Biology 202
1999 First Web Reports
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Music and the Brain: Processing and Responding (A General Overview)

Feyza Sancar

For any individual who either avidly listens to or performs music, it is understood that many melodies have amazing effects on both our emotions and our perception. To address the effects of music on the brain, it seems most logical to initially map the auditory and neural pathways of sound. In the case of humans, the mechanism responsible for receiving and transmitting sound to the brain are the ears. Briefly stated, the outer ear (or pinna) 'catches' and amplifies sound by funneling it into the ear canal. Interestingly, the outer ear serves only to boost high frequency sound components (1). The resonance provided by the outer ear also serves in amplifying a higher range of frequencies corresponding to the top octave of the piano key board. The air pressure wave travels through the ear canal to ultimately reach and vibrate the timpanic membrane (i.e.-- the eardrum). At this particular juncture, the pressure wave energy of sound is translated into mechanical energy via the middle ear. Here, three small bones, the ossicles, vibrate in succession to produce a unique pattern of movements that embodies the frequencies contained in every sound we are capable of hearing. The middle ear is also an important component in what music we actually keep out of our 'head'. The muscles grasping the ossicles can contract to prevent as much as two thirds of the sound from entering the inner ear. (1, 2)

The mechanical motions of the ossicles directly vibrate a small membrane that connects to the fluid filled inner ear. From this point, vibration of the connective membrane (oval window) transforms mechanical motion into a pressure wave in fluid. This pressure wave enters and hence passes vibrations into the fluid filled structure called the cochlea. The cochlea contains two membranes and between these two membranes, are specialized neurons or receptors called Hair cells. Once vibrations enter the cochlea, they cause the lower membrane (basilar membrane) to move in respect to the upper membrane (i.e. --the tectorial membrane in which the hair cells are embedded). This movement bends the hair cells to cause receptor potentials in these cells which in turn cause the release of transmitter onto the neurons of the auditory nerve. In this case, the hair cell receptors are very pressure sensitive. The greater the force of the vibrations on the membrane, the more the hair cells bend and hence the greater the receptor potential generated by these hair cells. The greater receptor potentials generated elicit higher frequencies of action potentials in the auditory axons (2). The pressure sensitivity of the hair cells dictate the intensity (loudness) of sound.

The membranes and the hair cells in the cochlea also serve to dictate pitch. The basilar membrane which acts as the vibrating membrane, varies in flexibility along the length of the cochlea. The membrane is most flexible and wider near the tip of the cochlea and this flexibility gradually decreases as the membrane nears the oval window. As such, higher frequencies cause the greatest vibration in the furthest regions of the cochlear membrane. Hence, the inputs from receptors towards the tip of the cochlea are interpreted as higher in pitch by the brain. From this, it can be inferred that the cochlea displays properties of anatomical specificity since signals received by the receptors farther along the cochlea connect only to certain parts of the brain which interpret progressively higher pitches.

The neuronal connections which ensue from this juncture of the auditory nerve is quite complex and difficult to distinguish. In order to process a melody, many 'higher' functioning areas of the brain (such as the frontal lobes) are greatly involved. The area of the brain which integrates the intensity and pitch information relayed from the cochlea is the brain stem. The brain stem is also important in localizing sound. This function is thought of as more rudimentary or primitive form of processing music as it is most related to a physical response (as in locating prey or a potential mate). It does, however, also work to define and shape sounds helping to identify individual notes. (1) This 'crude' form of information is presumably shunted to areas of the cerebral cortex where more complex assessment of notes are achieved.

In particular, the auditory cortex interprets sounds within the context of what has preceded. Specifically, the right-brain auditory cortex specializes in determining hierarchies of harmonic relations and rich overtones whereas the left auditory hemisphere deciphers relationships between successions of sounds (i.e.-- the sequencing of sounds and perception of rhythm)(1). It should be noted that the right-brain auditory cortex is particularly adept at analyzing the highly harmonic vowel sounds of language (1). It is very interesting to note that the left brain is also involved in the sequencing of words and ideas and is considered the 'seat' of language (1). In fact, through MRI scans, it has been recognized that one of the areas of the brain used to decipher language may also 'contain' the ability to conceive absolute pitch. This area, known as the planum temporale is not only used to decipher absolute pitch (for those with this skill), but it is also larger in individuals who have absolute pitch (3). Interestingly, abnormality in this area is presumed to be the cause of developmental dyslexia (4). From this information, it can be inferred that music and language may be interpreted and deciphered in similar ways as well as by similar brain structures. This may explain why, in some experiments, it has been found that prenatal exposure to music has produced an acceleration in the development of behaviors related to the acquisition of language (such as babbling) (5). Conversely, damage to areas of the brain involving language may also impair musical interpretation as well as the effects of music on cognition.

