NeuroSPECT technique: Experts show that each one of us "hears differently"

A study of sound stimulation influence on brain function means Chilean researchers are pioneers in Latin America. Similar research work has only been carried out in developed countries such as Japan, South Korea, Canada, and England.

Scientific research in general is a hot subject in Chile. It has been for many years. The country's economy has grown in a sustainable fashion since 1990 but based on the sale of raw materials; in other words, national production is limited and the country really only sells product. Chile invests just 0.5% of its gross domestic product (GDP) in science and technology, and researchers are few and far between, amounting to no more than 800 professionals. Developed countries, on the other hand, invest an average of 2.5% of GDP and keep an average of 5,000 specialised scientific researchers in work.

In this limited landscape, the state concentrates on solving energy problems, since the formula allows for no growth in the socio-economic system. For less prioritised areas, then, there are scarce possibilities. In Chile there are no official figures on scientific or technological research related to audiology. There are isolated efforts and studies in very controlled soft sciences, which is even more reason why the current efforts of a multidisciplinary group of experts backed by the Las Condes Clinic and immersed in studying sound stimulated brain function is attracting so much attention.

NeuroSPECT technique

Three internationally-renowned experts have been using technology called NeuroSPECT to study how the brain functions in relation to the auditory apparatus and the environment that generates these sounds. They are:

  • Ismael Mena, expert in nuclear medicine. Pioneer worldwide in central auditory processing with NeuroSPECT, the precursor of this technique at UCLA; in fact, he is the Emeritus Professor of Radiology at the University of California. He decided to return to Chile to apply this technology, and is now on the staff of professionals at the Las Condes Clinic. He was recently named Doctor Honoris Causa by the University of Auvergne in France.
  • Marcos Goycoolea, otorhinolaryngologist, who has more than 30 years of experience, has appeared in 160 national and international publications and published several books, among them an Atlas of Otological Surgery which was a best-seller in the USA in 1989. He is Associate Professor at the University of Minnesota, USA, and Visiting Lecturer at the University of Chile.
  • Sonia Neubauer, specialist in nuclear medicine at the Las Condes Clinic, and also an international authority on brain function studies.

These researchers have spent eight years submitting groups of volunteers to functional magnetic resonance imaging, aimed at understanding which areas of the human brain are activated and inhibited when given certain auditory stimuli.

Central processing

Most of the research is focussed on the peripheral organs of the system which allows us to hear: in the inner and middle ear. These Chilean doctors have opted to place emphasis on the central organ. The important aspect for them is how what is heard is processed at cerebral level; the knowledge extends to establishing that, in response to the same form of stimulation, every human being "hears differently", depending on our personal experience and history.

"Sound tells you things, and you interpret things through this sound," comments Dr. Marcos Goycoolea (above picture). "If we delve into one of our best known studies, we find examples such as this: "If you are made to listen to a piece of Bach, how do you know it is Bach's music? How do you recognise it? It is not because the ear processes the sound; you know it is Bach's music because there is a complete processing of sound stimulation going on, one in which, among other phenomena, auditory memory plays a part. So, what we have been doing is to submit volunteers to different auditory stiumuli while we measure their brain function activity."

Not only is the auditory area stimulated, but other zones too, such as those the brain uses for associating ideas and concepts, visual and frontal areas, which are related to emotions. "There is a lot of very interesting mental processing happening in interrelated areas. With sounds, there are certain areas of the brain which become excited, and others which are inhibited. Subjects who received stimulation with the same tones received stimulation in the same areas of their brains. Not all the ear captures; it is a kind of jumble of electric cables that reach up in a mechanised way. What you process in your brain is not just an electrical stimulation going up; it goes through a series of stages, and what gets up there is the final product of a lot of central processing. We drew a map of the different areas of the human brain and the results are very interesting," says Goycoolea.

Joint stimulation

Two of the most internationally famous articles are "Musical brains: a study of spontaneous and evoked musical sensations without external auditory stimuli*" and "Spontaneous musical auditory perceptions in patients who develop abrupt bilateral sensorineural hearing loss"**. Both have produced interesting and interrelated results.

"Many people listen to music, but musicians do not only listen; they also mentally modify what they hear," points out Doctor Goycoolea in relation to the aforementioned article. "Let me explain: conservatory composers and musicians relax and hear a song when there is nothing sounding; it is as if instead of switching on the radio they switch on their brains and listen by memory. In this process, they are able to modify the structures of that music within their heads. They mentally add instrument voices (violins, for example, or choirs), and they compose in this way. Schumann, Bach, Beethoven, and Mozart did this. We have now charted a cerebral map of this memory process in conservatory musicians and, among other conclusions, we realised that the same areas of the brain "light up" when these people are really hearing music as when they are composing music."

Doctor Goycoolea also summarises the second article, which won an award from the prestigious Scandinavian journal Acta Oto-Laryngologica. "This is very common: when patients lose their hearing in both ears in an abrupt fashion, shortly afterwards they hear music but don't dare to say so for fear of being called crazy. But a doctor discovers through to talking to such patients that this is a very common syndrome. We then ask ourselves where this music comes from. There are areas of auditory memory where this music is accumulated, and what the patient is hearing are old melodies. This is not psychotic, but totally functional, distinct from psychotic. So, we made cerebral maps of these people while they listened to music, and in all cases the brain area of auditory memory was activated. Later, we played music to them and the same area was activated. These areas were active in "freeing" music from the memory. What we proved, among other things, is that the brains of these people act in a different way to those of psychiatric patients. What we ultimately proved is that, on using auditory memory, very different zones are switched on to those used by patients who, for example, suffer from psychosis. The auditory areas and those of association are switched on."

Both studies revealed that the most stimulated brain area was that known as Brodmann area 39, which is located in the cerebral cortex in the posterior half of the brain and which belongs to the associative cortex. It is specifically auditory but is also related to the sensory memory, language comprehension, and grammar development.

The future

Meanwhile, these doctors will continue in their efforts to discover how the brain functions in response to sound stimulation. "We are now observing cochlear implants, evaluating them over time, and this has not been published. We are interested in finding out what brain areas are stimulated over time for patients with implants, how neuronal circuits are created, and how the brain changes from the visual to the auditory. This can be measured at brain function level. It is neither easy nor cheap, but it can be done."

Doctor Marcos Goycoolea is also interested in applying the same kind of imaging studies to subjects submitted to very specific sound stimuli such as mantras, since this team of experts is interested in exploring within the brain so that this knowledge can eventually lead to new treatments and ways of tackling different audiological problems. They are looking and working towards the future of medicine.

* GOYCOOLEA, M., MENA I., BERGER C.G. “Musical brains: a study of spontaneous and evoked musical sensations without external auditory stimuli.” Acta Oto-Laryngologica, 2007, 127: 711 - 721.

** GOYCOOLEA, M., MENA I., NEUBAUER S. “Spontaneous musical auditory perceptions in patients who develop abrupt bilateral sensorineural hearing loss. An uninhibition syndrome?” Acta Oto-Laryngologica, 2006,126: 368 - 374.

Gonzalo López Pardo

Translation: P.W., Photos: G.L.P.