Morphological Cerebral Asymmetries of Modern Man, Fossil Man, and Nonhuman Primate

Abstract

Cerebral asymmetries are common in modern and fossil man and the great apes. Those occurring most often are listed here: 1. The left sylvian fissure in man is longer than the right and in both fetal and adult brains the posterior end of the right sylvian fissure is commonly higher than the left. Associated with these findings, the left planum temporale is usually longer than the right. 2. The left occipital pole is often wider and usually protrudes more posteriorly than the right. 3. The left lateral ventricle, and especially the occipital horn, is usually larger than the right. 4. If one frontal pole extends beyond the other it is usually the right. 5. On X-ray computerized axial tomograms (CT) of the brain the right frontal lobe and the central portion of the right hemisphere more often measure wider than the left. 6. The CT studies commonly show a Yakovlevian anticlockwise torque (taking the nose as 12 o'clock), with the left occipital pole longer and often extending across the midline toward the right and a wider right hemisphere in its central and frontal portions and frequent forward protrusion of the right frontal pole. This is found also in newborns. 7. The posterior end of the sagittal sinus usually lies to the right of the midline and the sinus flows more directly into the right transverse sinus than into the left. 8. The right transverse sinus is usually higher than the left. 9. In left-handed and ambidextrous individuals the posterior ends of the sylvian fissures are more often nearly equal in height and the occipital regions are more often equal in width or the right may be wider. 10. The torque of the pyramidal tract and the hemispheral torque cannot at present be related to right- or left-handedness. Statistics concerning left-handedness are somewhat confounded, because it is likely that not a few individuals are left-handed because of an early injury of the left hemisphere in a normally right-handed individual. 11. Cerebral asymmetries are found in fossil man similar to those in modern man. 12. Asymmetries of the sylvian fissures similar to those of modern man have been found in the great apes and are particularly common in the orangutan. 13. The most striking and consistently present cerebral asymmetries found in adult and fetal brains are in the region of the posterior end of the sylvian fissures-- the areas generally regarded as a major importance in language function.

Endocast of Sambungmacan 3 (Sm 3): A new Homo erectus from Indonesia

“…Nevertheless, the features available on endocasts can provide some reasonable speculation as to the abilities of fossil individuals. The Sm 3 petalial pattern, while not distinct, suggests a torque pattern usually found in right-handed modern humans (LeMay, 1976). Such a pattern corroborates hemispheric dominance in H. erectus, albeit this is speculative.…”

“…Since Sm 3 only exhibits a clear right frontal petalia and no obvious occipital petalia, it is difficult to infer hemispheric dominance, and therefore handedness. Morphological data combined with the CT volumetric estimates, however, do indicate a left hemispheric dominance, suggesting a pattern consistent with right-handed individuals (Galaburda et al, 1978;LeMay, 1976LeMay, , 1977. Other Indonesian endocasts (Trinil 2, Sangiran 2) exhibit a left-occipital, right-frontal petalial pattern suggestive of right-handedness.…”

“…While the overall shape of the endocast is easily defined, the description of the petalial pattern possessed by Sm 3 is less straightforward. Using the petalial definitions set forth by LeMay (1976) and Holloway and de Lacoste-Lareymondie (1982) 2 , the Sm 3 endocast can be characterized as having a right frontal petalia with the right frontal wider from the midline to Broca's cap than the left (Fig. 3E).…”

“…These revised endocranial capacities and new measurements dismissed most of the gyral and sulcal interpretation attempted in early descriptions (e.g., Kappers, 1929;Kappers and Bouman, 1939). In addition, Holloway's observations of a left-occipital, right-frontal petalial pattern, and a well-developed inferior frontal region for Indonesian H. erectus, indicated possible cognitive lateralization (Holloway, 1980(Holloway, , 1981aLeMay, 1976). Despite the revised endocranial estimates and morphological observations of Indonesian H. erectus, one problem which has plagued the early Indonesian sample is a high degree of incompleteness.…”

Asymmetries of cortical shape: Effects of handedness, sex and schizophrenia

“…Welldocumented brain asymmetries identified in postmortem and imaging data include right frontal and left occipital hemispheric protrusions and petalias (LeMay, 1976;Chui and Damasio, 1980;Bear et al, 1986;Kertesz et al, 1990;Zilles et al, 1996), a leftward bias in the volume of the planum temporale, a posterior temporal lobe region and component of Wernicke's language area (Geschwind and Levitsky, 1968;Geschwind and Galaburda, 1985;Steinmetz, 1996;Shapleske et al, 1999), and hemispheric differences in Sylvian fissure (Galaburda et al, 1978;Ide et al, 1996;Thompson et al, 1998;Narr et al, 2001), planum parietale (Jancke et al, 1994) and parietal operculum (Habib et al, 1995) morphology. Asymmetries are also reported in anterior language-gifted cortices including the pars triangularis (Falzi et al, 1982;Foundas et al, 1998a;Amunts et al, 2003), the approximate site of Broca's area, the postcentral sulcus that marks primary sensory cortex (Hustler et al, 1998;Thompson et al, 1998;Narr et al, 2001), and motor cortex Zilles et al, 1996;Foundas et al, 1998b;Rademacher et al, 2001).…”