Gourt Home::Gourt :: Music and the brain
The difference between a particular sound being considered noise or being considered music may be the response that the sound elicits in the listener's brain; indeed, what may be noise to one listener's ears may be music to another's. Defining the factors that cause this 'mental response' (or simply defining what this response is), is a complex undertaking requiring a knowledge of many disciplines, including the studies of music, physics, and neuroscience.
There are many components of music that affect the way is it perceived, for example pitch, rhythm, timbre and amplitude. Of these, however, pitch and rhythm are the most influential, and much research in the area is based upon manipulations of pitch or timing.
Pitch
We, as humans, love resonant frequencies; they are present in all wave forms in physics, but when they are aurally perceived we call them keys or pitches. Some pitches, or combinations of pitches, seem more harmonious than others, and this can be partially explained by examining the octave scale.
In western music there are twelve chromatic pitch classes, which can be represented in many ways.
In eastern music there are more notes than in the west. For instance, in western music there is only one interval between a C and a C sharp; but in India this is a large jump and there are many notes in between what we call a C and a C sharp. Each of these pitches can be arranged into chords, which occur in characteristic sequences throughout Western music. For example, after two or three of these often-used chords are heard in sequence, the sequence of chords can be satisfactorily resolved only by a limited number of expected chords. This is a particular area of interest, as even musical laymen can detect these chord patterns and recognize when a chord progression has not resolved "correctly".
Recognizing pitches
Within our ear, there is a small membrane called the basilar membrane. When we hear a certain pitch, a corresponding part of the tonotopically organised membrane responds, and sends the signal to the auditory cotrex within the brain. Studies suggest that once it arrives here there are specific regions for each band of pitch, such that the area is organised into sections of cells that are responsive to certain frequencies from very low to very high pitches Arlinger, S., Elberling, C., Bak, C., Kofoed, B., Lebech, J., & Saermark, K. (1982). Cortical magnetic fields evoked by frequency glides of a continuous tone. EEG & Clinical Neurophysiology, 54, 642-653 . This organisation may not be stable though, in that the specific cells that are responsive to different pitches may change over days or months Janata P, Birk J, Van Horn J, Leman M, Tillmann B, & Bharucha J. 2002. The cortical topography of tonal structures underlying Western music. Science, 298, 2167–70. It has been suggested that in some people this organization is less variable, leading to perfect pitch, or the ability to recognize the musical scale label of a certain tone without hearing it in reference to other tones.
Rhythm
The circadian rhythm seems to be on a time scale which is far too large to contribute to music. The beats per minute in a song have been known to affect heart rate, and (coincidentally?) fall roughly in the same range of a normal human heart beat. A fast song can make the heart beat faster, while a slower paced song can make the heart beat slower . It would be interesting to see if there are any connections from the auditory cortex (or anywhere in the auditory network) which connect to the medulla to regulate heart beat. Perhaps even from the ear directly to the hypothalamus, analogous to the retino-hypothalamic tract.
Gray and McCormick
It has also been found that the brain has its own rhythm in several studies, one of which was by Charles Gray of UC Davis and another by David McCormick of Yale U. School of Medicine (Schechter 1996). The so-called “chatter cells” coordinate rhythmic firings of millions of cells in bursts around 30-60 hertz. The idea is that this may link anatomically distant neural structures and although it has not been directly tied to music, nothing relates more anatomically and functionally distant structures than the subject of this paper. It has been indicated that different parts of the auditory cortex are involved in processing rhythm, specifically the belt and parabelt areas of the right hemisphere. When individuals are preparing to tap out a rhythm of regular intervals (1:2 or 1:3) the “left frontal cortex, left parietal cortex, and right cerebellum are all activated”(Tramo, 2001). With more difficult rhythms such as a 1:2.5, more of the cortex and cerebellum are involved. Still, the structures involved in tonal comprehension and speech are better known than the rhythm and involve many distant structures.
Tonality and emotion
It has been indicated that the right auditory cortex a primary component for perceiving pitch, and parts of harmony, melody and rhythm (Tramo 2001). Janata found that there are tonally sensitive areas in the medial prefrontal cortex, the cerebellum, the Superior Temporal Sulci of both hemispheres and the Superior Temporal gyri (which has a skew towards the right hemisphere). When unpleasant melodies are played, the posterior cingulated cortex is activated, indicating a form of pain (Tramo, 2001). The right brain has also been found to be correlated with emotion, which can also activate areas in the cingluate in times of emotional pain, specifically social rejection (Eisenberger). This evidence, along with observations, has led many musical theorists, philosophers and neuroscientists to link emotion with tonality. This seems almost obvious; the tones in music seem like a characterization of the tones in human speech which indicate emotional content. The vowels in the phonemes of a song are elongated for a dramatic effect, and it seems as though speech tones and musical tones are one and the same.
