Currently reading a study with one of my favorite findings, so let's play an EEG game:

If I will report this as "normal," what is the OLDEST this patient can be? Vote in the next tweet ! #Tweetorial to follow #MedEd #neurology #MedTwitter #FOAMed

[Expand tweet to reveal poll if options not showing]

For this study to be normal, the patient must be UP TO:

Bonus question [again, might need to expand tweet to see the options]

Based on the finding above, What is the YOUNGEST this patient must be? CA = postconceptional age

First things first: what are we looking at? SLEEP SPINDLES (SS) How do we know?
1. SS appear, as defined by its name, during sleep (more on this later) – our patient is asleep, as evidenced by lack of myogenic artifact and slow background

2. SS tend be maximal over the central (C3, C4) electrodes and the vertex (Cz) – indeed, our patient’s waves can be seen maximal over these leads
3. SS are regular 12-14 Hz waves – Want to count the example I gave you? (Spoiler- it’s 13 Hz)

The most striking feature of the example above is that SS occur first over the left central region (C3/Cz) and about 2 seconds later, they occur over the right central region (C4/Cz). We say these SS are ASYNCHRONOUS

The reason I like SS is that they teach the huge difference between asynchronous and asymmetric findings on EEG:

ASYNCHRONY: findings occur in each hemisphere at different times, but their frequency "evens out" throughout the study

Compare this with:

ASYMMETRY: one side shows persistent differences in amplitude, rate (as in per-second) or frequency (as in how many times a finding occurs throughout the recording).

[BTW- this applies to any EEG element, not just SS]

The key point: ASYNCHRONOUS sleep spindles are normal, typically until the age of 24 months (on the contrary, *asymmetric* sleep spindles are NOT).

While most kids seem to show SS symmetry after 12 months, most authors see asynchronous SS as normal within 1st 2 years of life

SS change as we age:
1. Become more synchronous (full synch by age 24 mo)
2. Get shorter (typically 3-4 sec but up to 10 in babies vs. 1-2 sec but up to 4 in adults)
3. Go from arciform in infants to sinusoidal shape
4. Can start frontally max in infants, then move centrally max

SS also change as infants go thru sleep from lighter to deeper stages! Look at 3 captures from the same baby (CA 47-week) as the night progresses:
asynchronous SS (R only)
more synchronous SS (L and R co-occur, but L better formed first 2-3 seconds)
fully synchronous!

Even when SS are synchronous, they also change throughout the nights: if you pay attention, you can see them become more prominent in frontal regions as sleep deepens (and they may get slightly slower at 11-12 Hz!). Don't have screen captures of this now but will get some soon

Let's now answer the bonus question: when do SS appear? Most authors point to emergence between 44-46 weeks postconceptional age. See Libenson (blue) and Hrachovy atlas (black) diagrams for reference. I love keeping these handy, you should too!

We should end by saying that sleep spindles DEFINE the onset of stage II sleep. When they appear, you know you got to stage 2. The reticular nucleus of the thalamus is the generator of spindle activity.

You see why I said this is one of my fave EEG findings, who's with me?!

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