Zone Preference in the Visual Water Maze
June 26, 2025
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The right to liberty is one of the essential human rights. Evidence, however, shows that slavery didn’t end with the Slavery Abolition Act in the 19th century. Modern slavery or human trafficking is a global problem affecting millions of people and societies across the world. In fact, data shows there are twice as many trafficked people today as during the African slave trade. While human traffickers do not legally “own” their victims, they use threats, physical violence, psychological abuse, and manipulation to control and force people to act against their will.
Human trafficking is a global health problem. Alarmingly, more than 600,000 to 800,000 people are being trafficked across borders every year. Developed countries are not immune to the impact of human trafficking, defined as the fastest growing criminal industry in the world. Any country can be a source, a place of transit, or a destination. Note that the US is one of the largest markets and destinations, second to Germany (Dovydaitis, 2010). Domestic trafficking is also exorbitant. For example, according to data provided by the US State Department, 50,000 victims are trafficked into the US, and more than 400,000 domestic children are involved in trafficking every year.
Human trafficking generates more than $150 billions of dollars in profits, with forced labor, debt bondage, and sexual exploitation being three of the most common and “profitable” forms of human trafficking. Human trafficking involves three elements: a) the act (e.g., recruitment, kidnapping, transfer); b) the means (e.g., force, kidnapping, fraud); c) the purpose of exploitation (e.g., sexual exploitation, forced labor, removal of organs). Additionally, human trafficking takes on many forms, including drug trafficking, forced marriages, and child soldiers.
Modern slavery affects people of all age, race, nationality, and gender. Research on human trafficking is crucial to identify and help victims who according to data, reach 40.3 million across the world. Data shows that 81% of all victims are trapped in forced labor, and 75% are women. More than 10 million victims are children, and approximately 15.4 million people are forced into marriage. As many cases go unreported or neglected, health research is the most promising way to provide evidence-based data with real-life implications.
Sexual exploitation is one of the most extreme forms of modern slavery, with more than 54% of all victims being sexually exploited (UNODC, 2016). Human trafficking takes on different forms, including prostitution, Internet chat rooms, pornography, and sex tourism, and generates more than $99 billion in profits globally. Note that a large number of traffickers are women exploiting other women. While most of the trafficked individuals are females, men and boys also become victims of sexual exploitation.
In the US alone, Polaris’ National Hotline and Be Free text line identified 7,255 of sex victims in 2017, and not a single state was excluded. To provide an example, in 2014, the sex criminal industry generated $39.9 million in Denver, Colorado, and $290 million in Atlanta, Georgia. The majority of cases accounted for escort services, followed by residential cases and outdoor solicitation.
Due to extreme stress, violence, hazardous conditions, and deprivation of food and sleep, victims suffer tremendous consequences. Trafficked individuals often suffer physical injuries (e.g., cigarette burns, loss of teeth, broken bones) and long-term disabilities (Acharya, 2019), as well as depression, anxiety, and posttraumatic stress disorder (Hossain et al., 2010). Additionally, forced and unsafe abortions put female victims at risk and strip them from their reproductive rights.
Therefore, medical professionals play a crucial role in identifying victims of human trafficking. Often health care providers are the only professionals to interact with the victims while still in captivity. To set an example, data shows that 28% of victims saw a medical professional during their captivity. As many cases go under-reported, tattoo recognition also plays a vital role in prevention and recovery (Fang et al., 2018). Note that sex traffickers often “brand” their victims to indicate ownership. Due to the severe consequences of sexual exploitation, data shows that working with one trafficking victim can take the same amount of the health provider’s time as 20 other violence victims.
Labor trafficking is one of the most common forms of modern slavery, with more than 24.9 million people being victims of forced labor via human trafficking. Victims are often promised a high-paying job or better opportunities but are sent to horrendous working conditions. Victims are forced to work in inhumane conditions across various industries, such as domestic work, leather tanning, agriculture, construction work, factories, and even restaurants and massage businesses. Traffickers (including recruiters, contractors, and employers) exercise physical and psychological control to target vulnerable populations and ethnic communities. Factors, such as immigration status, recruitment debt, and weak labor protection policies, contribute to human trafficking. Women are highly affected by forced labor, accounting for 99% of victims in the sex industry and 58% in other industries. Many female victims of forced labor are often sexually exploited.
Forced labor practices occur in every industry, including manufacturing, hospitality, fishing, agriculture, and construction. Some of the means of human trafficking include the use of violence, retention of documents, and threat of exposure to immigration services. Descent-based slavery, which refers to people born into slavery to slave-owning families, should also be tackled. Note that descent-based still occurs in the Sahel belt in Africa and other parts of the world. As many victims experience abuse and live in inhumane and hazardous conditions, enslaved individuals often suffer from infections, malnourishment, and depression, which require medical assistance. Note that 22% of trafficking survivors in Southeast Asia reported severe injuries, such as loss of limbs (Zimmerman & Kiss, 2017).
