Cross-frequency coupling in psychiatric disorders: A systematic review.

Cross-frequency coupling (CFC), an electrophysiologically derived measure of oscillatory coupling in the brain, is believed to play a critical role in neuronal computation, learning and communication. It has received much recent attention in the study of both health and disease. We searched for literature that studied CFC during resting state and task-related activities during electroencephalography and magnetoencephalography in psychiatric disorders. Thirty-eight studies were identified, which included attention-deficit hyperactivity disorder, Alzheimer's dementia, autism spectrum disorder, bipolar disorder, depression, obsessive compulsive disorder, social anxiety disorder and schizophrenia. The systematic review was registered with PROSPERO (ID#CRD42021224188). The current review indicates measurable differences exist between CFC in disease states vs. healthy controls. There was variance in CFC at different regions of the brain within the same psychiatric disorders, perhaps this could be explained by the mechanisms and functionality of CFC. There was heterogeneity in methodologies used, which may lead to spurious CFC analyses. Going forward, standardized methodologies need to be established and utilized in further research to understand the neuropathophysiology associated with psychiatric disorders.

Dyspnea-fasciculation syndrome: early respiratory failure in ALS with minimal motor signs.

BACKGROUND: Respiratory failure (RF) in ALS typically occurs as a late manifestation. While there are uncommon patient reports of early RF, most had moderate limb and bulbar weakness. DESIGN/METHODS: We reviewed clinical and laboratory data from 3 patients with ALS, early RF, and minor motor signs. RESULTS: Patients were male, ages 62, 75 and 80 years. The patients presented with 6 months to 2 years of exertional and nocturnal dyspnea, daytime hypersomnolence, limb fatigability, and weight loss. Exam showed tachypnea, slight distal limb weakness, and hyperreflexia. All three patients had prominent fasciculations, insomnia, supportive EMG findings, FVC (32-74% predicted), PO2 (50-80 mmHg), PCO2(52-76 mmHg) and required BiPAP (Bi-level positive airway pressure). One patient had a reduced FEV1/FVC of 0.55 and a 15% increase in FEV1 post-bronchodilator suggesting concurrent chronic obstructive pulmonary disease (COPD). However, his P(A-a)O2 was only 7 mmHg suggesting COPD was not the major factor causing respiratory failure; his extreme hypercapnea could not be explained by ALS or COPD alone. CONCLUSIONS: ALS may present with unexplained RF, or sleep disturbance resembling sleep apnea, without significant bulbar or limb weakness. In our experience, such patients are elderly with dyspnea, fasciculations, and other minor motor signs: the Dyspnea-Fasciculation Syndrome. Concurrent COPD may augment the effect of ALS, resulting in earlier RF. FVC may be relatively preserved, despite hypercapnia.