The listening is still being done today in experiments. An experienced neurophysiologist (in the particular field of single cell recordings) can distinguish the

The listening is still being done today in experiments. An experienced neurophysiologist (in the particular field of single cell recordings) can distinguish the sound of an actual braincell firing, or groups thereof, from all surrounding noise. Which is sometimes more convenient than recording the signal, feeding it into rather complicated template matching algorithms and waiting for results. Especially since braincells might die while being recorded from, so you have to decide quickly.