Zone Preference in the Visual Water Maze
June 26, 2025
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Acids and Bases play an important role in chemistry. We see them everywhere in our day-to-day lives, from our cleaning agents; soaps and detergents, to baking soda. Acids and bases (alkaline earth metal chemical elements) are 2 categories of corrosive substances. Any compound with a pH value between zero to seven is considered acidic, whereas a pH value between seven to fourteen is a base. An acid is called a proton donor, while a base is called a proton acceptor (Kolb, 1978).
An acid is a molecule or substance that has a pH value of less than 7.0 when it is present in an aqueous solution. An aqueous solution is any solution where water is a solvent. Acids are termed as compounds that donate H+ (hydrogen ion) to another compound known as base.
A base (alkaline) is a molecule or substance that has a pH value higher than 7.0 when present in an aqueous solution. Bases are the exact chemical opposite of acids. In chemistry. They are substances that, in an aqueous solution, release hydroxide (OH−) ions.
As per Arrhenius Concept, an acid elevates the concentration of Hydrogen ions when dissolved in water.
As per Arrhenius Concept, a base is a compound that increases the concentration of hydroxide ions (OH–) when dissolved in water.
In the Bronsted-Lowry Concept, acids are substances that donate protons
Bases, on the other hand, are substances that accept protons
Ions that accept the pair of electrons (electron pair acceptor – an electrophile), and possess vacant orbitals are termed ‘Lewis acid’.
Ions that donate a pair of electrons (electron-pair donor – a nucleophile), and possess a lone pair of electrons are termed ‘Lewis base’.
Acids are classified as:
Bases are classified as:
The chemical formula for most acids starts with H. For Examples, Nitric acid (HNO3), Carbonic acid in soft drinks (H2CO3), Boric acid (H3BO3), Hydrochloric acid (HCl), Oxalic Acid (H2C2O4), Citric Acid or 2-Hydroxy-1,2,3-propane tricarboxylic acid (H3C6H5O7), and Sulfuric acid (H2SO4). However, there are exceptions like Acetic Acid (CH3COOH).
The chemical formula for most bases (compounds) has OH at the end. For example, Calcium hydroxide or slaked lime, Ca (OH)2 (paper, flocculant), Magnesium hydroxide (Mg (OH)2) or milk of magnesia, Sodium hydroxide (NaOH) or caustic soda (cleaning agent, pH regulator), Ammonium hydroxide (NH4OH) or ammonia water and KOH (Potassium hydroxide).
Acids have a pH of less than 7.0.
Bases have a pH higher than 7.0, and could even go up to 14 if the bases are very strong.
The strength of acids depends on the concentration of hydronium ions (Umansky, 1991).
The strength of bases depends on the concentration of hydroxide ions.
Both acids and bases are different in their physical properties.
When dissolved in water, acids
When dissolved in water, bases
Acids are species or compounds that break apart in H2O to form a hydrogen ion (H+). So, it can be said that acids form Hydronium ions on ionization (Schultz, 1997).
Bases result in Hydroxyl ions on ionization (Nyasulu et al, 2013).
Acids release H+ (Hydrogen ions) when mixed with water (H20).
Bases release OH– (Hydroxide ions) when mixed with water (H20).
Characteristics | Acids | Bases |
Definition | A substance, mostly liquid that donates a proton or accepts an electron pair in reactions. An acid increases the concentration of H+ ions. | A base is a substance that releases hydroxide (OH-) ions in aqueous solution, donates electrons and accepts protons. |
Bronsted Lowry Definition | An acid is a proton donor. | A base accepts a proton. |
pH (concentration of hydrogen ions in a solution) | Acids possess a pH value <7. | Bases possess a pH value >7. |
Phenolphthalein indicator | An acid remains colorless. | A base gives a pink color. |
Litmus paper test | Turns blue litmus paper to red color. | Turns red litmus paper to blue color. |
Chemical formula | The chemical formula begins with H in case of acids. For example, Hydrochloric acid (HCl). | The Chemical formula ends with OH in case of bases. For example, Sodium Hydroxide (NaOH). |
Strength | Depends on the concentration of hydronium ions. | Depends on the concentration of hydroxide ions. |
Dissociation | Acids dissociate to release hydrogen ions (H+) when mixed with water. | Bases dissociate to release hydroxide ions (OH–) when mixed with water. |
Uses | Used as a household cleaning agent, in carbonated drinks, in processing leather, and in preservatives and fertilizers. | Used in soaps, detergents, gastric medicines (antacid). |
Acids and bases impact daily life because they play a major and important role in many reactions, from digesting food to removing soap scum off a shower wall. Acids and bases are significant in balancing the pH levels in the body so that it stays at a level of 7. When a person consumes acidic foods, the body uses a buffering system to neutralize the positive ions produced by the acids. On the other hand, bases are required to regulate and control the body from becoming too alkaline.
We conclude that both acids and bases are an important part of life, and are found in the environment, in foods, and in chemicals, including pharmaceuticals. They are vital, not only in the chemistry laboratory but also in our daily lives.
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.
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:
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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 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.
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).
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.
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.
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.
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