Zone Preference in the Visual Water Maze
June 26, 2025
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A spectrophotometer is an invaluable tool that can help both professionals and hobbyists extract vital information from light measurements. Spectrophotometers are defined as optical devices that measure the amount of light absorbed by a substance. To be more precise, spectrophotometers provide a non-destructive way to measure the amount of light transmitted through a sample or that is reflected from it, including during photoluminescence.
Interestingly, the first spectrophotometer was invented by chemist Arnold Beckman in 1939. Now, spectrophotometers are invaluable tools in medicine, biomedical research, production facilities, forensics, environmental testing, and quality control management. Such instruments can help experts to measure a wide range of entities, such as cell culture density, food qualities, kinetics, clothing, cosmetics, minerals, lights, paint, and much more.
Here we should note there’s a difference between spectrometers and spectrophotometers. Spectrometers measure the emission spectrum and light properties over a specific portion of the electromagnetic field, while spectrophotometers measure the absorption and transmission spectrum of a sample. Also, while spectrometers detect spectra and can work over different wavelengths, including gamma and X-rays, spectrophotometers work in spectral areas near the visible spectrum. Note that the ultraviolet/visible/near-infrared range is essential in spectrophotometry; in fact, invisible spectrophotometry, the light properties of a sample can be observed by the color changes in it.
Furthermore, we should note that all spectrophotometers contain spectrometers. To be more precise, spectrophotometers consist of spectrometers and photometers: spectrometers transmit a beam of light and split it in different wavelengths; after the desired wavelength passes through the solution, the photometer detects the amount of light absorbed and sends data to a galvanometer or a digital display.
Spectrophotometers are popular optical instruments that can be used in a wide range of applications, such as environmental testing, chemistry, textiles, and forensics. Nevertheless, choosing a spectrophotometer can be challenging because detection limits, analytical working range, data quality, measurement time, and the wavelengths accepted by the grating are all factors to consider. Before buying a spectrophotometer, users should assess three major aspects:
Requirements: Spectrophotometers can be used in different settings, so it’s no surprise they come in all shapes and sizes. Thus, prospective buyers should evaluate their own goals and the instrument’s detection limits. Depending on the specific research goals, users can choose between different units that detect different wavelengths, such as visible light spectrophotometers, ultraviolet/visible spectrophotometers, near-infrared spectrophotometers, and nuclear magnetic resonance devices, atomic absorption spectrophotometers, mercury analyzers, and fluorometers. There are also microspectrophotometers to measure microscopic samples, suitable for thin-film measurements, microcalorimetry, and reflectometry. That said, wavelength limits are not the only factor that determines the classification of units. When it comes to sampling throughput, for instance, spectrophotometers can be divided into a single sample and multi-sample units. Last but not least, devices can be classified according to the light path employed: there are single beam, dual-beam, and split beam units.
Specifications: Although there are different types of units, which can be classified according to the wavelength spectrum, sample throughput, and light path – the basic mechanisms of spectrophotometers are the same. As mentioned above, spectrophotometers contain spectrometers and photometers. Such devices consist of a light/energy source, a filter/grater to set the desired wavelengths, a place for samples, and a radiation detector/phototube to convert the energy into a measurable unit. Note that solutions are placed in cuvettes or microplates and inserted into the device, after which spectrophotometers emit light and measure light intensity at different wavelengths.
Total costs: As stated above, detection limits, data quality, analytical working range, and measurement time are vital in determining purchasing choices and costs. Users should also consider if the unit has customizable or preconfigured testing method buttons, especially when it comes to consecutive analyses and measurement time. The actual footprint of the unit and its data export options can also impact prices. Last but not least, associated consumables should also be considered when calculating the total cost of a spectrophotometer.