This would be the case, however, studies on amusia suggest at least a slight separation between speech tonality and musical tonality. Congenital amusics are individuals who are incapable of distinguishing between pitches, they are unmoved by dissonance and a wrong key on a piano never bothers them. They cannot be taught to remember a melody or to recite a song. This being said, they are still capable of hearing the tonality of speech, for example, they can tell the difference between “You speak French” and “You speak French?” when spoken. Perhaps this suggests some sort of linear organization in the right brain for comprehending tone, analogous to the left hemisphere’s linguistic organization. Knowing this, it would be interesting to see if amusics have a flatter affect than a control, or if right brain damaged patients exhibit at least a partial amusia. It would also be interesting if anyone were to do a study to see if patients with amygdala damage exhibit some form of amusia. It seems as though tonality and rhythm are the most important and unique components to music, but lyrics play an important part too.
Linguistics and organization
Evolutionary neurobiologists have made endocasts of the skulls of early humans and have shown that society developed right along side the lateralization of the planum temporale to the left side. This area has been indicated in musical ability, linguistic ability and in word memory. Musicians have been shown to have significantly more developed left planum temporales, and have also shown to have a greater word memory (Chan et al.). Chan’s study controlled for age, grade point average and years of education and found that when given a 16 word memory test, the musicians averaged one to two more words above their non musical counterparts. Even though most scientists attribute this ability to the lateralization, or attribute the lateralization to this ability, it has been found that chimpanzees have the same lateralization as humans. Based on this evidence, the chimp should be able to have the linguistic ability associated with this. This is just another indication that there is much more needed to produce music than a left planum temporale.
Development
Malyarenko played music in a background setting for a group of four year old preschoolers for a period of six months. The musical group had significantly greater interhemispheric activity and range coherence than the control. Also, the musical four year olds were found to have greater left hemisphere intrahemispheric coherence (Strickland, 2001). Musicians have been found to have more developed anterior portions of the corpus callosum in a study by Cowell et al. in 1992 (Strickland, 2001). This was confirmed by a study by Schlaug et al in 1995 who found that classical musicians between the ages of 21 and 36 have significantly greater anterior corpora callosa than the non-musical control. Schlaug also found that there was a strong correlation of musical exposure before the age of seven greatly increases the size of the corpus callosum (Strickland, 2001). These fibers join together the left and right hemispheres and indicate an increased relaying between both sides of the brain. This suggests the merging between the spatial- emotiono-tonal processing of the right brains and the linguistical processing of the left brain. It has been thought that this large relaying across many different areas of the brain has contributed to music’s ability to aide in memory function.
Memory
Musical training has been shown to aid in memory functions in many different ways. Although the exact neural mechanism of how it helps it not fully agreed upon, it could be a neural exercise of different parts of the brain which are involved in memory. Another idea is that it could form neural connections from different angles to a single memory and help to create different pathways for the recall of a single memory. Altenmuller et al studied the difference between active and passive musical instruction and found the results to be equally effective in the short term. However, it was found that over a longer period of time, the actively taught students retained much more information than the passively taught students. The actively taught students were also found to have greater cerebral cortex activation; this would indicate that the musically taught students were more effectively taught. It should also be noted that the passively taught students weren’t wasting their time; they, along with the active group, displayed greater left hemisphere activity which is typical in trained musicians (Strickland, 2001).
There is also an anecdote of a woman with chronic dementia due to her age, she could not remember integral portions of her life such her place of birth, her place of residence for the majority of her life, or if she had had a short career singing on the radio. Despite this extreme dotage, she could remember every song she had sang perfectly (Skloot, 2002). It has also been indicated that simple melodies get “stuck” in our heads easier than more complex ones. Evolutionary biologists theorized that simpler tunes helped the ancient profession of the bard sing and remember oral histories. It has been shown that the more predictable the tune, the easier it is to get stuck in the head (Shouse, 2001). When subjects are asked to remember a song in their heads, the same parts of the brains light up except fainter and the primary auditory cortex is not activated as much.
Auditory cortices
This aligns with the studies of people remembering a song in their minds; they do not perceive any sound, but experience the melody, rhythm and overall experience of music. By deduction, when the primary auditory cortex is activated without auditory input, this should cause a hallucination. The going belief is that whole experience of music actually does terminate in the tertiary auditory cortex, which unites everything into the full experience. If so, it would be interesting to study a subject without a tertiary auditory cortex. This would be very difficult to do as the tertiary cortex is simply a ring around the secondary, which is a ring around the primary AC.
The power of music should not be underestimated. It is the neural triathlon, triggering an incredible concatenation of neural events, along with many parallel processes. The incredible, linguistic, emotional, rhythmic, mnemonic powers of music have been a great source of entertainment and functionality in both our modern and ancient human environments. There is little doubt that the discoveries of musical comprehension from a neurological standpoint have only just begun.
External links
References
"Music and the brain"