Background: Insufficient understanding of the mechanisms of
consciousness can make unconsciousness a diagnostic challenge, directly
effecting the treatment and the outcome of the patient. Consciousness is
a product of brainstem arousal (wakefulness, the level of
consciousness) and cortical information integration (awareness, the
contents of consciousness). The thalamus serves as a critical hub in the
arousal pathway. The nuclei within the internal medullary lamina,
together with the associated thalamocortical connections, have been
implicated as being especially important for human consciousness.



Case study: A 17-year old male migraineur developed a sudden episode
of unconsciousness after receiving a single dose of intranasal
sumatriptan for the treatment of prolonged migraine associated symptoms.
Diffusion-weighted magnetic resonance imaging revealed a small
bilateral thalamic infarction affecting the centromedian and
parafascicular nuclei and the associated non-specific thalamocortical
connections as the likely reason for the impairment of consciousness.
With the exception of occasional fatigue due to a persistent lesion on
the left thalamus, the patient experienced full recovery. Corresponding
to the injury, diffusion tensor tractography imaging revealed a
distinctive defect on the thalamocortical fibres originating from the
left centromedian/parafascicular nuclei complex.



Conclusions: The presented case offers an outstanding example of the
importance of the arousal system and non-specific thalamocortical
connectivity for normal waking consciousness.