Vignesh Subramanian ’24

Traumatic brain injury (TBI) is a form of acquired brain disability caused by an external force exerted against the head. The causative trauma is typically severe enough to result in loss of consciousness and the conditions under which consciousness returns remain unclear. Clinical practice uses complex electroencephalography (EEG) activity to predict its return and level, predicated on the assumption that neuronal firing in the thalamus (the relay station of sensory and motor signaling in the brain) grants the surrounding cortex the flexibility to switch between different states of neuronal activity characteristic of varying degrees of alertness. To assess the capacity of thalamic inputs to facilitate complex activity and their impact on cortical function, researchers led by Dr. Mofakham of Stony Brook University aimed to characterize the EEG activity of the prefrontal cortex (PFC) in TBI patients with different degrees of thalamocortical projection injuries.

The researchers first obtained a sample of fifteen TBI patients and stratified them by their clinical outcomes and post-injury thalamo-prefrontal structural integrity, the latter being determined using diffusion tensor imaging (DTI) and magnetic resonance imaging (MRI) scans. The researchers then obtained scalp EEG recordings from all subjects and conducted multi-dimensional spectral density analyses using delay embedding methodology to reconstruct each subject’s underlying phase space, or relative and dynamic spatial pattern of brain activity, from their previous period of unconsciousness. Finally, these EEG signatures underwent a series of stochastic statistical analyses to ascertain the numbers of discoverable cortical brainwave states. 

The researchers found that in the absence of signaling along impaired thalamo-prefrontal connections, the phase space of cortical dynamics in the TBI patients presented as a low-dimensional global attractor state, a particular set of fixed points that neural activity tends to evolve towards and sustain as it becomes stable. In these cases of more severe thalamocortical projection injuries, the cortical state was constrained to a limited number of alternative states of neuronal activity it could visit, though these states followed a predictable transitional trajectory and were generally structured (meaning they tended not to shift between each other). 

These findings suggest that impaired thalamic input contributes to cortical dynamics engaging in prolonged state occupancy (e.g., remaining in the unconscious state rather than eventually shifting towards behavioral demands and wakefulness), and conversely, that sustained thalamic inputs are necessary for the cortex to remain flexible and ultimately enable a return to consciousness. Future studies may aim to determine how to induce or promote the establishment of a wider repertoire of cortical states that enable the return of attentional, conscious behavior. 

Works Cited:

[1] S. Mofakham, et al., Injury to thalamocortical projections following traumatic brain injury results in attractor dynamics for cortical networks. Progress in Neurobiology 210, 1-10 (2022). doi: 10.1016/j.pneurobio.2022.102215

[2] Image retrieved from: https://commons.wikimedia.org/wiki/File:Thalamus_-_DK_ATLAS.png