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Biomolecules

Biomolecules: Types and Functions

Introduction

The human body is composed of roughly 30 trillion cells that collectively perform the essential functions of life. The cells can perform these life-sustaining tasks with the help of several organic molecules present in them. These organic molecules are referred to as biomolecules.

The biomolecules have a wide range of sizes and structures, and they are involved in a vast array of life functions. They are composed of more than 25 naturally occurring elements, with the primary elements being carbon, hydrogen, oxygen, phosphorus, and sulfur.[1]

Carbon compounds have major involvement in the formation of biomolecules. They covalently bind with other elements to form several other compounds. Some biomolecules are considered derivatives of hydrocarbons, they’re formed by replacing hydrogen atoms from functional groups like alcohols, amines, aldehydes, ketones, and carboxylic groups.[1]

Given below is a list of small biomolecules and the macromolecules that are formed after the polymerization of these small monomer units.[1]

Small Biomolecules Macromolecules
Sugars
Carbohydrates
Fatty acids
Fats/lipids
Amino acids
Proteins
Nucleotides
Nucleic acids

This article briefly explains the major biomolecules and the functions they perform in our bodies.

Four Major Types of Biomolecules

Approximately 10,000 to 100,000 molecules are present in a cell to regulate bodily function. But the four major types of biomolecules include carbohydrates, lipids, nucleic acids, and proteins. Most of the other compounds are derivatives of these major primary compounds.

Every biomolecule has its characteristics and is designated to perform some specific function essential for life. So, let’s see what they are all about!!!

1. Carbohydrates

Carbohydrates are a vital part of a healthy diet. They provide the energy required to do work. Scientifically, it’s a polyhydroxy aldehyde or polyhydroxy ketone.[1] Carbohydrates are the most abundant biomolecules on earth.

Types of Carbohydrates and Their Functions

Depending on the number of products formed after hydrolysis, carbohydrates are classified into three groups.[1]

  1. Monosaccharides: These are composed of a single unit of polyhydroxy aldehyde or ketone. Monosaccharides are colorless, crystalline solids that are completely soluble in water.[1] They are involved in generating energy for the body.  Examples include glucose, fructose, ribose, and arabinose.
  2. Disaccharides: These are composed of two units of sugars joined by O-glycosidic bonds.[1] A list of disaccharides with their monomer units and functions is given below.[1]
  3. Polysaccharides: These consist of more than two sugar monomer units. They are also known as glycans. They are of two types:
    • Homopolysaccharides: They are composed of only a single type of sugar unit. Based on the function they perform, homopolysaccharides are classified into two groups:
      • Structural polysaccharides: They provide mechanical stability to cells, organs, and organisms. Examples are chitin and cellulose. Chitin is involved in the construction of a fungal cell wall, while cellulose is an important constituent of the diet for ruminants.[2]
      • Storage polysaccharides: They serve as carbohydrate stores that release sugar monomers when required by the body. Examples include starch, glycogen, and inulin.[2] Starch stores energy for plants. In animals, it is catalyzed by the enzyme amylase (found in saliva) to fulfill the energy requirement. Glycogen is a polysaccharide food reserve of animals, bacteria, and fungi.[2]
    • Heteropolysaccharides: They contain two or more different types of sugar units. It includes glycosaminoglycans like hyaluronic acid, heparan sulfate, keratan sulfate, and murein. These polysaccharides have diverse functions. For example, heparin is an anticoagulant (prevents blood clotting, it’s also known as blood thinners), hyaluronic acid is a shock absorber and lubricant, while peptidoglycans or mureins are present in the bacterial cell wall.[3]
No. Disaccharides Monomer units Function
1
Sucrose
Glucose and Fructose
It’s a product of photosynthesis
2
Lactose
Galactose and Glucose
A major animal energy source
3
Maltose
Glucose and Glucose (alpha-1,4 linkage)
Important intermediate in starch and glycogen digestion
4
Trehalose
Glucose and Glucose (alpha-1, alpha-1 linkage)
An energy source for insects
5
Cellobiose
Glucose and Glucose (beta-1,4 linkage)
Essential in carbohydrate metabolism
6
Gentiobiose
Glucose and Glucose (beta-1,6 linkage)
A constituent of plant glycosides and some polysaccharides