Bonded labor or debt bondage is a severe form of labor trafficking, which refers to the use of a bond to keep an individual under control. Bonded labor occurs when traffickers manipulate the victim via an initial debt considered part of the terms of employment, such as a significant amount paid for the “privilege” to work abroad. Abuse of contracts, inadequate local laws, and intentional impositions of illegal costs contribute to bonded labor, especially among migrant workers. Surprisingly, in the US, 71% of labor trafficking victims entered the US on lawful visas (Owens et al., 2014).
Domestic servitude is a specific form of forced labor. Given the fact that domestic servitude involves private properties, which are rarely inspected, many cases go underreported. Evidence shows that foreign workers from Asia, Africa, and Latin America often work as domestic servants in rich places, such as the Gulf States and the US. In fact, the International Labor Organization reports more than 67 million people to work as domestic workers across the world. Many victims are on call 24/7, confined to a home without their travel documents or money, and with no access to health services or social support. Alarmingly, if workers manage to escape from their abusive employers, they are often treated as criminals instead of victims.
Illegal organ trade is one of the most complex forms of human trafficking, which generates profits between $840 million and $1.7 billion per year, with more than 10% of all organ transplants being trafficked. Note that lungs, kidneys, livers, corneas, and hearts are the most trafficked organs. According to the World Health Organization, more than 10,000 kidneys are purchased on the black market across the globe, which equals more than one kidney every hour.
Organ harvesting is a global health problem as long waiting times for legal transplants are among the main contributing factors fueling today’s illegal organ trade. In Canada, for instance, the average wait time for a kidney is between 4 and 7 years.
Victims are often forced or lured to sell their organs for a low price through a middleman. Other victims do not consent, and their organs are forcefully removed. To provide an example, a person may go to the hospital for an unrelated condition, after which their organs can be removed without their knowledge or consent. Victims of forced labor and sex exploitation often become victims of organ harvesting. Additionally, individuals can be kidnapped, sold, and killed for organs. Note that the Chinese government admitted to harvesting organs from prisoners between 1990 and 2000. Alarmingly, doctors, nurses, and other “respected” health professionals often get involved in organ trafficking.
To target traffickers, a multidisciplinary collaboration between health professionals, anti-laundering specialists, and law enforcement agents is essential. Note that wire transfers, payments between medical tourism sites, and first-line banking information for large amounts of money transferred by ill clients to medical companies can indicate organ harvesting.
Trafficking for crime and forced begging refers to forced crimes, such as benefit fraud, ATM theft, pick-pocketing, and forced begging. In Europe, the Roma community is one of the main ethnic targets of human trafficking, with Romania being one of the major source countries. Romani women and children are particularly vulnerable to trafficking for various purposes, including sexual exploitation, labor exploitation, organ trafficking, illegal adoption, and forced begging. Identifying such victims is specifically complex due to social exclusion, poverty, illiteracy, and ethnic discrimination.
Research shows that the UK is one of the main destination countries for enslaved victims. In the UK, in particular, 2,555 victims of trafficking were identified in 2012, with 16% identified as trafficked for the purpose of criminal exploitation. Forcing people into cannabis production is also common, with 96% of victims being from Vietnam. Note that bond labor is a common means of controlling the victims who often turn to illegitimate lenders to pay off their “debt.” Additionally, trafficked victims are often treated as criminals. For example, statistics show that in the UK alone, 130 children have been arrested for crimes relating to the cultivation of cannabis since 2011 (Victim or Criminal? Trafficking for Forced Criminal Exploitation in Europe.).
In Central America, drug cartels also exploit people, including children, for the purpose of drug and sex trafficking. Some victims of human trafficking are used to transport drugs across borders. These victims are known as drug mules and go through hazardous procedures to swallow balloons with illicit drugs, which are then retrieved from their bodies. Victims suffer serious injuries, stress, prosecution, and death. Alarmingly, drug cartels are turning to sexual exploitation, and in some cities, such illicit sex trade is even encouraged. A survey showed that 16% of boys from San Miguel Tenacingo, Mexico, wanted to become a “pimp” and get involved in human trafficking.
In fact, drug and human trafficking are interconnected; many victims suffer from drug addictions and mental illnesses. A survey showed that 84.3% of sex trafficking victims in the US used drugs during their exploitation; 55% used alcohol, marijuana, and cocaine; and 22.3% heroin (Stoklosa, MacGibbon & Stoklosa, 2017).
Forced marriages are another severe form of human trafficking. Data shows that 15.4 million victims of human trafficking are in situations of forced marriage, and 84% are girls and women. Note that three types of forced marriages exist: the forced marriage of adults, child marriage, and trafficking for marriage. The means of trafficking, on the other hand, vary from fraud to abduction by an armed group. Other forms of forced marriage include a family member being involved in the trafficking network, confining and abusing the victim to obtain consent – sometimes defined as “honor”-based violence.
