It looks like they were doing single-cell recording in humans. Almost certainly, these were epileptic patients being prepped for surgery, because that's almost

It looks like they were doing single-cell recording in humans. Almost certainly, these were epileptic patients being prepped for surgery, because that's almost the only time when scientists have access to data from invasive recording techniques. Ah, yes: "The subjects were nine patients who were evaluated for possible surgical treatment of epilepsy using implantation of depth electrodes." As a result, it's pretty typical to have small sample sizes like this. It's certainly possible to achieve statistical significance with this few subjects.