2. Proteins

Proteins are unbranched polymers of amino acid residues. There are about 22 amino acids that are involved in the synthesis of proteins according to their location and function.[1] Proteins are categorized into four groups depending on their structural organization:

  • Primary structure: It is formed by the formation of a peptide bond between amino acids.
  • Secondary structure: It is a folded structure within a polypeptide that’s due to the formation of hydrogen bonds between amide hydrogen and the carbonyl oxygen of the peptide backbone.[4] It includes structures like alpha-helix and beta-sheet.
  • Tertiary structure: It is a three-dimensional conformation that’s formed due to the interaction between R-groups or side chains of the amino acids that make up the proteins.[1] Bonds that contribute to the formation of this structure include hydrophobic interaction, electrostatic interactions, hydrogen bonds, and Van der Waals forces of interaction.[1]
  • Quaternary structure: This structure forms between two or more polypeptide chains. Each polypeptide chain is called a subunit.[1] The quaternary structures may occur between identical or different polypeptide chains. The bonds involved in the formation of these structures include hydrophobic bonds, electrostatic bonds, hydrogen bonds, and covalent cross-links.[1]

Functions of Proteins

Proteins are essential components of organisms. It participates in almost every process within cells. It is involved in the processes of DNA replication, cell signaling, catalyzing metabolic reactions, construction of cell and tissue structures, and transportation of molecules from one place to another.[5]

Given below are eight groups of proteins that are categorized based on their functional properties.[6]

  1. Structural proteins: These proteins are fibrous proteins that are tough and insoluble in water. They form the structural component of connective tissues, bones, tendons, cartilages, nails, hairs, and horns. Examples of structural proteins are collagen, elastin, and keratin.[6]
  2. Enzymes: These are globular conjugated proteins that are also known as biological catalysts. They catalyze metabolic reactions by reducing the activation energy that increases the rate of the reaction. Some examples of protein enzymes are DNA polymerase, lysozyme, nitrogenase, and lipase.[6]
  3. Hormones: These are long polypeptides composed of long chains of linked amino acids.  They play critical roles in regulating the physiological processes of the body, these processes include reproduction, growth and development, electrolyte balance, sleep, etc.[7] Some examples of these hormones are growth hormone (GH) and follicle-stimulating hormone (FSH).[7]
  4. Respiratory pigments: These are globular protein pigments that are usually soluble in water. Examples include myoglobin which provides oxygen to the working muscles and hemoglobin which transfers blood to all the tissues and organs through the blood.[6]
  5. Transport proteins: These are structural components of the cell membrane. They form channels in the plasma membrane to transfer selective molecules inside the cells. Some of them also form components of blood and lymph in animals. Examples of transport proteins are serum albumin (transport hemin and fatty acids), channel proteins, and carrier proteins.[6]
  6. Motor proteins: These proteins are involved in the contraction and relaxation of the muscle (muscle movement). It includes actin, myosin, kinesin, and dynein.
  7. Storage proteins: These proteins are the storage reserve of amino acids and metal ions in cells. They are present in eggs, seeds, and pulses. Examples of storage proteins include ferritin, ovalbumin, and casein.
  8. Toxins: These proteins are generally produced by bacteria. They include diphtheria toxin, Pseudomonas exotoxin, and ribosome-inactivating proteins.[8] They help bacteria to attack and kill their host organism by creating cytotoxicity.

3. Nucleic Acids

Nucleic acids are macromolecules present in cells and viruses, and they are involved in the storage and transfer of genetic information. The nucleic acid was first discovered by Friedrich Miesher in the nuclei of leukocytes.[1] Later, further studies showed that it’s a mixture of basic proteins and phosphorus-containing organic acid.

