New MRI evidence of attenuated rightward asymmetry in ADHD across executive networks
A new study published in Frontiers in Neuroscience in March 2026 reports structural MRI findings in 40 children and adolescents with ADHD compared to 30 age-and-sex-matched controls. The research, conducted at Istanbul Nişantaşı University, Beykoz University, and Üsküdar University, used the volBrain pipeline to compute hemispheric asymmetry indices for cortical lobes, cerebellar hemispheres, and key subcortical structures.
The findings are consistent across multiple regions. Compared to controls, the ADHD group showed significantly attenuated rightward asymmetry in frontal lobe volume (Cohen’s d ≈ 0.75), cerebellar hemispheres (d ≈ 0.60), caudate nucleus (d ≈ 0.70), putamen (d ≈ 0.63), and amygdala (d ≈ 0.52, with the asymmetry direction actually reversed to leftward). Cortical thickness asymmetry was similarly attenuated in frontal cortex (d ≈ 0.80), parietal cortex (d ≈ 0.61), anterior cingulate cortex (d ≈ 0.70), precentral gyrus (d ≈ 0.72), and postcentral gyrus (d ≈ 0.64).
Where typical development shows mild rightward dominance in these executive-related regions, the ADHD group showed near-symmetric or slightly leftward patterns. The frontal volume asymmetry index averaged +0.031 in controls (modest right-greater-than-left) versus +0.010 in ADHD (essentially symmetric). The amygdala showed the most striking pattern: rightward in controls (+0.006), reversed to leftward in ADHD (−0.007).
Effect sizes were robust across most regions. Temporal and occipital lobe asymmetries showed no group differences — confirming the pattern is region-specific rather than reflecting a generalised hemispheric imbalance.
Within-ADHD variation in asymmetry predicts attention, timing, and impulsivity performance
The more interesting finding sits within the ADHD group rather than between groups.
The researchers correlated regional asymmetry indices with performance on the MOXO-d-CPT, a continuous performance test producing standardised scores for Attention, Timing, Impulsivity, and Hyperactivity. Several correlations emerged within the ADHD group, surviving correction for multiple comparisons.
Greater rightward frontal cortical thickness asymmetry was associated with better Attention performance (r = 0.45, p = 0.008). A similar association appeared for the anterior cingulate cortex (r = 0.40, p = 0.020). Greater rightward parietal thickness asymmetry was associated with better Timing performance (r = 0.38, p = 0.030). Reduced rightward inferior frontal gyrus asymmetry was associated with greater Impulsivity (r = −0.42, p = 0.015). Greater rightward amygdala volume asymmetry was associated with lower Hyperactivity (r = 0.36, p = 0.040).
These correlations describe variation within the ADHD group. Children with more pronounced rightward asymmetry in specific executive regions performed better on specific cognitive measures. Children with less pronounced rightward asymmetry, or reversed asymmetry, performed worse on those same measures. The asymmetry pattern is not categorical — it is dimensional, varying within ADHD and predicting performance variation.
This is a more substantive finding than the group-level difference. Group-level differences confirm something exists. Within-group correlations describe how that something behaves at the individual level. The data suggest hemispheric organisation is meaningfully related to cognitive variation in ADHD — not as a binary marker of presence or absence, but as a continuous dimension along which performance varies.
Region-specific, not global — the lateralisation pattern is targeted
The pattern is anatomically specific, which strengthens the findings.
Temporal and occipital asymmetries showed no group differences. Both groups showed near-symmetric patterns in these regions, as expected — they are not typically right-lateralised in development. The researchers included occipital lobe asymmetry as a negative control, and the absence of group differences there confirms the analytic approach is detecting genuine regional effects rather than producing artefactual differences across the whole brain.
The regions where asymmetry differed are precisely those implicated in attention and executive control: frontal cortex, anterior cingulate, parietal cortex involved in dorsal attention networks, basal ganglia structures involved in inhibitory control, and cerebellar hemispheres involved in motor timing and higher-order cognition. The amygdala asymmetry difference connects to limbic regulation of arousal and emotional response, with the observed correlation to Hyperactivity scores making functional sense.
The pattern is coherent. ADHD is associated with attenuated rightward asymmetry specifically in regions involved in the cognitive functions ADHD affects — and the degree of attenuation predicts the degree of cognitive variation.
