Pain is a leading cause of insomnia
and sleep disruption is one of the complaints of patients who suffer chronic pain
during normal sleep a gating mechanism isolates the upper
brain from the barrage of sensory information
this disengagement from the environment allows sleep to continue without interruption
however a long-lasting pain sensation is perceived by the central nervous system as
a potential danger and this continuous barrage of pain signals reaching the thalamus breaks
down the gating mechanism allowing a free flow of neural impulses onward to the cortex. So what is
this gating mechanism? and how does it work? At the level of the thalamus the reticular
nucleus generates inhibitory postsynaptic potentials that maintain sleep continuity
This is done by the release of gamma-aminobutyric acid or GABA
and by the binding of GABA molecules to their receptors. This binding triggers
the gating mechanism to reduce pain perception by allowing the chloride ions to flux through
causing inhibitory postsynaptic potentials and a slower firing range of lamech relay neurons
This block in the thalamus then causes the cortical cortical connections to breakdown
as well, leading to fading of consciousness known as sleep. Compared to wakefulness where sensory
stimulation induces a sustained cortical response represented here by sustained recurrent waves
of brain activity, during sleep waves of brain activity quickly diminish and do not propagate
to other cortices. Thus the gating mechanism at the level of the thalamus plays a significant
role in allowing continuation of sleep. However when there is a long lasting painful sensation
the brain perceives this as perturbation of equilibrium and this continuous barrage of
pain impulses reaching the thalamus breaks down the gating mechanism causing sleep disruption
and pain exacerbation. Awakening of various brain regions from pain during sleep is part of
a natural survival response to protect the body from potential damage. However continuous sleep
disruption can lead to more pain and result in a vicious cycle of less sleep and more
pain. Current research which targets mechanisms that excite or inhibit the gating mechanism may
eventually offer patients with chronic pain better management of their sleep quality and continuity