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Tag: Ketamine

  • PET brain scans map ketamine’s rapid antidepressant effect, pointing to a potential biomarker for treatment-resistant depression

    PET brain scans map ketamine’s rapid antidepressant effect, pointing to a potential biomarker for treatment-resistant depression

    Researchers in Japan have reported some of the clearest human evidence yet of how ketamine can relieve symptoms of treatment-resistant depression, using PET brain imaging to track changes in key glutamate receptors. The work adds molecular detail to a treatment already known for acting faster than standard antidepressants.

    Major depressive disorder is a leading cause of disability worldwide, and a substantial share of patients do not improve after trying multiple first-line therapies. For those with treatment-resistant depression, ketamine and the related medicine esketamine have drawn attention because some patients feel relief within hours or days rather than weeks.

    What the PET scans measured

    The study, published in Molecular Psychiatry, used a PET tracer called [11C]K-2 designed to visualize AMPA receptors, proteins that help regulate communication between brain cells. Scientists have long suspected that AMPA receptor activity is central to ketamine’s antidepressant effects, but direct confirmation in living people has been limited.

    The researchers combined data from three clinical trials, comparing 34 patients with treatment-resistant depression against 49 healthy participants. Patients received intravenous ketamine or placebo over a two-week period, with PET scans taken before treatment and after the final infusion.

    Receptor shifts tied to symptom relief

    Before treatment, the PET data suggested patients with treatment-resistant depression had region-specific differences in AMPA receptor availability compared with healthy controls. After ketamine, the brain changes were not uniform, instead appearing as shifts in particular areas involved in mood and reward processing.

    Crucially, the degree and location of AMPA receptor changes tracked with how much a patient’s depressive symptoms improved. The authors highlighted especially notable shifts in regions linked in prior research to depression circuitry, arguing the images provide a direct bridge between earlier animal findings and human clinical response.

    Why it could matter clinically

    If replicated, AMPA receptor PET imaging could become a candidate biomarker to help predict who is most likely to benefit from ketamine, and to guide dosing or treatment strategies. That could be valuable because ketamine response can vary, and clinicians are seeking ways to personalize care while balancing benefit, side effects, and monitoring needs.

    The researchers caution that PET imaging is complex and not widely available, and larger studies would be needed before it could influence routine practice. Still, mapping ketamine’s effects at the receptor level may also support development of new rapid-acting antidepressants that target similar pathways with fewer practical barriers.

  • Stanford study maps how brief stimuli can sustain emotions, revealing a shared brain timing signature in humans and mice

    New research from Stanford Medicine offers a clearer look at how fleeting sensory events can set off emotional states that linger well beyond the trigger. The findings, reported in Science, point to a conserved brainwide timing pattern seen in both humans and mice.

    To create a safe, precisely timed negative experience across species, the team used brief air puffs to the eye, similar to a common eye exam test. Participants described the sensation as annoying or uncomfortable, and repeated puffs led to a longer-lasting feeling of irritation.

    A two-phase brainwide response

    In hospitalized epilepsy patients who already had intracranial electrodes implanted for clinical monitoring, researchers recorded widespread neural activity during the eye-puff task. They observed a fast burst of activity within about 200 milliseconds, followed by a slower phase lasting roughly 700 milliseconds that involved emotion-linked circuits.

    When the same task was run in mice, the brain response showed a comparable two-phase pattern. Repeated puffs also produced a more persistent negative state, reflected in reduced reward-seeking behavior after the stimulus ended.

    Ketamine hints at a mechanism

    The team then tested ketamine, a drug known to blunt typical emotional reactions at certain doses while leaving basic sensory awareness intact. In both humans and mice, ketamine preserved the reflexive blink but reduced longer, self-protective eye closure between puffs.

    Neural recordings suggested why: ketamine selectively shortened the slower, sustained phase of activity without eliminating the initial rapid sensory broadcast. By compressing this integrative window, the drug appeared to limit the brain’s ability to maintain an emotional state from a brief event.

    Why timing may matter clinically

    Researchers say these measurable timing properties could help explain emotional symptoms that are either too persistent or too fleeting across psychiatric conditions. They also argue that brainwide synchrony and the duration of integrative activity may be key variables for future diagnostics and treatment research.

    The work builds on a cross-species approach designed to isolate fundamental, evolutionarily conserved principles of emotional processing. While the study focused on mildly aversive input, the authors say similar timing rules may also apply to positive experiences, an area they are continuing to investigate.