x
[quotes_form]
Request a Quote
Request a Quote
Biomolecules

Amino Acids: Building Blocks of Proteins

Reference to this article: ConductScience, Amino Acids: Building Blocks of Proteins (2022). doi.org/10.55157/CS20220612

Introduction and History

Amino acids are organic compounds consisting of carbon, hydrogen, and nitrogen. They are monomers or building blocks of proteins. Proteins are one of the major biomolecules required for the proper functioning of living organisms. Moreover, they are the first biomolecules that were first recognized for their biological roles in organisms than the other biomolecules including carbohydrates, nucleic acids, and lipids.[1]

Moreover, proteins have well-defined physicochemical properties. The linearly arranged amino acid sequence, or one-dimensional protein, guides the formation of the 3-D structure of the protein that determines its interaction with other molecules.[1]

It’s been a century since the observation that when proteins are exposed to hydrolytic actions of boiling acids, they split up into small molecular substances.[2] The amino acid, Glycine, was first discovered and isolated by scientists from gelatin. Soon after this discovery, other amino acids were unmasked including cystine, asparagine, leucine, and threonine — the last of the 20 common amino acids to be found, in 1935.[2]

Several studies led to the discovery of about 500 amino acids by 1983. But, only 20 were found to be present in the genetic code and considered to be the essential building blocks of proteins.[1]

This article brings you an overview of amino acids (monomeric units of proteins), their structures, functions, and applications in the real world.

Classifications of Amino Acids

1. Classification based on the nutritional requirement

Out of 20 amino acids, 9 can be synthesized by the human body, and the others are gotten through the food we eat. These criteria categorize these amino acids into two groups: Essential amino acids and non-essential amino acids.

1.1. Essential amino acids

The amino acids not synthesized by the body and required from dietary sources are called essential amino acids. It includes histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.[4]

They can be obtained from various food sources such as quinoa, egg, meat, chicken, and vegetables.[4] These essential amino acids help the body repair muscle tissues and form precursor molecules for neurotransmitters.

1.2. Non-essential amino acids

The amino acids synthesized by the body are called non-essential amino acids. They are involved in proper brain function, the production of red blood cells (RBCs) and white blood cells (WBCs), and the removal of toxins from the body. It includes arginine, aspartic acid, glutamic acid, asparagine, glutamine, glutamic acid, proline, glycine, serine, and tyrosine.[5]

Even though they are produced by the body from scratch, the dietary sources containing these amino acids can enhance their availability and functions in the body.[4]

2. Classification based on the polarity of the side chain

The amino acid structure is composed of an amino group and a carboxyl group along with a side chain R. All amino acids have different side chains, as a result, they show different physicochemical properties and functions.[1] The key elements of the amino acid structures are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

All the amino acids, except proline, are known as alpha-amino acids. Proline contains a secondary amine where an alpha carbon is attached to two other carbons. Thus, it is referred to as the alpha-imino group.

General structure of alpha-amino acids and proline

Figure: (a) General structure of alpha-amino acids, and (b) structure of proline showing secondary carbon and imino group.[1]

The amino acids are categorized into three groups based on their side-chain structures:

2.1. Amino acids with nonpolar side chains

Nine amino acids have a non-polar side chain in their structures. These include glycine, alanine, valine, leucine, isoleucine, methionine, proline, phenylalanine, and tryptophan.

Glycine has the smallest side chain with an H atom; alanine, valine, and leucine contain an aliphatic hydrophobic side chain; methionine contains a thiol ether side chain; proline has cyclic secondary amino acids; phenylalanine has a phenyl moiety; while tryptophan has a bulky indole aromatic side chain.[3] The aliphatic or aromatic groups attached to these amino acids make them hydrophobic (repel water).

While building proteins, the globular proteins bury these hydrophobic amino acids in the interior of their 3-D shape to prevent them from any water contact.[6]

Structure of non-polar amino acids

Figure: Structure of non-polar amino acids.[6]

2.2. Amino acids with polar side chains

Six amino acids fall in the category of uncharged polar side-chain amino acids. These include serine, threonine, asparagine, glutamine, tyrosine, and cysteine.

