What does "rings around the brain" mean?

I'm watching the movie "Mary Poppins Returns".

At one point Marry Poppins sings:

Too much glee leaves rings around the brain

I'm not quite sure what "rings around the brain" means. From context I can imagine it means that too much delight/joy will diminish your logical thinking capabilities and degenerates your intellect. Putting imagination/joy/creativity in contrast to rigorous mathematical thinking. I also assume that the phrase "rings around the brain" comes from the idea that when you are hit on the head you feel rings/stars/birds circle around your head, like in cartoons.

But I'm lost and these are all assumptions that may be the result of too much glee and imagination.

Thanks

This is a metaphor. When we take a bath and we are very dirty, the particles of dirt washed from our bodies float on the surface of the water. When we pull out the bath plug, the water level descends, and a 'ring' of dirt can often be seen clinging to the sides of the bath ('bathtub' in US English). It is a residue which tidy people remove, and its occurrence is a sign that the bath user should wash more often (or works in a coal-mine). Too much glee, asserts Mary Poppins, leaves an undesirable residue in the brain. The following line confirms this: "Take that joy and send it down the drain". The washing metaphor, and references to baths and mental 'cleanliness' or 'tidiness' occur repeatedly in the song, e.g. "For intellect can wash away confusion".