Abstract
Despite the ancestral evidence of an asymmetry in motor predominance, going through the inspiring discoveries of Broca and Wernicke on the localization of language processing, continuing with the subsequent noise coinciding with the study of brain function in commissurotomized patients—and the subsequent avalanche of data on the asymmetric distribution of multiple types of neurotransmitters in physiological and pathological conditions—even today, the functional significance of brain asymmetry is still unknown. Currently, multiple evidence suggests that functional asymmetries must have a neurochemical substrate and that brain asymmetry is not a static concept but rather a dynamic one, with intra- and inter-hemispheric interactions between its various processes, and that it is modifiable depending on changing endogenous and environmental conditions. Furthermore, based on the concept of neurovisceral integration in the overall functioning of an organism, some evidence has emerged suggesting that this integration could be organized asymmetrically, using the autonomic nervous system as a bidirectional communication pathway, whose performance would also be asymmetric. However, the functional significance of this distribution, as well as the evolutionary advantage of an asymmetric nervous organization, is still unknown.
Highlights
If we briefly review the milestones in the knowledge of brain asymmetry, we could first highlight motor strength and ability
The lizard, like humans and other primates, alternates ovulation between the left and right ovary. These results somehow take us beyond simple brain asymmetry, suggesting a neurovisceral integration, mediated, in part and in these cases, hormonally
From all the reported studies, we can clearly establish the existence of a cerebral asymmetry that extends to an asymmetric neurovisceral integration in which a neurochemical asymmetry underlies, but we can conclude that this asymmetry changes neurochemically and functionally depending on the modification of multiple endogenous and exogenous factors
Summary
The concept of neurovisceral integration comes from Claude Bernard [1], developed more recently by Thayer and Lane [2]. The lizard, like humans and other primates, alternates ovulation between the left and right ovary These results somehow take us beyond simple brain asymmetry, suggesting a neurovisceral integration, mediated, in part and in these cases, hormonally. Its functional meaning remains to be elucidated In any case, these data suggest that handedness is integrated into a broader and more complex biological context, as we will see throughout this review. Roger Sperry, who received the Nobel Prize in 1981 [25] for their discoveries regarding the functional specialization of the cerebral hemispheres They carried out their study largely in commissurotomized patients, in which the corpus callosum—as the main bundle of fibers that connects both hemispheres—had been sectioned to alleviate the consequences of massive epileptic seizures. From studies in split brains, Michael Gazzaniga speaks about two brains in one head, but connected to each other, informing and influencing each other, leading to integrated cognitive processing [24]
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