Key findings

• Brain scans from people with ME/CFS and those with long COVID were analysed to determine the volumes of different regions of the hippocampus.

• The hippocampus is a brain structure involved in memory and learning.

• Compared with healthy control subjects, individuals in both patient groups had significantly larger volumes of several areas (subfields) of the hippocampus.

• Hippocampus subfield volumes were similar in ME/CFS and long COVID patients.

• These volumes also correlated with symptom severity for measures of pain, illness duration, fatigue, concentration, unrefreshing sleep and physical function.

• Structural alterations in the hippocampus may therefore contribute to the symptoms of both ME/CFS and long COVID.

Their findings in ME/CFS to date include brainstem volume changes (which correlated with measures of pain and breathing difficulty), impaired functional connectivity between specific brain regions, and raised brain neurochemical levels.

Another, earlier study also found differences in the hippocampus in people with ME/CFS. The hippocampus is a brain structure involved in memory and learning, and is comprised of different areas, or subfields, which each have specific jobs.