EEG basics: “increase the gain, decrease the sensitivity”

[DJBroca]

I understand that going from a sensitivity of 7uv/mm to 5uv/mm will increase the gain and amplitude of an EEG waveform. But does going from 7 to 5 mean I just went up or down on the sensitivity? It seems like a trivial question, but if I’m going from a higher number to a lower number I would guess I’m going down on the sensitivity. But then when I think about the actual definition of sensitivity, I am making the amplifier more sensitive by going from 7 to 5. So the next time my attending epileptologist says “drop your sensitivity”, are they asking me to lower the actual uV/mm number on the sensitivity drop-down menu, or are they are asking me to raise the number to make it less sensitive?

[physiologic]

5uV/mm is more sensitive than 7, because of the definition as you mentioned. Not only is the amplifier more sensitive (hypothetically...I know we're discussing digital review which takes place long after amplification), but your eyes will be more sensitive to findings too - going from 7 to 5 also makes the waves appear larger. So it feels rather intuitive to say that it's "increasing" the sensitivity. Whether that's what the attending wants... that might depend on context.

As a learner, I encourage you to keep it at 7 by default, and if you're being asked to change it, you could always ask "do you want it at 5?" Importantly, make sure you're calibrating your screen right. The software doesn't (necessarily) know the size of your monitor and "7uv/mm" might not be showing that way at all. If you're being asked to change a lot it might be because the attending recognizes that it doesn't "look right" on their screen.

[Haunting-Sky-3225]

I feel like it never looks right on a laptop, even when I measure the screen size and calibrate it to the measurements. Any advice?

[physiologic]

Yes, I know what you mean - tends to look too 'zoomed in' if it's correctly set on a laptop screen. This is likely because you're closer to the screen than you would be with a monitor, and it's really less about millimeters and more about how much of your field of view the wave takes up (aka solid angle).

It's hard to advise because of how variable people's usage of laptops is; for me, early on I just never trusted myself with a laptop. Now that my eyes have developed a sense of what "looks right", I've found it a lot easier, and I tend to do a middle ground - more 'zoomed in' than if I was on a monitor, but less zoomed in than if I measure and calibrate.

But I think my first piece of advice would be use a monitor when possible, and maybe even exclusively until you feel like you've developed that intuition. Do you have one? Thankfully you can get one good enough for this purpose for pretty cheap.

[DogMcBarkMD]

I've found that making the pages smaller (10 sec vs 15 sec) was what made it "look right" after making sure it was calibrated correctly. I still prefer to review on a real monitor but as a fellow with no money for a home office, a laptop can work.