Research Reports - The neural basis of impaired self-awareness after traumatic brain injury

Brain. 2014 Feb;137(Pt 2):586-97

Ham TE(1), Bonnelle V, Hellyer P, Jilka S, Robertson IH, Leech R, Sharp DJ

Self-awareness is commonly impaired after traumatic brain injury. This is an
important clinical issue as awareness affects long-term outcome and limits
attempts at rehabilitation. It can be investigated by studying how patients
respond to their errors and monitor their performance on tasks. As awareness is
thought to be an emergent property of network activity, we tested the hypothesis
that impaired self-awareness is associated with abnormal brain network function.
We investigated a group of subjects with traumatic brain injury (n = 63) split
into low and high performance-monitoring groups based on their ability to
recognize and correct their own errors. Brain network function was assessed using
resting-state and event-related functional magnetic resonance imaging. This
allowed us to investigate baseline network function, as well as the evoked
response of networks to specific events including errors. The low
performance-monitoring group underestimated their disability and showed broad
attentional deficits. Neural activity within what has been termed the
fronto-parietal control network was abnormal in patients with impaired
self-awareness. The dorsal anterior cingulate cortex is a key part of this
network that is involved in performance-monitoring. This region showed reduced
functional connectivity to the rest of the fronto-parietal control network at
'rest'. In addition, the anterior insulae, which are normally tightly linked to
the dorsal anterior cingulate cortex, showed increased activity following errors
in the impaired group. Interestingly, the traumatic brain injury patient group
with normal performance-monitoring showed abnormally high activation of the right
middle frontal gyrus, putamen and caudate in response to errors. The impairment
of self-awareness was not explained either by the location of focal brain injury,
or the amount of traumatic axonal injury as demonstrated by diffusion tensor
imaging. The results suggest that impairments of self-awareness after traumatic
brain injury result from breakdown of functional interactions between nodes
within the fronto-parietal control network.

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