Self Comes to Mind

activity in those maps, as we shall see, corresponds to primordial feelings.
    Mapping applies not only to visual patterns but to every kind of sensory pattern the brain is involved in constructing. For example, the mapping of sound begins in the ear’s equivalent of the retina: the cochlea, located in our inner ear, one on each side. The cochlea receives the mechanical stimuli that result from the vibration of the tympanic membrane and of a small collection of bones located underneath it. The equivalent of the retinal neurons for the cochlea are the hair cells. At the top of a hair cell, a wisp of hair (the bundle) moves under the influence of sound energy and provokes an electrical current captured by the axon terminal of a neuron located in the cochlear ganglion. This neuron sends messages into the brain across six separate stations that form a chain—the cochlear nucleus, the superior olivary nucleus, the nucleus of the lateral lemniscus, the inferior colliculus, the medial geniculate nucleus, and finally the primary auditory cortex. The latter is comparable, in terms of hierarchy, to the primary visual cortex. The auditory cortex is the beginning of yet another signaling chain within the cerebral cortex itself.
    The very first auditory maps are formed in the cochlea, just as the very first visual maps are formed in the retina. How are the sound maps achieved? The cochlea is a spiral ramp with an overall conical shape. It resembles a snail shell, as the Latin root of the word cochlea suggests. If you have ever been at the Guggenheim Museum in New York, you can easily picture what goes on inside the cochlea. All you need to do is imagine that the circles tighten as you go up and that the overall shape of the building is a cone pointing up. The ramp that you walk on wraps around the vertical axis of the cone, just like the cochlea’s. Within the spiral ramp the hair cells are located with an exquisite ordering determined by the sound frequencies to which they are capable of responding. The hair cells that respond to the highest frequencies are located at the base of the cochlea, which means that as you ascend the ramp, the other frequencies follow in descending order until the apex of the cochlea is reached, as that is where the hair cells respond to the lowest frequencies. It all starts with lyric sopranos and ends with deep basses. The upshot is a spatial map of possible tones ordered by frequency, a tonotopic map. Remarkably, a version of this sound map is repeated at every one of the five subsequent stations of the auditory system on the way to the auditory cortex, where the map is finally laid out in a sheath. We hear an orchestra playing or the voice of a singer when neurons along the auditory chain become active and when the final cortical layout distributes spatially all the rich substructures of the sounds coming to our ears.
    The mapping scheme applies far and wide to patterns having to do with body structure, such as a limb and its movement or the breakage in the skin caused by a burn, or to the patterns that result from touching the car keys you hold in your hand, surveying their shape and the smooth texture of their surface.
    The closeness between mapped patterns in the brain and the actual objects that prompt them has been demonstrated in a variety of studies. For example, it is possible to uncover, in a monkey’s visual cortex, a strong correlation between the structure of a visual stimulus (e.g., a circle or a cross) and the pattern of activity it evokes. This was first shown by Roger Tootell in brain tissue obtained from monkeys. However, under no circumstances can we “observe” the monkey’s visual experience—the images the monkey itself sees. Images—visual, auditory, or of whatever other variety one may wish—are available directly but only to the owner of the mind in which they occur. They are private and unobservable by a third party. All the third party can do is guess.
    Neuroimaging studies of the human brain are also beginning to uncover such correlations. Using multivariate pattern analysis, several research groups, ours included, have been able to show that certain patterns of activity in human sensory cortices correspond distinctively to a certain class of object. 3
Maps and Minds
     
    A spectacular consequence of the brain’s incessant and dynamic mapping is the mind. The mapped patterns constitute what we, conscious creatures, have come to know as sights, sounds, touches,