“…Most of the time the search turned up empty-handed, although sometimes we would come upon neurons that responded to categories of objects, such as animals, outdoor scenes or faces in general. But a few neurons were much more discerning.
One hippocampal neuron responded only to photos of actress Jennifer Aniston but not to pictures of other blonde women or actresses; moreover, the cell fired in response to seven very different pictures of Jennifer Aniston. We found cells that responded to images of Mother Teresa, to cute little animals and to the Pythagorean theorem, a2 + b2 = c2. Such cells, together with their sisters—for there are probably thousands of such cells in the medial temporal lobe for any one idea—encode a concept, such as Jennifer Aniston, no matter whether the patient sees or hears her name or looks at her picture. Think of them as the cellular substrate of the Platonic ideal of Jennifer Aniston. Whether the actress is sitting or running, whether her hair is up or down, as long as the patient recognizes Jennifer Aniston, those neurons are active. […]
Let me walk you through one example. Cerf recorded from a neuron that fired in response to images of actor Josh Brolin (whom the patient knew from her favorite movie, The Goonies) and from another neuron that fired in response to the Marilyn Monroe scene I just mentioned. The patient looked at a monitor where these two images were superimposed, with the activity of the two cells controlling the extent to which she saw Brolin or Monroe in the hybrid image.
Whenever the patient focused her thoughts on Brolin, the associated neuron fired more strongly. Cerf arranged the feedback such that the more this cell fired relative to the other one, the more visible Brolin became and the more the image of Monroe faded, and vice versa. The image on the screen kept changing until only Brolin or only Monroe remained visible and the trial was over. The patient loved it, as she felt that she controlled the movie purely with her thoughts. When she focused on Monroe, the associated neurons increased their firing rate, the cells for the competing concept, Brolin, dampened their activity, whereas the vast majority of neurons remained unaffected.
It might appear as if there are two people involved in this experiment, the way the puppeteer Craig occupied the head of actor John Malkovich in the 1999 movie Being John Malkovich. One is the patient’s mind, instructing her brain to think of Monroe. The other is the one that is acting out the mind’s desire—namely, the nerve cells in the medial temporal lobe that up- and down-regulate their activity accordingly. But both are part of the same brain. So who is in control of whom? Who is the puppeteer, and who the puppet?”