Hippocampal Damage Links Memory Loss to Apathy in Encephalitis Patients

Neurological Research Uncovers Biological Mechanisms Behind Memory Loss and Apathy

Hippocampal Damage and Behavioral Changes in Encephalitis

For patients diagnosed with autoimmune limbic encephalitis, memory impairment and a lack of motivation often occur in tandem. A study published July 20, 2026, in JNeurosci, titled "Working Memory Deficits in Hippocampal Amnesia are Associated with Apathy" (DOI: 10.1523/JNEUROSCI.0543-26.2026), was led by Bahaaeddin Attaallah of Imperial College London and Maria Raquel Maio of the University of Oxford. The researchers explored the mechanics behind this association by comparing patients with the condition to healthy controls.

The study found that patients were less able than healthy controls to pair objects with specific locations in a memory task. The researchers noted that, among patients alone, errors in the task were linked to apathy independent of depression symptoms or general cognitive ability. Imaging revealed that patients who made more errors had smaller hippocampi. These individuals also exhibited weaker connections between the hippocampus and prefrontal cortex. This behavioral and mechanistic link was observed only in the patient population. The research points to a brain mechanism in patients with autoimmune limbic encephalitis that may explain their impaired memory and dampened motivation. Moreover, these findings may have implications for other conditions that affect the hippocampus, such as Alzheimer’s disease, in which memory loss and apathy can also occur together.

Dopamine System Dysfunction in Long COVID Patients

While encephalitis patients show structural hippocampal issues, recent findings suggest long COVID symptoms—such as brain fog, memory problems, difficulty concentrating, and lack of motivation—may be rooted in the brain’s dopamine system. A study published in eBioMedicine used positron emission tomography (PET) brain imaging to measure vesicular monoamine transporter 2 (VMAT2), a marker of dopamine neuron integrity, in 24 adults with long COVID and persistent neuropsychiatric symptoms and in 24 healthy controls.

The research team, led by a team from the Brain Health Imaging Centre in Toronto and the University of Toronto, found lower levels of VMAT2, which indicates reduced dopamine nerve terminal density, in the brains of people with long COVID and neuropsychiatric symptoms compared with the control group. These lower levels were identified in the striatum, a region of the brain that plays key roles in reward and motivation, movement and motor control, and cognition. Specifically, participants with long COVID had 16% to 20% lower VMAT2 across three regions in the striatum compared with healthy controls. The largest differences were observed in the dorsal putamen, which is involved in movement, and the dorsal caudate, which is associated with memory. The smallest difference was observed in the ventral striatum, which is involved with motivation and reward.

"Our findings provide compelling evidence that long COVID involves the loss of dopamine-releasing neurons," said Jeffrey Meyer, MD, PhD, senior scientist at the Brain Health Imaging Centre and senior study author, in a news release from the Centre for Addiction and Mental Health. "This kind of injury is well known to produce symptoms like lack of motivation and motor slowing, and may contribute to memory difficulties in other neurological conditions. Our results suggest a similar process is occurring in long COVID."

Experts noted that these findings represent a shift in how the medical community approaches long COVID. Eric Guedj, MD, PhD, of Aix Marseille University in France, and Danielle Beckman, PhD, PharmD, of Helmholtz Munich, noted in an accompanying commentary: "This work shifts the discussion from symptom description to mechanistic stratification. By linking neuropsychiatric symptoms to a presynaptic dopaminergic marker, it reframes part of the long COVID spectrum as a measurable brain-network phenotype." Guedj and Beckman also noted that these changes are not necessarily permanent, and more longitudinal studies are needed to determine their clinical significance.

Future Directions for Neurological Research

The convergence of these findings suggests that apathy and memory loss are not merely psychological descriptors but are tied to distinct, measurable biological markers. Researchers remain cautious regarding the permanence of these changes. Meanwhile, investigators are expanding their scope regarding the overlap of memory and motivation. Speaking about future experimental plans, Bahaaeddin Attaallah said, "We are investigating the link between apathy and cognition in different cohorts with Parkinson’s disease and dementia using different methods, including large data analytics and experimental tasks. This will allow us to have a deeper understanding of how human memory and motivation overlap in these diseases."

If you are experiencing persistent neurological symptoms, please consult your healthcare provider for evaluation and personalized medical guidance.

Sources: Medicalxpress, miragenews.com.