Structurally, nucleic acids are polymers of nucleotides (or polynucleotides) which are phosphate esters of nucleosides.[1] The nucleotides are comprised of three components:[1]

  • Nitrogenous base: These are heterocyclic, planar, and aromatic molecules. It is of two types: purines and pyrimidines. Purines include adenine and guanine, both of which are found in both DNA and RNA. Pyrimidines include thymine (found only in DNA), cytosine (found in both DNA and RNA), and uracil (found only in RNA).
  • Five carbon sugar: The two types of pentose sugar are ribose (present only in RNA) and deoxyribose (present in DNA). These sugars in nucleic acids have the D-stereoisomeric configuration.[1]
  • Phosphoric acid ion: It’s a phosphate group involved in the polymerization of the nucleotides. A phosphodiester bond links two or more nucleotides leading to the formation of polynucleotides.

Types of Nucleic Acids and Their Functions

Based on nature, structure, and function, the nucleic acids are categorized into two groups: Deoxyribonucleic acids (DNA) and Ribonucleic acids (RNA).

a. Deoxyribonucleic acids (DNA)

DNAs are the hereditary material that resides inside the nucleus. In 1953, the first structure of DNA double helix (B-form of DNA) was discovered by Watson and Crick.[1] DNA has two other forms as well, A and Z forms. The conformation DNA will adopt depends on the hydration level, DNA sequence, chemical modification of the bases, the type, and concentration of a metal ion in the solution.[1]

The double helix structure represents two polynucleotides DNA coiled around a central helix. The two strands are antiparallel and interact by hydrogen bonds between complementary base pairs. In some cases, like at low pH, the triple helix form of DNA also exists. It’s formed by laying a third strand into the major groove of the DNA.

It is the genetic material that stores all the information required to be transferred to the progeny. It specifies the biological development of all living organisms and viruses.

b. Ribonucleic acids (RNA)

RNA is present in all living cells. It has different roles to play in different organisms. It acts as genetic material in some viruses and has enzymatic activity in other organisms (where it is called ribozyme). Three types of RNA are present among organisms: rRNA, mRNA, and tRNA. All three have essential roles in the development and maintenance of life.

The importance of RNA and DNA is incomparable. DNA carrying the genetic information can’t leave its home, the nucleus, and this is why RNA exists. They are involved in the transfer of genetic information for protein synthesis via the processes of transcription and translation (outside the nucleus), and they control gene expression as well.[1]

Structurally, RNA exists in both single-stranded (primary structure) and double-stranded (secondary structure) forms.[1] The double-helical structure of RNA is present in the A form.

4. Lipids

Lipids are organic compounds that are insoluble or poorly soluble in water but soluble in organic solvents (like dissolves like) such as ether, benzene, or chloroform.[1]

They are hydrophobic and structurally composed of a chain of hydrocarbons. They are chemically more diverse than other biomolecules, and they are primarily involved in membrane structure and energy storage.

Classes of Lipids and Their Functions

Different classes of lipids include:

  1. Fatty acids: These are the simplest forms of lipids. They are composed of hydrocarbon chains of 4-36 carbons and one acidic group.[9] They can be linear or branched. Moreover, fatty acids are the building blocks of other types of lipids.
  2. Waxes: These are esters of fatty acids and long-chain alcohols. They are composed of hydrocarbon chains of 14-36 carbons. They are synthesized by many plants and animals. However, the best-known wax is bee wax which is composed of an ester of palmitic acid with triacontanol alcohol.[1]
  3. Phospholipids: These are composed of fatty acids, an attachment platform for fatty acids, a phosphate, and an alcohol attached to phosphate. They are part of the cell membrane of the organisms.
  4. Glycolipids: These are lipids containing saccharide groups. They are constituents of the cell membrane and are involved in signal transductions.
  5. Steroids: These are complex derivatives of triterpenes. For example, cholesterol is a constituent of the cell membrane and acts as a precursor for the biosynthesis of steroid hormones and bile acids.[1]
  6. Eicosanoids: They arise from the 20 carbons of polyunsaturated fatty acids.[1] They perform several functions. For example, prostaglandins stimulate uterine contraction and lower blood pressure, leukotrienes are involved in chemotaxis and inflammation, and thromboxanes act as vasoconstrictors and stimulate platelet aggregation.[1]

Other than these lipid molecules, some plasma lipoproteins also exist that are structurally a lipid-protein complex. These complexes function as lipid transport systems in blood. Some examples of lipoproteins are chylomicrons, low-density lipoproteins, and high-density lipoproteins.[1]

Conclusion

Biomolecules are vital for life as it aids organisms to grow, sustain, and reproduce. They are involved in building organisms from single cells to complex living beings like humans, by interacting with each other. The diversity in their shape and structure provides diversity in their functions.