Child marriages, in particular, are a major health problem as they lead to numerous psychological and health issues, with risks stemming from early and multiple pregnancies. Data shows that 37% of people in forced marriage were children at the time of the marriage and were stripped from their right to education. Alarmingly, child marriages are integrated into various cultures throughout the world.
When it comes to the phenomenon of trafficking for marriage, 1.4% of victims of human trafficking were trafficked for marriage. According to data, due to the sex imbalance in China, men often purchase or lure foreign brides from countries such as Thailand, Vietnam, Laos, Cambodia, and North Korea. Forced marriage increases the risk of further abuse and enslavement with the inability to leave.
Forced marriages lead to a variety of health and emotional issues, including a high risk of self-harm and suicide. Family harassment, including harassment for dowry, also increases the risk of mental problems and premature death.
Trafficking of children spans all forms of modern slavery, including sexual exploitation, forced labor, removal of organs, forced marriage, and forced criminality. Alarmingly, 20% of all victims are children. In some parts of Africa and Asia, these numbers reach up to 100%. Statistics show more than 1.2 million children are being trafficked annually. According to the Polaris Project database, there are 100,000 to 300,000 children prostituted in the US, and more than two million children are held in sexual bondage across the globe.
Runaways are at high risk of being trafficked, with 1/3 forced into prostitution within 48 hours of leaving their homes. Data shows there are more than 450,000 child runaways; in 2017, one out of seven reported runaways were child sex trafficking victims. Alarmingly, 88% were in the care of social services or foster care seeking escape from a bad environment.
A specific form of child trafficking is the exploitation of children by extremist groups (e.g., child soldiers in Colombia and Nigeria, the enslavement of Yazidi women by Islamic State). Child soldiers, in particular, is a global problem as child soldiers are used for frontline combat, informants, and other acts of crime. Although empirical research is lacking, health professionals report that trafficked children suffer emotional trauma, developmental problems, and degradation (Rafferty, 2008).
Last but not least, child selling is another severe form of trafficking in children. We should note that global surrogacy arrangements, particularly in India, have also risen concern about human trafficking; human rights defenders claim that women in low-resource nations are particularly vulnerable to exploitation and discrimination.
Human trafficking is a growing problem. According to data provided by the International Labor Organization, there were 12.3 million trafficking victims in 2005, 21 million victims in 2012, and 40.3 million victims in 2016. In contrast, evidence shows there were only 14,894 trafficking prosecutions and 9,071 convictions in 2016. Moreover, victims, especially homeless people, LGBT youth, and minorities, often experience revictimization by the police or medical professionals. To provide an example, American Indians who represent 2.2% of the population in Hennepin County, Minnesota, account for 24% of women arrested for prostitution (Martin & Rud, 2007).
Human trafficking is also a global health problem. As explained above, health professionals are sometimes the only people who are in contact with the victim while still in captivity. Careful examination and training are mandatory to identify victims and save lives. As explained above, victims suffer tremendous injuries and mental problems. Data collected from 207 trafficked women across 14 countries reported that 95% of women had experienced extreme physical violence and emotional abuse. Forced abortions are also common; 71% of sex trafficking victims reported at least one pregnancy, 21% more than five pregnancies, 55% at least one abortion, and 30% multiple abortions. Note that forced abortions can lead to scar tissue, infections, and hysterectomy. Additionally, victims suffer from serious illnesses and long-term disabilities. To provide an example, a study on trafficked Nepalese girls and women found that 23% of them tested positive for HIV.
Therefore, evidence-based research is crucial to help authorities and health professionals identify and combat human trafficking. A recent bibliometric analysis, however, showed there is a significant underrepresentation of health literature on human trafficking (Sweileh, 2018).
When it comes to human trafficking, raising social awareness is one of the essential steps to end modern slavery. From pornography to social stigma, human trafficking is closer than people think, with the demand and supply circle being a vicious aspect of it. Alarmingly, the U.S. Department of Labor has identified more than 148 goods from over 76 countries made by forced labor, so smart purchasing choices are essential.
Human trafficking or modern slavery refers to the exploitation of people via violence, fraud, and threats. From forced labor and sex trafficking to domestic servitude and the use of child soldiers; trafficking represents horrendous violations of human rights. More than 40.3 million people across the globe become victims of human trafficking and suffer extreme physical, emotional, and social abuse. Alarmingly, victims who manage to escape are often treated as criminals and experience revictimization and discrimination.
Due to the covert nature of modern slavery, research and evidence-based information are mandatory to help authorities and health professionals identify and save victims who are often “hidden in plain sight.” Note that human trafficking is a global health concern as victims suffer from long-term disabilities and mental problems, and medical professionals are often the only people who can help the victim while in captivity.
While proper training and strict anti-trafficking legislation are mandatory, human trafficking is also a social concern. In demand for cheap products and accessible pornography, products of human trafficking are closer than people think. It’s no surprise trafficking is defined as the fastest growing criminal industry with more than $150 billion in profits annually.
Human trafficking, however, is not a business. Human trafficking is a crime against humanity – because people are not for sale.
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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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