The Effect of Handedness on fMRI Language Activation in Adolescents with Autism Spectrum Disorder

Background:   Handedness and language functions are highly associated, although the exact nature of this relationship remains unclear.  Language deficits are one of the core features of autism spectrum disorder (ASD) and previous studies have demonstrated an increased rate of left-handedness in this disorder.  Although studies have examined language laterality in typically developing right- and left-handers, few studies have examined language laterality and handedness in ASD. 

Objectives:   The purpose of this study was to examine brain activation during a language task in left- and right-handers with ASD and typically developing left- and right-handers. 

Methods:   We used fMRI to examine activation during a visual response naming task in a small sample of left-handed boys with ASD (n = 6), left-handed typically developing boys (n = 6), right-handed boys with ASD (n = 6), and right-handed typically developing boys (n = 6).  Percent signal change was calculated in 2 regions of interest, frontal language regions (pars triangularis and pars opercularis) and temporal language areas (posterior superior temporal gyrus, including the planum temporale), in each hemisphere and asymmetry quotients (AQs) were calculated. 

Results:   In left-handers, there were significant group differences for the temporal region (p = .005).  Left-handed controls had leftward asymmetry of activation while ASD left-handers showed rightward asymmetry.  In contrast, in right-handers, there were no significant AQ differences between ASD and controls.  When right- and left-handers were compared, in the ASD group, temporal AQs were significantly different (p = .003), with left-handers demonstrating rightward asymmetry and right-handers having leftward asymmetry.  In the control group, there were not significant differences between right- and left-handers. 

Conclusions:   These findings suggest that language functions may be different in left-handers with ASD.  Differences were found relative to typically developing individuals as well as compared to right-handers with ASD, emphasizing the importance of examining left- and right-handers separately.