Transcript SYLVIAN FISSURE ASYMMETRY IN NORMAL YOUNG ADULTS …

LATERAL ASYMMETRY IN SHAPE OF HESCHL’S GYRUS
C.M. Leonard, S.D. Towler, S. Welcome, L. Halderman, R. Otto, C. Chiarello
Department of Neuroscience, McKnight Brain Institute, University of Florida, Gainesville,
Department of Psychology, University of California, Riverside & MRI Diagnostic Imaging Center, Riverside CA
# 850.14
Examples
Background
There is considerable evidence that the left and right auditory systems are specialized for the
detection of different auditory cues. Such specialization has a long evolutionary history as rodents also
show evidence of lateralized strategies for detecting specific auditory cues (Fitch et al. 1993; Wetzel et al.
2008). In humans the left hemisphere is specialized for temporal processing while the right hemisphere
favors pitch or spectral processing. (Liegeois-Chauvel et al. 1999; Robin et al. 1990) More recently it has
been found that in the right but not the left planum temporale, activation to different pitches is
proportional to the distance between them (Hyde et al. 2008) while activation to rapid formant transitions
(Belin et al. 1998; Liegeois-Chauvel et al. 1999) and auditory streaming (Deike et al. 2004) is higher in
left auditory cortex.
There is a very reliable difference in the size of Heschl’s gyrus (HG) in the two hemispheres (Leonard
et al. 1998; Penhune et al. 1996) and the size of the left Heschl’s gyrus predicts the ease with which
English speakers can learn to use the pitch patterns of a foreign language for word identification (Wong
et al. 2008). There is growing evidence for localized specializations in HG. Primary auditory cortex is
restricted to the posterior medial portion (Liegeois-Chauvel et al. 1991), a correlate of pitch salience has
been found in a small region of nonprimary auditory cortex on the anterolateral margin of HG (Penagos et
al. 2004) and an MR correlate of koniocortex (primary cortex) is more extensive in the left HG than the
right, suggesting greater myelination (Sigalovsky et al. 2006).
Here we report evidence for two anatomical specializations which are more frequent in HG in the left
hemisphere. In each case a large Heschl’s gyrus is deformed slightly, either by an indentation in the
superior surface (“heart”) or an elongated Heschl sulcus that causes an asymmetrical stretching in the
posterior direction. We have named this second specialization “snoopy” because of its’ distinct
resemblance to Schultz’ famous beagle.
Left hemisphere: Twelve examples of Heschl’s Gyri) that were classified as “heart.” Best examples
are inside red ellipses. Key features are the pinched neck joining the gyrus to the superior temporal plane
and the indentation in the crown. Hearts are found more frequently in the left hemisphere. The two sides
of the heart rarely become two separate HG.
Left hemisphere: Twelve examples of Heschl’s Gyri that were classified as “snoopy.” Key feature is the
elongated Heschl’s sulcus. Snoopies are found more frequently in the left hemisphere. They are a transient
feature. The examples chosen were randomly selected. The best examples are encircled.
The examples chosen were randomly selected. In these images the cortical ribbon (gray matter) is white and white matter is black.
The brightness of each pixel represents the probability that the voxel contains gray matter (partial volume estimate (PVE) image). Anterior is to the left.
Method
200 college students were recruited for a study comparing asymmetries in linguistic processing and
brain structure. They received volumetric (MPRage) brain scans in a 1.5 T GE scanner in Riverside CA.
The images were sent to UF and processed with FSL software. The surface area and volume of Heschl’s
gyrus were measured on consecutive 1 mm thick sagittal images between 40 and 44 mm (normalized for
brain width) from the midline by raters blind to hemisphere and subject id. Each image was categorized
as either round, multiple (mult), heart or snoopy (see examples below) and then a summary
categorization was mad. Chi square analyses tested if the ratings differed by hemisphere, sex,
consistency of hand preference or reading skill.
