Neurophysiology

Recording electrical activity in the brainhttp://play.psych.mun.ca/~smilway/

Types of RecordingAcute or chronicSpontaneous or EvokedSensory (touch, light, sound)Chemical (injection, pipette, microdialysis)Electrical (Electode)Intracellular, extracellular, juxtacellularIn Vivo, In Vitro

Simplest PreparationRecord Spontaneous Electrical Activity using a single electrode.Recording ElectrodesMicropipette(intra-, extra- or juxtacellular)Fine wire (extracellular)Carbon fibre (extracellular)Ground or Reference

Recording ElectrodesStimulating Electrodes

The not so simple setup

RecordingThe 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)

AmplifierThe Amplifier amplifies and filters the signal.Amplifier output goes to:OscilloscopeA to D Converter

OscilloscopeX-axis: TimeY-axis: Voltage

A to D ConverterAnalog to Digital Voltages -10V to +10V are assigned a digital value 0 4095Digital value can be stored on computer.

A to D conversion

Sampling Rate Temporal ResolutionDigitization Range Voltage Resolution

Ato D Sampling Rate & Temporal Resolution

A to D Digital Range & Voltage Resolution4096 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.

20V20V

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

Electrical StimulationMonopolarAnodalCathodal (electrons flow cathode anode)BipolarTwisted wireConcentric

D to A ConveterThis 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.

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

ComputerA 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.

The Circuit

The PreparationRecording Electrode in Granule Cell Layer of Dentate GyrusStimulating Electrode in Perforant PathCannula in Locus Coeruleus

The Evoked Response