Structural and functional brain asymmetries in the early phases of life: a scoping review

Abstract

Asymmetry characterizes the brain in both structure and function. Anatomical asymmetries explain only a fraction of functional variability in lateralization, with structural and functional asymmetries developing at different periods of life and in different ways. In this work, we perform a scoping review of the cerebral asymmetries in the first brain development phases. We included all English-written studies providing direct evidence of hemispheric asymmetries in full-term neonates, foetuses, and premature infants, both at term post-conception and before. The final analysis included 57 studies. The reviewed literature shows large variability in the used techniques and methodological procedures. Most structural studies investigated the temporal lobe, showing a temporal planum more pronounced on the left than on the right (although not all data agree), a morphological asymmetry already present from the 29th week of gestation. Other brain structures have been poorly investigated, and the results are even more discordant. Unlike data on structural asymmetries, functional data agree with each other, identifying a leftward dominance for speech stimuli and an overall dominance of the right hemisphere in all other functional conditions. This generalized dominance of the right hemisphere for all conditions (except linguistic stimuli) is in line with theories stating that the right hemisphere develops earlier and that its development is less subject to external influences because it sustains functions necessary to survive.

Anti-phasic oscillatory development for speech and noise processing in cochlear implanted toddlers

“…Interestingly, after auditory deprivation early in life, the only cortical region responsive to sounds is the right ATL (Figure 2C & S1). This observation is consistent with previous brain imaging demonstrations that the normal hearing neonates showed clear right hemisphere dominance for non-linguistic aspects of auditory processing (Perani, Saccuman et al 2010, Arimitsu, Uchida-Ota et al 2011, Bisiacchi and Cainelli 2021, Bourke and Todd 2021). In normal hearing adults, the rATL is associated with voice and speaker identity processing (Kriegstein and Giraud 2004, Elia, Formisano et al 2008, Andics, Mcqueen et al 2010, Bestelmeyer, Belin et al 2011, Andics, Mcqueen et al 2013, Bonte, Hausfeld et al 2014).…”

“…Overall, the current study indicates a clear distinction in developmental emphases for the left and right hemisphere from the onset of (restored) hearing: The left hemisphere, primarily the areas next from the auditory cortex in the ventral and dorsal streams of speech processing, appears to strive to acquire listening and speaking abilities concurrently, while the right hemisphere appears responsible for non-linguistic aspects of auditory processing. Thus, the current results provide longitudinal developmental evidence for theories of functional asymmetries of the brain (Perani, Saccuman et al 2010, Arimitsu, Uchida-Ota et al 2011, Bisiacchi and Cainelli 2021, Bourke and Todd 2021, Hartwigsen, Bengio et al 2021).…”

Development of laterality: Asymmetrical human behaviors and perceptual biases

“…The former is supposed to have a greater need for oxygen due to a more active metabolism (Bakan et al, 1973). Also, the late development of the left hemisphere over the right suggests it to be more vulnerable to external influences (Bisiacchi & Cainelli, 2022;Sanches et al, 2013). Such influences, like hypoxia, could lead to NRH.…”

Normal development of the brain: a survey of joint structural-functional brain studies

“…Investigating the laterality of brain development is another subject of joint S-F development studies. Brain lateralization starts from the fetus and continues during development and is known as a maturation index for networks like language-related networks (Bisiacchi & Cainelli, 2021;Dubois et al, 2014;Güntürkün et al, 2020). While the structural asymmetry and functional lateralization are supposed to be related, the development of joint S-F laterality demands more study.…”