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Abstract

Background
Auditory stimulation is often used to elicit responses in unresponsive patients who have suffered severe brain injury. To investigate visual responses, we examined visual evoked potentials (VEPs) and behavioral responses to visual stimuli in vegetative patients during recovery to consciousness.

Methods
Behavioral responses to visual stimuli (visual localization, understanding of written commands, and object manipulation) and flash VEPs were repeatedly examined in eleven vegetative patients every two weeks for an average period of 2.6 months, and patients' VEPs were compared to a healthy control group. The long-term outcome of the patients was assessed 2-3 years later.

Results
Visual response scores increased during recovery to consciousness for all scales: visual localization, understanding of written commands, and object manipulation. VEP amplitudes were smaller and the latencies were longer in the patient group compared to the controls. The characteristics of VEPs at the first measurement were related to the long-term outcome up to three years after the injury.

Conclusions
Our findings show the improvement of visual response with restoration of the vegetative state to consciousness. Basic visual processing is present, but according to VEP responses, worse in vegetative and minimally conscious state than in healthy controls, and remains worse when patients regain consciousness. However, initial VEPs are related to long-term outcome.

Keywords
Brain injury, Vegetative state, Unresponsive vigilance syndrome, Minimal conscious state, Consciousness, Visually evoked potential