Fluid Filled Pipette Electrodes; Making Differential Recordings - Digitimer SPP-100 Operator's Manual

Digitimer Limited SPP-100 Operator's Manual Issue 1
Single-ended recordings can be accomplished by grounding the -INP input of the headstage
with the input cable fitted with the "U"-shaped 1mm jumper (supplied); the "U"-shaped
plug is pushed into the -INP and COM inputs and the flying lead is used to provide the ONLY
ground connection for the preparation. In this way any common-mode interference picked
up at both the +INP and -INP inputs of the headstage can be summed out by the SPP-100
main unit.
A DC path must be provided from each input of the headstage to the system ground. This
DC path may of course be through a high resistance microelectrode. It is also essential, for
the best noise performance, to make the ground connection to the biological preparation
through the COM terminal of the headstage. When used differentially, with both +INP and -
INP inputs connected through electrodes to the preparation, a connection to the COM
(Ground) input should still be made to the preparation.

Fluid Filled Pipette Electrodes

When using fluid filled pipette electrodes it is recommended that a compatible electrode
chamber with a 2mm pin is used. Digitimer supplies a range of holders (NL111) with and
without side ports.

Making Differential Recordings

Although the SPP-100 is most frequently used with high resistance microelectrodes where
the signal of interest is referenced to Ground, its very low-noise performance allows it to be
used with low-resistance electrodes (e.g. for differential recordings of compound action
potentials through pairs of gross electrodes).
WARNING - It should be pointed out that if the input device of, or cable to, the headstage
should fail there is a possibility of current flowing though the preparation to ground causing
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an inadvertent lesion . This is limited by the design to approximately 650mA. Should this be
a problem (and it is a remote possibility) please contact Digitimer for advice.
Do NOT attempt to use oversize plugs with the headstage sockets, as pins greater than
1.00/2.00mm diameter will damage the sockets.
(1)-Recording of Brain Potentials with FET-Circuits: Hazard of Inadvertent Lesions, by J. A. W.
M.Weijnen and N.Chedhade in Brain Research Bulletin, Vol. 18, pp617-618.
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