP Components
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ERP Components

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

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EEG/ERP

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

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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

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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

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PET
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PET

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

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PET
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PET

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

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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

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fMRI
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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

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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

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EROS
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EROS
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EROS
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EROS

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

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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

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Thank you for your attention!
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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

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Review Anatomy of the Neuron

• Dendrites
• Soma
• Axon
• Nodes of Ranvier
• Terminal Boutons

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Review Action Potential
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Review Neurotransmitters

• Neurotransmitter
• Chemical substances used in neural communication
• Made in soma
• Packaged in vesicles
• Transported down the axon to the terminal boutons

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Review Neurotransmission

• Arrival of AP stimulates release
• Crosses synaptic cleft to stimulate post-synaptic
  neuron