The study of these biomolecules is known as biochemistry. Biochemistry deals with the study of their structures, functions, interactions, and reactions. Several functions of these biological molecules are still a mystery and current advanced techniques are being used to discover more molecules and understand their role in life-sustaining processes.

References:

  1. Kumar, Pranav & Mina, Usha. (2016). Life Sciences, Fundamentals, and Practice, Part I.
  2. M. Manisha. Types of Polysaccharides (3 Types). Retrieved from https://www.biologydiscussion.com/carbohydrates/polysaccharides/types-of-polysaccharides-3-types/44929
  3. Heteropolysaccharides. Retrieved from https://www.britannica.com/science/carbohydrate/Heteropolysaccharides
  4. Orders of protein structure. Retrieved from https://www.khanacademy.org/science/biology/macromolecules/proteins-and-amino-acids/a/orders-of-protein-structure
  5. Protein. Retrieved from https://en.wikipedia.org/wiki/Protein
  6. Classification of Proteins Based on Structure and Function. Retrieved from https://www.easybiologyclass.com/classification-of-proteins-based-on-structure-and-function/#
  7. Hormones. Retrieved from https://courses.lumenlearning.com/suny-ap2/chapter/hormones/#
  8. Protein Toxins. Retrieved from https://www.creative-biolabs.com/adc/protein-toxins.htm#
  9. Overview of Biomolecules. Overview of molecules. Retrieved from http://med.fau.edu/students/md_m1_orientation/Overview.pdf

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Introduction

In behavioral neuroscience, the Open Field Test (OFT) remains one of the most widely used assays to evaluate rodent models of affect, cognition, and motivation. It provides a non-invasive framework for examining how animals respond to novelty, stress, and pharmacological or environmental manipulations. Among the test’s core metrics, the percentage of time spent in the center zone offers a uniquely normalized and sensitive measure of an animal’s emotional reactivity and willingness to engage with a potentially risky environment.

This metric is calculated as the proportion of time spent in the central area of the arena—typically the inner 25%—relative to the entire session duration. By normalizing this value, researchers gain a behaviorally informative variable that is resilient to fluctuations in session length or overall movement levels. This makes it especially valuable in comparative analyses, longitudinal monitoring, and cross-model validation.

Unlike raw center duration, which can be affected by trial design inconsistencies, the percentage-based measure enables clearer comparisons across animals, treatments, and conditions. It plays a key role in identifying trait anxiety, avoidance behavior, risk-taking tendencies, and environmental adaptation, making it indispensable in both basic and translational research contexts.

Whereas simple center duration provides absolute time, the percentage-based metric introduces greater interpretability and reproducibility, especially when comparing different animal models, treatment conditions, or experimental setups. It is particularly effective for quantifying avoidance behaviors, risk assessment strategies, and trait anxiety profiles in both acute and longitudinal designs.

What Does Percentage of Time in the Centre Measure?

This metric reflects the relative amount of time an animal chooses to spend in the open, exposed portion of the arena—typically defined as the inner 25% of a square or circular enclosure. Because rodents innately prefer the periphery (thigmotaxis), time in the center is inversely associated with anxiety-like behavior. As such, this percentage is considered a sensitive, normalized index of:

  • Exploratory drive vs. risk aversion: High center time reflects an animal’s willingness to engage with uncertain or exposed environments, often indicative of lower anxiety and a stronger intrinsic drive to explore. These animals are more likely to exhibit flexible, information-gathering behaviors. On the other hand, animals that spend little time in the center display a strong bias toward the safety of the perimeter, indicative of a defensive behavioral state or trait-level risk aversion. This dichotomy helps distinguish adaptive exploration from fear-driven avoidance.

