Studies by neuroscientists at MIT’s Picower Institute for Learning and Memory: Adult humans can retain only about four items “in mind” at a time. Using monkeys as subjects, researchers recorded simultaneously from neurons in two brain areas related to encoding visual perceptions (the parietal cortex) and holding them in mind (the prefrontal cortex. Results showed that the monkeys (and supposedly humans, as well) have a capacity of two objects in each hemisphere. If the object to remember appears on the right side of the visual space, it does not matter how many objects are on the left side; as long as the right side contains only two, the monkeys can easily remember an object on the right side. Or if the right side contains three objects and the left side only one, their capacity for remembering the key object on the right is exceeded and so they may forget it.