For the brain, and specifically the auditory cortex, to assimilate notes and melodies, both long-term and short-term memory as well as learning processes are thought to be involved. Although the auditory cortex does have some capabilities of short-term memory of musical line, long term memory is important in relating different musical pieces to one another as well as differentiating between different styles of music (1). The hippocampus (located below the auditory cortex) is implicated in this task. It is presumed that listening to music integrates the function of both the auditory and memory/learning related structures in the brain such as the hippocampus. The hippocampus is also implicated in many learning tasks which relate to spatial-temporal orientation (4). This may shed some light on the recent experimental observations obtained regarding the effects of classical music composed by Mozart.

It has been observed that animals exposed to Mozart (as opposed to other or no auditory stimulation) completed spatial mazes faster and with fewer errors (3) . From these observations, it is has been theorized that music and spatial temporal reasoning may activate the same neural pathways in the hippocampus of the brain (3). It could be argued that listening to and interpreting music with complex patterns activate the neuronal pathways in the hippocampus, which can lead to an increased efficacy of the neurons. The increase in the efficacy of neurons, may in turn encourage the formation of new synaptic connections. This touches upon the idea of physical contiguity, where signals can from one place to another only if there are synaptic connections between the two areas. In terms of this principal, it has been proposed that musicians (who both extensively listen and perform music) may possess a larger number of biochemical links or pathways between and within structures in the brain that are common to everybody (3).

The priming and involvement of learning and memory structures in the processing music can also be supported by anecdotal evidence. For example, many Alzheimer's patients have been known to 'retrieve' lost memory through listening to particular types of music (3) . It seems that processing music involves the use of memory and also aids in the retrieval of past memories. From this, it may be speculated that there is a strong connection between memory centers of the brain as well as those that process music. Another interesting effect of music is observed in patients with Parkinson's (3). Some immobile patients have been observed to get up and walk around when the 'right' kind of music is playing. This implies that particular kinds of music can elicit complex motor behavior . Whether this response is due to the musical memory which serves to prompt the retrieval of a lost 'motor score' is unknown. It has been experimentally shown, however, that certain types of music can synchronize brain waves (6), which may, in turn, aid synchronizing neural patterns involved in complex behavior such as walking or running. This particular observation may also implicate the possibility of emotional arousal produced by music which may ultimately cause both the retrieval of memories and the volition for movement.

The involvement of emotion in the process of interpreting music is also very important in the effect of music on the brain. It has been established that certain melodic and harmonic elements may prove more pleasing to the brain. The brain is mainly an organizer. Information that is organizeable normally produces some sort of pattern or structure. In music, pattern and structure are greatly related to the contour and line of melodies. It is interesting to note that contiguous notes (those that remain close together) demonstrate successful melodies (1). It seems that this type of line or contiguity is not only anticipated but pleasure provoking due to the fact that it is organizeable by the brain(1).

The pleasing effect of melodies and harmonies are mediated by personal as well as cultural preference. It has been theorized that individuals are greatly influenced by the tones found in their native language which in turn influence their native music. This may imply that individuals raised in different cultures have brains which are 'wired' to respond to different melodic/ harmonic contours and lines (3). Similarly, varying neuronal contiguity would theoretically dictate which lines are thought to be organizeable and anticipated by the brain. Hence, the emotions provoked would also vary based on the fulfillment of the anticipated harmony (1). As such, it could be that melodies are first processed, at the same time they are remembered, and finally organized to produce an emotional (i.e.-physiological) response based on the fulfillment of anticipatory harmonic balance.

As it might be suspected, in order for music to provoke an emotional response, the areas used in deciphering, learning, and remembering music must be connected or related to areas of the brain which produce a emotional responses. In this case, the areas of the brain which have been implicated are the frontal lobes and limbic system. Liking certain types of music also depends on the state of emotional arousal which they exhibit (5). Exciting and festive music has been observed to be both well-liked and arousing (5). The root cause of liking and disliking as well as pleasurable effects of music are currently associated with the production of endorphins.

Anecdotal evidence seems to imply that music and activate areas of the limbic system which are important in producing arousing as well as pleasurable effects. In fact, it has been observed that music which increases arousal (is 'uplifting') activates areas in the limbic system which release endorphins. This release in endorphins has been observed to combat certain forms of depression such as SAD (seasonal affective disorder) (6). Similar observations display a physiological effect which would signal a positive emotional state but are not strong enough to elicit a conscious effect in the alleviation of depressive symptoms (5). This information provides intriguing possibilities in the way of musical therapy. What seems key in the emotional response is the integration of all of the areas of the brain involved in the processing of music. If one area is in dysfunction, then the effects of music are lost. As it can be seen, the losses are immense, considering the known and unknown mechanisms in the brain involved in the processing of music.

Sources

1)Jourdain, Robert. Music, the Brain, and Ecstasy: How Music Captures Our Imagination. New York: William Morrow and Company, 1997.

2) Audesirk, Gerald and Teresa. Biology: Life on Earth (fourth edition). New Jersey: Prentice Hall, 1996.

3) Gray Matters: Music and the Brain, TV and Radio Transcripts

4)Physiology of Behavior (sixth edition). Massechusettes: Allyn and Bacon, 1998.

5)Musica Research Notes, 1996, 1998, 1999

6)Braintuning News and Braintuning quiz answers




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