  • Emotional reactivity: Fluctuations in center time percentage serve as a sensitive behavioral proxy for changes in emotional state. In stress-prone or trauma-exposed animals, decreased center engagement may reflect hypervigilance or fear generalization, while a sudden increase might indicate emotional blunting or impaired threat appraisal. The metric is also responsive to acute stressors, environmental perturbations, or pharmacological interventions that impact affective regulation.

  • Behavioral confidence and adaptation: Repeated exposure to the same environment typically leads to reduced novelty-induced anxiety and increased behavioral flexibility. A rising trend in center time percentage across trials suggests successful habituation, reduced threat perception, and greater confidence in navigating open spaces. Conversely, a stable or declining trend may indicate behavioral rigidity or chronic stress effects.

  • Pharmacological or genetic modulation: The percentage of time in the center is widely used to evaluate the effects of pharmacological treatments and genetic modifications that influence anxiety-related circuits. Anxiolytic agents—including benzodiazepines, SSRIs, and cannabinoid agonists—reliably increase center occupancy, providing a robust behavioral endpoint in preclinical drug trials. Similarly, genetic models targeting serotonin receptors, GABAergic tone, or HPA axis function often show distinct patterns of center preference, offering translational insights into psychiatric vulnerability and resilience.

Critically, because this metric is normalized by session duration, it accommodates variability in activity levels or testing conditions. This makes it especially suitable for comparing across individuals, treatment groups, or timepoints in longitudinal studies.

A high percentage of center time indicates reduced anxiety, increased novelty-seeking, or pharmacological modulation (e.g., anxiolysis). Conversely, a low percentage suggests emotional inhibition, behavioral avoidance, or contextual hypervigilance. reduced anxiety, increased novelty-seeking, or pharmacological modulation (e.g., anxiolysis). Conversely, a low percentage suggests emotional inhibition, behavioral avoidance, or contextual hypervigilance.

Behavioral Significance and Neuroscientific Context

1. Emotional State and Trait Anxiety

The percentage of center time is one of the most direct, unconditioned readouts of anxiety-like behavior in rodents. It is frequently reduced in models of PTSD, chronic stress, or early-life adversity, where animals exhibit persistent avoidance of the center due to heightened emotional reactivity. This metric can also distinguish between acute anxiety responses and enduring trait anxiety, especially in longitudinal or developmental studies. Its normalized nature makes it ideal for comparing across cohorts with variable locomotor profiles, helping researchers detect true affective changes rather than activity-based confounds.

2. Exploration Strategies and Cognitive Engagement

Rodents that spend more time in the center zone typically exhibit broader and more flexible exploration strategies. This behavior reflects not only reduced anxiety but also cognitive engagement and environmental curiosity. High center percentage is associated with robust spatial learning, attentional scanning, and memory encoding functions, supported by coordinated activation in the prefrontal cortex, hippocampus, and basal forebrain. In contrast, reduced center engagement may signal spatial rigidity, attentional narrowing, or cognitive withdrawal, particularly in models of neurodegeneration or aging.

3. Pharmacological Responsiveness

The open field test remains one of the most widely accepted platforms for testing anxiolytic and psychotropic drugs. The percentage of center time reliably increases following administration of anxiolytic agents such as benzodiazepines, SSRIs, and GABA-A receptor agonists. This metric serves as a sensitive and reproducible endpoint in preclinical dose-finding studies, mechanistic pharmacology, and compound screening pipelines. It also aids in differentiating true anxiolytic effects from sedation or motor suppression by integrating with other behavioral parameters like distance traveled and entry count (Prut & Belzung, 2003).

4. Sex Differences and Hormonal Modulation

Sex-based differences in emotional regulation often manifest in open field behavior, with female rodents generally exhibiting higher variability in center zone metrics due to hormonal cycling. For example, estrogen has been shown to facilitate exploratory behavior and increase center occupancy, while progesterone and stress-induced corticosterone often reduce it. Studies involving gonadectomy, hormone replacement, or sex-specific genetic knockouts use this metric to quantify the impact of endocrine factors on anxiety and exploratory behavior. As such, it remains a vital tool for dissecting sex-dependent neurobehavioral dynamics.
 The percentage of center time is one of the most direct, unconditioned readouts of anxiety-like behavior in rodents. It is frequently reduced in models of PTSD, chronic stress, or early-life adversity. Because it is normalized, this metric is especially helpful for distinguishing between genuine avoidance and low general activity.

