Sunday, December 21, 2008

There’s more to auditory cortex than meets the ear

Zatorre, Robert J. (2007) “There’s more to auditory cortex than meets the ear” Hearing Research 229 (2007) 24-30

Sharon Dutton

Dr. Zatorre’s paper challenges us to think outside of traditional definitions, particularly of the auditory cortex, which, he states, are based “either on anatomical criteria, as the cortex which receives input from the medial geniculate, or physiologically as the cortex containing neurons responsive to acoustic stimulation” (p 1). Such definitions were previously useful, but a more currently apt description needs to incorporate a sense of complex relational interactions.

Dr. Zatorre identifies three influences or variables that affect the patterns of activity in the auditory cortex. The first is memory, or prior learning and experiences, which may assign or associate meaning to the auditory stimulus, and which consequently affects the manner in which physical sounds are processed. The second factor is attention, which, Zatorre claims, has been known to affect responses, specifically; “evoked responses are larger to attended than to unattended stimuli” (p 3). Of particular note (to music teachers), “One of the more consistently reported interactions involving auditory cortex is that it often shows decreases in activity (relative to a no-stimulus baseline) in the presence of a visual stimulus”.1 However, he notes that the opposite can also be true, that “presentation of an auditory signal recruits some visual cortical areas, rather than inhibiting them” .2

The third influencing factor is imagery, or the ability of the brain to imagine sounds when they don’t actually exist. The auditory cortex becomes engaged while there is no actual auditory stimulus. Clearly, this occurs because of activity in other regions of the brain, and Dr. Zatorre cites lip-reading, as an example. Dr. Zatorre cites several research studies that support the relational aspect of the auditory cortex, and likely of the rest of the brain, (and the organism, and the planet). The traditional approach to understanding the brain in terms of anatomy and function does not accommodate these three capacities; memory, attention, and imagery. Considering the auditory cortex “in terms of its position in a distributed system, rather than in isolation” (p 2) is crucial to advancing our understanding of its role.


In his discussion, Dr. Zatorre concludes that “one cannot consider sensory systems as isolated processors; instead, they exert mutual, reciprocal influences” (p 4). This suggestion is becoming rather common among scientists. Whereas modern scientific truths are based on objectifying, deconstructing, rationalizing and verifying the nature of the world, Eastern, artistic, and ancient views of reality emphasize understanding relationships between earthly beings, between our own bodies, minds, and spirits, and between our past, the present and the future. Rather than objectifying the auditory cortex, as traditional Western science and philosophy would have us do, he is suggesting that we approach it with a consideration for its relationship with other stimuli.

Science is entering the realm of qualitative research, of understanding a thing in its entirety, not only its function and physical presence, but its relationship to everything else, including its past and future existence. We can ever entirely know anything; we can only know what we think we know; therefore, what we think we know needs to be questioned. Such is the craft of the bricoleur, to always question our assumptions, remaking them anew as our knowledge and understanding grows. By approaching a subject from yet another point of view, we advance our understanding of it, specifically as it exists in relation to our other constructs. In a healthy brain, nothing is isolated. Every thought, every impulse, every perception exists in tandem with everything else, and all activity seems to be known simultaneously – even, in some cases, anticipated – by every other activity.

1 Laurienti, P., Burdette, J., Wallace, M, Yen, Y.-F., Field, A., Stein, B. (2002)"Deactivation of sensory-specific cortex by cross-modal stimuli". Journal of Cognitive Neuroscience 14, 420-429
Zatorre, R.J., Mondor, R.A., Evans, A.C. (1999) "Functional activation of right parietal and frontal cortex during auditory attention to space and frequency" Neuroimage 10, 544-554
2 Zatorre, R.J., Evans, A.C., Meyer, E., (1994) "Neural mechanisms underlying melodic perception and memory for pitch" Journal of Neuroscience 14 (4), 1908-1919

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