MIND Lust for Danger : Why We Gamble and Have Affairs Hearing Colors , Tasting Shapes Smarter on Drugs ?

connections between seemingly unrelated inputs. COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC. refl ected from a scene hits the cones (color receptors) in the eye, neural signals from the retina travel to area 17, in the occipital lobe at the back of the brain. There the image is processed further within local clusters, or blobs, into such simple attributes as color, motion, form and depth. Afterward, information about these separate features is sent forward and distributed to several far-fl ung regions in the temporal and parietal lobes. In the case of color, the information goes to area V4 in the fusiform gyrus of the temporal lobe. From there it travels to areas that lie farther up in the hierarchy of color centers, including a region near a patch of cortex called the TPO (for the junction of the temporal, parietal and occipital lobes). These higher areas may be concerned with more sophisticated aspects of color processing. For example, leaves look as green at dusk as they do at midday, even though the mix of wavelengths refl ected from them is very different. Numerical computation, too, seems to happen in stages. An early step also takes place in the fusiform gyrus, where the actual shapes of numbers are represented, and a later one occurs in the angular gyrus, a part of the TPO that is concerned with numerical concepts such as ordinality (sequence) and cardinality (quantity). (When the angular gyrus is damaged by a stroke or a tumor, the patient can still identify numbers but can no longer divide or subtract. Multiplication often survives because it is learned by rote.) In addition, brain-imaging studies in humans strongly hint that visually presented letters of the alphabet or numbers (graphemes) activate cells in the fusiform gyrus, whereas the sounds of the syllables (phonemes) are processed higher up, once again in the general vicinity of the TPO. Because both colors and numbers are processed initially in the fusiform gyrus and subsequently near the angular gyrus, we suspected that number-color synesthesia might be caused by cross wiring between V4 and the number-appearance area (both within the fusiform) or between the higher color area and the number-concept area (both in the TPO). Other, more exotic forms of the condition might result from similar C R O L D O N N E R www.sc iammind.com 19 V4 TPO junction Occipital lobe Area 17 Numberappearance area Temporal lobe Optic nerve Light Retina Parietal lobe Mixed Signals In one of the most common forms of synesthesia, looking at a number evokes a specifi c hue. Brain areas that normally do not interact when processing numbers or colors do activate one another in synesthetes. 3 Ultimately, color proceeds “higher,” to an area near the TPO (for temporal, parietal, occipital lobes) junction, which may perform more sophisticated