Left
Heart
Right
Snoopy
Round
Multiple
Results and Discussion
Graph at left shows a striking hemispheric asymmetry in
Heschl’s gyrus morphology that is independent of medial –
lateral position between 40 and 44 mm lateral to the midline
(more laterally, HG loses definition and merges with the
superior temporal gyrus). On the right, round and multiple
are most frequent, while on the left, hearts and snoopies are
most frequent. Chi square analysis demonstrated significant
asymmetry at all lateral positions, p < .0001. There were no
significant associations with sex, hand preference, reading
skill or visual field asymmetry.
A search of the literature was unsuccessful in locating earlier discussions of these asymmetries. In our
previous studies we failed to distinguish between hearts and other forms of multiple HG that are more
frequent on the right. These asymmetries do not appear to be limited to this particular sample as they have
been found in three other samples (Leonard unpublished data).
Given the speculation that gyral morphology reflects early developmental gradients and axonal
trajectories it is tempting to speculate that some functional asymmetries are associated with these
morphological specializations. This idea could be tested with individualized fMRI investigations.
Right hemisphere: Twelve examples of Heschl’s Gyri that were classified as “heart.” The examples
were randomly selected. Squares designate the best examples. Note that most right hemisphere HG that
were classified as hearts lack the pronounced indentation and narrowed neck seen in the left hemisphere.
Anterior is to the right.
Right hemisphere: Twelve examples of Heschl’s Gyri that were classified as “snoopy.” The examples
chosen were randomly selected. Squares designate the best examples. Note that few right hemisphere
snoopies have the pronounced elevation or asymmetry that characterizes left hemisphere examples.
References
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Belin P, Zilbovicius M, Fontaine A et al. Lateralization of speech and auditory temporal processing. Journal of Cognitive Neuroscience 1998; 10:536-40.
Deike S, Gaschler-Markefski B, Brechmann A et al. Auditory stream segregation relying on timbre involves left auditory cortex. Neuroreport 2004; 15 (9):1511-4.
Fitch RH, Brown CP, O'Connor K et al. Functional lateralization for auditory temporal processing in male and female rats. Behavioral Neuroscience 1993; 107:844-50.
Hyde KL, Peretz I, Zatorre RJ. Evidence for the role of the right auditory cortex in fine pitch resolution. Neuropsychologia 2008; 46 (2):632-9.
Leonard CM, Puranik C, Kuldau JM et al. Normal variation in the frequency and location of human auditory cortex landmarks: Heschl's gyrus: Where is it? Cerebral Cortex 1998; 8:397-406.
Liegeois-Chauvel C, de Graaf JB, Laguitton V et al. Specialization of left auditory cortex for speech perception in man depends on temporal coding. Cereb Cortex 1999; 9 (5):484-96.
Liegeois-Chauvel C, Musolino A, Chavel P. Localization of the primary auditory area in man. Brain 1991; 114:139-53.
Penagos H, Melcher JR, Oxenham AJ. A neural representation of pitch salience in nonprimary human auditory cortex revealed with functional magnetic resonance imaging. J Neurosci 2004; 24 (30):6810-5.
Penhune VB, Zatorre RJ, MacDonald JD et al. Interhemispheric anatomical differences in human primary auditory cortex; probabilistic mapping and volume measurement from magnetic resonance scans. Cerebral Cortex 1996; 6:661-72.
Robin DA, Tranel D, Damasio H. Auditory perception of temporal and spectral events in patients with focal left and right cerebral lesions. Brain and Language 1990; 39:539-55.
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Sigalovsky IS, Fischl B, Melcher JR. Mapping an intrinsic MR property of gray matter in auditory cortex of living humans: a possible marker for primary cortex
and hemispheric differences. Neuroimage 2006; 32 (4):1524-37.
Upadhyay J, Ducros M, Knaus TA et al. Function and connectivity in human primary auditory cortex: a combined fMRI and DTI study at 3 Tesla. Cereb Cortex 2007; 17 (10):2420-32.
Wetzel W, Ohl FW, Scheich H. Global versus local processing of frequency-modulated tones in gerbils: an animal model of lateralized auditory cortex functions. Proc Natl Acad Sci U S A 2008; 105 (18):6753-8.
Wong PC, Warrier CM, Penhune VB et al. Volume of left Heschl's Gyrus and linguistic pitch learning. Cereb Cortex 2008; 18 (4):828-36.
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This research was supported by NIDCD grant no R01 006957.