Spectrophotometers are versatile scientific products used in a variety of research and production settings. As stated earlier, there’s a wide range of spectrophotometers prospective buyers can choose from:
With a variety of units on the market, choosing a spectrophotometer might be a challenging task. Note that some of the most notable manufacturers of spectrophotometers include Agilent, Shimadzu, Thermo Fischer Scientific, Hach Technology, Perkin Elmer, and GE Healthcare. Based on different characteristics and user reviews, here are the best spectrophotometers for sale:
Hach DR1900-01H DR 1900 Portable Spectrophotometer is a powerful portable unit. This spectrophotometer comes with over 220 built-in preprogrammed methods, which allows it to perform a large number of tests. Note that the model supports testing with a wavelength range of 340 nm to 800 nm. With its large display and clear interface, the unit is an easy to operate field instrument, suitable for various laboratory analyses and fieldwork.
Bespick Digital Display Spectrophotometer (Ray Spectrometer/Visible Spectrometer for Medical Testing, Food, Petrochemical Industry) is a versatile product that can be used in medical testing, environmental control, petrochemical settings, criminal investigations, and geological explorations. The unit consists of tungsten illumination and a large sample chamber. Also, it has an automatic wavelength adjustment and storage functions to ensure high accuracy. Last but not least, this spectrophotometer is equipped with an RS232 output port in order to connect to a printer or a computer.
MXBAOHENG UV–5100 UV/VIS Spectrophotometer (Photometer 200–1000nm, Bandwidth 4nm) is a great unit with a photometric performance in the 200–1000 nm range. The unit has both tungsten and deuterium lamps, which can be turned on and off individually in order to extend the unit’s lifetime. Also, this spectrophotometer has a large screen (128×64) that facilitates use and readings. Note that there is optional software UV-Professional, which can expand the unit’s applications to kinetics and quantitative measurements.
UV–5200 UV/VIS Spectrophotometer with Scanning Software, 190-1100nm Wavelength Range, 2nm Bandwidth is a great single beam unit that operates within a 190-1100 nm wavelength range. Note that its bandwidth is 2 nm. The unit’s large screen can display a total of 200 groups of data (five per screen), as well as a standard curve and curve equation. Furthermore, this spectrophotometer ensures easy transfer and storage of data to facilitate research and interoperability.
CGOLDENWALL Digital Spectrophotometer Spectrometer (Tungsten Lamp) for Lab Medical Testing, Food, Petrochemical Industry is a small single-chip system with advanced optics, a sealed grating monochromator, and easy to replace tungsten halogen lamps. This visible spectrophotometer combines calculation accuracy and beautiful design, ensuring high user experience.
Thermo Electron 840-301000 Biomate 160 UV/Visible Spectrophotometer (110V, 35.5 cm Length, 38.5 cm Width 19.5 cm Height) is an easy to use automated UV/VIS unit. Note that this spectrophotometer offers pre-programmed assay methods ideal for acid and protein concentration and cell culture analyses. Additionally, the unit comes with a high-resolution color touchscreen and Wi-Fi connectivity to facilitate usability.
Spectrophotometers are sophisticated tools, and as such, they require adequate maintenance. Taking care of spectrophotometers is essential to ensure a long lifetime and accurate measurements:
Spectrometers are sophisticated optical units that measure the amount of light transmitted through a sample, or that reflected off it, which is highly needed in medicine, biomedical research, production facilities, forensics, environmental testing, and quality control management. Given their diverse applications, it’s no surprise spectrophotometers come in different shapes and sizes, with visible light spectrophotometers, ultraviolet/visible spectrophotometers, near-infrared spectrophotometers, nuclear magnetic resonance devices, atomic absorption spectrophotometers, mercury analyzers, and fluorometers being popular models.
Before choosing a spectrophotometer, however, prospective buyers should consider three major factors: requirements, specifications, and total costs. Note that detection limits, data quality, analytical working range, light path, size, sample throughput, and measurement time are all factors to consider. Adequate maintenance is also a must to ensure long life and accurate use.
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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