A vegetative state is caused by having massive damage to the mesencephalon, which can include both the pontine nuclei and the thalamus (Plum and Posner 1980). During this state, the metabolic activity of the neocortex can be reduced by as much as 50% (Blacklock et al. 1987), well below the activity during slow-wave sleep (Maquet et al. 1990). Patients in a vegetative state lose all consciousness, while still exhibiting a sleep-wake cycle and autonomic functions (Owen 2008; Schiff, Llinas et al. 2002). As well, they retain many brain stem and spinal cord reflexes such as the righting reflex, the vestibulo-ocular reflex, and the stretch reflex. The ability to learn is abolished in vegetative patients, however (Owen 2008). The vegetative state is caused by a disruption of connectivity loops between the neocortex and cerebellum, two structures that must be connected for learning and consciousness (Tehovnik, Hasanbegović, Chen 2024).
Hasanbegović and her collaborators (Gao et al. 2018; Guo, Hantman et al. 2021; Hasanbegović 2024; Zhu, Hasanbegović et al. 2023) have shown that silencing any part of a neocortico-cerebellar loop (including at the neocortex, the pons, the cerebellum, or the thalamus) disrupts discrimination behavior. Mice were trained to detect a tactile probe that signaled whether a left or right water-spout needed to be contacted to receive a reward. Optogenetics was used to silence a loop during a memory period, which systematically interrupted a mouse’s performance. Using resting-state-functional connectivity fMRI, it has been established that islands of association neocortex are connected to corresponding regions of the cerebellum (Buckner 2013; Buckner et al. 2011; Diedrichsen et al. 2019; Marek et al. 2018). For example, it is known that prism adaptation is subserved by distinct neocortico-cerebellar regions such that damage to these regions compromises the adaptation (Kurata and Hoshi 1999; Morton and Bastian 2004a). The same correspondence exists for visually guided saccades and visual pursuit (Tehovnik, Hasanbegović, Chen 2024). Finally, some 95% of the neurons are found in the neocortex and cerebellum of all mammals (Herculano-Houzel 2009, 2012), which means these two structures together account for most of the neurons in the brain and these neurons must be connected (via loops) for learning and consciousness to be realized (Plum and Posner 1980; Owen 2008).
Once patients in a vegetative state begin to recover, islands of neocortical tissue start to become responsive (Levy et al. 1987; Monti et al. 2010; Owen 2008; Owen et al. 2006; Schiff, Llinas et al 2002). We would suggest that this responsivity is dependent on recovery of not only neocortical tissue, but also cerebellar tissue. The recovery process should be based on loop recovery, since it is the loops that must be functional to mediate behavior (Gao et al. 2018; Guo, Hantman et al. 2021; Hasanbegović 2024; Zhu, Hasanbegović et al. 2023). For instance, the restoration of all language loops following mesencephalic damage should restore all languages that were initially lost (Mariën et al. 2017; Ojemann 1991).
- Badges
- Science topic
- Similar topics
- Biological Science
- Molecular Biology
- Biomolecules
- Nucleic Acids
- RNA