Neuroimaging confirms that sleep apnea takes a toll on brain function.


One in 15 adults has moderate to severe obstructive sleep apnea (OSA), a disorder in which a person’s breathing is frequently interrupted during sleep, as many as 30 times per hour.  People with sleep apnea also often report problems with cognition such as poor concentration, difficulty with memory as well as decision-making, depression, and stress.  Now, a study from researchers at the UCLA School of Nursing shows significant changes in the levels of two important brain chemicals in people with sleep apnea, which could be a reason that many have symptoms that impact their day-to-day lives.  The opensource study is published in the Journal of Sleep Research.

Previous studies show structural brain alterations in OSA could arise from multiple pathologies. MRI differences appear in the insular cortex during autonomic challenges. The processes underlining those differences could be elucidated by determining the levels of the neurotransmitters glutamate and γ-aminobutyric acid (GABA), which can now be measured non-invasively. Levels of these chemicals are sensitive to neural reorganization in response to injury, and can reflect different functional states. High levels of glutamate, in particular, are associated with excitotoxicity, a probable mechanism of injury in some brain areas in OSA.  GABA is a chemical messenger that acts as an inhibitor in the brain, which can slow things down and help to keep people calm. GABA affects mood and helps make endorphins.  Glutamate, by contrast, is like an accelerator; when glutamate levels are high, the brain is working in a state of stress, and consequently doesn’t function as effectively. High levels of glutamate can also be toxic to nerves and neurons.  The current study investigated GABA and glutamate in the anterior insular cortex in OSA patients, relative to healthy subjects.

The current study observed 14 OSA patients and 22 healthy subjects, no participants had a history of head trauma or disease, current mental illness, use of psychoactive medications, cancer or cardiac disease.  The lab investigated levels of the neurotransmitters glutamate and GABA, in the insula brain region, with magnetic resonance spectroscopy (MRS).

Results show that people with sleep apnea had decreased levels of GABA and unusually high levels of glutamate.  The lab explain that it is rare to have this size of difference in biological measures and were surprised to see the drop in GABA.  They go on to state that this suggests that there is a reorganization of how the brain is working.

The team surmise that their findings show that what comes with sleep apnea are these changes in the brain, so in addition to prescribing continuous positive airway pressure (CPAP) physicians now know to pay attention to other symptoms such as stress, concentration and memory loss.  For the future, the researcher hope to determine whether treating the sleep apnea, using CPAP or other methods, returns patients’ brain chemicals back to normal levels; if not, they will turn to the question of which treatments could be more effective. They go on to conclude that they are also studying the impacts of mindfulness exercises to see if they can reduce glutamate levels by calming the brain.

Source: UCLA School of Nursing

 

Left: example insula voxel is shown in red (15 mm3) overlaid an individual anatomical scan. Right: example two-dimensional magnetic resonance spectroscopy (2D-MRS) spectra from right insulae in obstructive sleep apnea (OSA) (56-year-old female) and control (53-year-old male) subjects, with resonances of various neurochemicals indicated (Cho, choline; Cr, creatine; mI, myo-inisotol; MM, other macromolecules; NAA, N-acetylaspartate; Tau, taurine).  Obstructive sleep apnea is associated with low GABA and high glutamate in the insular cortex.  Thomas et al 2016.

Left: example insula voxel is shown in red (15 mm3) overlaid an individual anatomical scan. Right: example two-dimensional magnetic resonance spectroscopy (2D-MRS) spectra from right insulae in obstructive sleep apnea (OSA) (56-year-old female) and control (53-year-old male) subjects, with resonances of various neurochemicals indicated (Cho, choline; Cr, creatine; mI, myo-inisotol; MM, other macromolecules; NAA, N-acetylaspartate; Tau, taurine). Obstructive sleep apnea is associated with low GABA and high glutamate in the insular cortex. Thomas et al 2016.

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