The amino acids, serine, and threonine contain aliphatic hydroxyl groups of different sizes; glutamine and asparagine have amide groups of different sizes; tyrosine has phenolic group, an aromatic group like tryptophan and phenylalanine; and cysteine has a unique thiol group attached to it.[3]

These amino acids have available electron pairs that are involved in hydrogen bonding with water and other molecules.[6]

The structure of polar uncharged amino acids

Figure: The structure of polar uncharged amino acids.[4]

2.3. Amino acids with charged polar side chains

The side chain of these amino acids can be positively charged or negatively charged at physiological pH. It includes lysine, glutamic acid, aspartic acid, histidine, and arginine.[3]

Lysine contains a butylammonium side chain; arginine has a guanidino group; histidine bears imidazolium moiety; glutamic acid and aspartic acid carries a carboxylic acid group on their side chain.[3]

In an aqueous solution, at physiological pH, aspartic acid and glutamic acid carry an overall charge of (-1) and are called glutamate and aspartate in their ionic forms. These are also known as acidic amino acids.[6] Whereas, lysine, histidine, arginine possess a (+1) charge at their physiological pH and are called basic amino acids.[4]

Structures of polar and charged amino acids

Figure: Structures of polar and charged amino acids.[4]

Physicochemical Properties of Amino Acids

The amino acids possess different physicochemical properties. These include optical activity, polarity, acidity and basicity, aromaticity, confirmation flexibility, and chemical reactivity. Some of the properties are discussed here in brief.

1. Stereochemistry

All the amino acids exist in L-configuration and are superimposable mirror images of each other. This configuration was given by Emil Fischer.[3] L- configuration represents all amino acids that are majorly involved in the translation process for protein synthesis. In some rare cases, D-amino acids are also found in some proteins.

According to the Fischer convention, the configuration of a group around a chiral center can be related to that of glyceraldehyde structure. For alpha-amino acids, the arrangement of the amino, carboxyl, R, and H groups about the C atom is related to that of the hydroxyl, aldehyde, CH2OH, and H groups, respectively, of glyceraldehyde.[3]

Fischer convention configuration of glyceraldehyde

Figure: Fischer convention configuration of glyceraldehyde to which all groups can be related.[3]

2. Peptide bond formation

The number and type of amino acids linked together to form proteins ultimately determine the shape, size, and function of the proteins.[7] The amino acids are covalently attached through a peptide bond, which is a result of a condensation reaction.

The carboxyl group of one amino acid combines with the amino group of another amino acid releasing a water molecule, this reaction is called a dehydration or condensation reaction.[7]

Peptide bond formation between two amino acids

Figure: Peptide bond formation between two amino acids with the release of a water molecule.[7]

Less than 50 amino acids linked together with the peptide bond are called oligopeptides and more than 50 amino acids are combined to form polypeptides. So, the proteins are the result of polypeptide formation, whereas individual amino acids are known as amino acid residues.[6]

It’s also essential to note that an individual amino acid possesses acid-base properties, which are lost in proteins because of the involvement of the carboxyl group in the peptide bond formation. So, the acidity-basicity of proteins depends on the overall ionization characteristics of individual R groups of the amino acid components.

3. Optical properties

Amino acids, except glycine, isolated after mild hydrolysis of protein can rotate plane-polarized light. This property is known as optical activity. The optically active molecules possess chiral carbons, having four different groups attached to a carbon, called a chiral center.[3]

The asymmetry due to chiral carbons results in non-superimposable mirror images of the molecule, called enantiomers. Glycine has two hydrogens attached to its alpha-carbon and is therefore not optically active.

Structure of alanine isomers

Figure: Structure of alanine isomers.[1]

The concept of enantiomers should not be confused while performing ordinary chemical synthesis. The chemical or physical processes have no stereochemical bias, thus, during the chemical synthesis of chiral molecules, racemic mixtures are produced.[3] Racemic mixtures contain an equal amount of right-hand and left-hand enantiomeric forms of a molecule.

