AAromatherapy is the most widely used complementary therapy in the National Health Service, and doctors use it most often for treating dementia. For elderly patients who have difficulty interacting verbally, and to whom conventional medicine has little to offer, aromatherapy can bring benefits in terms of better sleep, improved motivation, and less disturbed behaviour. So the thinking goes. But last year, a systematic review of health care databases found almost no evidence that aromatherapy is effective in the treatment of dementia. Other findings suggest that aromatherapy works only if you believe it will. In fact, the only research that has unequivocally shown it to have an effect has been carried out on animals.

BBehavioural studies have consistently shown that odours elicit emotional memories far more readily than other sensory cues. And earlier this year, Rachel Herz, of Brown University in Providence, Rhode Island, and colleagues peered into people’s heads using functional Magnetic Resonance Imaging (fMRI) to corroborate that. They scanned the brains of five women while they either looked at a photo of a bottle of perfume that evoked a pleasant memory for them, or smelled that perfume. One woman remembered how as a child living in Paris she would watch with excitement as her mother dressed to go out and sprayed herself with that perfume. The women themselves described the perfume as far more evocative than the photo, and Herz and co-workers found that the scent did indeed activate the amygdala and other brain regions associated with emotion processing far more strongly than the photograph. But the interesting thing was that the memory itself was no better recalled by the odour than by the picture. “People don’t remember any more detail or with any more clarity when the memory is recalled with an odour,” she says. “However, with the odour, you have this intense emotional feeling that’s really visceral.”

CThat’s hardly surprising, Herz thinks, given how the brain has evolved. “The way I like to think about it is that emotion and olfaction are essentially the same things,” she says. “The part of the brain that controls emotion literally grew out of the part of the brain that controls smell.” That, she says, probably explains why memories for odours that are associated with intense emotions are so strongly entrenched in us, because the smell was initially a survival skill: a signal to approach or to avoid.

DEric Vermetten, a psychiatrist at the University of Utrecht in the Netherlands, says that doctors have long known about the potential of smells to act as traumatic reminders, but the evidence has been largely anecdotal. Last year, he and others set out to document it by describing three cases of post-traumatic stress disorder (PTSD) in which patients reported either that a certain smell triggered their flashbacks, or that smell was a feature of the flashback itself. The researchers concluded that odours could be made use of in exposure therapy, or for reconditioning patients’ fear responses.

EWhether odour-linked memories can be eliminated by some kind of therapy remains to be seen. For now, Herz is working with patients who suffer from drug addiction. She is trying to discover whether a drug-related odour can be used as a cue to intensify drug cravings in the laboratory setting, in order to enable patients to deal with it, and thereby overcome the addictive pull of the drug itself. A drug-related odour could act as a cue to trigger a craving in patients in a controlled environment, in order to allow the craving to be overcome, and the patient to eventually end their addiction. If such methods prove to be successful, it will be the first time that a purely olfactory cue has been used therapeutically. “What’s exciting for me,” says Herz, “is that this would be a case where odour memory is being used to erase or attenuate emotional memories.”

FThe evidence suggests that odour-linked memories can be strong, but are they really more accurate than other kinds of memories? Research suggests not. Chris Miles, a psychologist at Bournemouth University, UK, and his colleagues tested whether adding an odour to events during a learning session affects memory. They found that it didn’t, and in a separate study, Miles found that even though people thought their memories of an event were clearer when the associated odour was present, they were not actually any more accurate. “People may have a metacognitive illusion when it comes to odour,” he says – in other words, they believe they are recalling more clearly when they are not.

GPerhaps the most compelling evidence that smell has direct access to the emotional memory centres comes from a study using people with a neurological condition called temporal lobe epilepsy. Normally when we recall an event, we can also remember where and when we learned something about it, as well as general information about the topic. But some people with temporal lobe epilepsy have an impaired ability to remember the source or context of a memory. It turned out that odour was no better than other cues at triggering these specific kinds of memories in epileptics, suggesting that the emotional tagging of odour memories is carried out by neural circuits that can be disrupted by seizures, in the same way as other circuits controlling memory sources.

AMusic and the brain are both endlessly fascinating subjects, and as a neuroscientist specialising in auditory learning and memory, I find them especially intriguing. So I had high expectations of Musicophilia, the latest offering from neurologist and prolific author Oliver Sacks. And I confess to feeling a little guilty reporting that my reactions to the book are mixed.

