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VI. Life’s Cerebral Cognizance Becomes More Complex, Smarter, Informed, Proactive, Self-Aware

2. Laterality: A Bicameral Brain Emerges with the Nested Scales

    Another prime aspect of an oriented advance of cerebral topology and cognitive sentience is an asymmetrical brain with left and right hemispheres. Each bicameral half then has characteristic abilities of either fine detail or wider spatial focus which much serves sustenance and survival. Until recently these features were thought to only exist in humans. As major paradigm change, many research findings now identify the presence of similar bilateral qualities throughout the animal kingdom from primates to birds, reptiles, amphibians, and onto invertebrates and insects. Further studies trace this dual reciprocity to the earliest neural sensitivities. To this cover volume, we add Divided Brains (2013), Lateralized Brain Functions, (2017) and references herein to confirm this revolutionary and auspicious realization.


2020: Still another 21st century discovery of much import is the steady presence of a bilateral, hemispheric, archetypal endowment across every Metazoan creature. This common property was unknown before 2000 but has since been robustly verified from our human double brain through mammalian, avian, reptilian, and aquatic kingdoms all the way to insects and invertebrates. It is surmised that a broad reciprocal ability to peck for seeds with the right eye which informs the left side while the left view which goes to the right brain scans for predators is optimum for evolutionary survival. In regard this binocular quality of characteristic dot focus and holistic image to left and right hemispheres seems to hold through all past and present instances. And as this optimum bigender complementarity reaches our homo to anthropo to Earthomo sapience, a true microuniverse could be seen to ordain our cerebral capacity.

In this year, we have added a citation as Laterality Entering the Next Decade: The 25th Anniversary of a Journal Devoted to Asymmetries of Brain, Behavior and Cognition by Markus Hausmann, et al as a record of the consummate advances in this now universe to human study to an extent that, as its text says, a profound, salutary realization has been achieved.

Corballis, Michael and Isabelle Haberling. The Many Sides of Hemispheric Asymmetry. Journal of the International Neuropsychological Society. 23/9-10, 2017.
Forrester, Gillian, et al, eds. Cerebral Lateralization and Cognition. Progress in Brain Research. Volume 238, 2018.
Giljov, Andrey, et al. Facing Each Other: Mammal Mothers and Infants Prefer the Position Favouring Right Hemisphere Processing. Biology Letters. 14/1, 2018
Godfrey-Smith, Peter. Integration, Lateralization, and Animal Experience. Mind & Language. 36/2, 2021.
Gunturkun, Onur, et al.. Brain Lateralization: A Comparative Perspective. Physiological Reviews. 100/1019, 2020.
Hausmann, Markus, et al. Laterality Entering the Next Decade: The 25th Anniversary of a Journal Devoted to Asymmetries of Brain, Behavior and Cognition. Laterality. 26/3, 2021.
Letzner, Sara, et al. Visuospatial Attention in the Lateralized Brain of Pigeons. Nature Scientific Reports. 7/15547, 2017.
Moskovitz, Ted, et al. A Unified Theory of Dual-Process Control. arXiv:2211.07036.
Vallortigara, Giorgio and Lesley Rogers. A Function for the Bicameral Mind. Cortex. Online December, 2019.


Andics, Attila, et al. Neural Mechanisms for Lexical Processing in Dogs. Science. 353/1030, 2016. Within their Family Dog Project, Eotvos Lorand University, Budapest, researchers use MRI imaging to quantify that our canine companions are indeed able to understand when we often speak to them. This delightful achievement gained much press coverage for it quantifies why they seem so intelligent and responsive, as they are. Just as human brains, it is noted, use the left hemisphere for discrete words and the right for prosody rhythms, dogs avail the same asymmetry and synthesis. As a result, further evidence is affirmed of a consistent “functional analogy” across life’s evolution.

During speech processing, human listeners can separately analyze lexical and intonational cues to arrive at a unified representation of communicative content. The evolution of this capacity can be best investigated by comparative studies. Using functional magnetic resonance imaging, we explored whether and how dog brains segregate and integrate lexical and intonational information. We found a left-hemisphere bias for processing meaningful words, independently of intonation; a right auditory brain region for distinguishing intonationally marked and unmarked words; and increased activity in primary reward regions only when both lexical and intonational information were consistent with praise. Neural mechanisms to separately analyze and integrate word meaning and intonation in dogs suggest that this capacity can evolve in the absence of language. (Abstract)

Andrew, R., et al. Motor Control by Vision and the Evolution of Cerebral Lateralization. Brain and Language. 73/2, 2000. A research report on the ancient roots of complementary functions.

