Jill Bolte Taylor: Most Replayed Moment: The 4 Personalities Living In Your Brain! How To Switch Between Them

Asked what the "four personalities" in everybody's brain are, the guest starts with anatomy instead of a list. She describes evolution in stages. Some creatures have only a spinal cord, like worms. Then a small medulla forms at the top of that tissue and begins to control and streamline information processing for the rest of the system. The pons comes next, which she calls "just a structure of cells."

The cerebellum sits in relation to the pons, and she uses it to make a point about structure and function. Its Purkinje cells (transcribed as "pergenji") are flat, two-dimensional, hand-like cells that line up in rows with fibres running through them. She says this alignment is part of the timing mechanism that makes movement fluid. Her general principle is that cells are not all alike.

Cells have the right shape for the right job.

In the mammalian brain she adds the hippocampus, "for learning and memory," and the amygdala, a group of cells she says is "scanning constantly am I safe? Am I safe? Am I safe?" The interviewer sums this up as threat detection, and she agrees: "Yes, that's exactly what it is."

Her first hemispheric contrast is about threat. There are two emotional systems, one in each hemisphere. The right asks whether you are safe "in the right here right now." Her example is a snake suddenly going by. The startle comes from the right amygdala asking whether you are safe. The left hemisphere then names the threat and decides what to do: "oh my gosh, it's a snake, no, I'm not safe. Push it away."

She notes there are two amygdalae and two hippocampi, one of each per hemisphere. Learning depends on the threat system settling first. When the amygdalae are calm and you feel safe, you can learn and focus, and she ties focus to the anterior cingulate gyrus (transcribed as "singular gyrus").

To show that abilities depend on specific groups of cells, she gives three brief lesion examples. Wipe out an amygdala and "you're not going to feel any fear." Wipe out a language centre and "you're not going to have any language." Wipe out the motor control for your index finger and you are paralyzed. Her conclusion is that every ability you have exists because brain cells perform that function. These are flat statements. The segment gives no case evidence or caveats for them.

The four characters come from a two-by-two grid: an emotional system and a thinking system in each hemisphere. She first describes the right emotional system as purely present-focused.

That's all it has. Don't have the past. Don't have the future. Don't know who you are.

She corrects herself at once. She first says the right emotional system doesn't have anxiety or depression, then adds "Well, it has anxiety. But most of that is going to be based in the left hemisphere." Her reason is that the left hemisphere "has linearity across time." Because it tracks time, the left emotional system remembers "every traumatic event that ever happened to you that you don't want to have happen again."