Causes of Disorders of Consciousness

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What causes disorders of consciousness?
With Joseph Giacino, PhD

Lower Third
Joseph Giacino, PhD
Project Director,
Spaulding-Harvard Traumatic Brain Injury Model System

There are a number of different kinds of injuries, if you will, to the brain that can cause a disorder of consciousness. Traumatic brain injury … can begin with that, where there is literally a traumatic injury to the brain. That can be a car accident, a fall, a blunt injury to the head. Second type or etiology would be stroke, for example. That affects certain portions of the network that control consciousness. Anoxic brain injury, where there is loss of oxygen to the brain. So somebody might have a heart attack, cardiac arrest, loss of oxygen flow to the brain, starves the brain of oxygen, and does it in a diffuse manner, enough loss of oxygen that again, will cause alteration of consciousness. Can also have metabolic and infectious processes that disturb the brain globally, that impact multiple areas, again, either in large volume, enough to suppress consciousness or certain parts of that network being involved to cause loss of consciousness.

Disorders of consciousness can occur from any type of injury to the brain, but there are really a number of mechanisms that play in when we're talking about disturbance and consciousness, a brain injury that's significant enough to cause disturbance in consciousness. So it can happen when the brain experiences diffuse bi-hemispheric injury. So both hemispheres of the brain — the brain is comprised of the left and the right hemisphere — are both damaged significantly at the level of the cortex. There needs to be a significant volume of damage in order to disturb consciousness if that's where the location of the injury is. But we can also have disturbance in consciousness result from injury to the brain at lower levels. So if you have bilateral — meaning both sides of the thalamus — that's sort of an intermediate level of the brain. If bilateral thalamic lesions occur, that can disturb consciousness. Or it can occur when we get down to the level of the brainstem, and we have injury to both sides of the brainstem.

So that's from a structural standpoint how one may develop a disturbance in consciousness. If we think about it from a mechanistic level, there are certain structures in the brain that are tied deeply into the consciousness network, if you will. And if any part of that circuit is directly damaged, it's structurally damaged, it may perturb the whole system, and we get disturbance in consciousness. So that can be a single lesion in a strategic part of the brain. Another mechanism is that the brain has to maintain connectivity along all of its levels, basically. So if we have an injury that causes a disruption in the connectivity of the brain, no single lesion is responsible or no single structural injury is responsible for that disturbance in consciousness. But we have these interruptions or disruptions in circuits in many different regions of the brain. So this loss of connectivity is probably the most common mechanism, especially after traumatic brain injury that results in loss or disturbance in consciousness.