Cortical-Subcortical Interactions and the Regulation of the Functional State of the Brain in Acute Hypoxia in Humans

Abstract

The mechanisms regulating the functional state (FS) of the brain were studied in humans in conditions of dosed acute hypoxia (breathing a mixture of 8% oxygen in nitrogen for 15-25 min). The dynamics of the FS of the brain due to changes in the balance of the activities of brain regulatory structures in hypoxia were reflected in rearrangements of EEG spatial relationships (factor and cluster analysis of EEG crosscorrelation matrixes) and the redistribution of intracerebral locations of electrically equivalent dipole sources (EEDS), with increases in EEDS density in the projections of the medial and basal parts of the temporal lobes of the hemispheres (EEDS tomography data). Changes in cortical-subcortical interactions were characterized by a decrease in the tone of the activatory brain system, a decrease in the inhibitory control of subcortical structures by neocortical formations, and activation of limbic system and hypothalamic structures. Switching of the integrative regulatory mechanisms from the cortico-thalamic level to the limbic-diencephalic level may allow release of the energy-consuming nonspecific components of hypoxic stress and more stable regulation of physiological parameters by the major vital systems in conditions of increasing oxygen deficit.

Acute and chronic hypoxia: implications for cerebral function and exercise tolerance

“…Normobaric hypoxia was administered in the form of a lowered fraction of inspired O 2 (F I O 2 = 0.08) to participants for 15–25 min (S p O 2 ≤75%). In line with the EEG-hypoxia literature, it was found that the acute exposure to hypoxia was accompanied by slowing and synchronisation of the EEG signals (50). Such a reduction and synchronisation of the EEG signal was said to characterise a functional brain state that was relatively lower compared to baseline (i.e.…”

“…Due to the differences in the severity and time of hypoxic exposure or methods utilised, direct comparisons between previous investigations are difficult to make. However, it does seem that the greatest change in EEG occurs at a similar S p O 2 or oxygen tension (PO 2 ) (≤75% or ≤40 mmHg; 35, 44, 48, 50). Nevertheless, such slowing of the EEG signal might reflect the previously discussed widespread depolarisation of cerebral neurons known to occur in AH.…”

“…Rozhkov and colleagues (50) investigated changes in the balance of brain regulatory structures and rearrangement of the multi-channel EEG signal at rest during a period of AH. Normobaric hypoxia was administered in the form of a lowered fraction of inspired O 2 (F I O 2 = 0.08) to participants for 15–25 min (S p O 2 ≤75%).…”

“…This is, however, a functionally necessary state for the brain to adopt as transferring from a high level of function to a lower level state, would lead to a reduction in neuronal energy cost providing the essential reserves for survival in hypoxia (27, 50). Moreover, in addition to changes in characteristics of the EEG signal, the authors report rearrangements in temporospatial relationships between oscillations of cortical potentials, demonstrating reorganisation of the inter-centre interactions within the CNS (50). Specifically, acute hypoxia led to a rearrangement of electrical activity in a lateral direction which may have reflected involvement of structures within the medial and basal area of temporal lobes (Figure 2).…”

“…Specifically, acute hypoxia led to a rearrangement of electrical activity in a lateral direction which may have reflected involvement of structures within the medial and basal area of temporal lobes (Figure 2). Such an increase in the electrical activity in these regions of the brain is thought to reflect activation of the limbic system (hippocampus, denate nucleas and amygdaloid complex; 50). The limbic system plays a central role in integrating the emotional-motivational and autonomic-visceral components of the body’s activity under different conditions (54); thus, the limbic system occupies an important position to initiate the body’s adaptation when in an oxygen deprived environment.…”