This post summarizes “Acute Effects of Sceletium tortuosum (Zembrin), a Dual 5-HT Reuptake and PDE4 Inhibitor, in the Human Amygdala and its Connection to the Hypothalamus” by Terburg et al., published in Neuropsychopharmacology (2013). Read the full study.
What the study asked
This was the first human brain-imaging study on a kanna extract. The question: does a single serving change how the amygdala — the brain's threat-detection hub — responds to threatening faces?
Design
Sixteen healthy participants, aged 18 to 21, received a single 25mg serving of a standardized research extract (Zembrin) or a placebo in a double-blind, cross-over design, with sessions 5 to 9 days apart. Scanning ran two hours after administration.
Two fMRI tasks were used: a perceptual-load task measuring amygdala reactivity to fearful faces, and an emotion-matching task measuring amygdala connectivity with other brain regions.
Findings
Amygdala reactivity to fearful faces under low perceptual load was reduced after the extract compared to placebo. Coupling between the amygdala and the hypothalamus was also decreased. Other connectivity — midbrain, brainstem, prefrontal cortex — did not change, and participants reported no side effects.
The authors read this as attenuated threat responsivity in the amygdala and its subcortical connections, consistent with the extract's two laboratory activities: serotonin reuptake inhibition and PDE4 inhibition.
Limits
A small sample of healthy young adults, one low serving, and a focus on threat circuitry alone. The authors point to higher servings, repeated administration, and broader populations as next steps.
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