The hippocampus is frequently damaged in epilepsy. It is deeply involved in Alzheimer’s disease and dementia. It is sensitive to stress, oxygen deprivation, inflammation, and aging. Scientists have long known that the hippocampus can shrink in disease, but understanding the chemistry that changes inside it while a person is still alive has remained an enormous challenge.

A series of studies from Prof. Jullie Pan of the University of Missouri Columbia and colleagues has helped illuminate this hidden chemistry. Taken together, these studies reveal a remarkable story about how the living brain manages energy, balances excitation and inhibition, and responds to injury. They also show how advanced magnetic resonance spectroscopy can detect subtle biochemical differences in the hippocampus that may eventually help researchers understand why some brains are more vulnerable to disease than others.

The most recent study, published in 2025, focused on a deceptively simple question. Are the left and right hippocampi chemically identical in healthy people? At first glance, the answer might seem obvious. The two hippocampi appear nearly symmetrical on brain scans. Yet neuroscientists have long known that the left and right sides of the brain are not functionally identical. The left hippocampus, in particular, plays a major role in verbal memory formation. Damage to this region can severely impair the ability to form and retrieve words and narratives.

Measuring the chemistry of the hippocampus in a living person, however, is extraordinarily difficult. The structure is small, curved, and buried deep within the brain. It sits near air-filled spaces in the skull that distort magnetic fields and complicate magnetic resonance imaging. Detecting tiny concentrations of molecules such as glutamine or creatine inside living human tissue requires remarkable technical precision.

To overcome these obstacles, Prof. Pan and colleagues used an advanced form of ultra high-field magnetic resonance spectroscopy at 7 Tesla, a magnetic field far stronger than most conventional hospital MRI systems. The researchers combined sophisticated radiofrequency control with highly specialized magnetic field shimming techniques to create unusually accurate measurements from the hippocampus.

The participants were healthy middle-aged and older adults who were cognitively normal and carried no APOE4 genetic risk factor for Alzheimer’s disease. Importantly, the researchers measured the left and right hippocampi separately rather than averaging them together.

What they found was striking. The left hippocampus consistently showed higher levels of several key metabolites than the right, in particular creatine and glutamine, with these two compounds known to be strongly associated with energy metabolism and excitatory glutamatergic neurotransmission, respectively.

Creatine is well known to be a key part of muscle physiology, stabilizing the energy supply in the face of large sporadic motor movement. It is similar in the brain, where neurons consume enormous amounts of energy with their fluctuating communication through electrical and chemical signals. Creatine and phosphocreatine provide a crucial energy buffering system to ATP to maintain cellular function during periods of high demand.

Glutamine, meanwhile, is tightly linked to glutamate, the brain’s primary excitatory neurotransmitter. Glutamate drives much of the signaling activity involved in learning and memory. After glutamate is released between neurons, surrounding support cells called astrocytes help recycle it through the glutamine pathway. Elevated glutamine can therefore reflect increased neurotransmitter cycling and metabolic activity.

The left hippocampus not only contained higher levels of these two metabolites, but the concentrations were also correlated with one another. This relationship appeared specifically in the left hippocampus and not the right.

These findings suggest that the left hippocampus operates with a distinct bioenergetic profile even in healthy people. In other words, consistent with the difference in cognitive function between the left and right, the two hippocampi are not mirror images. They appear to exhibit a different metabolic “poise” or balance.

This observation could have major implications. Previous imaging studies have shown that the left hippocampus may be more vulnerable to environmental stressors such as air pollution and age-related degeneration. Neuropsychological research has also demonstrated that verbal memory function depends heavily on the left hippocampus. The new findings raise the possibility that the left side’s greater metabolic activity may help explain both its specialized cognitive role and its potential vulnerability.

Prof. Jullie Pan has noted that preliminary data from a small group of cognitively normal APOE4 carriers showed markedly different measurements in the left hippocampus compared with this healthy control group. Although the APOE4 carrier group was too small for formal publication, the observation hints at the possibility that subtle metabolic differences may emerge long before symptoms of dementia appear.

If confirmed in future studies, this kind of chemistry-based imaging could eventually provide an early window into brain vulnerability decades before disease becomes clinically obvious.

The 2025 study was highly methodological in nature, emphasizing the importance of accurate measurements. Yet the biological meaning of these metabolic differences becomes even clearer when viewed alongside two earlier studies that explored what happens when the hippocampus is placed under extreme physiological stress.

In 2015, Prof. Pan and collaborators published a study examining the metabolic consequences of status epilepticus in rats. Status epilepticus is a prolonged seizure state that can produce severe neuronal injury and increase the likelihood of developing chronic epilepsy later in life.

The researchers used magnetic resonance spectroscopy together with imaging and histological analysis to track metabolic changes after seizures. Although the work was performed in rats, the study was designed to model processes relevant to human epilepsy and neurological injury.

The results revealed a dynamic and evolving biochemical response inside the hippocampus. One of the clearest findings was a decline in N-acetylaspartate, often abbreviated as NAA. NAA is widely considered a marker of neuronal health and mitochondrial function, with the mitochondria ultimately responsible for maintaining appropriate levels of energy currency, i.e., ATP and phosphocreatine. Lower NAA levels generally indicate impaired neuronal metabolism or injury.

