Affiliations: Department of Neuropsychiatry, The Barberry Building,
UK Centre for Mental Health, Edgbaston, Birmingham, UK
Note: [] Address for correspondence: Department of Neuropsychiatry, The
Barberry Building, UK Centre for Mental Health, 25, Vincent Drive, Edgbaston,
Birmingham, UK, B15 2FG. Tel.: +44 (0)121 301 2294; E-mail: manny.bagary@bsmhft.nhs.uk
Abstract: Consciousness is often disrupted in epilepsy. This may involve
altered responsiveness or changes in awareness of self and subjective
experiences. Subcortical arousal systems and paralimbic fronto-parietal
association cortices are thought to underpin current concepts of consciousness.
The Network Inhibition Hypothesis proposes a common neuroanatomical substrate
for impaired consciousness during absence, complex partial and tonic-clonic
seizures. Neurostimulation in epilepsy remains in its infancy with vagal nerve
stimulation (VNS) as the only firmly established technique and a series of
other methods under investigation including deep brain stimulation (DBS),
intracranial cortical stimulation and repetitive transcranial magnetic
stimulation (rTMS). Many of these systems impact on the neural systems thought
to be involved in consciousness as a continuous duty cycle although some
adaptive (seizure triggered) techniques have been developed. Theoretically,
fixed duty cycle neurostimulation could have profound effects on
responsiveness, awareness of self and subjective experience. Animal studies
suggest vagal nerve stimulation positively influences hippocampal long term
potentiation. In humans, a chronic effect of increased alertness in VNS
implanted subjects and acute effect on memory consolidation have been reported
but convincing data on either improvements or deterioration in attention and
memory is lacking. Thalamic deep brain stimulation (DBS) is perhaps the most
interesting neurostimulation technique in the context of consciousness. Neither
bilateral anterior or centromedian thalamic nucleus DBS seem to affect
cognition. Unilateral globus pallidus internus DBS caused transient wakefulness
in an anaesthetised individual. As intracranial neurostimulation, particularly
thalamic DBS, becomes more established as a clinical intervention, the effects
on consciousness and cognition with variations in stimulus parameters will need
to be studied to understand whether these secondary effects of neurostimulation
make a significant positive (or adverse) contribution to quality of life.
