What are the two brains of the human body?

The human brain has long been considered the master controller of the body, directing everything from our thoughts and emotions to our physical movements. But new research reveals that we have a "second brain" located in our gut. This blog explores how our central nervous system collaborates with the enteric nervous system—home to trillions of gut microbes—to shape our overall health. We delve into the fascinating function of both brains, the science behind the gut-brain axis, and the pivotal role gut microbiome testing plays in deciphering this connection. Readers will discover how this integrative relationship impacts everything from mood and mental clarity to immune function and digestive health.

Introduction

The term “two brains of the human body” might sound like a figure of speech, but modern science validates this concept with compelling evidence. The human brain, located in the skull, has traditionally held the spotlight for its role in controlling bodily processes and interpreting the world around us. However, nestled within our gut exists an equally intricate and autonomous system: the enteric nervous system (ENS), often referred to as the “second brain.”

This enteric brain contains over 100 million neurons and can operate independently of the central nervous system. Recent breakthroughs in neuroscience, gastroenterology, and microbiology affirm that this gut-based system does more than digest food—it communicates constantly with the brain, affecting behavior, mood, and cognitive function. This interplay, known as the gut-brain axis, has emerged as a focal point in health and wellness research.

An invaluable tool in understanding and optimizing the gut-brain connection is gut microbiome testing. Through analyzing the trillions of microorganisms residing in our digestive tract, microbiome tests can reveal the balance or imbalance within this ecosystem, offering insights into both physical and mental health. Understanding this connection not only helps us address conditions like anxiety, depression, and brain fog but also informs personalized interventions to support neurobiological and microbiome health simultaneously.

In this article, we explore the science of the two brains, their interdependent roles, and how microbiome testing provides a personalized roadmap for healing and performance optimization.

1. The Human Brain and the Gut: Bridging Neurobiology and Microbiology

The human brain has always occupied the central position in discussions of intelligence, consciousness, and bodily coordination. Enclosed within the skull, it comprises more than 85 billion neurons organized into complex networks that orchestrate thoughts, emotions, movements, and vital physiological processes. However, findings from the past two decades have sparked a paradigm shift, revealing that the gut, specifically the enteric nervous system (ENS), holds remarkable neurological capabilities.

The ENS resides within the walls of the gastrointestinal tract, spanning from the esophagus to the rectum. Sometimes called the “second brain,” this network contains sensory neurons, interneurons, and motor neurons amounting to roughly 100 million nerve cells—more than the spinal cord. Importantly, the ENS communicates bidirectionally with the central nervous system through the vagus nerve and biochemical signaling.

What sets the gut “brain” apart is its intimate interaction with the gut microbiome. The human gut harbors trillions of microorganisms, including bacteria, archaea, fungi, and viruses. These microbes regulate digestion, synthesize vitamins, train the immune system, and, notably, produce neuroactive compounds such as serotonin, dopamine, and gamma-aminobutyric acid (GABA). In fact, approximately 90% of the body’s serotonin is produced in the gut.

This ongoing crosstalk between the human brain and the gut impacts a wide range of cognitive functions. For example, mood disorders such as depression and anxiety have been linked with imbalances in the gut microbiota. Similarly, conditions like Alzheimer’s disease, Parkinson’s disease, and autism spectrum disorders correlate with dysbiosis—a disrupted microbiome.

Gut microbiome testing serves as a bridge connecting science with actionable health insights. By analyzing fecal samples, these tests identify the presence, type, and relative abundance of microbes in a person’s gut. This data can be used to identify pathogenic imbalances or deficits in beneficial bacteria crucial for neurotransmitter production and immune modulation.

With growing awareness of the gut-brain axis, individuals are turning to microbiome testing not only for digestive issues but also for improving mental clarity, reducing symptoms of chronic fatigue, and supporting emotional regulation. It allows us to intervene proactively using diet, prebiotics, probiotics, and lifestyle changes that restore microbial balance and support both biological and neurological health. Bridging neurobiology and microbiology unlocks a holistic strategy to optimize the full spectrum of our well-being.

