Illustration of the experiment. Right panel shows an illustration of the entire experiment, broken into 5 blocks. The experiment had 3 repetitions of the control presentation (blocks 1, 3, 5), and 2 fading blocks (2 and 4). Real feedback in block 2 was given to two out of the four units, while the remaining two received feedback from a previous trial (sham feedback). The pairs alternated in block 4. Central panel shows an illustration of 6 targets in a fading block, corresponding to fading 1 on the right. While in this example the subject is receiving feedback coming directly in real‐time from four MTL units in his head that respond selectively to pictures of Johnny Cash and the first author, he receives false feedback (from a previous trial) for the picture of the spider and the man. Left panel illustrates a single trial in the experiment (corresponding to a single trial in the central panel), where the subject had the first author as his target, after which he faded in and out of images of the author and Johnny Cash until he reached a 100% visual presentation of Johnny Cash (‘failed’ trial).
Scientists from Germany, Israel, Korea, the United Kingdom, and the United States have performed experiments in which they were able to monitor individual neurons in a human brain associated with specific visual memories. They then taught people to will one visual memory onto a television monitor to replace another.
The results suggest that scientists have found a neural mechanism equivalent to imagination and daydreaming, in which the mental creation of images overrides visual input. And, if technology someday advances to enable reading the electrical activity of many thousands or millions of individual neurons (as opposed to the dozens typically available by hard-wiring methods today), scientists might begin to access snippets of real daydreams or actual dreams.
Daily life continually confronts us with an exuberance of external, sensory stimuli competing with a rich stream of internal deliberations, plans and ruminations. The brain must select one or more of these for further processing. How this competition is resolved across multiple sensory and cognitive regions is not known; nor is it clear how internal thoughts and attention regulate this competition. Recording from single neurons in patients implanted with intracranial electrodes for clinical reasons here we demonstrate that humans can regulate the activity of their neurons in the medial temporal lobe (MTL) to alter the outcome of the contest between external images and their internal representation. Subjects looked at a hybrid superposition of two images representing familiar individuals, landmarks, objects or animals and had to enhance one image at the expense of the other, competing one. Simultaneously, the spiking activity of their MTL neurons in different subregions and hemispheres was decoded in real time to control the content of the hybrid. Subjects reliably regulated, often on the first trial, the firing rate of their neurons, increasing the rate of some while simultaneously decreasing the rate of others. They did so by focusing onto one image, which gradually became clearer on the computer screen in front of their eyes, and thereby overriding sensory input. On the basis of the firing of these MTL neurons, the dynamics of the competition between visual images in the subject’s mind was visualized on an external display.
There are about 5 million neurons [in your brain] that encode for the same concept, Cerf says. There are many neurons that fire all together when you think of Michael Jackson. But, he adds, each neuron also codes for numerous other people, ideas, or images, which is partly how we associate one memory with another thought, place, idea, or person.
When at least two reliable image-linked neurons (say, associated with actors Josh Brolin and Marilyn Monroe) were attached to the microwires, the experiment could begin. In one experiment [see video], Josh Brolin’s face appeared on-screen, but the subject was told to think of Marilyn Monroe. The subject viewed an image of Brolin on-screen while making a conscious attempt to repress the image and replace it with an image of Monroe. Meanwhile, a computer monitored the patient’s neural activity. If it determined that the patient was squelching the firing of the Josh Brolin neuron, it made Brolin’s image fade from the screen. If it read that the patient was boosting the activity of the Marilyn Monroe neuron, it would bring up the image of Monroe. For all 12 subjects in Cerf’s group, what each wanted—or was told—to see trumped what he was actually watching 69 percent of the time.