Who's in Control?: the NOVA documentary on how much of what we do we actually decide

Someone wakes up to find they have painted one wall in the living room and another in the kitchen, and drawn a perfect triangle besides. They did it all asleep. At a sleep center at the Icahn School of Medicine at Mount Sinai, in New York, tests show what happens in those hours: part of the brain wakes up and runs the body, while the prefrontal cortex, the region of deliberate choices, stays in deep sleep.

That is the starting point of Your Brain: Who's in Control?, the second episode of NOVA's Your Brain series, broadcast by PBS in May 2023. The host is Heather Berlin, a neuroscientist and clinical psychologist, who visits laboratories to measure how much of what we do passes through consciousness.

Consciousness by degrees

Neuroscientist Emery Brown shows on the electroencephalogram how anesthesia turns the varied activity of the waking brain into a slow hum, and points to the thalamus, a relay station for information, as a key piece of that disconnection. With Michael Gazzaniga and Michael Miller, Berlin revisits split-brain patients, whose bridge between the hemispheres was cut to treat epilepsy. In a famous case, one patient's left hand draws a cowboy hat prompted by the word Texas, which only the right hemisphere saw, while the side that speaks cannot explain the drawing.

Emotion, trauma and inheritance

Luke Chang measures guilt in an investment game and locates the signal in the insula. Bianca Jones Marlin pairs the smell of almond with mild shocks in mice and finds their offspring born with more cells sensitive to that smell. The film links the research to the Dutch famine of 1944 and 1945, whose health effects also appeared in the children and grandchildren of those who lived through it.

The feeling of deciding

The most unsettling moment comes with neuroscientist Uri Maoz, who uses magic tricks to anticipate Berlin's choices in an envelope handed over before the test. In a lab, researcher Alice Wong uses magnetic stimulation to move a volunteer's finger; when the machine interferes with a movement he started himself, the volunteer says it was not him. Finally, Charles Limb shows that the prefrontal cortex switches off in musicians who improvise.

Caveats, and why watch

The idea that the unified self is an illusion is the interpretation of some interviewees, not a consensus conclusion, and the transmission of experiences across generations, seen in mice, has only hints in humans, such as those from the Dutch famine. Even so, the episode explains classic and recent experiments with rare clarity, and leaves an uncomfortable question about who decides when we say "I".