2. Neural Hemispheres: Symmetry and Specialization in the Brain and Gut-Brain Axis

The human brain is structurally divided into the left and right hemispheres, each with distinct but interrelated functions. The left hemisphere typically governs logical reasoning, language, and analytical tasks, while the right hemisphere is associated with creativity, emotional processing, and spatial reasoning. Although both sides of the brain contribute to all activities, this lateralization of function influences how we think and react to our environment.

Interestingly, emerging science suggests that the gut-brain axis may exhibit similar forms of lateral specialization. Research indicates that certain microbiome-related activities may correlate more strongly with either the left or right hemisphere depending on the type of neural processing affected. For example, the right hemisphere’s emphasis on emotional regulation seems to be acutely sensitive to microbial imbalances, which can aggravate conditions like generalized anxiety or social stress. Meanwhile, left-hemispheric activities such as cognitive planning or language fluency may be influenced by microbial species involved in nutrient absorption and neurotransmitter production.

Functional magnetic resonance imaging (fMRI) studies show asymmetric activation in response to inflammatory signals originating in the gut. These signals, conveyed through the vagus nerve and inflammatory cytokines, influence neuroplastic changes in the cerebral cortex, and lateralization plays a role in how these changes manifest. The implication is clear—neuronal hemispheric dominance may skew which symptoms or vulnerabilities a person experiences from a disrupted gut environment.

Microbiome testing reveals clues about these interactions. By identifying specific deficiencies or overgrowths—such as too much Proteobacteria (linked to anxiety), or low Bifidobacterium (crucial for GABA production)—clinicians and individuals can map microbial signatures to psychological and cognitive patterns. When integrated with neuropsychological assessments that identify hemispheric dominance (e.g., via response-based tests or EEGs), tailored interventions become feasible.

For instance, someone with right-hemisphere dominance and microbiome-induced emotional dysregulation might benefit more from strains like Lactobacillus rhamnosus, which facilitate stress resilience and mood stability. Conversely, left-dominant individuals with cognitive fatigue and microbiome imbalance might prioritize strains known to increase brain-derived neurotrophic factor (BDNF).

Understanding the gut-brain axis through the lens of neural hemispheres enables a novel framework for designing highly personalized health plans. As we continue to unravel the symmetries between brain and gut functionality, microbiome testing proves critical in navigating this complexity with precision and purpose. The end goal is balanced interhemispheric communication fueled by an optimally diverse and resilient gut microbiota—a true harmony between our two brains.

3. Brain Functions: Cognitive Processes, Emotional Regulation, and Gut Microbiota

The brain executes a wide range of functions that govern memory, learning, problem solving, decision-making, attention, and emotional control. These activities rely on intricate electrical and chemical signaling between neurons—networks that rely heavily on a supportive and stable biological environment. Recent advances in psychobiotics and neurogastroenterology reveal that our gut microbiota plays a substantial role in facilitating or disrupting these brain functions.

One of the most direct influences of gut microbes on the brain is through the production of neurotransmitters and neuromodulators. For instance, certain strains of Lactobacillus and Bifidobacterium contribute to the synthesis of GABA, serotonin, and dopamine. These compounds are critical for maintaining a stable mood, reducing anxiety, and enhancing focus and memory retention.

Furthermore, gut microbes affect brain function through the regulation of the immune system and the integrity of the gut lining. When harmful bacteria proliferate, they may create systemic inflammation and increase intestinal permeability (often referred to as “leaky gut”). This inflammatory cascade can cross the blood-brain barrier, leading to neuroinflammation, which has been closely linked to cognitive decline, depression, and even the onset of neurodegenerative diseases.

Microbiome testing offers a practical window into this complex ecosystem. Results from these analyses highlight microbiota diversity, richness, and the relative abundance of key families such as Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Deviations from optimal proportions may point to dysbiosis affecting mental health.

Microbiome tests can also detect microbial metabolites like short-chain fatty acids (SCFAs), particularly butyrate, which plays a vital role in neurogenesis and blood-brain barrier integrity. Butyrate-producing bacteria like Faecalibacterium prausnitzii and Roseburia are known to protect against inflammation and oxidative stress in the brain.

