Magnesium L-Threonate (Magtein) Supports Cognition and Brain Health Dietary Supplement MagMind (Magnesium L-Threonate, or Magtein) is the only form of magnesium that has been shown, by promising research, to readily cross the bold-brain barrier and provide significant positive effects on cognition, memory and brain health. MagMind may also improve relaxation and sleep quality.