Greetings from Maryland, where the official state sport is jousting!

I don't think we can definitively state either way that the accident is the sole cause for his tyrannical behavior. Indeed, it is unlikely that his tyrannical behavior has one single, solitary cause. In addition, the injury to his brain was not nearly as severe as neuropsychology's first well-studied case for frontal lobe damage, Phineas Gage. From the description of the accident given by an eyewitness, George Cavendish, there was no foreign object penetration of any kind - "just" an acute, blunt blow to the head, an injury that we often see today in things like car accidents and full contact sports. It generally takes more than a single impact such as this to cause massive, permanent personality change due to traumatic brain injury (TBI). Indeed, thousands of people who received TBI from lobotomies performed in the first half of the last centuries did not exhibit that kind of drastic personality change.

Let's take a small break from history to talk brains and frontal lobe injury. What does the frontal lobe do? It plays a significant role in "higher" mental functions:motivation, planning, social behavior, speech production and a lot of little things we take for granted - behavioral control, suppression of emotional states that would otherwise lead to outbursts, and even self-censoring (i.e. not telling your mother-in-law what you really think of her). I'm not a huge fan of referring to these functions as 'higher' brain functions, though it is common parlance. A better way to say it is that the frontal lobe plays a huge part in making humans, well, human.

Damage to this part of the brain, especially bilaterally (Henry likely had unilateral damage), results in the type of frontal lobe disinhibition that causes individuals to lose some, most, or even all behavioral control. You essentially lose your brain's editor: the neurological decision-making process is interrupted in a way that is similar to young children, whose frontal lobes aren't well developed.

Did Henry's behavior change after the accident? Historical records seem to indicate so, and neuropsychology and our understanding of frontal lobe TBI support this. Was it the source of all his tyrannical behavior? I think that that is unlikely. Brains are surprisingly adept at compensating for injury - brain damage is permanent, and yet there are thousands of people who have, through hard work and determination, regained the loss of a particular function/functions.

We can also look at Henry's personal history, specifically his childhood. The surrounding environment in a person's formative years has an impact on who they become that is so great that it cannot be ignored.

Putting aside the uniqueness and often malignant experience of growing up royal, Henry's family dynamic plays a part in who he was and how he behaved later in life. He was never meant to be king. As such, not much is known about his early life, which may tell us volumes - if his early years remain largely unrecorded, it is not a stretch to say that he was second best and was treated as such, which will have consequences later on in life. Even after his brother's death, his father gave him few tasks, did not allow him to appear in public - this behavior seems to indicate that he ignored the child Henry. This is of fundamental importance to his later life - as an adult, Henry exhibited a behavior pattern that demonstrated his desperate, near pathological need to be recognized, adored, even worshiped. He spent his whole life trying to compensate for what he likely did not get in childhood.

I am not an expert on Henry VIII. I am, however, an expert on psychopathology, and I can tell you that every human's adult personality, mental state, and behavior is shaped quite a bit by their childhood, and that, based his behavior from the period prior to his TBI, he was already exhibiting a personality pattern that fits with what little we know and can hypothesize about his childhood.

And then there is the process of aging. By age 44 you start to see a minor progression of frontal lobe disinhibition, which would most certainly be magnified in a king who has absolute authority and absolute power, a man who had already asserted his power over the Holy Roman Church itself.

If all we knew was pre-injury Henry, we could see the seeds of narcissism and the flowering of authoritarion behavior. He did not handle the Church's decision not to annul his first marriage very well, and there are recorded instances of his anger at the situation flaring up. He was egomaniacal but had a somewhat fragile ego, and did not tolerate the word "no" very well - especially when what he perceived to be an affront was as public as this particular refusal was. Henry had already been established as a king who could be domineering and totalitarian sometimes. It would appear that his frontal lobe injury magnified a personality style that was already there. The pain from his ulcerated legs may have contributed to his pre-injury behavior as well.

To summarize: I do not believe that Henry's jousting injury was serious enough to cause a drastic change in personality, resulting in his change from a solid, even-keeled ruler to a tyrant where there was none such person before. We cannot discount the role of his childhood in forming his behavior, whatever it may have been. Henry was already aging as well, and as a king with absolute power, he had free reign to act like a tyrant. Moreover, we can see authoritarian behavior in his pre-injury years. I do not doubt for a second that the jousting injury permanently alter his behavior for the worse, but I don't think that the accident alone can account for who he was and who he eventually became.