Mapping this data to real-world symptoms—such as brain fog, impulsivity, poor concentration, or emotional volatility—enables individuals to make data-driven changes. These may include increasing dietary prebiotics to nourish beneficial microbes, introducing targeted probiotic strains, or reducing sugar intake to hinder pathogenic fermentation.

As scientific understanding evolves, gut-focused interventions are increasingly seen as powerful complements to traditional neurological and psychiatric treatments. From enhancing cognitive sharpness to stabilizing mood disorders, treating the gut coequally with the brain leads to holistic improvements. The message is clear: a healthy microbiome is not just good for digestion—it’s crucial for mental acuity and emotional freedom.

4. Cerebral Cortex: Higher-Order Thinking and the Microbiome's Role in Neuroplasticity

The cerebral cortex is the outer layer of neural tissue covering the brain and is responsible for some of the most advanced human capabilities, including conscious thought, language processing, imagination, and reflective thinking. It plays a key role in what makes us uniquely human. Concerns such as memory retention problems, decreased attention span, and decision-making difficulties often stem from imbalances or stagnation in this brain layer's function.

Neuroplasticity—the brain's remarkable ability to reorganize itself by forming new neural connections—underpins learning, recovery from injury, and adaptation to new experiences. Researchers are now uncovering that certain gut microbes have profound influence over this process.

Microbiota influence neuroplasticity both directly and indirectly. Short-chain fatty acids like acetate, propionate, and butyrate, created through the fermentation of dietary fiber by gut bacteria, modulate gene expression involved in neuron growth. These SCFAs act as epigenetic modifiers and promote BDNF, a key protein involved in learning and memory.

Beyond this, some microbial metabolites mimic neurotransmitters or interact with receptors in the brain, fine-tuning the degree to which neurons respond and adapt. Gut-derived tryptophan, for example, acts as a precursor to serotonin, which influences mood and decision-making. Alterations in the microbial manufacturing of these substances can impair neuroprogression and learning capacity.

Microbiome testing can detect if an individual’s gut flora lacks the diversity or composition required to sustain robust neuroplastic functionality. Low populations of Bifidobacterium longum, Akkermansia muciniphila, and Prevotella copri could diminish production of enteric neuroactive compounds, thereby stalling cognitive adaptability.

Personalized intervention based on microbiome testing not only addresses existing cognitive limitations but can actively support learning endeavors, creative expression, and intellectual performance. A microbiome rich in diversity and beneficial metabolites enhances cerebral cortex function just as surely as sleep, exercise, or academic engagement.

Overall, gut microbes do not merely assist cognitive function—they appear indispensable to the architecture of thought itself. Recognizing the gut's role in nurturing neuroplasticity marks a revolutionary shift in our approach to education, therapy, and personal development.

5. Neural Communication: The Gut-Brain Axis and Signaling Pathways

Communication between the two brains—the central brain and the enteric nervous system—occurs across the gut-brain axis, a complex bidirectional network comprising neural, hormonal, and immune pathways. Understanding these signaling routes is essential to decipher how our thoughts, emotions, and behaviors are shaped from below the neck.

The vagus nerve operates as the primary neural highway between brain and gut, transmitting information about the state of the gut environment back to the brain. This sensory feedback can influence everything from food cravings and satiety to mood and motivation. For example, increased vagal tone—a sign of healthy vagus nerve function—is linked with reduced inflammation and greater emotional regulation.

Hormonal signaling also plays a vital part in gut-brain communication. The hypothalamic-pituitary-adrenal (HPA) axis drives stress responses, and its feedback loops are modulated by gut microorganisms. Imbalance in the microbiota affects circadian rhythms and cortisol output, leading to chronic stress states, insomnia, and impaired impulse control.

Likewise, microbial influence on the immune system is profound. Excessive endotoxins like lipopolysaccharides (produced by gram-negative bacteria) compromise the blood-brain barrier and trigger systemic inflammation. This inflammatory state can disorient neural signaling and impair synaptic plasticity.

Gut microbiome testing pinpoints key biomarkers indicating dysfunction in these pathways. Imbalances like low diversity, high pathobiont count, or insufficient SCFA production often mirror imbalanced stress responses, fatigue, and disorders rooted in neural signaling problems.

