Hello, Hammah Payne,

We do electrophysiological recordings with NeuroNexus electrode which are silicone probes. We find that some electrodes will record light-induced artifacts and some electrodes won't. It seems that electrode quality depends. So we choose those electrodes without light-induced artifacts when we do optogenetics recordings.

I am not sure if you can try other eletrodes.

I never try #3 solution. 

I hope that helps you. Let me know if you have any further questions.

Best

Dinghong

Thanks Dinghong. Any idea what differentiates the probes that have artifacts from those that don't?

Hi Hannah,

You should also ground your laser source and fiber optic cable which is likely to be source of the noise. Often simply grounding the equipment (including the microscope) close to the recording chamber helps to get rid off the noise. I usually use couple of crocodile clips connecting equipment to the Faraday cage or the Table, which are connected into the recording amplifier's ground.

Best wishes, Refik

 In order to find out whether Refik is right and it is an "electrical artifact", did you trigger the laser, but had unplugged the fiber before, so no light reaches the tissue? And I really mean UNPLUGGED aka physicallyY BLOCK the LIGHT?  If you still see an artifact, the method of Refik might work... or some more thoughts about ground connections in your setup. 

If it really is the light itself - is it intensity dependent? If you need to stick with single wires, go for stainless steel or Pt (FHC and many others...) or glass coated PtIr  multisites (AlphaOmega or Thomas Recording). We do see light artifacts when illuminating MEA arrays - but I doubt it is a very specific photoelectric effect...  More of a thermal-electric effect (thats why I was asking about the light intensity dependence...)  

If you go to apply silicon probes, be aware, that (very much dependent on the lithography process), the interface between metal and electrolyte might affect the semiconductor below. It may very well be a depletion layer down there, thus establishing a real photodiode perpendicular to the electrode into the Si-bulk.... Thats why I prefer Si-probes based on the Silicon-on-Insulator over p-doped Si-probes.... ;-)  So, I am not quite sure which process Neuronexus is using for all their probes (it is recognizable from their spec sheet), but you might want to look into the Atlas Si-Probes as alternative... Their newest ones should not show these photo-currents. 

And last but not least, refering to template-subtraction: An artifact is an artifact and if it is big enough to be a nuisance, it's subtraction is big enough to spoil your data. 

I know everybody is using this method, but I am not really fond of it - but alternatively blanking your signal is really worse!

Good luck!

uli

We use the Michigan probes from Neuronexus (such as A1x16-5-50-703-OALP). We simply filter out the artifact for MUA/SUA analysis by applying a filter from 500 - 5000Hz. If you wish to investigate the LFP effect you might have bigger problems as the artifact is not that trivial to get rid of there.

Hi Hannah,

I believe there might be the ELECTRICAL GROUND or SHIELDING effect but more I suspect of 1)  the cross-talk between the laser excitation and the sensor and 2) the Electrical noise associated with the pulse itself..

I can explain this further -

There are two events happening at the same time instance - First, the electronic pulse  (2ms) that stimulates or TRIGGERs your laser source has some noise (harmonics) associated with it that is seen your sensor output.

Secondly, as you have stated, your light inserted is through the same guide tube as that of the sensor, therefore, this is the CROSS_TALK or direct induction of light response in the sensor.

Remedy:

1) Try isolate your exciting fiber from your sensor electrode, use different cables or jacket if possible.

2) You can use a digital filter in your data acquisition system to get rid of the noise but it will also have direct effect on your signal acquired and you might loose some information due to this filtering. Therefore, identify the "2ms pulse related only" noise and try to filter out if possible.

I hope this idea suits to solve our problem.

Best wishes!

-Prasanna Waichal

For clarification, I am using a very long fiber optic (~4 m) and the laser source is in a separate room, so I doubt there are any artifacts from the electrical trigger pulse. Also, the artifact does seem to be intensity dependent.

I've realized there are two components:

1. direct light-related artifacts (i.e. present in non-expressing tissue)

2. increased background activity during stimulus trains (in highly expressing transgenic ChR2 mice).

I can now get some recordings without the light-related artifact (1) by moving the electrode, but the background activity (2) due to nearly synchronous activation of the population is a bit more difficult -- it just raises the bar higher for a well-isolated spike.

I think I'll avoid the artifact subtraction method if possible based on your responses.

While we are on the topic, does anyone know if carbon fiber electrodes have light artifacts?

Thanks all!

Hi Hannah,

Do you use single channel recordings?

If yes, then you may try the novel combined carbon fiber optrode of Kation Scientific Ltd (http://kationscientific.com/products/carbon-optrodes).

In this probe, the light is projected by the glass sheating of the carbon fiber, and the light is emitted directly at the recording site of the carbon tip.

We tested it for extracellular electrophysiology in anesthetized rats (and for electrochemical measurements), but if the head is fixed, it may work also in awake animals.

Light-induced artifacts were also assessed, and the carbon fiber optrode performed much better than a typical tungsten electrode. Take a look at our very recent paper on the performance of these electrodes.

Article A novel carbon tipped single micro-optrode for combined opto...

Regards,

Zsolt

Light-induced artifacts in electrophysiological recording, particularly in in vitro patch-clamp recordings, can arise from various sources, including stray light, photobleaching, and photoelectric effects. These artifacts can interfere with the accurate measurement of neuronal activity and complicate data interpretation. Here are some strategies to mitigate light-induced artifacts in electrophysiological recordings:

By implementing these strategies and optimizing experimental conditions, researchers can minimize light-induced artifacts in electrophysiological recordings and improve the accuracy and reliability of their data.

l Check out this protocol list; it might provide additional insights for resolving the issue.