Methodological Considerations

  • Zone Definition: Accurately defining the center zone is critical for reliable and reproducible data. In most open field arenas, the center zone constitutes approximately 25% of the total area, centrally located and evenly distanced from the walls. Software-based segmentation tools enhance precision and ensure consistency across trials and experiments. Deviations in zone parameters—whether due to arena geometry or tracking inconsistencies—can result in skewed data, especially when calculating percentages.

     

  • Trial Duration: Trials typically last between 5 to 10 minutes. The percentage of time in the center must be normalized to total trial duration to maintain comparability across animals and experimental groups. Longer trials may lead to fatigue, boredom, or habituation effects that artificially reduce exploratory behavior, while overly short trials may not capture full behavioral repertoires or response to novel stimuli.

     

  • Handling and Habituation: Variability in pre-test handling can introduce confounds, particularly through stress-induced hypoactivity or hyperactivity. Standardized handling routines—including gentle, consistent human interaction in the days leading up to testing—reduce variability. Habituation to the testing room and apparatus prior to data collection helps animals engage in more representative exploratory behavior, minimizing novelty-induced freezing or erratic movement.

     

  • Tracking Accuracy: High-resolution tracking systems should be validated for accurate, real-time detection of full-body center entries and sustained occupancy. The system should distinguish between full zone occupancy and transient overlaps or partial body entries that do not reflect true exploratory behavior. Poor tracking fidelity or lag can produce significant measurement error in percentage calculations.

     

  • Environmental Control: Uniformity in environmental conditions is essential. Lighting should be evenly diffused to avoid shadow bias, and noise should be minimized to prevent stress-induced variability. The arena must be cleaned between trials using odor-neutral solutions to eliminate scent trails or pheromone cues that may affect zone preference. Any variation in these conditions can introduce systematic bias in center zone behavior. Use consistent definitions of the center zone (commonly 25% of total area) to allow valid comparisons. Software-based segmentation enhances spatial precision.

Interpretation with Complementary Metrics

Temporal Dynamics of Center Occupancy

Evaluating how center time evolves across the duration of a session—divided into early, middle, and late thirds—provides insight into behavioral transitions and adaptive responses. Animals may begin by avoiding the center, only to gradually increase center time as they habituate to the environment. Conversely, persistently low center time across the session can signal prolonged anxiety, fear generalization, or a trait-like avoidance phenotype.

Cross-Paradigm Correlation

To validate the significance of center time percentage, it should be examined alongside results from other anxiety-related tests such as the Elevated Plus Maze, Light-Dark Box, or Novelty Suppressed Feeding. Concordance across paradigms supports the reliability of center time as a trait marker, while discordance may indicate task-specific reactivity or behavioral dissociation.

Behavioral Microstructure Analysis

When paired with high-resolution scoring of behavioral events such as rearing, grooming, defecation, or immobility, center time offers a richer view of the animal’s internal state. For example, an animal that spends substantial time in the center while grooming may be coping with mild stress, while another that remains immobile in the periphery may be experiencing more severe anxiety. Microstructure analysis aids in decoding the complexity behind spatial behavior.

Inter-individual Variability and Subgroup Classification

Animals naturally vary in their exploratory style. By analyzing percentage of center time across subjects, researchers can identify behavioral subgroups—such as consistently bold individuals who frequently explore the center versus cautious animals that remain along the periphery. These classifications can be used to examine predictors of drug response, resilience to stress, or vulnerability to neuropsychiatric disorders.

Machine Learning-Based Behavioral Clustering

In studies with large cohorts or multiple behavioral variables, machine learning techniques such as hierarchical clustering or principal component analysis can incorporate center time percentage to discover novel phenotypic groupings. These data-driven approaches help uncover latent dimensions of behavior that may not be visible through univariate analyses alone.