The specializations of the LES (left eye system) (right hemisphere) probably have continued to be shaped during evolution of vertebrates other than mammals by the fact the LE tends not to be used in viewing the immediate target of motor response, leaving the LES free to record environmental layout and contextual cues. (232)

Banich, Marie and Wendy Heller. Evolving Perspectives on Lateralization of Function. Current Directions in Psychological Science. 7/1, 1998. An introduction to a special issue on the subject, which reports the general consensus of finer or coarser modes for the brain hemispheres.

Rather, the left hemisphere may be better conceptualized as being specialized for processing information in a piecemeal, analytic, and sequential manner, which just happens to be a good method for processing verbal information, and the right hemisphere may be better conceptualized as being specialized for processing information in an integrative and holistic manner which just happens to be ideal for processing spatial information. (1)

Bisazza, Angelo and Culum Brown. Lateralization of Cognitive Functions in Fish. Brown, Culum, et al eds. Fish Cognition and Behavior. Oxford: Blackwell, 2011. In this compendium about fishy traits and schooling activities, a University of Padova comparative psychologist, and Macquarie University, Sydney, biologist thoroughly observe, as found in every other Metazoan class, the rudimentary neural architecture of fish similarly avails the evolutionary advantage of asymmetric cerebral faculties.

Butterworth, Brian, et al. Introduction: The Origins of Numerical Abilities. Philosophical Transactions of the Royal Society B. 373/1740, 2018. Butterworth, University College London, Claude Gallistel, Rutgers University, and Giorgio Vallortigara, University of Torento orient and survey 18 authoritative entries from a Royal Society meeting in February 2017 to discuss new findings about a common, innate ability of animals from early rudiments to primates and human children to estimate and count. Typical papers are The Deep History of Number Words, Numerical Assessment in the Wild, Evolution of Cognitive and Neural Solutions Enabling Numerosity Judgments, Understanding the Origin of Number Sense, Counting Insects, and Reassessing Lateralization in Calculation. The issue merited an article. Many Animals Can Count, Some Better Than You by Natalie Angier, in the New York Times for February 7, 2018.

Chernigovskaya, Tatiana. Evolutionary Perspective for Cognitive Function. Semiotica. 127/1-4, 1999. A Russian neuroscientist finds in both phylogeny and ontogeny a sequential path for brain function of an initial right hemisphere emphasis followed by left side maturation. The entire issue is devoted to “biosemiotica,” the communicative signs of life.

It allows us to discuss two main semiotic oppositions of ‘mythological’ and ‘logical’ antithesis in association with cerebral lateral mechanisms. Both developmental and cross-cultural data demonstrate semiotic evolution from the right-hemisphere ‘archaic’ mentality characteristic of traditional societies towards the left-hemispheric ‘modern’-‘eurocentric’ guided by Aristotleian logic….Evolutionary physiology gives us evidence of the older age of the right-hemisphere function in comparison to the left hemisphere. It is also shown that small children (up to 10 years of age) are, in the majority, much more right-hemispheric than adults: the older they are, the more left-hemispheric components they gain. Therefore, we argue that in this sense both phylo- and ontogenesis have a certain vector. (229)

Chiang, Ann-Shyn, et al. Three-Dimensional Reconstruction of Brain-wide Wiring Networks in Drosophila at Single-Cell Resolution. Current Biology. 21/1, 2011. A 25 person team of Taiwanese neuroscientists, at work for a decade, describe their breakthrough achievement of a three-dimensional atlas of this fruit fly brain. The work has received much praise, as a New York Times article “Decoding the Human Brain, With Help from a Fly” (Nicholas Wade, December 14, 2010) reports. The upshot is to come upon at this rudimentary phase a micro-exemplar and progenitor of mammalian and homo sapiens cerebral architectures. The same bilateral, asymmetric hemispheres, with corpus callosum fibers and small-world network geometries, as in people appear already in this elementary insect. In Wade’s report Indiana University’s Olaf Sporns notes that in both disparate brains, a “high local clustering of neurons, together with long-range connections” can be similarly found.

The Drosophila brain consists of two symmetric hemispheres connected by numerous fibers. We found 14 commissural tracts that link an LPU or hub to its counterparts at the same level in the opposite hemisphere; ten pairs of decussate tracts that obliquely cross from one hemisphere to the other; and 12 pairs of associated tracts linking two LPUs in the same hemispheres. The central complex develops from interhemispheric commissures (i.e., bridge-like aggregates of neurons and glia across the midline) that may share a similar origin with the corpus callosum of mammalian brains. Analysis of numerous short-range interhemispheric connections among member elements of the central complex, presumably serving fast information exchange between the two brain hemispheres, will be addressed in the future. (7)

Corballis, Michael. The Evolution and Genetics of Cerebral Asymmetry. Philosophical Transactions of the Royal Society B. 364/867, 2009. From a special issue on the subject, (see its Introduction by Luca Tommasi below) a senior researcher provides an overview of the emergent Metazoan pervasiveness and continuity of brain hemisphere complements. And here is another example of a significant recent discovery that has not registered because it is due to many scientists in different areas, will be not rewarded by a single prize, nor are we prepared to philosophically wonder what it means. For it reveals, in a natural genesis, that the masculine and feminine, yang and yin, archetypes grace and evolve in tandem, which then constitute an exemplary microcosm in our own cognizant intellect.