Through customized intervention plans based on testing outputs—such as probiotic supplementation, vagal nerve toning practices (like breathing exercises), or polyphenol-rich nutrition—individuals can restore this communication axis to a state of resilience. Treating both ends of the gut-brain axis ensures optimal systemic harmony and a clearer mental state.

6. Brain Hemispheres and the Gut: Lateralization and Microbiome Differences

As evidence continues to emerge around the brain’s hemispheric influence on bodily regulation, researchers are beginning to probe how each side might uniquely engage with gut functions. This concept, referred to as lateralization, implies specialized communication patterns between specific brain regions and the gut—and it may shape the microbial ecosystem itself.

For example, right-hemisphere-related mood centers in the limbic system show enhanced vagal connectivity with the gut during emotional arousal or stress situations. As a result, individuals with right-hemispheric dominance may face a greater psychosomatic burden from gut-related issues. Conversely, the left hemisphere’s association with executive function and planning may reflect microbial interactions impacting cognitive regulation.

Microbiome testing adds dimension to this idea of functional lateralization. People displaying mental health conditions linked to right-brain hyperactivity (such as social anxiety or trauma responsiveness) tend to exhibit patterns of dysbiosis associated with neurotoxic byproducts or depleted butyrate. Conversely, those with left-brain dominant challenges (such as obsessive cognition or reduced task motivation) often show microbial signatures suggesting poor SCFA metabolism or improper folate cycling.

By aligning test results with neurobehavioral profiles, health practitioners can tailor gut-based strategies according to hemispheric needs. For instance, individuals with right-brain emotional dysregulation might benefit from serotonin-enhancing strains, whereas those with left-brain cognitive fatigue might benefit from prebiotic interventions targeting BDNF enhancement.

This direction opens a futuristic path—using personalized data to align mental and gut functioning based on neurological patterns. Testing reveals our gut's microbial code, and when integrated with knowledge about cerebral dominance, it becomes a powerful script for therapeutic precision. As gut microbiome science continues to evolve, so too will our tools for understanding and treating the complexities of the two human brains in synchrony.

Conclusion

The notion of the human body possessing two brains—the central nervous system and the enteric nervous system—is no longer a metaphor but a scientifically endorsed truth. These two neural control centers engage in a continuous biological and chemical conversation that influences nearly every aspect of our wellbeing, including mood, memory, digestion, immune function, and stress resilience.

Gut microbiome testing stands at the forefront of efforts to decode this dialogue. With personalized data on microbial makeup, we can strategically approach both mental and physical health using interventions calibrated to our unique biochemistry. The benefits extend beyond relief from symptoms; they empower individuals with the knowledge needed to proactively nurture and optimize their two brains.

Now is the time to embrace the transformative power of microbiome health. By understanding and respecting the intricate relationship between the gut and the human brain, we evolve toward a new model of integrative wellness—one that truly begins from within.

Q&A Section

What are the two brains of the human body?

The two brains refer to the central nervous system (the brain in the skull) and the enteric nervous system (the gut's neural network). These systems work in tandem to regulate physiological and emotional health.

How does the gut microbiome influence mental health?

Gut microbes produce and regulate neurotransmitters like serotonin, dopamine, and GABA. An imbalance can affect mood, cognition, and emotional regulation.

What is gut microbiome testing?

This testing analyzes the gut's microbial composition to determine abundance, diversity, and health status. It identifies imbalances that may impact overall health and brain function.

Can microbiome testing help improve brain function?

Yes, by identifying problem areas in gut ecology, targeted interventions like probiotics, diet changes, and prebiotics can improve cognitive performance and emotional well-being.

How do brain hemispheres relate to gut microbiota?

Each hemisphere has unique roles that may associate with certain microbiota. Emotional functions, often attributed to the right hemisphere, can be affected more by gut-related imbalances leading to mood disruptions.

Important Keywords

• Human brain
• Gut-brain axis
• Microbiome testing
• Enteric nervous system
• Neuroplasticity
• Cognitive health
• Brain hemispheres
• Gut microbiota
• Neurotransmitters
• Vagus nerve