Cerebral Lateralization

Geschwind, Norman; Galaburda, Albert M.

doi:10.1001/archneur.1985.04060060019009

Cited by 896 publications

(39 citation statements)

References 369 publications

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“…One problem for estimating hemispheric asymmetry in non-epileptics from these studies is that, of course, many people suffering from severe epilepsy will have had congenital abnormalities, which may in some instances at least, lead to a change in speech and language dominance from one hemisphere to another. Of course, this caveat should apply to the estimates of speech dominance in the dextrals as well as the adextrals (assuming, probably wisely, that epileptogenic foci are rather agnostic about which hemisphere they choose to appear in), unless of course a more complicated “pathological left handedness” argument is made (e.g., Geschwind and Galaburda, 1985a,b,c). Claims for increased incidence of adextrality in epilepsy are extremely common.…”

Section: Discussionmentioning

confidence: 99%

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

2014

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Speech and language-related functions tend to depend on the left hemisphere more than the right in most right-handed (dextral) participants. This relationship is less clear in non-right handed (adextral) people, resulting in surprisingly polarized opinion on whether or not they are as lateralized as right handers. The present analysis investigates this issue by largely ignoring methodological differences between the different neuroscientific approaches to language lateralization, as well as discrepancies in how dextral and adextral participants were recruited or defined. Here we evaluate the tendency for dextrals to be more left hemisphere dominant than adextrals, using random effects meta analyses. In spite of several limitations, including sample size (in the adextrals in particular), missing details on proportions of groups who show directional effects in many experiments, and so on, the different paradigms all point to proportionally increased left hemispheric dominance in the dextrals. These results are analyzed in light of the theoretical importance of these subtle differences for understanding the cognitive neuroscience of language, as well as the unusual asymmetry in most adextrals.

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Section: Discussionmentioning

confidence: 99%

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

2014

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“…It has been shown that the magnitude, if not also the direction, of cortical asymmetry predicts the relative numbers of neurons comprising a given pair of hemispheric architectonic homologs such that the more asymmetric the region is, the smaller the number of neurons (Geschwind and Galaburda, 1985a,b,c; Galaburda et al, 1990). Similarly, the more asymmetric a region is, the smaller the density of interhemispheric connections and (probably) the greater the density of intrahemispheric connections.…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, the more asymmetric a region is, the smaller the density of interhemispheric connections and (probably) the greater the density of intrahemispheric connections. In general, more symmetrical brains appear to have a larger corpus callosum and thus showed increased interhemispheric connectivity (Geschwind and Galaburda, 1985a,b,c; Galaburda et al, 1990; Aboitiz et al, 1992c; Dorion et al, 2000). For example, fewer callosal projections between the plana temporales were found when their minicolumn spacing was more asymmetrical (Chance et al, 2006) and there is a correlation between the magnopyramidal neuron density in the planum temporale and axon number in the isthmus of the corpus callosum and this correlation seems to be absent in schizophrenia (Simper et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

The hypothesis of neuronal interconnectivity as a function of brain sizeâ€”a general organization principle of the human connectome

Hänggi

Fövenyi

Liem

et al. 2014

Front. Hum. Neurosci.

118

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Twenty years ago, Ringo and colleagues proposed that maintaining absolute connectivity in larger compared with smaller brains is computationally inefficient due to increased conduction delays in transcallosal information transfer and expensive with respect to the brain mass needed to establish these additional connections. Therefore, they postulated that larger brains are relatively stronger connected intrahemispherically and smaller brains interhemispherically, resulting in stronger functional lateralization in larger brains. We investigated neuronal interconnections in 138 large and small human brains using diffusion tensor imaging-based fiber tractography. We found a significant interaction between brain size and the type of connectivity. Structural intrahemispheric connectivity is stronger in larger brains, whereas interhemispheric connectivity is only marginally increased in larger compared with smaller brains. Although brain size and gender are confounded, this effect is gender-independent. Additionally, the ratio of interhemispheric to intrahemispheric connectivity correlates inversely with brain size. The hypothesis of neuronal interconnectivity as a function of brain size might account for shorter and more symmetrical interhemispheric transfer times in women and for empirical evidence that visual and auditory processing are stronger lateralized in men. The hypothesis additionally shows that differences in interhemispheric and intrahemispheric connectivity are driven by brain size and not by gender, a finding contradicting a recently published study. Our findings are also compatible with the idea that the more asymmetric a region is, the smaller the density of interhemispheric connections, but the larger the density of intrahemispheric connections. The hypothesis represents an organization principle of the human connectome that might be applied also to non-human animals as suggested by our cross-species comparison.

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“…In an alternative model, W itelson and Now akowski (1991) proposed that testosterone mediates lateralisation of function in men through the pruning of axons in the corpus callosum , and that som e com pletely different mechanism operates in wom en, a theory that they interpreted to be consistent with a leftshift in both gay m en and lesbians. Geschw ind and Galaburda (1985) invok ed the notion of``maternal stress' ' in com bination with testosterone levels to speculate on the possibility of a left-shift in homosexuals. These theories have been difficult to test experimentally.…”

Section: Discussionmentioning

confidence: 99%

A Crossover Interaction Between Sex, Sexual Orientation, and Handedness

Pattatucci¹,

Patterson²,

Benjamin³

et al. 1998

Laterality: Asymmetries of Body, Brain and Cognition

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The distribution of handedness scores was analysed in 1414 heterosexual, bisexual, and homosexual men and women. Hand preference was assessed by a questionnaire that distinguishes consistently right-handed from partially or completely left-handed individuals, and sexual orientation was measured by the Kinsey scales. As expected from population-based studies, heterosexual men were, on average, more left-handed than heterosexual women. By contrast, gay men were more right-handed than lesbians or heterosexual men, and lesbians were more left-handed than gay men or heterosexual women. This crossover interaction suggests that a common variable influences sex, sexual orientation, and hand preference.

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Cerebral Lateralization

Cited by 896 publications

References 369 publications

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

The hypothesis of neuronal interconnectivity as a function of brain sizeâ€”a general organization principle of the human connectome

A Crossover Interaction Between Sex, Sexual Orientation, and Handedness

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