A right-hemisphere bias has also been documented for social responses in a number of fishes, chicks, and monkeys, and may relate to the right hemispheric involvement in social understanding in humans. (869) For example, pigeons tend to discriminate patterns projected to the left hemisphere in a categorical fashion, and those projected to the right hemisphere in a more holistic (‘coordinate’) fashion. The same appears to be true of humans, and may well have set the stage for language to be lateralized to the left hemisphere. (870)

Corballis, Michael. The Evolution of Hemispheric Specializations of the Human Brain. Kaas, Jon, editor-in-chief. Evolution of Nervous Systems. Amsterdam: Elsevier/Academic Press, 2007. This article appears in Volume 3: Mammals. The University of Auckland cognitive neuroscientist concisely surveys nonhuman bicameral precursors as they involve handedness, vocalization, facial and visual modes, and behaviors. Of much significance, as this section reports, the same left detail and right image propensities holds throughout. This scientific, quantified finding of a bilateral commonality is quite recent and not yet assimilated in its import.

But it is becoming increasingly clear that cerebral and behavioral asymmetries are widespread in nature, and that at least some of the asymmetries observed in other species seem to operate according to principles similar to those documented in humans. (382) The above review is by no means an exhaustive coverage of the now voluminous literature on behavioral and cerebral asymmetries in nonhuman species. It should serve, however, to illustrate that humans are not unique in displaying such asymmetries. Moreover, some of the principles underlying these asymmetries seem to apply to both human and nonhuman species. There appears to be right-hemispheric specialization for emotion, aggression, social behavior, and for the more holistic aspects of perception. The left hemisphere seems to be the more specialized for detailed visual analysis, feeding behavior, and species-specific communication. (384)

Corballis, Michael. The Lopsided Ape. New York: Oxford University Press, 1991. Right hemisphere spatial representation appears earlier in evolution, complemented by a later arriving left side which takes up the role of language and its generation of technical detail.

In summary, the picture of hemispheric duality in humans that emerges is not very different from the popular account of the left hemisphere as more analytic, rational and propositional and the right as more holistic, intuitive and appositional. (273)

Corballis, Michael and Isabelle Haberling. The Many Sides of Hemispheric Asymmetry. Journal of the International Neuropsychological Society. 23/9-10, 2017. . In a special issue for the 50th anniversary of this society, University of Auckland and University Hospital of Psychiatry, Zurich psychologists review the course of brain lateralization studies over this span from Roger Sperry’s 1960s CalTech work, in which the lead author participated. While Corballis has been opposed an excess attribution of cognitive qualities such as analytic language or holistic creativity to a fixed neural area, it now be well averred that reciprocal complements do indeed grace all manner of neural cognitive activities. A major advance in recent years has been to trace this dual quality through creaturely species as they

Hemispheric asymmetry is commonly viewed as a dual system, unique to humans, with the two sides of the human brain in complementary roles. To the contrary, modern research shows that cerebral and behavioral asymmetries are widespread in the animal kingdom, and that the concept of duality is an oversimplification. The brain has many networks serving different functions; these are differentially lateralized, and involve many genes. Unlike the asymmetries of the internal organs, brain asymmetry is variable, with a significant minority of the population showing reversed asymmetries or the absence of asymmetry. This variability may underlie the divisions of labor and the specializations that sustain social life. (Abstract)

De Kovel, Carolien, et al. Subtle Left-Right Asymmetry of Gene Expression Profiles in Embryonic and Foetal Human Brains. Nature Scientific Reports. 8/12606, 2018. MPI Psycholinguistics and Newcastle University researchers are able to trace via sophisticated genetic studies an occasion of hemispheric neural formations to an organism’s earliest embryonic stages, and by extension throughout evolutionary species.

Left-right laterality is an important aspect of human and in fact all vertebrate brain organization for which the genetic basis is poorly understood. Using RNA sequencing data we contrasted gene expression in left and right-sided samples from several structures of the anterior central nervous systems of post mortem human embryos and foetuses. While few individual genes stood out as significantly lateralized, most structures showed evidence of laterality of their overall transcriptomic profiles. Brain asymmetry may therefore originate in multiple locations, or if there is a single origin, it is earlier than 5 weeks post conception, with structure-specific lateralized processes already underway by this age. (Abstract excerpts)

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