How is a woodpecker like a football player?

As the National Football League (NFL) approaches its most prestigious game of the year, the Superbowl, fans are often treated to video montages of the big plays and hard hits that either led their teams to victory or contributed to the end of their season. While these clips serve to instill a sense of excitement in rapt fans, they also often elicit a muttered “ouch…” As a neuroscientist, watching the tackles in which necks, heads, and backs are crunched in the process sends particular chills down my spine. Though it has long been understood that the physical jobs of athletes like football players can cause both sudden injury and chronic cognitive impairment, a 2005 study from researchers at the University of Pittsburgh showed the first evidence of chronic traumatic encephalopathy (CTE), a specific type of long-term brain damage, in an ex-NFL player’s postmortem brain tissue. This study truly brought the issue of cognitive decline following years of mild traumatic brain injury and concussions into the public spotlight [1].

 

CTE and its prevention

Though symptoms become obvious in middle to old age, CTE can only be diagnosed after death by looking at hallmark signs of damage in the person’s brain tissue. Most notable are the presence of neurofibrillary tangles in the neurons near blood vessels and deep in the folds in the brain [2]. These clumps are made up of the protein called tau, which normally would help form the microtubules that make up the skeletal structure of neurons. These clumps, however, clog up the neurons, reducing their ability to move important molecules around and send information to other cells. Interestingly, these tangles are also a feature of other neurodegenerative disorders, such as Alzheimer’s Disease. Though it remains a mystery how exactly chronic head trauma leads to the formation of these tangles (check out this 2014 NeuWrite article about the history of CTE in football and this 2016 article about brain injury in combat sports!), some neuroscientists hypothesize that the trauma can change the structure of a variety of proteins that work together to cause these characteristic brain defects [3].

human tau

Staining for the protein tau in an ex-NFL players brain reveals neurons with neurofibrillary tangles indicative of CTE. Image adapted from [1].

Since these findings about CTE in football were published, the NFL has started to make changes that will hopefully promote the brain health of its athletes. At the first sign of a hit to the head, players are put through the “concussion protocol” to assess for a head injury. In order to prevent further head injuries, much research has gone into technology that can be used in sports helmets to ameliorate the forces that cause head trauma upon impact.

As with other advances (like the invention of velcro to mimic plant burrs sticking to fabric or fur), we can look at the animal kingdom and natural world for clues to increasing our own safety and efficiency. In the case of brain protection, some researchers have received inspiration from a surprising source – the woodpecker.

 

Woodpeckers and their brains

You may have heard these special birds while out for a hike as they tap-tap-tap away at the trunk of a tree. Woodpeckers obtain their food by pecking holes into the trunks of trees, then using their long tongues to scoop out hidden insects. The process of pecking, however, is quite a bit more violent than you might have guessed. As the woodpecker pecks, its beak can reach speeds of up to 16 miles per hour, and as its beak makes contact with the tree, the head of the bird experiences a deceleration of around 1000 g-force or more. For reference, humans can sustain concussions at decelerations around 300 g, meaning that woodpeckers are consistently sustaining three times or more the force that would cause head trauma in humans [4]. And the woodpecker pecks about 12,000 times on average per day [5].

red-bellied_woodpecker

A red-bellied woodpecker pecks away at the trunk of a tree (source: https://www.audubon.org/field-guide/bird/red-bellied-woodpecker)

Just how do these birds withstand such forces and continue to peck away to find their food? A variety of tested hypotheses exist for their resilience. First, the woodpecker’s small size, especially its scaled-down brain, helps. Because of its small and simple build, there is simply less brain per unit surface area to worry about in a collision. Additionally, biophysics experts suggest that since each peck is so short – in some species only about 1 millisecond – higher forces can be tolerated. Still others point out that the strong neck muscles of these birds help minimize damaging forces [4].

Other lines of woodpecker research look at how their brains are situated in their skulls. The woodpecker brain fits very snugly into the skull. In contrast, our brains and spinal cords are surrounded by cerebrospinal fluid (CSF), which is meant to cushion our fragile tissues from banging around in our sharp, bony skull. In cases of extreme forces on the head, however, the presence of CSF around the brain causes brain ‘slosh,’ which, exactly as it sounds, is the phenomenon in which the brain slips around inside the skull. Woodpeckers, on the other hand, have very little CSF [4]. Though CSF is meant to be brain protective, the birds actually benefit from the tighter brain fit through the reduction of slosh.

Another way woodpeckers are thought to prevent the thumping around of their brains inside their skulls with each peck is their uniquely structured “hyoid apparatus,” which is made up of the bones, muscles, and cartilage of the tongue. Unlike humans, birds have a bony structure underlying the soft tissue of their tongues.

woodpecker tongue

Shown here in red, the woodpecker tongue, when not in use for scooping up food, wraps entirely around the back of the skull. Image adapted from [6].

