Cortical metabolic changes in disorders of consciousness follow canonical functional gradients
Poster No:
2022
Submission Type:
Abstract Submission
Authors:
Elizaveta Baranova-Parfenova1, Timothy Lane2, Niall Duncan1
Institutions:
1Graduate Institute of Mind Brain and Consciousness, Taipei Medical University, Taipei, Taiwan, 2Institute of European and American Studies, Academia Sinica, Taipei, Taiwan
First Author:
Elizaveta Baranova-Parfenova
Graduate Institute of Mind Brain and Consciousness, Taipei Medical University
Taipei, Taiwan
Graduate Institute of Mind Brain and Consciousness, Taipei Medical University
Taipei, Taiwan
Co-Author(s):
Niall Duncan, Dr
Graduate Institute of Mind Brain and Consciousness, Taipei Medical University
Taipei, Taiwan
Graduate Institute of Mind Brain and Consciousness, Taipei Medical University
Taipei, Taiwan
Introduction:
Disorders of consciousness (DoC) are serious pathological states in which an individual has lost all conscious awareness or has limited consciousness for an extended period of time. Such a state may result from a variety of insults that cause damage to the brain. Understanding these conditions is important from a clinical perspective, to guide treatment and to allow accurate prognosis. They are also of interest from a purely scientific perspective as they represent a condition in which humans can have preserved physiological functions but no consciousness. The brain changes seen in such conditions may therefore provide clues as to necessary neural correlates of consciousness.
Amongst prominent theories of consciousness there is a consistent idea that it requires the integration of information from sources such as sensation and memory. At the same time, recent work has pointed to organisational principles in the brain that follow a general gradient from unimodal sensory regions to associative cortex. We might expect, therefore, that loss of consciousness may correspond more with changes in such associative regions than in sensory regions.
Amongst prominent theories of consciousness there is a consistent idea that it requires the integration of information from sources such as sensation and memory. At the same time, recent work has pointed to organisational principles in the brain that follow a general gradient from unimodal sensory regions to associative cortex. We might expect, therefore, that loss of consciousness may correspond more with changes in such associative regions than in sensory regions.
Methods:
To investigate the supposition that associative regions are more affected in consciousness loss than sensory, we obtained cortical glucose metabolism measures (FDG-PET) from a group of DoC patients (n = 69) and from fully conscious controls (n = 19). DoC patients included people diagnosed with unresponsive wakefulness syndrome and in a minimally conscious state. FDG-PET values were normalised for each individual relative to values in non-neural tissue. An average group difference (i.e., controls-patients) in glucose metabolism was then calculated for each of the 180 regions in the right HCP-MMP1 atlas. Gradient values from the first five canonical functional gradients reported by Margulies et al. (2016) were then obtained for the same 180 regions. Finally, metabolism difference values were correlated with gradient values. (See Figure 1 for an overview.)
Results:
Differences in glucose metabolism were positively correlated with the first functional gradient, going from unimodal to associative gradient ends (r = 0.17, pFDR = 0.035; Figure 2A). No association with the second or fourth gradients was seen (Figure 2B&D). A negative correlation between glucose metabolism difference and gradient position was seen for the third (r = -0.19, pFDR=0.024; Figure 2C) and fifth gradients (r = -0.21, pFDR=0.018; Figure 2E).
Conclusions:
These results support a model of consciousness based upon the necessity of information integration as neural function appears to be more retained in unimodal regions than at the associative end of the primary functional gradient. This suggests that, regardless of retained activity in sensory regions, consciousness does not arise without corresponding activity potential in brain regions involved in information integration. The third gradient follows a pattern similar to a progression from default to salience network. The negative correlation observed therefore raises interesting questions about the relationship between these networks in consciousness, with both of them having been previously highlighted in studies adopting different measures of brain activity. Finally, the fifth gradient has been associated with the olfactory system (Waymel et al., 2020). A correlation between this and loss of consciousness may be related to work showing that retention of olfactory responses is associated with recovery of consciousness (Arzi et al., 2020). Together, these results provide new insights into the patterns of neuro-metabolic changes seen in DoC patients, highlighting how these correspond to core organisational principles of the brain.
Novel Imaging Acquisition Methods:
PET
Perception, Attention and Motor Behavior:
Consciousness and Awareness 1
Physiology, Metabolism and Neurotransmission:
Cerebral Metabolism and Hemodynamics 2
Keywords:
Consciousness
Neurological
Positron Emission Tomography (PET)
1|2Indicates the priority used for review
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Margulies, D. S. (2016). Situating the default-mode network along a principal gradient of macroscale cortical organization. Proceedings of the National Academy of Sciences, 113(44), 12574–12579. https://doi.org/10.1073/pnas.1608282113
Waymel, A. (2020). Anchoring the human olfactory system within a functional gradient. NeuroImage, 216, 116863. https://doi.org/10.1016/j.neuroimage.2020.116863