MUSIC AND THE BRAIN Essay Cognitive Neuroscience – 24 April 2008 Ben Spruit (student nr: 0404764) 2975 words In our modern society music is almost everywhere, whether you like it or not. To listen to our favourite music wherever we are, we even bring music with us in our iPods, mp3-players or radios. Hearing the first notes of our favourite song in the morning can give us a thrill that can brighten up our day. Music can cause people to jump and move to the rhythm in a thing we call dance. It is wonderful that music, basically some waves in the air that can be picked up by our ears, can cause such a strong emotional or physical reaction. Apparently our brains are able to recognise these waves as music and process them very rapidly, resulting in such a response. In music production musicians are able to perform very complex motor actions that take years of practice. Still everyone is able to produce some kind of music, even if it is only the tapping of your finger to the beat or singing a children’s song. Both listening to and producing music involve many tasks, in which the role of the brain seems to be very complex. In this essay, by summarising the current knowledge of the role of the brain in music perception and production, I hope to answer the question how the brain deals with music. What is music? Most music is composed of a combination of melody and rhythm. It is often the melody that is stuck in our mind after listening to a song. A musical melody is formed by a sequence of tones of a different frequency. Humans can perceive frequencies ranging from 20 Hz to 20,000 Hz, but this upper limit is decreasing with age. The fundamental frequency of a tone that we perceive is called the pitch. A presentation of more than one pitch at the same time forms a chord, while a simultaneous presentation of more than one melody forms a harmony. Not all combinations of tones sound good to us, therefore rules are set up to organise tones that ‘sound good’ together in keys. A melody is often made with a restricted number of tones that are allowed in one key. A combination of tones that do not belong to the same key sound bad together, and then we consider them as false tones. Besides pitch, music is organised in time. The first level of temporal organisation of music is the interval between two sounds, either tones or beats. Several intervals form a more complex pattern; a rhythm. A higher level of temporal organisation is metre, which is the general organisation of a rhythm extending in a piece of music. Metre defines the hierarchy of beats within a rhythm, the length a rhythm; often three or four seconds, and the number of repetitions of the same rhythm. A third fundamental aspect that forms a piece of music is timbre. Timbre can be described as the ‘colour’ of a sound. It is an aspect that discerns different musical instruments and even musical streams. Different musical instruments can play the same melody and rhythm, yet both instruments sound different because of the timbre. Even though it cannot be easily described or measured, timbre is a fundamental aspect of music. The organisation of music in melody and rhythm, and the use of timbre can vary over different musical streams and cultures. Our assessment of good or false music is partly culturally determined, but also for a large part regulated by the brain. In the next parts, the role of the brain in perceiving and producing music will be discussed. Methods of detecting music in the brain The role of the brain in perceiving and producing music can be studied by several different methods. The traditional method is making associations between defects in the brain and the symptoms the patients with these defects have. This can be done from two different approaches: a symptom-led and a lesion-led approach. In the symptom-led approach, people with limitations in their musical abilities are tested for brain defects. According to the lesion-led approach, patients with the same brain defect are categorised, and they are tested for their musical abilities. In both cases, the defective brain area is then assigned to the impaired function or ability. Both approaches have their Figure 1: The anatomy of the brain limitations, but have been Brain areas are indicated with a letter: used in studies for many A) Primary motor cortex, B) Supplementary motor areas, C) Premotor cortex, D) Prefrontal cortex, E) Insula, F) Auditory cortex, G) Cerebellum years. Edited from Zatorre et al., 2007 Because of the recent advances in brain imaging techniques, much more knowledge of the function of brain area’s can be acquired rapidly by functional imaging. Techniques like fMRI, PET and EEG can show what different brain area’s are active during different musical tasks and thereby probably involved in the respective task. Since there are similarities in brain structure and function between animals and humans, animal models can, in addition to research in humans, give insight in the neural mechanisms of brain functions that overlap with those involved in the processing of music. How does the brain perceive music? Like any sound, music is perceived by the auditory system and processed in the auditory cortex. In humans, the auditory cortex is located on the superior temporal gyrus, next to the lateral (Sylvian) fissure on the temporal lobe of the brain. Besides the primary auditory cortex, secondary auditory cortical areas and the planum temporale are additional brain areas that are important in the processing of auditory stimuli. Some brain anatomy and the location of several brain areas are shown in Figure 1. Pitch Pitch perception is one of the fundamental properties of listening to music. Pitch perception seems to evoke responses in the secondary auditory cortex rather than the primary cortex. It is suggested that a pitch centre in this secondary auditory cortex is responsible for the processing of pitch. (Stewart et al., 2006) Neuronal networks involving the frontal lobes are responsible for the processing of more complex levels of pitch, like harmonies and melodies. The processing of melodies requires the analysis of pitch contour, which is relation between the pitches of multiple tones in a sequence. In the analysis of pitch contour the brain recognises the pattern of frequency intervals between tones, while not much attention is given to the determination of the absolute frequency of tones. The value of the pitch itself instead of the contour is only recognised by the brain if it is trained to do so, which is the case with musicians. For non-musicians, it is hard to distinguish between the