Woodpeckers have super long, skinny tongues that are crucial to reaching into trees and poking around for insects to eat. However, when not in use for eating, their tongues wrap completely around the back of the skull and forward again, providing bone and muscle support for the brain during pecking [6]. In other words, woodpeckers use their tongues as a seatbelt for their brains [5].

 

tongue

The process of woodpecker tongue unfurling for food retrieval (source: https://www.birdwatchingdaily.com/news/science/woodpeckers-hammer-without-headaches/)

 

Are woodpeckers a good model?

So, it seems that we have a lot to learn from how woodpeckers go about their daily business of pecking at trees. One proposed technological advance for humans based on the woodpecker is the fashioning of a neck collar designed to compress the veins of the neck to help the brain fit more snugly in the skull and prevent brain slosh like in our feathered model system. This isn’t to say that everyone is on board with using these birds as a good model species for head trauma resistance. In a recent opinion article titled “Woodpeckers don’t play football,” two researchers look at the proposed collar with skepticism. The authors correctly remind us that woodpeckers don’t play football: they have different brain structures and adaptations, their collisions look different from a football player’s tackle, and they themselves don’t use neck compression collars [7].

Most importantly, however, is this remaining question: do all of these evolutionary adaptations prevent chronic neurotrauma? Until recently, we continued to use the woodpecker as a model organism for brain health in the face of continued collisions without knowing that their brains remain in pristine condition.

Unfortunately, according to a 2018 article from researchers at Boston University, it looks like woodpecker brains have a similar fate to the studied NFL football players. Using preserved woodpecker brains from museums, these neuroscientists found that woodpecker brain tissue contains neurofibrillary tangles whereas blackbird brains do not, suggesting that persistent head trauma does affect the brain health in our concussion-resistant model species [8].

This does not mean that all of the current research into woodpecker brains is in vain. Woodpeckers have still evolved ways to withstand forces that would be dangerous or fatal for human beings and continue to peck away at tree trunks. We don’t know if the birds have similar behavioral and emotional symptoms of cognitive decline as human patients with CTE. Finally, we don’t know what the presence of neurofibrillary tangles in the brains of woodpeckers means. Because this study doesn’t indicate whether the neurofibrillary tangles cause neurons to die, it is possible that the tangles function differently in the woodpecker brain in ways that do not disrupt neuron function or might even have protective effects.

 

How do neuroscientists pick a model organism?

The study of woodpeckers as neurotrauma models provides an interesting example of how neuroscientists may look to unexpected animals to learn more about ourselves. In many cases, researchers like to look at the brains and behavior of mammals, as the similarities are more easily drawn between those animals and ourselves. However, in other cases, there are other animals that do things better than we do which we can learn from. Despite the evidence of trauma in the woodpecker brain and the fundamental differences between birds and humans, woodpeckers have evolved ways to sustain forces that would severely damage our brains. The creativity of neuroscientists to look into the natural world for answers can reveal interesting insights to better our own lives.

 

 

 

 

References

  1.     Omalu BI, DeKosky ST, Minster RL, Kamboh MI, Hamilton RL, Wecht CH (2005) Chronic traumatic encephalopathy in a national football league player. Neurosurgery, 57:128-134
  2.     McKee AC, Cairns NJ, Dickson DW, Folkerth RD, Keene CD, Litvan I, Perl DP, Stein TD, Vonsattel JP, Stewart W, Tripodis Y, Crary JF, Bieniek KF, Dams-O’Connor K, Alvarez VE, Gordon WA (2016) The first NINDS/NIBIB consensus meeting to define neuropathological criteria for the diagnosis of chronic traumatic encephalopathy. Acta Neuropathol, 131:75-86
  3.     Chen L (2018) What triggers tauopathy in chronic traumatic encephalopathy? Neural Regeneration Research, 13(6):985-986
  4.     Gibson LJ (2006) Woodpecker pecking: how woodpeckers avoid brain injury. Journal of Zoology, 270:462-465
  5.     Wang L, Cheung JT, Pu F, Li D, Zhang M, Fan Y (2011) Why do woodpeckers resist head impact injury: a biomechanical investigation. PLoS ONE, 6(10):e26490
  6.     Jung JY, Naleway SE, Yaraghi NA, Herrera S, Sherman VR, Bushong EA, Ellisman MH, Kisailus D, McKittrick J (2016) Structural analysis of the tongue and hyoid apparatus in a woodpecker. Acta Biomaterialia, 37:1-13
  7.     Smoliga JM, Wang L (2018) Woodpeckers don’t play football: implications for novel brain protection devices using mild jugular compression. Br J Sports Med, 0:1-2
  8.     Farah G, Siwek D, Cummings P (2018) Tau accumulations in the brains of woodpeckers. PLoS ONE, 13(2):e0191526

Cover image source: https://www.audubon.org/news/how-woodpecker-bangs-without-brain-damage

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