[The Rosenbergs' execution] had nothing to do with me, but I couldn't help wondering what it would be like, being burned alive along your nerves.
I thought it must be the worst thing in the world. (1.1)
The Rosenbergs' death by execution looks ahead to Esther's nightmarish experience with electroshock therapy later in the novel. Their shared experience with, well, let's just call it "bad electricity" suggests that madness may not be just a physiological issue for Esther. Madness could just be another name for people who don't fit in with the values of mainstream society, like the Rosenbergs.
The silence depressed me. It wasn't the silence of silence. It was my own silence. (2.37)
This is a particularly vivid passage about Esther's descent into suicidal depression. For a girl who spends her life working with words – as a magazine intern, as a literature major – silence is terrifying.
[Buddy] was very proud of his perfect health and was always telling me it was psychosomatic when my sinuses blocked up and I couldn't breathe. (6.84)
Buddy, as a medical student, is one of the voices of the medical profession in the novel. His condescending attitude toward Esther indicates how the medical profession can be sexist in the way that it dismisses the validity of women's concerns.
I saw my life branching out before me like the green fig tree in the story.
From the tip of every branch, like a fat purple fig, a wonderful future beckoned and winked [...] I saw myself sitting in the crotch of this fig tree, starving to death, just because I couldn't make up my mind which of the figs I would choose. (7.20-21)
One aspect of Esther's depression is that she feels paralyzed, unable to act. The fig tree here represents all of the possibilities for action that she just can't muster up the initiative to pursue.
A small answering point in my body flew toward it. I felt my lungs inflate with the inrush of scenery – air, mountains, trees, people. I thought, "This is what it is to be happy."
I plummed down past the zigzaggers, the students, the experts, through year after year of doubleness and smiles and compromise, into my own past. (7.121-122)
While Esther is certainly mentally ill, she experiences moments of almost visionary clarity, such as the one described in this passage. It is this clarity that comes through when she makes her biting critique of the hypocrisy of modern society. Her experience suggests that her "madness" is not an either/or kind of thing, but a composite of physiological, emotional, and social factors. Simply put, both Esther and society contribute to her suicidal depression.
I made out men and women, and boys and girls who must be as young as I, but there was a uniformity to their faces, as if they had lain for a long time on a shelf, out of the sunlight, under siftings of pale, fine dust. (12.9)
The "uniformity" of these patients is distressing when you consider that Dr. Gordon, who runs the institution, also happens to be prone to uniformity, as seen when he repeats the things he said about Esther's college. These patients basically represent how even "sane" or "normal" people are trapped in habits and routines.
Then something bent down and took hold of me and shook me like the end of the world [...] with each flash a great jolt drubbed me till I thought my bones would break and the sap fly out of me like a split plant.
I wondered what terrible thing it was that I had done. (12.32-33)
This passage describes Esther's first experience with electroshock therapy, and significantly, she feels that it's a punishment. Not a cure, but a punishment. This underscores her connection to the Rosenbergs (see Quote #1).
[...] I felt dumb and subdued. Every time I tried to concentrate, my mind glided off, like a skater, into a large empty space, and pirouetted there, absently. (12.53)
Again, after her first experience with electroshock therapy at Dr. Gordon's, Esther loses, well, her mind. She's unable to put thoughts together, and she feels "dumb," another way of saying she's lost her voice (see Quote #2). The therapy seems just as bad as her illness.
If Mrs. Guinea had given me a ticket to Europe, or a round-the-world cruise, it wouldn't have made one scrap of difference to me, because wherever I sat – on the deck of a ship or at a street cafe in Paris or Bangkok – I would be sitting under the same glass bell jar, stewing in my own sour air (15.10)
The bell jar is a recurring symbol in the novel that captures how Esther feels trapped in her depression, and, as this passage emphasizes, isolated from the rest of the world. (See "What's Up with the Title?" for more on the bell jar.)
All the heat and fear had purged itself. I felt surprisingly at peace. The bell jar hung, suspended, a few feet above my head. I was open to the circulating air. (18.5)
As with Quote #9, the bell jar appears in this passage as a symbol for depression. But in this instance, after a successful bout of electroshock therapy (guided by the female Dr. Nolan), the bell jar is lifted and Esther feels relief.