How Animal Personalities Are Revolutionizing Brain Science
The secret to understanding aggression, anxiety, and even ourselves might be scurrying through a field or laboratory maze.
Why does one mouse boldly explore every corner of its environment while another hesitates, cautiously assessing potential threats? The answers to these questions are shaping our understanding of the complex relationship between genes, the brain, and behavior. For decades, behavioral neuroscientists have relied on animal models to unravel the mysteries of the brain, drawing a direct line from the aggressive displays of a betta fish to the nuanced social interactions of humans 7 .
This field rests on a powerful evolutionary principle: the conservation of critical biological systems across species 1 . The same basic brain structures and neurochemical pathways that govern fundamental behaviors like fighting, fleeing, and mating have been preserved throughout vertebrate evolution.
This means studying behavior in mice can reveal general principles that apply much more broadly 1 . By observing how natural and artificial selection shape behaviors like aggression and anxiety, scientists are not just learning about animals—they are uncovering the fundamental blueprint of our own brains.
The theoretical foundation for this research dates back to Charles Darwin, who first scientifically addressed the implications of natural selection for the evolution of behavior 1 . Modern behavioral neuroscience builds on this groundwork, using a comparative approach to understand how behaviors have evolved in related species sharing homologous brain structures 1 .
The vertebrate brain showcases this "conservative" nature of evolution. Systems critical for survival and reproduction, such as the serotonergic system that modulates socio-sexual behaviors, maintain a remarkably similar basic structure and function across different animal classes 1 .
A major breakthrough came when scientists began applying the principles of selection in the laboratory. Researchers can create distinct genetic lines of animals by selectively breeding individuals that show extreme expressions of a specific trait, like high or low aggression 1 .
This method was pioneered by K. M. Lagerspetz in the 1960s, who demonstrated that by selectively breeding the most and least aggressive mice from a population, she could create two dramatically different lines in just a few generations 1 .
Foundation for understanding how natural selection shapes behavior across species.
Studying related species with homologous brain structures to trace behavioral evolution.
Pioneered by Lagerspetz in the 1960s, creating distinct behavioral lines in just a few generations.
Using advanced methods to pinpoint specific genes and neural circuits underlying behavior.
To understand how selection shapes behavior, consider a comprehensive series of experiments that compared four different genetic lines of mice: wild mice, outbred Swiss-CD1 mice, and two inbred strains (DBA/2 and C57/BL6N) 3 .
The researchers used ethologically-based paradigms—tests designed around the natural behavioral repertoire of mice—to analyze both social (aggression) and non-social (novel environment exploration) contexts 3 . The experiments proceeded in three phases:
Measuring various forms of aggression, including intrasexual aggression and maternal aggression 3 .
Evaluating anxiety-related behaviors using tests like the free exploratory paradigm 3 .
Administering anxiolytic drugs to examine neurobiological mechanisms across genetic lines 3 .
The results revealed a compelling pattern: different forms of aggression consistently covaried across genetic lines 3 . Mice from the lines that showed the highest levels of intermale attack (Wild and Swiss-CD1) also displayed the highest levels of infanticide, interfemale attack, and maternal aggression 3 .
Interestingly, the most aggressive lines showed the lowest levels of anxiety-like behavior. They explored more freely and showed less "risk assessment" behavior compared to the less aggressive DBA/2 and C57/BL6N strains 3 .
| Genetic Line | Aggression Level |
|---|---|
| Wild Mice | High |
| Swiss-CD1 | High |
| C57/BL6N | Low |
| DBA/2 | Low |
| Genetic Line | Exploration |
|---|---|
| Wild Mice | High |
| Swiss-CD1 | High |
| C57/BL6N | Low |
| DBA/2 | Low |
| Genetic Line | Sensitivity |
|---|---|
| Swiss-CD1 | High |
| C57/BL6N | Low |
| DBA/2 | Low |
The pharmacological phase provided the crucial link: the different genetic lines showed varying sensitivity to the anxiety-reducing effects of chlordiazepoxide 3 . This suggested that artificial selection of different genotypes had not just changed outward behavior but had actually modified the proximate neural mechanisms—likely the GABAergic system—that modulate aggression and anxiety 3 .
Contemporary behavioral neuroscience relies on a sophisticated array of tools to connect behavior with its biological underpinnings.
Mice, Rats, Zebrafish, Drosophila 5
Provide conserved neurobiological systems for studying behavior and testing interventions.
Automated tracking, AI-based pattern recognition 4
Objectively quantify complex behavioral dynamics with high precision.
Immunoassays for Tau, Amyloid-β, α-Synuclein 2
Measure specific protein levels or aggregates linked to neurological conditions.
Anxiolytics like Chlordiazepoxide 3
Probe the neurochemical systems that regulate behavior (e.g., GABA).
Programmable syringe pumps 8
Automate and standardize reward delivery in learning and decision-making tasks.
Robotic animals for social interaction studies 7
Enable controlled experiments on social behaviors with unprecedented precision.
The field of behavioral neuroscience is rapidly evolving, propelled by technological advances that were once the realm of science fiction. Today, researchers are using robotic animals to decode social interactions with unprecedented control. For example, scientists using robotic guppies have discovered that "an adaptive leader is a better leader than a static leader"—a finding only possible through controlled robot-animal interaction 7 .
Advanced robotic systems allow precise control over social stimuli, enabling researchers to systematically study how animals respond to specific behavioral cues in their conspecifics 7 .
Tools like advanced motion tracking, virtual reality, and artificial intelligence algorithms are allowing researchers to detect behavioral dynamics with unmatched precision 4 .
Major initiatives like the NIH BRAIN Initiative are fostering interdisciplinary collaborations to accelerate this progress, with a focus on understanding the brain at multiple levels—from individual cells to complex circuits governing behavior . The ultimate goal is a comprehensive understanding of how dynamic patterns of neural activity are transformed into cognition, emotion, perception, and action in health and disease .
The research into selected lines of mice reveals a profound insight: subtle genetic alterations can cause profound effects on behavioral strategies and their adaptive value 3 . The coupling of high aggression with low anxiety in certain genetic lines is not a random coincidence but likely represents an evolved behavioral syndrome—a suite of traits that work together in specific ecological contexts.
These findings underscore the importance of studying behavior in ecologically-relevant contexts that emphasize its function 3 . As we continue to develop more sophisticated tools for measuring and manipulating brain activity, the humble mouse and other animal models will undoubtedly continue to illuminate the intricate dance between our genes, our neurons, and our behaviors—revealing the deep evolutionary heritage that shapes who we are.
Animal behavior research demonstrates that conserved neurobiological systems across species provide powerful insights into the fundamental mechanisms underlying human behavior, emotion, and cognition.