All Jazzed Up: Looking for a Jazz Center Within the Folds of the Brain
Before talking about these brain areas it is important to understand the basics of brain mapping.
Much of our modern understanding of localizationwhere major functions are located in the braincomes from the work of German Neurologist Korbinian Brodmann who, in 1909, published a treatise in which he identified 52 distinct areas on the surface or cortex of each hemisphere of the brain, based on the type of cells and the way they were structured into layers. The brain is made up of two hemispheresa dominant and non-dominant onethat are mirror images of each other. Dominance is purely based on where language is localized and, in over 90% of the population (all right handed and ambidextrous and 50% of left handed people), it is in the left one.
Some of the Brodmann areas were later found to have distinct functions. Areas 41-42 are now known to be the areas responsible for hearing. These areas are not only the primary relay for sound, but they also communicate with areas of language understanding (Wenicke's area), language production (Broca's area), and their corresponding areas on the right. In addition, they have a close relationship with the secondary auditory area or the supramarginal gyrus (area 40), and the tertiary auditory area or the angular gyrus (area 39). See Figure 1 for a map of where these areas are located.
The primary auditory area identifies the fundamental elements of music such as pitch and loudness and the secondary area processes the harmonic and melodic patterns, while the tertiary area is more concerned with the overall music appreciation. Incidentally, this is also the area responsible for higher processing of language and mathematics. These areas also link to the Limbic system (figure 1b), which is responsible for emotions and, hence, the emotional impact of music.
Generally speaking, rhythmthe relative duration and distribution of notesis perceived in the left or dominant areas 41-42, when the sounds are brief, but tends to involve the corresponding regions in the non-dominant hemisphere, when the sounds are longer. Harmonythe relation of simultaneous tones to each other---and timbrethe specific difference in sound of more than one instrument playing the same notesare usually assigned to the non-dominant hemisphere.
The advent of functional magnetic resonance imaging (fMRI), a scientific tool that is able to map brain function and superimpose it on brain structure, has helped scientists identify yet another area that becomes active in music appreciation: Brodmann area ten, or the rostromedial prefrontal cortex, which is usually involved in high level planning, executive function and memory. Furthermore, there is evidence that when a listener expresses enjoyment, the regions of the brain usually associated with sexual and food pleasure and addiction also activate. Therefore, music appreciation involves processes of memory, emotion and higher mental functioning, in a way unifying all levels of brain activity into an integrated whole. Interestingly, people exhibit the same response whether they are actually listening to or imagining music (playing a song in their head).
This is obviously a very simplified version of a complex and dynamic phenomenon.
So what happens in the brains of musicians? Studies utilizing fMRI have shown that musicians activate a larger area of their dominant hemisphere's primary auditory areas than non-musicians when listening to music, but not when listening to other sounds. Other studies have also demonstrated that, in fact, not only do musicians activate greater parts of their auditory areas, but they also have larger auditory areas where size is commensurate with level of training. Moreover, other parts of brain involved in coordination and manual dexterity also are larger in musicians than they are in non-musicians, and the size again correlates with years of experience.
What about jazz and improvised music? A recent discovery demonstrated that certain brain regions are more active, and others virtually shut down when improvising, as opposed to playing a preset series of notes. Areas of the brain involved in planning, monitoring one's self and self-censorship are virtually shut down, while areas involved in storytellingand those involved in risk taking and intense pleasureshow increased activation.