  We use Kepler/K2 lightcurves to measure rotation periods of brown dwarfs and
very low mass stars in the Upper Scorpius star-forming region. Our sample
comprises a total of 104 periods. Depending on the assumed age of Upper
Scorpius, about a third of them are for brown dwarfs. The median period is 1.28
d for the full sample and 0.84 d for the probable brown dwarfs. With this
period sample, we find compelling evidence for early rotational braking in
brown dwarfs, caused by the interaction between the central object and the
disk. The median period for objects with disks is at least 50% longer than for
those without. Two brown dwarfs show direct signs of 'disk-locking' in their
lightcurves, in the form of dips that recur on a timescale similar to the
rotation period. Comparing the period samples for brown dwarfs at different
ages, there is a clear need to include rotational braking into period evolution
tracks between 1 and 10 Myr. A locked period over several Myr followed by
spin-up due to contraction fits the observational data. We conclude that young
brown dwarfs are affected by the same rotational regulation as stars, though
they start off with significantly faster rotation, presumably set by initial
conditions.