4. Acid-base properties

Amino acids are amphoteric molecules, as they can either act as an acid or a base. The acidity and basicity of amino acids are due to charges either on their carboxyl or amino groups.[6]

The pKa value of the basic amino group is between 9 and 10 while that of an acidic carboxyl group is close to 2. The pKa value indicates the strength of amino acids. It is defined as the negative base (-10) log of the acid dissociation constant (Ka) of a solution.

pKa = -log10Ka

The pKa is also defined as the pH value at which the concentration of protonated group is equal to that of the unprotonated group.[6] So, at physiological pH, the amino acids have a balanced charge, equal number of negative and positive charges, on their structure and are called dipolar ion or zwitterion. The pH at which this phenomenon occurs is called the isoelectric point, donated by pI.

General structure of amino acid, and its zwitterionic form

Figure: (1) General structure of amino acid, and (2) its zwitterionic form.[1]

Note: At the isoelectric point, amino acids have a net-zero charge but amino acids are never considered to have an absolute zero charge.[6] Moreover, in an aqueous solution, amino acids never assume a neutral form.

5. Chemical reactions

The amino acids undergo several reactions by involving their functional groups. Some chemical reaction processes of amino acids are given below:

  • Deamination is the transfer of the amino group of one amino acid to a compound that forms another amino acid. For example, the transfer of an amino group to alpha-ketoglutarate results in glutamate formation.[1]
  • The Condensation reaction is the combination of two components into a single compound while releasing a small molecule. Two or more amino acids undergo a condensation reaction to form polymers of amino acids by forming a peptide bond and releasing one or more water molecules at the same time.[4]
Formation of tripeptide chain
  • Figure: Condensation reaction of three molecules of glycine into a tripeptide chain by releasing two molecules of water.[8]
  • Cysteine oxidation is the oxidation of two molecules of cysteine that result in cystine production by forming disulfide bonds. The reaction occurs due to the high reactivity of the thiol group of cysteines that are involved in this reversible oxidation reaction.[4] The reaction is mainly essential for proteins. The disulfide bridges formed in the reaction provide stability to proteins.

Functions of Amino Acids

All amino acids have some central role to play in the body’s metabolism and functioning. So, given below is a list of essential functions performed by some amino acids:

  1. The thiol side chain of the cysteine is involved in the formation of a unique disulfide bond by cross-linking with the thiol group of another cysteine. This bonding has a crucial role in protein formation and stability.[3]
  2. Threonine plays a major role in signal transduction and boosting the immune system.[8]
  3. Phenylalanine is a precursor molecule in the synthesis of tyrosine, dopamine, norepinephrine, epinephrine, and melanin. The genetic disorder, phenylketonuria, is caused due to an inability to synthesize and metabolize phenylalanine.[8] This is because of a lack of phenylalanine hydroxylase.
  4. Tryptophan helps in anchoring cell membranes along with tyrosine. They are also precursor molecules for the production of neurotransmitters (serotonin), hormones (melatonin), and the vitamin, niacin.[8]
  5. Alanine plays a crucial role in the glucose-alanine cycle between tissue and liver. This cycle removes and transfers pyruvate and glutamate from muscle to liver. An imbalance in the glucose-alanine cycle increases the level of ALT (Alanine transferases) which leads to type II diabetes.[8]
  6. Valine is essential for the self-renewal of hematopoietic stem cells that give rise to other blood cells.[8]
  7. Leucine is a ketogenic molecule that gives an end product of acetyl CoA and acetoacetate.[8] These molecules are precursors of ketone bodies and myelin that are especially required during early childhood for brain development.
  8. Isoleucine has multiple functions including assisting wound healing, detoxification of nitrogenous wastes, stimulating immune function, and promoting secretion of several hormones.[8]
  9. Methionine is a precursor for compounds like cysteine and taurine, versatile compounds such as S-adenosyl methionine, and the antioxidant, glutathione. Methionine is regenerated in the body by using homocysteines, and improper conversion leads to the accumulation of homocysteine that causes atherosclerosis.[8]
  10.  Histidine is a precursor for histamine that plays a major role in inflammation. It is converted into ammonia and urocanic acid by the action of the enzyme histidine, ammonia-lyase.[8] The deficiency of this enzyme causes a rare metabolic disorder, histidinemia.
  11. Lysine is involved in protein stability, epigenetic regulation by histone modification, structural proteins of connective tissues, calcium homeostasis, and fatty acid metabolism. Any interruption in lysine catabolism results in lysine accumulation that causes hyperlysinaemia.[8]