same melodies with a different pitch, for example when shifted to another key. The analysis of intervals between tones is performed by two separable functions. First, there is a detection of change in pitch, second, the brain determines the direction of the change, either higher of lower. The perception of pitch interval is also called relative pitch perception, since only the relationships between frequencies is analysed. Absolute pitch perception, when the frequency of a tone is assessed without another reference or contour, is used in two different contexts. Musical absolute pitch, as mentioned above, is not used very often but can be improved after musical training. Every normal brain used estimation of general absolute pitch, the frequency of a tone in general, to, for example, identify the frequencies of voices and distinguish between voices of men, women and children. Besides humans, animals also use general absolute pitch perception in communication. Pigeons, rats and humans seem to have equal capacities in estimating absolute pitch value, while zebra finches, a songbird species, perform much better. (Friedrich et al., 2007) This implies a highly specified role of absolute pitch in vocal communication across different animal species, especially in birdsong. Rhythm Like pitch, rhythm is built up in different hierarchical levels. The analyses of pitch and rhythm seem to be separable for the simple hierarchical levels, but from a certain point the analyses of complex melodies and rhythms interact. Since temporal organisation has a large role in complex melodies, its analysis cannot be done without analysis of rhythm. Unlike pitch analysis, where different brain areas are responsible for processing the different levels of pitch, the processing of all levels of rhythm seems to involve the cerebellum and basal ganglia. Auditory-motor interactions seem to play a large role in the perception of rhythm. The brain areas responsible for processing rhythm perception also seem to underlie the motor production of rhythm. (Stewart et al., 2006) This suggests, like the motor theory of speech, a motor theory of rhythm perception, whereby the perception of rhythm depends on the motor mechanisms that underlie the production of rhythm. Timbre The perception of timbre consists of the perception of different characteristics of music. There is evidence that timbre is processed by a network of areas in the superior-temporal lobe of the right hemisphere, together with areas that are also involved in pitch pattern analysis. Discrimination of timbres in voices and environmental sounds is processed in the same way. Emotion and Memory Listening to music is an experience that is larger than the sum of the different aspects. Therefore, an additional component in musical listening is the emotional experience. Listening to pleasant music activates the same brain areas as doing other pleasant activities, mainly in the mesiolimbic areas, the amygdala in particular, and the insula. There also seems to be a difference in brain activity when listening to music that is appreciated and music that is experienced as unpleasant. Recognition of familiar tunes is a common aspect of listening to music. The anterior superior-temporal gyrus and the right insula are likely to be involved in music recognition and musical memory. How does the brain play music? Production of music involves several sensory and motor tasks. In all motor control functions there is a hierarchy of actions that lead to the execution of movements: first different areas of the neocortex that have information of the position of the body and the environment, together with the basal ganglia, make up a strategy for a movement. Then, the motor cortex and the cerebellum exactly plan the movement that is needed. The final step is execution of the movement by activating the associated muscles, which is performed by the brain stem and the spinal cord. In playing music exact planning of the movement, the second step, is very complex. In general, this can be divided into three basic motor control functions: timing, sequencing, and spatial organisation. Timing Timing, the organisation of rhythm, has been studied extensively during the past years, but it still remains impossible to draw any general conclusion about the neural mechanisms responsible for timing. For many years, the overall idea has been that timing is regulated by a neural clock or counting mechanism in the brain. It is supposed that there is a pacemaker that produces regular pulses, which are stored. (Buhusi and Meck, 2005) At the moment of feedback, the number of pulses that the pacemaker has emitted from the moment of action is counted and memorised. This model has proved successful in explaining some, but not all, observations in rhythm experiments. Recently, other theories have been proposed that also explain some part of the observations. The theory involving ‘neural oscillators’ hypothesises that somehow a prediction of time can be made by the degree of simultaneous firing of two coincidentally firing neurons in the cortex. Data that support this hypothesis comes from studies with animals that were trained to time the intervals between rewards. (Fiorillo et al., 2003) The dopaminergic system, responsible for rewarding, seems to be involved in timing, but it is unclear whether this mechanism is responsible for timing of rhythm during music production. More research is needed to find a mechanism that is supported by all research on a neural mechanism of timing, and timing of musical rhythm in particular. Of the brain areas that are active during timing tasks, the cerebellum seems to have an important role. The cerebellum might predict timing of movements and seems to be responsible for error correction of movement, and the precise control of movements on the short timescales; around hundreds of milliseconds. Movements on longer timescales of more than a second are organised by supplementary motor areas (SMA). The formation of actual patterns of rhythm that are required to play music involve a higher level of timing, and this is attributed to the basal ganglia and the premotor cortex. Overall, timing seems to be regulated by a network of brain areas, instead of a specific brain area. Sequencing The formation of a sequence of individual movements in time is necessary to play more than just one tone or beat of music. The frontal cortex and basal ganglia seem to be involved in the learning of a sequence, while the cerebellum integrates individual movements into that sequence. Chunking, the re-organisation of complex