Through monitoring brain function after traumatic brain injury (TBI), new research has revealed potential to better predict who will ‘wake up’ and what brain circuits to target to potentially treat disorders of consciousness.
Through studying TBI patients, scientists have identified the brain circuits that lead to unpredictable behaviour, which they believe is a core feature common to human consciousness.
“After brain injury, unconscious and semi-conscious patients don’t do much, they don’t engage in goal-oriented behaviour, and their behaviours are highly predictable,” said Dr Charles Mikell, assistant professor in the Department of Neurosurgery at Stony Brook University.
“This predictability is apparent in patients’ brain signals that we recorded with special electrodes on the scalp and the brain,” co-author Dr Sima Mofakham, assistant professor in the university’s Department of Surgery, explained.
“By studying brain injury patients in this state, we have identified the brain circuits required for unpredictable behaviour.
“Specifically, we found that injuries to a brain region called the thalamus results in ‘attractor dynamics’ in the brain. ‘Attractors’ are ways of describing repetitive activity, which the brain has trouble escaping, like trying to escape a whirlpool.”
The research, which comprised a series of studies, centred on the thalamus, a walnut-sized piece of brain tissue that coordinates activity in other parts of the brain.
“For cortical networks, attractors limit the availability of different brain states, and consequently behaviours,” Dr Mofakham said.
“We found the integrity of the thalamocortical connections may support the behavioural and electrophysiological unpredictability associated with consciousness.”
The first paper involved using electrodes implanted in the brain to look at brain dynamics in comatose patients as they recovered consciousness following brain injury.
This use of implanted electrodes made this the first study of its kind and opened a new window into brain dynamics after injury in comatose patients.
They assessed five patients in a unique study that combined brain wave recording with brain imaging, in an attempt to understand how thalamus injury affects cortical function.
Stony Brook researchers identify the role of the thalamus as key therapeutic target for TBI patients. Photo courtesy of Sima Mofakham.
Their main finding was that thalamus input facilities the formation of cortical ensembles required for the return of cognitive function and consciousness. This observation supports the view that thalamic input to the cortex enables rich cortical dynamics associated with consciousness.
In a further paper, Dr Mofakham and Dr Mikell and their team found in another cohort of patients that the number of cortical states is limited, and brain activity is predictable in patients with injuries to their thalamus and its projections to the cortex.
They found that withdrawal of thalamic input results in a cortical attractor state with a limited number of states available, which leads to limited behaviours.
They write that the “results are in line with the new view of the thalamus: the thalamus is not simply a relay centre, but it can dynamically control the distributed adaptive dynamics within and across cortical networks to support the ongoing cognitive task.
“Multiple reports support this view and define a new role for the thalamus, in particular higher-order thalamic nuclei such as the mediodorsal nucleus, as the regulator of connectivity.”
Further research showed that people with thalamic injury and injuries to their mediodorsal nucleus, are less likely to recover the content of consciousness.
This study involved analysing 25 patients after severe TBI. They investigated whether the integrity of the thalamo-prefrontal circuits, assessed via diffusion tensor imaging, was associated with the return of goal-oriented behaviour.
Some patients recovered, but some did not, and more than half returned to a state where they could follow commands or engage in other goal-oriented behaviour.
All of the researchers’ data from their imaging and testing of patients supported that intact thalamo-prefrontal connectivity was essential to the return to goal-oriented behaviour.
