Neuromagnetic Evidence for a Pitch Processing Center in Heschl's Gyrus

Abstract

There have been several attempts to use the neuromagnetic response to the onset of a tonal sound (N100m) to study pitch processing in auditory cortex. Unfortunately, a large proportion of the N100m is simply a response to the onset of sound energy, independent of whether the sound produces a pitch. The current study describes a novel stimulus paradigm designed to circumvent the energy-onset response and thereby isolate the response of those neural elements specifically involved in pitch processing. The temporal resolution of magnetoencephalography enables us to show that the latency and amplitude of this pitch-onset response (POR) vary with the pitch and pitch strength of the tone. The spatial resolution is sufficient to show that its source lies somewhat anterior and inferior to that of the N100m, probably in the medial part of Heschl's gyrus.

Human Auditory Cortical Processing of Transitions Between ‘Order’ and ‘Disorder’

“…Interestingly, these transition responses are similar to the properties of the 'pitch onset response' (POR; Krumbholz, Patterson, Seither-Preisler, Lammertmann and Lütkenhöner 2003;Gutschalk, Patterson, Scherg, Uppenkamp, and Rupp 2004;Ritter, Gunter Dosch, Specht and Rupp 2005;Chait, Poeppel and Simon 2006). The POR, hypothesized to reflect cortical pitch processing mechanisms, is evoked by transitions between irregular click trains, which do not have a pitch and regular click trains which are perceived to have a sustained temporal pitch (Gutschalk et al, 2004) or by transitions between white noise and iterated rippled noise (Krumbholz et al, 2003).…”

“…The POR, hypothesized to reflect cortical pitch processing mechanisms, is evoked by transitions between irregular click trains, which do not have a pitch and regular click trains which are perceived to have a sustained temporal pitch (Gutschalk et al, 2004) or by transitions between white noise and iterated rippled noise (Krumbholz et al, 2003). However, it is also possible to describe the shift as a transition between states that differ along a more abstract dimension, such as degree of 'regularity' or 'order'.…”

Functional imaging of the auditory processing applied to speech sounds

“…So, while it is the case that the latency of the N100m varies with pitch, the response is fundamentally confounded with the activation of other generators that reflect features like loudness and timbre rather than pitch. To isolate the pitch component of the N100m, Krumbholz et al (2003) developed a continuous stimulation technique in which the sound begins with a stationary noise and then, after a second or so, when the N100m has passed and the AEF has settled into a sustained response, the fine structure of the noise is regularized to produce a RI sound (RIS) without changing the energy or spectral distribution of the energy. There is a marked perceptual change at the transition from noise to RIS, and it is accompanied by a prominent negative deflection in the magnetic field, referred to as the pitch onset response (POR).…”

Competition Between Cortical Ensembles Explains Pitch-Related Dynamics of Auditory Evoked Fields

“…In order to assess quantitatively the relation between the N100m and the model's output, we computed the latency of the component for pure tones and HCTs and compared them with available results in the literature [5,7,8]. Results are shown in Figure 4.…”

“…The exact N100m's latency is correlated with the perceived pitch of a wide range of stimuli [5,7,8], suggesting that the cortical source of the transient component has an important role on the processing of pitch in auditory cortex [9]. However, the biophysical substrate of the relationship between pitch decoding and the N100 morphology remains an enigma.…”