Traumatic Brain Injuries in the Modern Age

Traumatic brain injuries (TBIs) have become an increasing concern in modern society, particularly over the past century. Historically, our ancestors faced external forces that shaped the evolution of the human skull into a robust structure capable of protecting the brain from direct impacts (Lieberman, 2011). However, despite these evolutionary adaptations, modern TBIs primarily result from acceleration, deceleration, and rotational forces—forces that bypass the skull's protective capabilities (Meaney & Smith, 2011). This post explores the origins of brain injuries during early human evolution, the protective role of the skull, how technological advancements have led to a rise in TBIs that exploit the brain's vulnerabilities in ways our ancestors never experienced, and what can be done to reduce these injuries.

The Evolution of the Skull: Built for External Blows

The evolution of the skull was driven by the need to protect against external blunt-force trauma. Early hominins, who often fell from trees in their arboreal habitats, developed thicker and more durable skulls capable of withstanding impacts (Schwartz, 2007). Large predators posed another significant threat, frequently targeting the head, making stronger skulls a crucial survival advantage for those who could pass on their genes (Pickering et al., 2004). Evidence from fossilized skulls suggests that interpersonal violence was prevalent, with some skulls showing healed fractures that indicate survival after severe blows from weapons or fists (Walker, 2001). As humans created tools and engaged in hunting, accidents involving blunt force trauma likely contributed to the selective pressures for thicker skull bones (McHenry, 1994). These evolutionary pressures resulted in a dense, dome-shaped cranium designed to disperse external forces, providing formidable protection against direct impacts.

A New Kind of Injury: Acceleration, Deceleration, and Rotation

Despite these adaptations, the human brain remains vulnerable to various forces introduced by modern technology. Unlike direct impacts, acceleration and deceleration forces act within the skull, damaging the brain (Giza & Hovda, 2001). Sudden stops, such as those occurring during car crashes, cause the brain to slam against the inside of the skull, leading to concussions and diffuse axonal injuries (Smith et al., 2003). Whiplash from high-speed impacts stretches and damages neural connections (Bayly et al., 2005). The human brain is not rigidly fixed within the skull; rather, it is suspended in cerebrospinal fluid, which makes it particularly vulnerable to twisting motions (Hardy et al., 2007). Rapid rotation, common in contact sports, causes shearing injuries to nerve fibers, disrupting communication between different brain regions (Meaney & Smith, 2011). Repetitive minor shocks, such as those experienced in boxing, football, and soccer, accumulate damage over time, increasing the risk of chronic traumatic encephalopathy (CTE), a degenerative brain disease associated with repeated head trauma (McKee et al., 2009). While these injuries often go unnoticed at first, they can result in long-term cognitive decline.

The Role of Modern Technology in the Rise of TBIs

The modern world has introduced rapid movements and forces that the human brain did not evolve to manage. High-speed transportation, including automobiles, motorcycles, and trains, subjects humans to extreme acceleration and deceleration forces that did not exist in evolutionary history (Guskiewicz et al., 2007). Although seatbelts and airbags reduce external impact, they do little to prevent the brain from shifting violently within the skull. Extreme sports and contact athletics, such as football, hockey, and mixed martial arts, present frequent opportunities for high-speed impacts and rotational injuries (Broglio et al., 2011). While protective gear can prevent skull fractures, it does not address the underlying brain movement responsible for concussions.

Military advancements have introduced new sources of brain injury, particularly from explosions, which generate blast waves that shake the brain violently within the skull (Taber et al., 2006). Unlike traditional head injuries, blast-induced TBIs can affect brain function even without direct impact. Additionally, the increased human lifespan and medical advances have contributed to the prevalence of TBIs. In ancient times, individuals with severe head injuries often did not survive. However, modern medicine now allows many to recover from previously fatal injuries, leading to an increase in cases of long-term brain damage being studied (DeKosky et al., 2010).

The Future of Brain Protection

Understanding the difference between external trauma and internal motion-related injuries is essential for developing better protection strategies. Innovations in helmet technology, safer vehicle designs, and increased awareness in sports training are steps toward reducing TBIs. However, since the primary challenge lies in the movement of the human brain inside the skull, solutions must go beyond traditional protective barriers. Research into improved diagnostic tools, treatment methods, and neurological rehabilitation is crucial for adapting to modern technology's challenges. Episode 5 of my podcast, Extreme Brains, explores these issues in greater depth.