motor sequences into small parts, is performed by the supplementary motor areas and seems to improve the accuracy of the movements in a motor sequence. Subsequently, the premotor and motor cortices have a role in the planning and execution of the complete motor sequence. Spatial organisation The spatial organization of movement is the co-ordination of the direction of individual movements. Exact planning of movements of specific body parts, of the fingers for example, is needed to make the complex and accurate movements that are required for producing music. Like with most motor actions, these movements are planned by the parietal, sensory- motor and premotor cortices. Not much research has been performed on spatial organisation yet, because for a long time it has been considered as part of sequencing. Only the last couple of years specific research has led to some knowledge of the brain areas involved in spatial organisation of movements in music and the differences with less complex motor functions. Auditory-Motor interactions Besides motor action, playing music requires many interactions between the auditory and motor systems. During feedback interactions, auditory input is used to control and correct errors in the motor output. Auditory feedback is very important when pitch has to be controlled continuously, for example during playing musical instruments like the violin or singing. The produced music is heard and compared to a mental representation and expectation of the music. The brain then adjusts the motor output in order to correct for the errors in the music compared to the mental representation. An example of this is shown in Figure 2. Another type of auditory-motor interaction is feedforward interaction, when during listening to music the Figure 2: Feedback interactions in playing music From Zatorre et al., 2007 auditory input predicts motor output. Finger tapping to the beat and dancing are examples of feedforward interactions. Both the auditory and motor cortices are active during listening to music and playing of music. (Zatorre et al., 2007) The premotor cortex of musicians shows activity during listening to a familiar piece of music without actual playing the music. The other way around, the auditory cortex was active during production of music, without auditory input. This indicates the existence of strong interacting networks between both auditory and motor systems that work together in perceiving and producing music. The musician’s brain Even though the normal brain contains many auditory-motor interactions and features discussed before, mainly musician’s brains are studied in research on music production and perception. Musicians generally perform better in the experiments and differences with normal brains are supposed to be larger, and therefore more easily to be found. Besides functional differences, some structural differences between normal and musician’s brains have been discovered. Though only slight differences, the musician’s brain has a larger volume of the auditory cortex and the cerebellum. In the motor cortices, a greater grey matter concentration was found in the areas associated with the body parts used in music production. Guitar players for example, have a higher grey matter concentration in the motor cortex area responsible for the left hand. Some studies demonstrated brain reorganisation after even short periods of musical training, but it is unknown for how long after the training these changes endure. (Gaab et al., 2006) This however is debated, because it remains unclear whether these larger volumes and concentrations are acquired during musical training, or whether these structural differences existed from birth and allowed the musician to attend musical training. Conclusion More than any other activity, music requires highly complex tasks of the brain. The normal human brain already has the ability to perceive and produce music, but can be trained to perform better and more specialised. There are indications that even differences in brain structure can occur after musical training. Listening and playing music could therefore improve functioning of the brain in perception and motor accuracy and memory in general. Since there is a great overlap with other auditory and motor functions, for example with speech, music is an interesting and promising area of research. By understanding how the brain processes music, we would gain a lot of knowledge about the functioning of the brain itself. Therefore, besides defects in the perception and production of music, which were not discussed in this essay, the study of music might help to solve problems with other brain functions. Discovering a neural mechanism of rhythm production, for example, might help to find a treatment for Parkinson’s disease, where patients often have troubles in initiating movements. Also knowledge on perception of pitch contour might help people that have troubles in perceiving emphasis and intonation in speech. Besides auditory and motor functions, music also has a large psychological aspect that involves emotion and musical culture. It would be interesting to study if there is a neurological basis for the variation of musical preference, and the impact of music on emotion. Of the many tasks that the brain has to perform in the perception and production of music, only global neural mechanisms are, just slightly, revealed. Being able to listen to music seems to be a lot more complicated then just pressing the play button of the ghetto blaster, but it might be better not to think of that and just enjoy! References Buhusi CV, Meck WH (2005) What makes us tick? Functional and neural mechanisms of interval timing. Nature Reviews Neuroscience 6:755-765. Fiorillo CD, Tobler PN, Schultz W (2003) Discrete coding of reward probability and uncertainty by dopamine neurons. Science 299:1898-1902. Friedrich A, Zentall T, Weisman R (2007) Absolute Pitch: Frequency-Range Discriminations in Pigeons (Columba livia)—Comparisons With Zebra Finches (Taeniopygia guttata) and Humans (Homo sapiens). Journal of Comparative Psychology 121:95-105. Gaab N, Gaser C, Schlaug G (2006) Improvement-related functional plasticity following pitch memory training. Neuroimage 31:255-263. Stewart L, von Kriegstein K, Warren JD, Griffiths TD (2006) Music and the brain: disorders of musical listening. Brain 129:2533–2553. Zatorre RJ, Chen JL, Penhune VB (2007) When the brain plays music: auditory–motor interactions in music perception and production. Nature Reviews Neuroscience 8:547- 558.
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