Whether you’re a fan of classical quartets or acid house, one thing is certain; we all love a good tune! Music has the amazing ability to drive our emotions, bring people together and encourage us to dance till dawn. But why should this be the case? It’s easy to understand how pleasure can be derived from food and sex and why bereavement makes us sad. But, what is so special about music? The ability to write a good tune has no evolutionary advantage….or does it?
Novel research from our own fair city (Manchester) is now combining evolutionary biology, physics and neuroscience in an attempt to uncover the mysteries of music and its effect on the brain. This work, led by academic and musician Dr. Neil Todd, has uncovered a biological pathway linking sound, movement and pleasure in the brain. This pathway may have remained elusive for so many years because of its unusual origins. Neil has found evidence that, contrary to the traditional textbook theories, the cochlea is not the only sensory organ in the inner ear capable of responding to sound. His research suggests that the vestibular apparatus, normally associated with balance and spatial orientation, is also sensitive to certain frequencies of sound.
This may seem like a kooky idea but, viewed from an evolutionary standpoint, it actually makes perfect sense. In mammalian anatomy, we know that the cochlea is responsible for perception of sound. But, looking back down the evolutionary scale we find that this organ is not always present. Taking bony fish as an example, we find no sign of a cochlea. But, fish are far from deaf; in fact they use their otolith organs (part of the vestibular system) to detect vibrations. Similar to the human cochlea, the fish otolith organ contains an array of tiny hair-cells which can detect vibrations and translate these into a sensation of sound. Alongside fish, there are also many further examples of creatures utilising their vestibular sensors as sound detectors. So, there’s certainly evolutionary precedence for a mammalian vestibular sound processor. But, can humans use this system to perceive sound and, if so, why might this be advantageous?
Using electrodes which measured electrical signals from the neck and eyes (specifically from muscles responsive to vestibular activation). Neil found that the human vestibular system was sensitive to air-conducted sound frequencies ranging from 50-1000Hz, peaking between 300 and 350Hz – just above middle C on a musical scale and a similar frequency to male and female voices. For head vibration the peak sensitivity is even lower, at around 100 Hz. Taking this work one step further, Neil’s group wired up a number of participants looking at electrical activity in the brain and vestibular activated neck/eye muscles simultaneously. This method enabled the group to discern how responses in the brain differed between sounds which activated the vestibular system and those which didn’t. It was discovered that sounds falling within vestibular-activating frequency bands caused activity in auditory cortex and cingulate limbic areas, as well as sub-cortical areas traditionally associated with vestibular activation. This strongly suggests that certain sounds can indeed activate the human vestibular system, but why might this be useful?
Once again peering back through our evolutionary past, we find that many creatures use vestibular-activating sounds as mating signals. Have you ever heard a fish sing? Well, he may not get a turn from the judges on ‘the Voice’, but the male Haddock is one of the most vocal of fish and he uses his alluring voice to snag himself a mate. Male haddock vocalise by drumming on their swim bladder and, if surrounding females, are charmed by this song the music can cause both fish to simultaneously release eggs and sperm. Again, it seems that many creatures use this sense when finding a mate, and many also accompany this behaviour with a kind of dance. Therefore, it is possible that the vestibular sound-sensing system represents an ancient pathway used in mating behaviour – perhaps similar to the recently discovered vomeronasal system used to choose a mate based on pheromones and smell.
Post by: Sarah Fox