At the same time, the researchers observed increases in glutamine and myo-inositol. Similar to but also distinct from the above human hippocampal studies, here the increase in glutamine can reflect the consequences of the dramatically increased abnormal activity from seizures. With glutamine and myo-inositol identified as key astrocytic compounds, these observations are consistent with the astrocyte’s role as support cells that regulate neurotransmitter recycling, maintain chemical balance, and help protect neurons during stress. Their activation is often a hallmark of brain injury and inflammation.

The study also identified important changes in glutathione, one of the brain’s key antioxidant molecules. Glutathione helps protect cells from oxidative stress generated during intense neuronal activity. In animals with more prolonged seizures, glutathione levels showed patterns suggesting that antioxidant defenses were being consumed as injury progressed.

Together, the findings paint a picture of the brain struggling to maintain metabolic stability under the extreme functional demand of seizures. Excitatory neurotransmission surged. Astrocytes increased their activity in an attempt to clear excess glutamate and protect neurons. Antioxidant systems were mobilized. Yet despite these responses, markers of neuronal mitochondrial integrity declined.

The work highlighted an important principle of brain biology. Neuronal activity is inseparable from energy metabolism. Every thought, memory, or electrical impulse carries an energetic cost. The human hippocampus, with its central role in learning and memory, may operate near the limits of metabolic demand. During seizures, that demand can become overwhelming.

This idea connects directly to the final study in the series, published in 2008. Unlike the 2015 rat study, this investigation involved living human epilepsy patients undergoing intracranial monitoring before brain surgery.

The study was unusual and remains rare even today because it combined intracranial microdialysis with pre-operative magnetic resonance spectroscopy. Microdialysis allows researchers to measure extracellular neurochemicals directly within living brain tissue. In this case, the team focused on extracellular GABA, the brain’s principal inhibitory neurotransmitter.

GABA acts as a counterbalance to glutamate. If glutamate accelerates neuronal signaling, GABA applies the brakes. Healthy brain function exhibits a delicate balance between excitation and inhibition. It is believed that in seizures and epilepsy (particularly of the common “focal onset” type of epilepsy), this balance is not working correctly, particularly in the brain region of seizure onset.

In the seizure onset regions – which can be thought to harbor excessive excitation – the researchers discovered that higher extracellular GABA was associated with poorer mitochondrial function or NAA levels. This suggested a failure of extracellular GABA to inhibit this region as seen by the worsening neuronal mitochondrial function. Outside the seizure onset region, however, higher GABA levels were associated with better neuronal metabolic markers.

The findings implied that inhibitory signaling behaves differently in healthy versus diseased tissue. In the healthier brain outside the seizure onset region, increased GABA may reflect appropriate compensatory inhibition. In the diseased seizure onset region, it may indicate a failing system attempting to contain pathological excitation. Therefore, even though extracellular microdialysis GABA levels were similar in both groups of patients, it was the energetic and mitochondrial parameter that most clearly separated them.

Taken together, the three studies reveal a remarkably coherent picture of hippocampal biology. The hippocampus is a cognitively essential (especially for humans!) and metabolically intense region whose function depends on delicate coordination between neurons, glial cells, neurotransmitters, antioxidants, and energy buffering systems.

The 2025 study shows that even healthy hippocampi exhibit subtle metabolic asymmetries that may reflect specialized cognitive functions and differential vulnerability to disease. The 2015 study demonstrates how these systems respond dynamically during severe neuronal stress. The 2008 study provides direct evidence from living humans that mitochondrial function and inhibitory neurotransmission are intimately connected in epilepsy.

Across all three investigations, one theme repeatedly emerges. Brain function cannot be separated from brain metabolism. This insight is becoming increasingly important in modern neuroscience. For decades, neurological disease was often understood primarily through anatomy. Researchers focused on plaques, cell death, atrophy, or structural lesions visible on scans or under microscopes. But not surprisingly, metabolism changes well before structural damage becomes apparent. Measuring the chemistry of living brain tissue offers a chance to detect vulnerability earlier and perhaps intervene before irreversible injury occurs.

This is especially relevant for disorders such as Alzheimer’s disease, where pathology may begin decades before symptoms emerge. If future work confirms that metabolic signatures in the hippocampus differ in genetically at-risk individuals, spectroscopy could become a powerful tool for early detection and monitoring.

The work also highlights the importance of technical innovation in neuroscience. Measuring millimolar concentrations of metabolites inside a deep brain structure is not trivial. Small distortions in magnetic fields can significantly alter results. The methodological advances developed by Prof. Jullie Pan and collaborators were essential for detecting the subtle left-right differences observed in healthy hippocampi.

Scientific breakthroughs often depend not only on asking the right biological questions, but also on building the tools capable of answering them. Ultimately, these studies remind us that the brain is a living chemical ecosystem in constant motion. Neurons fire, astrocytes recycle neurotransmitters, mitochondria generate energy, antioxidants counter oxidative stress, and inhibitory systems struggle to maintain balance.

Within the hippocampus, these processes are especially intense because memory itself is metabolically expensive. Every remembered conversation, learned language, or emotional experience depends on this hidden chemistry operating correctly.