Phantoms in the Brain

This book is aimed squarely at the popular science market and, presumably because of this, presents neurology as an exhilarating voyage into the ‘twilight zone’. It seeks to convey recent insights into the workings of the human mind, as gleaned from studies of some of the more perplexing and counterintuitive deficits (or excesses) that can result from brain injury (or amputation). Though co-authored by Ramachandran (a psychologist with a medical background) and Blakeslee (a science writer and journalist), it is written entirely in the Ramachandran first person. The book largely comprises vignettes of Ramachandran’s encounters with various patients suffering from a diverse array of unusual neurological deficits. As such, it runs close to Oliver Sacks’ territory, and the authors seem happy to trade on this overlap. Nevertheless, the book is a highly original and personal statement of Ramachandran’s position on innumerable issues. This is both its strength and its weakness. Each chapter covers a different topic, the only commonality being the seemingly bizarre and paradoxical nature of the neurological deficits described. The description of Ramachandran’s celebrated work on referred sensation in patients with amputated (phantom) limbs is an early highlight of the book. Although referred sensations—that is, feelings in phantom limbs generated by touch elsewhere on the body—have been described before, Ramachandran’s insightful contribution relates them to the somatosensory ‘homunculus’ in the brain and to recent electrophysiological discoveries about neural plasticity. The subsequent chapter on ‘treatment’ of referred phantom limb pain—the patient views a mirror-reflection of their intact limb moving, apparently at the location of the amputated limb—is less successful. No systematic study of the effectiveness of this treatment has yet been done, and there is no clear notion why the mirror intervention should work. As with much of the book, we are in uncertain and speculative territory, although the journey is certainly a thought-provoking one. The chapter on unconscious processing in the visual system emphasizes the different potential uses of vision—control of immediate action versus recognition of objects—and is superb. Unlike the other chapters, it provides an overview of a large body of research by many groups, summarizing both the areas of consensus and the remaining controversies. It integrates important findings on healthy subjects with those from patients, and offers many fundamental insights into visual perception. This chapter stands headand-shoulders above the rest, which may reflect Ramachandran’s particular expertise in vision research (plus the fact that the visual system has been studied most extensively). Although it would be unfair for any criticism to stem from such an exceptional chapter, this highlight does cast something of a shadow over the remainder of the book. It is the only chapter to shift the focus from Ramachandran’s own studies to the field as a whole, and as any writer will admit, it is easier to be objective about other people’s work than one’s own. Staying with the visual theme, the authors next address visual ‘filling-in’ of the blindspot which every normal person has in each eye. This leads to the perception of something where there is in fact no retinal input, a venerable topic to which Ramachandran has made important new contributions. A somewhat forced analogy is made with pathological hallucinations in braindamaged patients (Charles Bonnet syndrome). It is well-known that such hallucinations can be restricted to particular regions of the visual field. The new claim here is that the hallucinations must therefore be due to the influence of backprojections, from higherto lower-level visual areas. Although this is certainly one interesting possibility, it does not as yet seem to be a certain conclusion, a comment that applies to many other intriguing claims in this provocative book. I found the authors to be the least convincing on the subjects that I know best (neglect and anosognosia), which is perhaps inevitable given their maverick tendency to dismiss orthodox views. The discussion of unilateral neglect focuses on Ramachandran’s observation that some, but not all, neglect patients reach towards their ‘good’ ipsilesional side even when what is seen there is a mirrorreflection of an object whose true location lies on the impaired contralesional side. However, many interpretations seem possible for this (for example, motor rather than perceptual neglect; frontal deficits in overriding prepotent response tendencies). Moreover, journalistic comments such as “mere confrontation with a mirror flips these patients into the twilight zone” seem more sensationalist than revealing about the plight of neglect patients. The section on anosognosia (unawareness of deficit after brain damage)—for example, patients with left hemiparesis after right-hemisphere stroke often have no insight into their inability to control the affected limbs—may be the most controversial part of an unashamedly controversial book. Ramachandran takes a neo-Freudian view, arguing that patients actively deny information that they possess about their deficit due to putative differences in ‘processing style’ between the cerebral hemispheres. The left hemisphere supposedly seeks to maintain the status quo, whereas the normal right hemisphere seeks to ‘rock the boat’ in true Ramachandran style. If so, anosognosia may offer unique insights into the confabulatory style of the conservative left hemisphere. However, as yet the evidence seems insufficient to rule out a more cautious interpretation. Anosognosia for hemiparesis after large right parietal/frontal lesions may arise simply because the affected structures subserve ‘body image’, and so the patient lacks new information about the disruption to their movements. This would certainly explain why anosognosia is typically restricted just to body movement and position. But no doubt Ramachandran would think that I myself am stuck in conservative left-hemisphere denial here. © 1999 Nature America Inc. • http://medicine.nature.com