Meditation significantly improves global cognitive performance, sleep quality, and health status in older adults with subjective cognitive decline, mild cognitive impairment, and Alzheimer's disease. A meta-analysis of 25 randomized controlled trials involving 2,095 participants found that meditation raised Mini-Mental State Examination scores by an average of 2.22 points, improved Pittsburgh Sleep Quality Index scores by 1.40 points, and increased 36-Item Short Form Health Survey scores by 3.50 points. No significant effect on depression was detected. The findings suggest meditation is a useful adjunct therapy, though results should be interpreted cautiously due to heterogeneity and limited sample sizes.
Ketamine, a racemate of S-ketamine and R-ketamine, produces rapid and sustained antidepressant effects in rodent models and patients with treatment-resistant depression at subanesthetic doses. Its mechanisms involve glutamate receptors (NMDAR, AMPAR, mGluR5), molecular pathways (mTOR, ERK-CREB, PI3K/Akt), metabolites, opioid receptors, inflammation, and monoamines. S-ketamine has received FDA approval as a novel antidepressant. In rodent depression models (forced swimming test, novelty suppressed feeding, chronic social defeat stress, learned helplessness), R-ketamine showed more potent and prolonged effects without psychotomimetic side effects or abuse potential, though its clinical effects remain unclear. This review overviews ketamine's antidepressant mechanisms and differences between the two enantiomers.