Functional Imaging Reveals Numerous Fields in the Monkey Auditory Cortex

Abstract

Anatomical studies propose that the primate auditory cortex contains more fields than have actually been functionally confirmed or described. Spatially resolved functional magnetic resonance imaging (fMRI) with carefully designed acoustical stimulation could be ideally suited to extend our understanding of the processing within these fields. However, after numerous experiments in humans, many auditory fields remain poorly characterized. Imaging the macaque monkey is of particular interest as these species have a richer set of anatomical and neurophysiological data to clarify the source of the imaged activity. We functionally mapped the auditory cortex of behaving and of anesthetized macaque monkeys with high resolution fMRI. By optimizing our imaging and stimulation procedures, we obtained robust activity throughout auditory cortex using tonal and band-passed noise sounds. Then, by varying the frequency content of the sounds, spatially specific activity patterns were observed over this region. As a result, the activity patterns could be assigned to many auditory cortical fields, including those whose functional properties were previously undescribed. The results provide an extensive functional tessellation of the macaque auditory cortex and suggest that 11 fields contain neurons tuned for the frequency of sounds. This study provides functional support for a model where three fields in primary auditory cortex are surrounded by eight neighboring “belt” fields in non-primary auditory cortex. The findings can now guide neurophysiological recordings in the monkey to expand our understanding of the processing within these fields. Additionally, this work will improve fMRI investigations of the human auditory cortex.

Orthogonal acoustic dimensions define auditory field maps in human cortex

“…Here, we report conclusive fMRI evidence for the existence of orthogonal tonotopic and periodotopic gradients forming complete AFMs in human core and belt auditory cortex. The presence of orthogonal gradients allowed the identification of 11 maps consistent with the human cytoarchitectural measurements (19)(20)(21)(22) and with proposed homology to the 11 core and belt auditory subfields in macaque auditory cortex (10,11,17,18). More broadly, we found that the 11 AFMs are organized into the radially orthogonal "clover leaf" clusters, similar to what has been reported as an organizing principle of VFMs in human visual cortex (4,6,7,9,(35)(36)(37).…”

“…In audition, there has been only one dimension of sensory topography clearly mapped in cortex, which makes it impossible to use sensory topography to accurately differentiate specific human cortical auditory field maps (AFMs). Current estimates of human AFMs rely primarily on a monkey model that is well characterized by cytoarchitectonics (10,11), single-and multiunit physiology (12)(13)(14)(15)(16), tracer studies (17), and functional magnetic resonance imaging (fMRI) (18). Human cytoarchitectonic measurements generally resemble those in macaque monkey and indicate that the small subfields of primary auditory cortex are confined to Heschl's gyrus (HG; or between HG-1 and HG-2, in cases where a double gyrus exists) and oriented medial to lateral along HG (19)(20)(21)(22).…”

“…1073/pnas.1213381109/-/DCSupplemental. TE = 3.7 ms, flip = 8°, SENSE factor = 2.4), one T1-weighted inplane anatomical scan to align the functional and anatomical data (1 × 1 × 3 mm voxels), and 12-16 functional auditory field mapping scans (T2-weighted, gradient echo imaging, TR = 10s, TA = 2s, TE = 30 ms, flip = 90°, SENSE factor = 1.7, reconstructed voxel size of 1.875 × 1.875 × 3 mm, no gap), with six to eight scans of narrowband noise for tonotopy in one session and six to eight scans of broadband noise for periodotopy in the other (SI Text).We used narrowband noise instead of pure tones because it has been demonstrated that narrowband noise in monkey fMRI drives voxels in auditory belt regions more robustly than do pure tones, without any cost in responses in auditory core (18,38). Our broadband noise stimuli were similarly modeled after those used in previous studies [ Fig.…”

Monkey drumming reveals common networks for perceiving vocal and nonvocal communication sounds

“…S4A). To further localize the caudal auditory region with respect to functionally defined auditory fields, we exploited a described mapping procedure, which provides a functional parcellation of auditory cortex based on the tonotopic organization of auditory fields (30). This positioned the region of overlapping activations as within the caudal belt (caudo-medial and caudo-lateral fields), but also extending into primary field A1 and the caudal parabelt (including region Tpt), a location that is consistent with a vocalizationsensitive region reported in a previous study (16).…”

From sounds to words: A neurocomputational model of adaptation, inhibition and memory processes in auditory change detection

“…We defined as "active" any link from a cell x such that the output O(x,t) of cell x at time t is larger than θ pre , where θ pre ∈]0,1] is an arbitrary threshold representing the minimum level of presynaptic activity required for LTP (or LTD) to occur. Thus, given any two cells x and y linked with weight w t (x,y), the new weight w t+1 (x,y) is calculated as follows: (Romanski et al, 1999;Petkov et al, 2006) indicates that the auditory system consists of three main areas, A1, AB and PB; although these systems have been studied mainly in macaques, homologous areas of the human auditory cortex (Brodmann Areas 41, 42 and 22) lend themselves to an analogous parcellation (Uppenkamp et al, 2006). …”