Zone Preference in the Visual Water Maze
June 26, 2025
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While both reflecting and refracting models continued improving over the years, advancements in lens technology outside the field of telescopy led to the development of the catadioptric telescope – a combination of refracting (lenses) and reflecting (mirrors) optics. To provide an example, in 1820, physicist Augustin-Jean Fresnel developed the prominent catadioptric lighthouse reflector, in 1859 scientist Leon Foucault used catadioptric optics to build a microscope, and in 1876 officer Alphonse Mangin developed the so-called Mangin mirror integrated into today’s catadioptric units. Additionally, two main models of telescopes enhanced the design of contemporary catadioptric telescopes: the catadioptric dialytes (with the Hamiltonian telescope being the first dialyte unit patented in 1814) and the Schupmann medial telescope. Note that in 1931, optician Bernard Schmidt introduced the first full-diameter corrector plate to correct spherical and chromatic aberration in telescopes. Now popular catadioptric models include Schmidt–Cassegrain, Maksutov, Maksutov-Cassegrain, Argunov-Cassegrain, and Klevtsov-Cassegrain.
Given the interest in telescopes and research, it’s no surprise many people invest in telescopes. Telescopes can be used to study scenery, animals, and celestial objects. When it comes to amateur astronomy, telescopes can be used to study bright celestial objects, such as planets and the fascinating craters of the Moon, as well as deep-sky objects, such as distant nebulae and galaxies. Catadioptric units, in particular, are popular among astronomy lovers as they are compact and powerful at the same time. We should note that the three companies that popularized Schmidt-Cassegrain and Maksutiv-Cassegrain telescopes were Questar created by Lawrence Braymer in 1950, Celestron founded by Tom Johnson, and Meade Instruments started by John Diebel in 1972. Now, as stated above, popular catadioptric models include Schmidt–Cassegrain, Maksutov, Maksutov-Cassegrain, Argunov-Cassegrain, and Klevtsov-Cassegrain.
Because of the wide variety of units and brands on the market, choosing a catadioptric model can be difficult. Users should consider three main factors before purchasing a telescope:
Requirements: Users should refine their requirements and familiarize themselves with the basics of telescopes. As stated above, there are three types of telescopes: 1) refracting telescopes that employ lenses; 2) reflecting telescopes that consist of mirrors; 3) catadioptric telescopes that have both mirrors and lenses. Catadioptric models, in particular, use a combination of optical parts. Their unique design allows the folding of light within the unit without diminishing its focal length; it also eliminates various optical problems (e.g., coma, spherical aberration, and chromatic aberration).
Also, buyers should decide what they’ll be using the telescope for (e.g., terrestrial, nautical, or astronomical use). When it comes to amateur astronomy, users should decide what objects they want to see (e.g., deep-sky or bright objects) and where they’ll be viewing them (e.g., light-polluted or rural areas).
Specifications: Before purchasing a catadioptric telescope, users should consider two major specifications: aperture and magnification. Aperture refers to the diameter of the telescope’s main optical part through which light passes; a bigger aperture is ideal for observing deep-sky objects (e.g., galaxies, nebulae, clusters). As explained earlier, catadioptric units use both lenses and mirrors to create and focus a beam of light, resulting in sharp and detailed images.
Magnification is another vital characteristic to consider. However, excessive magnification can lead to blurry images, with magnification ranges of up to 300X being the maximum useful magnification. Note that a unit’s power can be adjusted by changing its eyepieces.
Total costs: Catadioptric or compound units are highly versatile and compact products as they use both mirrors and lenses to collect and focus light within a small tube. This optical configuration supports their compact and portable design and makes them easy to use and maintain. Yet, aperture, materials used, and additional features can increase the cost of a catadioptric unit. Large and computerized models, for instance, are more costly.
Additionally, telescope accessories, such as mounts, eyepieces, tripods, and carry bags, can increase the final cost of a catadioptric unit.
With diverse features and compact design, catadioptric telescopes are highly popular among seasoned users, astronomy lovers, outdoor enthusiasts, and young learners. Some of the most popular models are Schmidt-Cassegrain, Maksutov-Cassegrain, Schmidt-Astrograph, and Schmidt-Newtonian. Based on different specifications and user reviews, here are the best catadioptric models available on the market:
Celestron CPC 1100 StarBright XLT GPS Schmidt-Cassegrain 2800 mm is one of the best catadioptric models on the market. The unit features a 2800 mm aperture, a computerized altazimuth mount, a 9×50 finderscope, and premium optical coatings. With an internal GPS system and database of 40,000 celestial objects, this sophisticated catadioptric telescope provides excellent alignment and tracking accuracy. Additionally, Celestron CPC 1100 StarBright XLT GPS Schmidt-Cassegrain 2800 mm comes with a sturdy tripod, which facilitates both night sky viewing and astrophotography.