BSacks himself is the best part of Musicophilia. He richly documents his own life in the book and reveals highly personal experiences. The photograph of him on the cover of the book – which shows him wearing headphones, eyes closed, clearly enchanted as he listens to Alfred Brendel perform Beethoven’s Pathetique Sonata – makes a positive impression that is borne out by the contents of the book. Sacks’ voice throughout is steady and erudite but never pontifical. He is neither self-conscious nor self-promoting.

CThe preface gives a good idea of what the book will deliver. In it, Sacks explains that he wants to convey the insights gleaned from the “enormous and rapidly growing body of work on the neural underpinnings of musical perception and imagery, and the complex and often bizarre disorders to which these are prone.” He also stresses the importance of “the simple art of observation” and “the richness of the human context.” He wants to combine “observation and description with the latest in technology,” he says, and to imaginatively enter into the experience of his patients and subjects. The reader can see that Sacks, who has been practicing neurology for 40 years, is torn between the “old-fashioned” path of observation and the new-fangled, high-tech approach: He knows that he needs to take heed of the latter, but his heart lies with the former.

DThe book consists mainly of detailed descriptions of cases. Part I, “Haunted by Music,” begins with the strange case of Tony Cicoria, a nonmusical, middle-aged surgeon who was consumed by a love of music after being hit by lightning. He suddenly began to crave listening to piano music, which he had never cared for in the past. He started to play the piano and then to compose music, which arose spontaneously in his mind in a “torrent” of notes. How could this happen? Was the cause psychological? Or was it the direct result of a change in the auditory regions of his cerebral cortex? Electroencephalography (EEG) showed his brain waves to be normal in the mid-1990s, just after his trauma and subsequent “conversion” to music. There are now more sensitive tests, but Cicoria has declined to undergo them; he does not want to delve into the causes of his musicality. What a shame!

EPart II, “A Range of Musicality,” covers a wider variety of topics, but unfortunately, some of the chapters offer little or nothing that is new. For example, chapter 13, which is five pages long, merely notes that the blind often has better hearing than the sighted. The most interesting chapters are those that present the strangest cases. Chapter 8 is about “amusia,” an inability to hear sounds like music, and “dysharmonia,” a highly specific impairment of the ability to hear harmony, with the ability to understand melody left intact. Such specific “dissociations” are found throughout the cases Sacks recounts.

FTo Sacks’s credit, part III, “Memory, Movement and Music,” brings us into the underappreciated realm of music therapy. Chapter 16 explains how “melodic intonation therapy” is being used to help expressive aphasic patients once again become capable of fluent speech. In chapter 20, Sacks demonstrates the near-miraculous power of music to animate Parkinson’s patients and other people with severe movement disorders, even those who are frozen into odd postures. Scientists cannot yet explain how music achieves this effect.

GTo readers who are unfamiliar with neuroscience and music behaviour, Musicophilia may be something of a revelation. But the book will not satisfy those seeking the causes and implications of the phenomena Sacks describes. For one thing, Sacks appears to be more at ease discussing patients than discussing experiments. And he tends to be rather uncritical in accepting scientific findings and theories.

HIt’s true that the causes of music-brain oddities remain poorly understood. However, Sacks could have done more to draw out some of the implications of the careful observations that he and other neurologists have made. For example, he might have noted that the many specific dissociations among components of music comprehension, such as loss of the ability to perceive harmony but not melody, indicate that there is no music centre in the brain.

IAnother conclusion one could draw is that there seem to be no “cures” for neurological problems involving music. A drug can alleviate a symptom in one patient and aggravate it in another or can have both positive and negative effects in the same patient. Treatments mentioned seem to be almost exclusively antiepileptic medications, which “damp down” the excitability of the brain in general; their effectiveness varies widely.

JFinally, in many of the cases described here the patient with music-brain symptoms is reported to have “normal” EEG results. Although Sacks recognises the existence of new technologies, among them far more sensitive ways to analyse brain waves than the standard neurological EEG test, he does not call for their use. In fact, although he exhibits the greatest compassion for patients, he conveys no sense of urgency about the pursuit of new avenues in the diagnosis and treatment of music-brain disorders. This absence echoes the book’s preface, in which Sacks expresses fear that “the simple art of observation may be lost” if we rely too much on new technologies. He does call for both approaches, though, and we can only hope that the neurological community will respond.