Interhemispheric Anatomical Differences in Human Primary Auditory Cortex: Probabilistic Mapping and Volume Measurement from Magnetic Resonance Scans

Abstract

The gyral morphology of the region of the primary auditory cortex (PAC) in the human brain is highly variable, and possible asymmetries between the hemispheres have been noted since the beginning of the century. We mapped the location and extent of PAC as identified from gross anatomical landmarks in magnetic resonance scans that had been transformed into Talairach-Tournoux stereotaxic space. Individual maps were averaged to produce a probabilistic map of the region which can be co-registered with any image of brain structure or function that has been similarly transformed. The map can be used to localize a region of interest, such as a lesion, or an activation focus from position omission tomography or functional magnetic resonance imaging, within a specified range of probability. We also measured the total volume of the region and found a significant L > R asymmetry both on average and in the majority of subjects. Automatic segmentation of the volumes into grey and white matter revealed larger volumes of white, but not grey matter on the left. This larger volume of cortical connecting fibres may be related to the known left-hemisphere dominance for speech, and a preferential role for left PAC in processing temporal aspects of auditory stimuli is suggested.

Illusory Vowels Resulting from Perceptual Continuity: A Functional Magnetic Resonance Imaging Study

“…By contrasting signal strength of illusory speech-like sounds (illusion) with acoustically very similar nonspeech sounds (illusion break) in the core (primary) auditory cortex and speech areas (speech ROI), we can perhaps identify functionally distinguishable regions in the auditory cortex. To do this, we first estimated the coordinates of HG by averaging across four separate estimates of the center of either HG (Patterson, Uppenkamp, Johnsrude, & Griffiths, 2002;Penhune, Zatorre, MacDonald, & Evans, 1996) or cytoarchitectonically defined the PAC Rademacher et al, 2001). All four sets of coordinates are published in Patterson et al (2002, Table 1).…”

Estudo da vantagem da orelha direita em teste de detecção de gap

“…28 The primary auditory cortex is located approximately in half of the first gyrus or in half of the first gyrus and in part of the second gyrus; it covers about the central two thirds of Heschl's gyrus. 25,[28][29][30] Many studies have demonstrated the existing asymmetry between the right and left Heschl's gyruses. The left gyrus is larger than the right gyrus; thus, the left primary auditory cortex is also larger than the right primary auditory cortex.…”

“…The increased left size volume results from more gray and white matter present in this side. 28,31,32 The larger neural substrate (more neurons and more intra-and interhemispheric interconnections) in these left hemisphere anatomic structures provides the basis for better language development compared to the corresponding (smaller) areas in the right side. 32 Left hemisphere speech specialization may be related to an identification of specific acoustic parameters for sound and speech discrimination.…”

An MRI study of spatial probability brain map differences between first-episode schizophrenia and normal controls

“…Accordingly, many groups have noted the importance of probabilistic atlases and have made probability maps using different modalities and different methodologies. Probability maps for subregions of normal brains have been reported (Amunts et al, 1999(Amunts et al, , 2000Kennedy et al, 1998;Leonard et al, 1998;Loftus et al, 1995;Paus et al, 1996;Penhune et al, 1996;Rademacher et al, 2001aRademacher et al, ,b, 2002Thompson et al, 1996a;Tomaiuolo et al, 1999;Varnavas and Grand, 1999;Westbury et al, 1999;White et al, 1997).…”

“…Probability maps of planum temporale and primary auditory cortex, using MRI parcellations (Penhune et al, 1996), and primary auditory cortex, using cytoarchitectonic parcellations (Rademacher et al, 2001b), have been published for normal control subjects. However, little is known of the anatomical and distributional abnormalities in these areas and, to our knowledge, no probability maps have been created based on manually delineated ROIs in first-episode schizophrenia.…”