Neurophysiology Recording electrical activity in the brain smilway

NeurophysiologyNeurophysiology

Recording electrical activity in the Recording electrical activity in the brainbrain

http://play.psych.mun.ca/~smilway/

Types of RecordingTypes of Recording

Acute or chronicAcute or chronic

Spontaneous or EvokedSpontaneous or Evoked Sensory (touch, light, sound)Sensory (touch, light, sound) Chemical (injection, pipette, microdialysis)Chemical (injection, pipette, microdialysis) Electrical (Electode)Electrical (Electode)

Intracellular, extracellular, juxtacellularIntracellular, extracellular, juxtacellular

In Vivo, In VitroIn Vivo, In Vitro

Simplest PreparationSimplest Preparation

Record Spontaneous Electrical Activity Record Spontaneous Electrical Activity using a single electrode.using a single electrode.

Recording ElectrodesRecording Electrodes Micropipette(intra-, extra- or juxtacellular)Micropipette(intra-, extra- or juxtacellular) Fine wire (extracellular)Fine wire (extracellular) Carbon fibre (extracellular)Carbon fibre (extracellular)

Ground or ReferenceGround or Reference

http://www.psych.umn.edu/courses/fall05/burkhardtd/psy3031/images/microelectrode.jpg

Recording ElectrodesStimulating Electrodes

The not so simple setup

RecordingRecording

The recording electrode or the The recording electrode or the micropipette’s silver wire is connected to micropipette’s silver wire is connected to the G1 pole of the amplifier input.the G1 pole of the amplifier input.

The ground (screw) is connnected to the The ground (screw) is connnected to the G2 pole. The signal on G2 (background) is G2 pole. The signal on G2 (background) is subtracted from G1. (Differential subtracted from G1. (Differential amplification) amplification)

AmplifierAmplifierThe Amplifier amplifies and filters the signal.The Amplifier amplifies and filters the signal.Amplifier output goes to:Amplifier output goes to: OscilloscopeOscilloscope A to D ConverterA to D Converter

OscilloscopeOscilloscopeX-axis: TimeY-axis: Voltage

A to D ConverterA to D Converter

AAnalog nalog toto DDigital igital

Voltages -10V to +10V are assigned a Voltages -10V to +10V are assigned a digital value 0 digital value 0 4095 4095

Digital value can be stored on computer.Digital value can be stored on computer.

A to D conversionA to D conversion

Sampling Rate Sampling Rate

Temporal ResolutionTemporal Resolution

Digitization Range Digitization Range

Voltage ResolutionVoltage Resolution

Ato D Sampling Rate & Temporal Ato D Sampling Rate & Temporal ResolutionResolution

A to D Digital Range & Voltage A to D Digital Range & Voltage ResolutionResolution

4096 points4 settings:•-10V to +10V Resolution: 4.88mV•-5V to +5V Resolution: 2.44mV•-2.5V to +2.5V Resolution:1.22mV•-1.25V to +1.25V Resolution: 0.61mV

Maximize use of the range, but avoid clipping.

20V

20V

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

Add Electrical StimulationAdd Electrical Stimulation

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

Electrical StimulationElectrical Stimulation

MonopolarMonopolar AnodalAnodal Cathodal (electrons flow cathode Cathodal (electrons flow cathode anode) anode)

BipolarBipolar Twisted wireTwisted wire ConcentricConcentric

D to A ConveterD to A Conveter

This particular stimulator is gating a pulse This particular stimulator is gating a pulse from a computer to administer the from a computer to administer the stimulation.stimulation.

The D to A converter converts a digital The D to A converter converts a digital input to a voltage.input to a voltage.

HeaterHeater

Under anaethesia animal will not regulate Under anaethesia animal will not regulate temperature very well. temperature very well.

A heater can be added to maintain the A heater can be added to maintain the animals temperature at a constant levelanimals temperature at a constant level

ComputerComputer

A computer is usually used to control the A computer is usually used to control the experiment and collect and analyze the experiment and collect and analyze the data.data.

Specialized software packages for Specialized software packages for neurophysiology are available. We use neurophysiology are available. We use Expeimenter Workbench by DataWave.Expeimenter Workbench by DataWave.

The CircuitThe Circuit

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

The Evoked ResponseThe Evoked Response