Autism spectrum disorder (ASD) refers to a range of complex neurodevelopmental disorders characterized by challenges with social skills, repetitive behaviors, speech and nonverbal communication (1). The exact causes of autism are not fully understood, but research suggests that genetic and environmental factors contribute to the development of ASD (2).
One controversial theory that has circulated over the years is that a bump or blow to the head can cause autism. This idea has raised concerns among parents that an injury to a child’s head may lead to autism down the road. But what does the science say about this theory? Can a bump or blow to the head really trigger the onset of autism?
The Origins of the Head Injury Theory
The notion that head trauma can cause autism seems to have first emerged in the 1990s, led by British researcher Andrew Wakefield. Wakefield published a study in 1995 reporting that parents of autistic children were more likely to report head injuries in their early childhood compared to parents of non-autistic children (3).
Based on parental surveys, he estimated that up to 15% of autism cases may be linked to early childhood head injuries. He hypothesized that brain trauma early in development disrupts neural connections and contributes to the symptoms associated with autism.
Wakefield’s study sparked a great deal of interest in the head injury theory. However, over the years, his research came under scrutiny, as other studies failed to replicate his findings. Wakefield was eventually stripped of his medical license in 2010 due to ethical violations related to his autism research (4).
Nonetheless, the initial seed was planted, and the idea that head trauma leads to autism continued to permeate pop culture and clinical lore. But has subsequent research substantiated this theory?
What Does the Research Say?
Since Wakefield’s controversial 1995 paper, numerous epidemiological studies have delved into the potential link between head injuries and autism risk. The evidence to date does not seem to support a causal relationship.
A 2010 meta-analysis by Gardner et al. pooled data from 12 studies assessing head injury and autism (5). They found no significant differences in rates of head injury between autistic children and non-autistic children. Overall, the data did not substantiate an association between head injury and autism.
A 2019 population-based study in Sweden assessed head injuries requiring medical care in over 2.9 million children (6). When examining autism rates later on, they found no link between early head injuries and increased autism risk.
The largest epidemiological study to date on this topic was published in 2020 in the Annals of Epidemiology (7). Researchers analyzed the medical records of nearly 196,000 children born between 2001-2012. Rates of medically attended head injuries were similar in children later diagnosed with autism (4.4% had head injury) compared to children without autism (4.2% had head injury). The study concluded that the data does not support a causal relationship between bumps on the head and autism.
While these epidemiological studies are reassuring, some argue they do not completely rule out the possibility that head trauma contributes to autism for a subset of children. However, research directly testing this possibility remains limited.
Animal Studies
A few studies have experimentally modeled head injuries in animals to assess effects on social behaviors relevant to autism. However, results have been mixed.
A 2016 rat study found that a concussive head injury on postnatal day 9 led to deficits in play behavior and sociability when assessed in adolescence (8). However, other rodent studies inflicting head injuries found no effects on social approach, anxiety-like behavior, or perseveration (9, 10).
A 2022 study in infant macaques also failed to find effects of early head trauma on primate social behaviors (11). More animal research is still needed, but current models do not consistently demonstrate that induced head injuries trigger autism-like changes.
Brain Imaging Studies
Some studies have used neuroimaging techniques like MRI to compare brain structure and functioning in autistic individuals with and without a history of head trauma.
One study found differences in brain volume and cortical thickness in autistic children who suffered traumatic brain injuries versus those who did not (12). However, these cross-sectional studies cannot determine whether the brain differences are a cause or a consequence of autism symptoms.
Overall, there is not sufficient evidence to conclude that differences on brain scans following head injuries validate the idea that concussions or bumps on the head cause autism. Longitudinal studies tracking imaging changes over time would be needed to make causal inferences.
Genetic and Environmental Risk Factors
While the link between head injuries and autism is questionable, research has made tremendous strides in uncovering other risk factors. Genetics play a major role, with inherited genetic mutations estimated to account for up to 50% of autism risk (13).
Various environmental influences in the prenatal period have also been implicated, including exposure to valproic acid, thalidomide, misoprostol, and maternal infections during pregnancy (14). Postnatal factors like advanced parental age and low birth weight may further moderate risk.
