Neurophysiology

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Neurophysiology

• Recording electrical activity in the brain

http//play.psych.mun.ca/smilway/
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Types of Recording

• Acute or chronic
• Spontaneous or Evoked
• Sensory (touch, light, sound)
• Chemical (injection, pipette, microdialysis)
• Electrical (Electode)
• Intracellular, extracellular, juxtacellular
• In Vivo, In Vitro

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Simplest Preparation

• Record Spontaneous Electrical Activity using a
  single electrode.
• Recording Electrodes
• Micropipette(intra-, extra- or juxtacellular)
• Fine wire (extracellular)
• Carbon fibre (extracellular)
• Ground or Reference

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Stimulating Electrodes
Recording Electrodes
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The not so simple setup
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Recording

• The recording electrode or the micropipettes
  silver wire is connected to the G1 pole of the
  amplifier input.
• The ground (screw) is connnected to the G2 pole.
  The signal on G2 (background) is subtracted from
  G1. (Differential amplification)

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Amplifier

• The Amplifier amplifies and filters the signal.
• Amplifier output goes to
• Oscilloscope
• A to D Converter

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Oscilloscope
X-axis Time Y-axis Voltage
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A to D Converter

• Analog to Digital
• Voltages -10V to 10V are assigned a digital
  value 0 ? 4095
• Digital value can be stored on computer.

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A to D conversion

• Sampling Rate
• Temporal Resolution
• Digitization Range
• Voltage Resolution

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Ato D Sampling Rate Temporal Resolution
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A to D Digital Range Voltage Resolution

• 4096 points
• 4 settings
• -10V to 10V Resolution 4.88mV
• -5V to 5V Resolution 2.44mV
• -2.5V to 2.5V Resolution1.22mV
• -1.25V to 1.25V Resolution 0.61mV
• Maximize use of the range, but avoid clipping.

20V
20V
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Here the signals from the rat are seen in the
oscilloscope (top) and on the computer monitor
after being digitized by the AtoD Converter.
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Add Electrical Stimulation

• Many experiments examine connectivity by
  looking at response evoked by electrical
  stimulation to input.

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Electrical Stimulation

• Monopolar
• Anodal
• Cathodal (electrons flow cathode ? anode)
• Bipolar
• Twisted wire
• Concentric

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D to A Conveter

• This particular stimulator is gating a pulse from
  a computer to administer the stimulation.
• The D to A converter converts a digital input to
  a voltage.

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Heater

• Under anaethesia animal will not regulate
  temperature very well.
• A heater can be added to maintain the animals
  temperature at a constant level

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Computer

• A computer is usually used to control the
  experiment and collect and analyze the data.
• Specialized software packages for neurophysiology
  are available. We use Expeimenter Workbench by
  DataWave.

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The Circuit
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The Preparation

• Recording Electrode in Granule Cell Layer of
  Dentate Gyrus
• Stimulating Electrode in Perforant Path
• Cannula in Locus Coeruleus

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The Evoked Response