Hallucinations

The children and the little people lasted for a couple of weeks, and then they, too, vanished, in the mysterious way that such hallucinations tend to. Though Rosalie misses Spike, she has found other friends in the nursing home, and she is back to her usual routines of chatting and listening to audiobooks and Italian operas. She is rarely alone now, and — coincidentally or not — her hallucinations have, for the time being, disappeared.

If some or all sight is preserved, as with Charles Lullin and Zelda, there may be not only visual hallucinations but various disorders of visual perception: people or objects may appear too large or too small, too near or too far; there may be too little or too much color or depth; misalignment, distortion, or inversion of the image; or problems with motion perception.

If, of course, the person is completely blind, as Rosalie is, then there can only be hallucinations, but these may also show anomalies of color, depth, transparency, motion, scale, and detail. CBS hallucinations are often described as having dazzling, intense color or a fineness and richness of detail far beyond anything one sees with the eyes. There are strong tendencies to repetition and multiplication, so that one may see rows or phalanxes of people, all dressed similarly and making similar motions (some early observers referred to this as “numerosity”). And there is a strong tendency to elaboration: hallucinatory figures often seem to be wearing “exotic dress,” rich robes, and strange headgear. Bizarre incongruities often appear, so that a flower may protrude not from someone’s hat but from the middle of their face. Hallucinatory figures may be cartoonlike. Faces, in particular, may show grotesque distortions of the teeth or eyes. Some people hallucinate text or music. But by far the commonest hallucinations are the geometrical ones: squares, checkerboards, rhomboids, quadrangles, hexagons, bricks, walls, tiles, tessellations, honeycombs, mosaics. Simplest of all, and perhaps most common, are phosphenes, blobs or clouds of brightness or color, which may or may not differentiate into anything more complex. No single individual has all of these perceptual and hallucinatory phenomena, though some people may have a great range, like Zelda, while others tend to stick to a particular form of hallucination, like Marjorie, with her “musical eyes.”

In the last decade or two, Dominic ffytche and his colleagues in London have done pioneering research on the neural basis of visual hallucinations. Based on the detailed reports of dozens of subjects, they developed a taxonomy of hallucinations, including categories like figures with hats, children or small people, landscapes, vehicles, grotesque faces, text, and cartoonlike faces. (This taxonomy is described in a 2000 paper by Santhouse et al.)

With this classification in hand, ffytche went on to do detailed brain-imaging studies in which selected patients with different categories of visual hallucinations were asked to signal the beginning and end of their hallucinations while being scanned.

There was, as ffytche et al. wrote in a 1998 paper, “a striking correspondence” between the particular hallucinatory experiences of each patient and the particular portions of the ventral visual pathway in the visual cortex which were activated. Hallucinations of faces, of color, of textures, and of objects, for example, each activated particular areas known to be involved in specific visual functions. When there were colored hallucinations, there was activation of areas in the visual cortex associated with color construction; when there were facial hallucinations of a sketchlike or cartoonlike character, there was activation in the fusiform gyrus. Visions of deformed or dismembered faces or grotesque faces with exaggerated eyes or teeth were associated with heightened activity in the superior temporal sulcus, an area specialized for the representation of eyes, teeth, and other parts of the face. Text hallucinations are associated with abnormal activation in the visual word form area, a highly specialized area in the left hemisphere.

Ffytche et al. observed, moreover, a clear distinction between normal visual imagination and actual hallucination — thus, imagining a colored object, for example, did not activate the V4 area, while a colored hallucination did. Such findings confirm that, not only subjectively but physiologically, hallucinations are unlike imagination and much more like perceptions. Writing of hallucinations in 1760, Bonnet said, “The mind would not be able to tell apart vision from reality.” The work of ffytche and his colleagues shows that the brain does not distinguish them, either.