Total Distance Traveled

Total locomotion helps contextualize center time. Low percentage values in animals with minimal movement may reflect sedation or fatigue, while similar values in high-mobility subjects suggest deliberate avoidance. This metric helps distinguish emotional versus motor causes of low center engagement.

Number of Center Entries

This measure indicates how often the animal initiates exploration of the center zone. When combined with percentage of time, it differentiates between frequent but brief visits (indicative of anxiety or impulsivity) versus fewer but sustained center engagements (suggesting comfort and behavioral confidence).

Latency to First Center Entry

The delay before the first center entry reflects initial threat appraisal. Longer latencies may be associated with heightened fear or low motivation, while shorter latencies are typically linked to exploratory drive or low anxiety.

Thigmotaxis Time

Time spent hugging the walls offers a spatial counterbalance to center metrics. High thigmotaxis and low center time jointly support an interpretation of strong avoidance behavior. This inverse relationship helps triangulate affective and motivational states.

Applications in Translational Research

  • Drug Discovery: The percentage of center time is a key behavioral endpoint in the development and screening of anxiolytic, antidepressant, and antipsychotic medications. Its sensitivity to pharmacological modulation makes it particularly valuable in dose-response assessments and in distinguishing therapeutic effects from sedative or locomotor confounds. Repeated trials can also help assess drug tolerance and chronic efficacy over time.
  • Genetic and Neurodevelopmental Modeling: In transgenic and knockout models, altered center percentage provides a behavioral signature of neurodevelopmental abnormalities. This is particularly relevant in the study of autism spectrum disorders, ADHD, fragile X syndrome, and schizophrenia, where subjects often exhibit heightened anxiety, reduced flexibility, or altered environmental engagement.
  • Hormonal and Sex-Based Research: The metric is highly responsive to hormonal fluctuations, including estrous cycle phases, gonadectomy, and hormone replacement therapies. It supports investigations into sex differences in stress reactivity and the behavioral consequences of endocrine disorders or interventions.
  • Environmental Enrichment and Deprivation: Housing conditions significantly influence anxiety-like behavior and exploratory motivation. Animals raised in enriched environments typically show increased center time, indicative of reduced stress and greater behavioral plasticity. Conversely, socially isolated or stimulus-deprived animals often show strong center avoidance.
  • Behavioral Biomarker Development: As a robust and reproducible readout, center time percentage can serve as a behavioral biomarker in longitudinal and interventional studies. It is increasingly used to identify early signs of affective dysregulation or to track the efficacy of neuromodulatory treatments such as optogenetics, chemogenetics, or deep brain stimulation.
  • Personalized Preclinical Models: This measure supports behavioral stratification, allowing researchers to identify high-anxiety or low-anxiety phenotypes before treatment. This enables within-group comparisons and enhances statistical power by accounting for pre-existing behavioral variation. Used to screen anxiolytic agents and distinguish between compounds with sedative vs. anxiolytic profiles.

Enhancing Research Outcomes with Percentage-Based Analysis

By expressing center zone activity as a proportion of total trial time, researchers gain a metric that is resistant to session variability and more readily comparable across time, treatment, and model conditions. This normalized measure enhances reproducibility and statistical power, particularly in multi-cohort or cross-laboratory designs.

For experimental designs aimed at assessing anxiety, exploratory strategy, or affective state, the percentage of time spent in the center offers one of the most robust and interpretable measures available in the Open Field Test.

Explore high-resolution tracking solutions and open field platforms at
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References

  • Prut, L., & Belzung, C. (2003). The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review. European Journal of Pharmacology, 463(1–3), 3–33.
  • Seibenhener, M. L., & Wooten, M. C. (2015). Use of the open field maze to measure locomotor and anxiety-like behavior in mice. Journal of Visualized Experiments, (96), e52434.
  • Crawley, J. N. (2007). What’s Wrong With My Mouse? Behavioral Phenotyping of Transgenic and Knockout Mice. Wiley-Liss.
  • Carola, V., D’Olimpio, F., Brunamonti, E., Mangia, F., & Renzi, P. (2002). Evaluation of the elevated plus-maze and open-field tests for the assessment of anxiety-related behavior in inbred mice. Behavioral Brain Research, 134(1–2), 49–57.

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