Burst detection is trickier than you might think because they come in all shapes and sizes. There are many algorithms to do it. The two most prominent are
1. A simple threshold set at something like 5 to 10X the baseline firing rate. This is what is used in our recent paper:
2. Burstiness-index.
Bursts come
in different forms, so simply tallying up the
number of bursts is not sufficient to describe
the burstiness of a culture. It is essential to account
for the size of bursts, measured in terms
of number of participating neurons, aggregate
number of spikes, or duration. Fortunately, we
found that it is not necessary to identify individual
bursts to quantify the level of burstiness of a
recording. Instead, we used the following method:
divide a 5 min recording into 300 1-sec-long
time bins and count the number of spikes (total
across all electrodes) in each bin. Compute the
fraction of the total number of spikes accounted
for by the 15% of bins with the largest counts. If
the firing rate is tonic, this number, f15, will be
close to 0.15. Conversely, if a recording is so
bursty that most of the spikes are contained in
bursts, f15 will be close to 1, because even at the
highest burst rates observed during these experiments,
bursts did not occupy 45 1-seclong
bins (15%) in a 5 min recording. We then
defined a burstiness index (BI), normalized between
0 (no bursts) and 1 (burst dominated) as
BI ( f15 0.15)/0.85. (Statistical fluctuations
make the BI deviate slightly from zero even in
complete absence of bursts.)
Aside from this there are more complex ways to characterize the nature of sychronized spiking activity in cultures, e.g. looking at the distribution of sizes of sychronized events instead of looking at a single moment of the distribution. This is what Plenz has been doing for years.