Celestron CPC 800 GPS (XLT) Computerized Telescope is another powerful unit with a focal length of 2032 mm, advanced StarBright XLT optics, and SkyAlign alignment technology. Additionally, this 8-inch Schmidt-Cassegrain telescope comes with a computerized mount with GPS and a remote hand-control holder. Celestron CPC 800 GPS (XLT) Computerized Telescope is an ideal present for both astronomy experts and beginners.
Celestron NextStar Evolution 8 Telescope has an aperture of 203 mm, a focal length of 1500 mm (focal ratio of f/10), and 480X maximum magnification. The unit is equipped with StarBright XLT Multicoated Optics, a stainless steel tripod, and a single fork arm altazimuth mount. With numerous advanced settings, Celestron NextStar Evolution 8 Telescope is ideal for viewing both bright celestial objects (e.g., planets) and deep-sky clusters (e.g., nebulae).
Celestron 22097 NexStar 127 SLT Mak Computerised Telescope is a 127 mm Maksutov-Cassegrain telescope with a focal length of 1500 mm. The unit is equipped with a computerized altazimuth mount, StarPointer finderscope, and NexStar’s hand control. Additionally, its design ensures quick setup and straightforward use. Celestron 22097 NexStar 127 SLT Mak Computerized Telescope is an ideal product for exploring the secrets of the night sky.
Celestron CPC 925 GPS Computerized Telescope is a wonderful product equipped with SkyAlign alignment technology, 40,000 object database, internal GPS, hand control software, enhanced computerization, and quality optics. Note that this Schmidt-Cassegrain telescope has an aperture of 235 mm. Celestron CPC 925 GPS Computerized Telescope is simply perfect for both stargazing and astroimaging.
Celestron 11049 NexStar 4 SE Computerised Telescope is an advanced Maksutov-Cassegrain model with an aperture of 102 mm (4.02 inches). The unit comes with a red-dot StarPointer finderscope, 25mm Plossl eyepiece, astronomy software, hand control, and 40,000 object database. As users can easily connect their DSLR or astronomical camera, this telescope is great for astroimaging. With its orange tube, Celestron 11049 NexStar 4 SE Computerized Telescopes makes an exciting gift choice for both experts and beginners.
Celestron 11068 NexStar 6 SE Computerised Telescope is another powerful catadioptric product. The unit has a 150 mm aperture, ideal for viewing planets and deep-sky objects. Its compact design makes it an ideal addition to a camping trip or an outdoor adventure. Moreover, with Celestron’s iconic “orange tube” and single fork arm design, Celestron 11068 NexStar 6 SE Computerized Telescope can make a beautiful gift for any astronomy lover.
Orion 10022 StarMax 90mm TableTop Maksutov is a great grab-and-go tabletop Maksutov-Cassegrain unit. With its 90 mm aperture, the telescope provides sharp views of bright planets and deep-sky objects. The model comes with two 1.25-inch eyepieces (25mm and 10mm focal lengths), EZ Finder II reflex, and a 90-degree mirror diagonal to facilitate viewing. Given its beautiful design, Orion 10022 StarMax 90 mm TabelTop Maksutov is also a magnificent aesthetic unit.
Levenhuk Strike 1000 PRO is a Maksutov-Cassegrain telescope with an aperture of 102 mm and a focal length of 1300 mm. Note that this unit is powerful and light at the same time. The telescope comes with numerous features: a German equatorial mount, an adjustable tripod, four planetary filters, lunar and solar filters, a 2X Barlow lens, a red-dot finderscope, and a diagonal mirror. The kit also contains books and DVDs, ideal for astronomy lovers who want to dive into the secrets of the night sky.
Catadioptric units are highly popular among astronomy lovers. Catadioptric or compound telescopes are one of the three main types of telescopes available on the market: refractors, reflecting units, and catadioptric instruments. Catadioptric telescopes employ both refractive optics (lenses) and reflective optics (mirrors) to produce enlarged images of distant objects. As stated above, it was Questar, Celestron, and Meade Instruments that popularized Schmidt-Cassegrain and Maksutiv Cassegrain models among stargazers. With numerous features, large aperture, high optical quality, and compact design, compound telescopes are sought-after units.
Yet, choosing a catadioptric telescope can be a daunting endeavor. Buyers should consider three main factors: requirements, specifications, and budget. Aperture, magnification, and optical quality are also essential factors to consider. Note that large and computerized models are usually more costly than other products. Purchasers should also be aware of the fact that taking care of telescopes is essential to guarantee long use. Catadioptric units, in particular, have complex optical and moving parts, so dissembling them is not recommended.
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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