>> I'm having a bit of trouble with a simple experiment (or so I >
thought).
> I'm doing some extracellular single and multi-unit recording in visual
> areas
> of Equithesan anesthetised rats, looking for Critical Flicker Fusion
> thresholds. The visual stimulus is a strobe light presented at >
frequencies
> ranging from 1 Hz to 30 Hz.
>> I'm having trouble actually finding cells which can be driven by the >
strobe.
> I'm doing penetrations all over the occipital area but only seem to >
find 2
> or 3 cells (or small groups of cells) at most after many many >
penetrations.
> I honestly thought the numbers would be much higher than this. Has >
anyone
> here done anything similar to this and can tell me 1) about how many >
cells
> they find with each penetration and/or 2) what I'm doing wrong?
>> Another thing which is curious is that many of the cells I do find >
seem to
> be located about 4 mm below the surface of the brain and _not_ in the
> cortex. It looks more like the hippocampus to me and they are often >
found
> in an area where the cells have rhythmic, synchronized and continuous
> basal
> firing rates. Does this sound normal?
>
I don't do vision research but I had 2 ideas
1. Have other people used that anesthetic for cortical recordings in
rats? If you are not seeing any activity in the cortex (including
spontaneous spikes, then either your electrodes are bad or the cortex is
not in good shape.
2. If your strobe light is global it would stimulate both the center
and surround of most cells so they would be poorly driven. Have you
tried stimuli more restricted in space?
Doug Fitzpatrick
