So What Actually Hurts in a Primary Headache?
It’s a good question, if there is no underlying pathology, why do I get head pain?
While we have several different types of primary headache there is ultimately one common neurological process that underpins them all; a process called brainstem sensitisation.
Both head and neck pain is perceived consciously in a higher region of the brain called the sensory cortex. However, pain signals coming from nerve endings in head or neck don’t directly project to this region. The incoming signals are all directed to a structure called the trigeminocervical nucleus (TCN). This is group of nerve endings clumped together in the brainstem, which connects the upper spinal cord to the higher regions of the brain. This nucleus acts as a relay centre for the incoming signals before passing to the conscious parts of the brain.
Importantly, not all signals will make it past the TCN, as it has to reach a certain threshold before sending signals on. This threshold is maintained so that only relevant pain signals are felt consciously and this experience of head pain can only be felt if the TCN is triggered.
However, the TCN can become ‘sensitised’ so that the threshold of the TCN is lowered and more easily triggered and hence an over-reactive pain system is set up where the brain registers pain even in the absence of actual tissue injury. This is the essence of a primary headache sufferers issue – the brain itself has become over reactive to environmental stimuli that isn’t actually damaging to the body.
So how does this structure become sensitised?
The threshold level of the TCN is largely controlled by other regions of the brain that produce several key neurotransmitters such as serotonin, dopamine and noradrenaline. These chemicals have a dampening or inhibitory effect on the TCN, which prevents it from over reacting to normal sensations. This process is known as pain modulation.
We know that headache sufferers – in particular migraine sufferers – have alterations in the production of these substances due to genetic factors.
The ultimate irony is that the key deficiency that causes primary headache is an over protective pain system.
As a result we have a system that easily triggered by many factors such as diet, weather change, fatigue, stress, glare, hormonal changes, postural strain and on and on.
We also know that these same genetic impairments lead to a range of other syndromes such as irritable bowel syndrome, vertigo, anxiety, insomnia, ADHD, asthma, fibromyalgia, and epilepsy.