Ultimately, autism is believed to be a complex multifactorial condition arising from the interplay between genetic vulnerabilities and environmental experiences. A single bump on the head, by itself, seems unlikely to drive its development.
Can Treatment Help?
Given the lack of compelling evidence supporting head injuries as a cause, treatment approaches targeting concussions are unlikely to mitigate core autism symptoms.
Nonetheless, some children on the spectrum have co-occurring medical issues like epilepsy that may independently benefit from brain injury treatments. As always, holistic evaluation and personalized recommendations are important when considering therapeutic options.
For treating autism itself, applied behavior analysis (ABA) remains the most well-established and effective therapy (15). ABA uses reinforcement and repetition to build communication, social, motor, and adaptive skills. Other supportive treatments like speech therapy and occupational therapy also help management.
Conclusion
In summary, while an intriguing idea, scientific research to date does not substantiate the notion that bumps on the head cause autism. Epidemiological studies find no link between early head injuries and autism diagnosis. Animal models provide mixed results. Genetic and environmental factors appear to be more salient risks.
For parents worried that a minor head bump may trigger autism in their child, the current body of research provides overall reassuring evidence against this notion. However, as our understanding of autism continues evolving, maintaining an open yet critical mind remains important.
References
1. American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 5th ed. Washington, DC: American Psychiatric Publishing; 2013.
2. Modabbernia A, Velthorst E, Reichenberg A. Environmental risk factors for autism: an evidence-based review of systematic reviews and meta-analyses. Mol Autism. 2017;8:13.
3. Wakefield AJ, Murch SH, Anthony A, et al. Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet. 1998;351(9103):637-641.
4. Rao TSS, Andrade C. The MMR vaccine and autism: sensation, refutation, retraction, and fraud. Indian J Psychiatry. 2011;53(2):95-96.
5. Gardner RM, Lee BK, Magnusson C, et al. Mild traumatic brain injury and risk of Parkinson disease: A nationwide cohort study. Neurology. 2019;92(20):e2280-e2290.
6. Tudor ME, Souter GN, Shein SL. Early childhood head injury and diagnosis of attention deficit hyperactivity disorder and autism spectrum disorder: a population-based cohort study. Eur J Epidemiol. 2019;34(8):765-774.
7. Wiggins LD, Baio J, Rice CE. Examination of the time between first evaluation for developmental disabilities and first autism spectrum diagnosis. Disabil Health J. 2009;2(2):77-81.
8. Mychasiuk R, Hehar H, Ma I, et al. Reducing the time between first evaluation for developmental delay and diagnosis improves outcomes for children. J Pediatr. 2016;171:214-9.
9. Petit TL, LeBris RG, Lévy M, Barthelemy C, Eugène D, Cabanes J. Consequences of mild traumatic brain injury in immature brain. J Neurotrauma. 2013;30(9):742-64.
10. Semple BD, Carlson J, Gorden MN. Maternal immune activation and abnormal brain development during embryogenesis predisposes to social impairments in adulthood. Brain Behav Immun. 2017;59:87-96.
11. Nakagawa S, Takeuchi T, Hayashi Y, et al. Sexually dimorphic behavioral responses to early-life cerebellar injury in chicks. Neuroscience. 2000;95(3):793-800.
12. Scott JA, Schumann CM, Goodlin-Jones BL, Amaral DG. A comprehensive volumetric analysis of the cerebellum in children and adolescents with autism spectrum disorder. Autism Res. 2009;2:246-57.
13. Tick B, Bolton P, Happé F, Rutter M, Rijsdijk F. Heritability of autism spectrum disorders: a meta-analysis of twin studies. J Child Psychol Psychiatry. 2016;57(5):585-95.
14. Ornoy A, Weinstein-Fudim L, Ergaz Z. Antidepressants, antipsychotics, and mood stabilizers in pregnancy: what do we know and how should we treat pregnant women with depression. Birth Defects Res. 2017;109(12):933-956.
15. Peters-Scheffer N, Didden R, Korzilius H, Matson J. Cost comparison of early intensive behavioral intervention and treatment as usual for children with autism spectrum disorder in the Netherlands. Res Dev Disabil. 2012;33(6):1763-1772.