The findings replicate and extend earlier work. Postema and colleagues (2021) reported similar asymmetry patterns across 39 datasets in the ENIGMA consortium. Chen and colleagues (2021) reported reversed putamen asymmetry in ADHD. The new study uses a mean-normalised asymmetry index — each participant serves as their own internal control for overall brain size — and adds direct correlation with objective cognitive performance.
"Developmental lag" frame ASSUMES a maturational arc it claims to describe
The authors interpret their findings within a “right-hemisphere developmental lag” framework. The framework holds that typical development produces rightward asymmetry in executive regions, that ADHD reflects delayed maturation of this rightward dominance, and that the asymmetry differences observed in cross-sectional data reflect arrested or slowed progression along an expected trajectory. The language is woven through the paper. Frontal regions are “underdeveloped” in ADHD. Right-lateralised executive networks show “delayed maturation.” The pattern is consistent with “right-hemisphere developmental lag models.”
The framing is not the data. The framing is an interpretation laid over the data — and it carries embedded assumptions worth examining.
The first assumption: that the more right-leaning organisation observed in typical controls represents the maturational endpoint. That stronger rightward asymmetry in executive regions is what brains are supposed to produce, and that anything else is failure to arrive. But typical development is not the same as optimal development. The neurotypical pattern is descriptive — what most brains in the sample produce — not normative. Calling deviation from it “lag” requires assuming the deviation is along a single arc with a single endpoint, and that the endpoint is the typical pattern.
The second assumption: that the ADHD pattern reflects less development rather than different development. The cross-sectional data cannot distinguish between these. Children with attenuated rightward asymmetry might be on a delayed trajectory toward the typical pattern. They might also be on a different trajectory entirely — one that does not converge on the neurotypical endpoint, and was never going to. The longitudinal studies that would distinguish these scenarios have not been conducted at sufficient resolution. The “lag” interpretation is selected, not demonstrated.
The third assumption — and the most consequential — is what counts as the older, more foundational organisation in the first place.
An alternative framing is at least as defensible. Right-hemisphere processing is, in some accounts, more integrated, more holistic, more contextual, and more closely associated with the kind of broad-bandwidth attention and pattern-recognition that characterised cognition before high-specialisation literacy and screen-mediated symbolic processing came to dominate cognitive demand. Left-hemisphere processing, in those same accounts, is more specialised, more linear, more focused, and more recently dominant in the cognitive niche modern humans actually occupy. If that framing holds — and it is contested, but it is not absurd — then “typical” rightward executive asymmetry in modern controls might itself reflect a particular historical-cultural configuration rather than a neutral baseline. And the ADHD pattern of attenuated rightward dominance might not represent failure to mature into the typical configuration. It might represent a different configuration with different costs and different affordances, observed in a measurement environment (CPT performance, classroom function, productivity tasks) that selectively rewards left-lateralised processing.
This is not a settled position. It’s an off-the-cuff coherent counter — one that the data does not rule out, and that the “developmental lag” framing systematically forecloses without examining. The same correlation between rightward frontal asymmetry and CPT Attention score can be read as: rightward dominance produces better attention (the authors’ reading); or, rightward dominance happens to align with what the CPT measures, while leftward or symmetric organisation might align with cognitive functions the CPT does not measure. Continuous performance tests are designed around sustained vigilance for predictable targets — a narrow slice of attention. They were not designed to detect what attention configured differently might be good at.
The point is not that the alternative framing is correct. The point is that the authors’ framing is not neutral. Calling the ADHD pattern “underdeveloped” prejudges what the brain is for. Calling it “different” leaves the question open. The data — region-specific attenuation of rightward asymmetry, correlated with variation in CPT performance within ADHD — supports both readings equally. The choice between them is interpretive, not empirical.
For ADHD and neurodiversity research, this matters. Decades of “right-hemisphere deficit” framing have produced an enormous literature describing what ADHD brains lack. The same data could ground a literature describing what ADHD brains are. The structural findings reported here are real. The framing is a choice. The framing should be made visible as a choice — not absorbed as if it were the finding itself.
Citations
Çınaroğlu, M., Yılmazer, E., Ülker, S. V., & Tarlacı, S. (2026) — Attenuated rightward hemispheric asymmetry in ADHD: structural MRI evidence from a normalized asymmetry index and its association with cognitive performance
