Stimulus-specific adaptation detects sound novelty in macaque A1
The question of how the auditory system is able to automatically track unattended background sounds and detect novelty therein is one of the most intriguing ones in cognitive neuroscience. Electroencephalography and magnetoencephalography studies in humans have extensively documented associations between differential auditory cortex responses to sounds deviating from background stimulation (a.k.a. mismatch negativity responses) and the extent that these deviations in stimulation penetrate into the awareness of the subjects as reflected by disruptions of ongoing task performance. The underlying neural mechanisms have, however, been an issue of controversy, with a number of studies suggesting that stimulus-specific adaptation could serve as a relatively simple and ecological neurophysiological automatic sound deviance screening mechanism, and other studies arguing that there must be some other, more complex, mechanisms at play.
In their recent study, Fishman and Steinschneider (2012) studied carefully the underlying neural mechanisms by recording macaque primary auditory cortex responses to frequently repeating “standard” sounds and infrequently occurring “deviant” sounds in a conventional oddball paradigm and various control conditions. Taken together, their results suggest that stimulus-specific adaptation underlies detection of deviations in ongoing auditory stimulation in the macaque primary auditory cortex. The authors caution that their recordings were confined within the macaque A1, and thus there could always be other mechanisms at play in secondary auditory cortical areas that should be investigated in future studies. These findings are highly significant in that they bridge the gap between human mismatch negativity research and animal models. Indeed, it is fascinating to think that a relatively simple adaptation mechanism could underlie the relatively complex perceptual-cognitive level phenomena that the mismatch negativity response has been associated with, including auditory sensory memory and involuntary attention.
Reference: Fishman YI, Steinschneider M. Searching for the mismatch negativity in primary auditory cortex of the awake monkey: deviance detection or stimulus specific adaptation? Journal of Neuroscience (2012) 32: 15747–15758. http://dx.doi.org/10.1523/JNEUROSCI.2835-12.2012