Fixing BAK Electronics IMP-2 Electrode Impedance Tester

BAK IMP-2 Tests a 1MOhm Resistor, declares impedance to be 1MOhm. 

In getting ready to do some electrophysiology I fixed up a broken a BAK IMP-2 Electrode Impedance Tester.  This unit measures impedance at 1kHz.  The device I got was given to us free in a broken state.  My guess was that some op amps got fried by a "naughty" experimenter.  This was indeed the case, however, not one, but two op amps were destroyed.  The unit runs off of two LF442CN dual op amps and one OPA111A high precision op amp.  The burned out components were the OPA111A and one of the LF442CNs.  Lucky for me, we found replacements for both components the same evening and the unit is now as good as new!  I must thank my awesome tech for helping me verify the broken op amps and find replacements! Ready for electrodes.

Measuring Olfactometer Output in Odor Port

Odors are hard to measure and typical humans have little intuition for how they behave.  However, there are now ways to [relatively] easily measure the concentration of odors in clean air.  These devices are called photoionization detectors (PIDs) and they are used heavily in industry to detect specific volatiles.  Many of these devices are good at quantifying a stable odor source, but lack temporal resolution.  Some companies, however, have elected to make particularly fast PIDs.  One of these is the minPID from Aurora Scientific.  This device gives a measure of odor concentration in clean air with millisecond precision.

We use it routinely to calibrate our odor presentation and it is really the only reason we have solid idea about what odor concentration is being presented to the animal in our odor port.

Routine testing: miniPID (bottom) inserted into one of the odor ports.

Sniffs and Spikes

My next technical challenge in the lab is to set up simultaneous recording of sniffing and of neural spikes.  I am planning on putting together a compound device integrating a silicone probe for measuring neural activity and a pressure sensor for measuring sniffing simultaneously.  The trick will be to have all inputs and output go through a single tether wire.  Currently my thinking is that I can use a TDT ZIF-Clip with 64 channel capacity and use 32 of the channels for the electrodes and 4 channels for the pressure sensor (+V, -V, Gnd, Out).  For a commutator, I am thinking of getting a 36 channel slip ring system from the orbex group.

UPDATE:  Turns out there are issues with integrating other inputs/outputs into the ZIF-Clip from TDT.  Currently, the clip uses nearly all of its channels for electrode signals and it is difficult to break any channels out.  My alternate solution is to just put up with a second (third) wire to the head and continue attaching the sniff sensor via a magnet.  We are now miniaturizing our sniff sensor so that it may fit better on the head alongside the electrode and micro drive.

Tubing and odors, a non-ideal combination

In olfactometry, one is constantly fighting to produce temporally precise and stable concentration outputs.  This is especially critical when you want to make detailed measurements of perception or neural activity.  Unfortunately, investigators are constantly confounded by artifacts that can distort the temporal properties and concentration profile of odor output.  On this blog, I hope to eventually cover several issues that typically come up in calibrating olfactometers.  In this first installment, I will deal with the issue of tubing after the jump.

Cheap(ish) Commutator for Tethered Recordings

A friend pointed me to a very useful product for those of us who connect wires to freely moving animals.  It is a slip ring commutator manufactured in china by Hangzhou Prosper Mechanical and Electrical Technology Co and sold here in the US by adafru.it.  This commutator moves quite freely and is available with many channel options (the 6 channel goes for $17.50).  I got my hands on a few and am now contemplating using this as my commutator for ephys recordings.  The company makes a 32 channel version which is sold for about $350.  I will first test the one I have with my sniff sensor.

Human Olfactometer in Action

Today was a day of putting the new Alicat MFC powered human olfactometer through its paces.

We tested:

1. Onset Latency (NResearch final valve)
2. Concentration steps via flow dilution (Alicat MFC)
3. Concentration waveforms (Alicat MFC)
4. Odor sampling by human subject (YBS)

Here are pictures of our setup:

Olfactometer Test Setup 1: Kinetics.  The PID (photoionization detector) is sampling directly from  the nose port.  The scope is displaying PID output and flow from the flow sensor (below).  Scope is being triggered on final valve onset.

Closeup of nose port (Nasal Ranger) connected to our teflon odor injector (right top) and then Honeywell flow meter at exhaust (bottom).  Here the PID is sampling from the exhaust.

Behavioral Box

After a delay, I now have the new box running.  Here are some pictures of my setup: