The validity and reliability of quantifying hemispheric specialisation using fMRI: Evidence from left and right handers on three different cerebral asymmetries

Abstract

Neuroimaging has tremendous potential for quantifying hemispheric specializations.However, the possibilities remain under-utilized, in part, given some of the complexities in quantifying any differences in a reliable, transparent fashion. A second issue with hemispheric asymmetries is that they are extremely one-sided in most people. This skew limits the generalisability of any findings to those participants with rarer forms of cerebral asymmetry. Here, we demonstrate usefulness of an approach developed by Wilke and Lidzba, (J Neurosci Meth, 163, 2007), which allows for threshold-independent estimates of cerebral asymmetry to be calculated in individual participants. We compared these estimates from two separate runs for three different cerebral asymmetries in the same participants. We circumvented the skewed nature of this type of data in two ways; first, we scanned a large number of non-right handed participants, and second, we included asymmetries that favour the right hemisphere in right handers, which we had reason to believe were less skewed than those related to speech and language. Verbal fluency and two visuoperceptual asymmetries were localised in a sample of 33 right handed and 60 non-right handed participants.Laterality indices (LIs), which quantify the direction and strength of an asymmetry, were calculated for BOLD activity relating to language, face perception, and body perception in each run separately. Run 1 -run 2 correlations were all statistically significant and surprisingly sizeable (r = .89 to r = .62), considering the relatively short amount of time on task within our particular localizers. This noteworthy success validates a number of useful ways that functional neuroimaging can be used to advance understanding of cerebral asymmetries.

Mirrored brain organization: Statistical anomaly or reversal of hemispheric functional segregation bias?

“…We used fMRI to obtain participant-specific measures of hemispheric dominance for language (word generation task), praxis (tool pantomime task), spatial attention (line bisection judgment task), face recognition (dynamic faces one-back task), and emotional prosody (emotional intonation judgment task). A recent study showed that fMRI can reliably quantify hemisphere asymmetries (47).…”

Handedness Development: A Model for Investigating the Development of Hemispheric Specialization and Interhemispheric Coordination

“…It is my contention that much of the study of hemispheric specialization and interhemispheric communication (HS/HC) is constrained by conventional wisdom that inhibits the discovery of the developmental processes involved. Indeed, many critical reviews of HS/HC note problems of inadequate statistical power, missing details on proportion of those showing atypical lateralization, and the use of many different, often insufficiently validated, methods to ascertain functional lateralization [3,39,40]. Thus, there are too many instances of failures of replication [41], poor research designs [42], and the accumulation of conflicting evidence that fails to support any explanation of the character of HS/HC (e.g., [43,44]) or for the mechanisms responsible for the specialization [45].…”

Mapping brain asymmetry in health and disease through the ENIGMA consortium

“…Left-right asymmetry is an important aspect of human brain organization for multiple functions (Coan & Allen, 2004;Corballis, 2003;Hugdahl & Davidson, 2004;Vigneau et al, 2006;Wheeler, Davidson, & Tomarken, 1993;Zago et al, 2017;Zhen et al, 2017). For example, at least 85% of people have left-hemisphere language dominance, based on functional magnetic resonance imaging (fMRI) (Mazoyer et al, 2014), and a similar proportion are right-handed (Gilbert & Wysocki, 1992), although these proportions can vary depending on cut-off values applied to continuous data (Johnstone, Karlsson, & Carey, 2020). Some anatomical features of the brain are also lateralized at the population level, including the overall "torque" or clockwise twisting of the cerebral hemispheres (viewed from below) (Toga & Thompson, 2003), and the anatomy of cortical regions around the Sylvian fissure (Geschwind & Levitsky, 1968), although again the population proportions depend on cut-off values, as well as the precise methods for quantifying asymmetry.…”