Applications of Amino Acids

Amino acids have a variety of application in industries, some of them are listed below:

  1. They are used as additives in animal feed. Examples include lysine, methionine, threonine, and tryptophan.[1] The amino acids are chelated with the metal cation to improve the absorption of mineral supplements for the better health of animals.
  2. Aspartame (aspartyl phenylalanine 1-methyl ester) is used as an artificial sweetener worldwide.[1]
  3. Glutamic acid has a major application as a flavor enhancer.[1]
  4. Amino acids are also used as supplements to improve mineral absorption in the human body, especially for those dealing with mineral deficiencies.[1]
  5. Amino acids are used to manufacture drugs and cosmetic products.
  6. Amino acids are used to develop fertilizers to enhance mineral absorption in plants and prevent deficiencies. Thus, facilitating healthy production of plants without affecting overall productivity.[1]

Amino acids are used to manufacture biodegradable polymers that are used for developing eco-friendly packaging, drug delivery carriers, and prosthetic implants.[1]

Conclusion

Amino acids are building blocks of proteins that are involved in every metabolic function of organisms. The side chain of the amino acids determines their physical and chemical properties. The chemical nature of these amino acids is determined by their functional groups. These functional groups are involved in carrying out several chemical processes in the organisms.

Today, several tools are present to isolate and study amino acids in labs. The advanced technology has facilitated the sequencing of every protein to study from their basic unit, that is, the amino acid. Scientists are meticulously developing several other tools to tackle the challenges faced during the study of these molecules. The area of amino acid and protein research creates an intriguing possibility to discover and uncover several other mysterious properties of these amino acids and their functions in organisms.

References:

  1. Amino acids. Retrieved from https://en.wikipedia.org/wiki/Amino_acid
  2. Vickery, H. B., & Schmidt, C. L. A. (1931). The History of the Discovery of the Amino Acids. Chemical Reviews, 9(2), 169–318. doi:10.1021/cr60033a001
  3. Voet Donaly and Voet G. Judith (2010). Biochemistry. Hoboken, NJ: John Wiley & Sons.
  4. Sarah Knapp (2020). Amino acids. Retrieved from https://biologydictionary.net/amino-acids/
  5. Difference between essential and non-essential amino acids. Retrieved from https://www.vedantu.com/biology/difference-between-essential-and-nonessential-amino-acids#
  6. Amino acid: Chemical compound. Retrieved from https://www.britannica.com/science/amino-acid
  7. Amino acids. Retrieved from https://courses.lumenlearning.com/introchem/chapter/amino-acids/
  8. Kiran Meena (2019). Structure of amino acids. Retrieved from https://aiimsrishikesh.edu.in/aiims/document/Biochemistry/Structures%20of%20Amino%20Acids.pdf

Learn More about our Services and how can we help you with your research!

Click here

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
https://conductscience.com/open-field/
Go to

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.

Written by researchers, for researchers — powered by Conduct Science.

See more of Our Posts

Behavioral Neuroscience

All Resources

GO TO

Never miss our posts!

Facebook-f Twitter Instagram Linkedin-in
Facebook Twitter Youtube Instagram Reddit-alien

Our Location

Monday – Friday
9 AM – 5 PM EST

Conduct Science

Resources

Support

Customer service

DISCLAIMER: ConductScience and affiliate products are NOT designed for human consumption, testing, or clinical utilization. They are designed for pre-clinical utilization only. Customers purchasing apparatus for the purposes of scientific research or veterinary care affirm adherence to applicable regulatory bodies for the country in which their research or care is conducted.

© Conduct Science 2024