23/12/2025
“Horses do not experience training, handling, or environment through intention or ideology. They experience it through their nervous system.”
A very interesting content that deeps in the knowledge about horses and how behaviour, what we think that we see, is not always the way to understand them.
Horses do not experience training, handling, or environment through intention or ideology. They experience it through their nervous system.
Every cue, pressure, change in environment, and social interaction is filtered through a fast, unconscious biological process asking a single question:
Is this within my capacity to cope right now?
The concept known as the Window of Tolerance offers a framework for understanding why a horse may appear confident one day and reactive the next, compliant yet shut down, or “unpredictable” across contexts. It shifts the conversation away from attitude or resistance and toward physiological capacity.
This framework originates in interpersonal neurobiology (Siegel) and trauma research, but the underlying mechanisms are rooted in autonomic nervous system function, which is conserved across mammals, including horses.
What the Window of Tolerance Actually Describes
The window of tolerance refers to the range of autonomic arousal within which an organism can remain sufficiently regulated to process sensory information, adapt behaviour, and learn flexibly.
When a horse is within this range:
Sensory input can be processed without overwhelming threat response
Movement remains coordinated
Attention can shift and widen
Recovery after startle is possible
Learning is adaptive rather than defensive
When arousal exceeds or drops below this range, the nervous system shifts priorities from learning to protection.
This is not psychological. It is biological.
In the Window: Regulation, Not Sedation
A regulated horse is often misunderstood as a calm or quiet horse. This is inaccurate.
A horse within their window may be:
Energetic, forward, and expressive
Alert but orienting rather than scanning
Able to pause and respond to light aids
Curious rather than hypervigilant
Socially connected to herd and human
Capable of recovery after effort or surprise
Physiologically, this reflects:
Dynamic balance between sympathetic (mobilising) and parasympathetic (calming) systems
Engagement of ventral vagal pathways, the part of the nervous system that supports calm social connection, coordination, and flexibility
Prefrontal and hippocampal involvement in learning and memory
Stress hormones present at manageable, adaptive levels
Crucially, being in the window does not mean the absence of stress. It means stress remains within tolerable limits, allowing the nervous system to integrate experience rather than defend against it.
Above the Window: Hyperarousal and Mobilisation
When arousal exceeds capacity, the horse moves into sympathetic dominance, often described behaviourally as fight or flight.
Common signs include:
Heightened startle response
Bolting, rushing, spinning
Increased muscle tone, especially through neck and back
High head carriage, wide or fixed eyes
Rapid or shallow breathing
Reduced responsiveness to subtle cues
Loss of fine motor control
Neurologically:
The brain prioritises speed and escape over precision
Sensory processing narrows (threat-focused attention)
Prefrontal modulation reduces
The amygdala plays a stronger role in rapid threat learning
A necessary nuance on learning here
Learning does not fully stop in hyperarousal. What becomes unavailable is flexible, context-sensitive learning.
Procedural and motor learning can still occur, which is why horses can appear to “learn” tasks under stress. However, memory formed in this state is more likely to be:
Rigid
Context-bound
Fear-associated
Less adaptable across environments
This helps explain why behaviours learned under high arousal are often context-bound, break down under pressure, or later reappear as heightened reactivity.
Below the Window: Hypoarousal, Freeze, and Shutdown
Hypoarousal is frequently mistaken for calmness or good behaviour. It is neither.
Here, the nervous system reduces output when mobilisation feels ineffective or unsafe.
Observable signs may include:
Dullness or absence
Delayed or minimal responses
Low curiosity or engagement
Reduced facial expression
Fixed posture, immobility, or “stillness”
A horse that appears compliant but emotionally unavailable
From a physiological perspective:
Parasympathetic pathways dominate behavioural output
Metabolic activity is reduced
Stress hormones such as cortisol may remain elevated internally
There is often a mismatch between internal stress and external stillness
This state is particularly concerning because it is easily misinterpreted as training success.
The horse is not relaxed. The horse has suppressed expression.
State-Dependent Learning: Why Capacity Matters
Neuroscience consistently shows that learning is state-dependent.
Excessive arousal impairs hippocampal processing and flexible memory formation. Hypoarousal reduces engagement, attention, and motivation. Only within a regulated range can information be evaluated, updated, and integrated
This is why:
A horse may perform well at home but unravel at a show
A behaviour may “disappear” under stress
Repetition does not equal consolidation
The behaviour is not lost. The nervous system state has changed.
Normal Stress vs Dysregulation
It is important to be clear:
Not all arousal is harmful.
Horses are biologically designed to experience:
Brief startle
Alert curiosity
Excitement
Physical exertion
Environmental novelty
Short excursions outside the window are normal and often unavoidable. What determines impact is:
Intensity
Duration
Frequency
Whether escape or recovery is available
Stress becomes problematic when it is:
Overwhelming
Inescapable
Repeated without adequate recovery
Layered across multiple domains (physical, social, environmental)
Recovery is not optional. It is what allows the window to remain open.
How to Assess Where a Horse Is
There is no single indicator. Assessment requires pattern recognition, not isolated behaviours.
Key considerations:
Baseline: What is normal for this individual?
Context: Does this behaviour change across environments?
Recovery: How quickly does the horse return to baseline?
Expression: Is the horse able to show variation, curiosity, softness?
Consistency: Are responses organised or fragmented?
Examples:
A high-headed horse may be alert and curious or hypervigilant
A quiet horse may be regulated or shut down
Stillness may reflect focus or freeze
Physiological measures such as heart rate variability (HRV) research in horses support these distinctions, but careful observation remains central.
Recovery: What It Actually Looks Like
Recovery does not mean the horse looks “fine” again.
Adequate recovery may include:
A visible softening of posture and breath
Return of curiosity or exploratory behaviour
Ability to disengage attention voluntarily
Restoration of normal movement rhythm
Emotional availability rather than emotional absence
Recovery may take minutes, hours, or longer, depending on the intensity and accumulation of stress. Both active recovery (movement, grazing, social contact) and passive recovery (rest, predictability, safety) play a role.
Without recovery, capacity does not expand.
It contracts.
Expanding the Window: Skill Building, Not Avoidance
Respecting the window does not mean avoiding challenge.
Athletic development, confidence, and learning require controlled stress exposure.
The difference lies in:
Staying close to the edge without overwhelming
Allowing retreat and choice
Building predictability
Layering difficulty gradually
Ensuring clarity and release
For example, with trailer loading:
Initial exposure may involve allowing investigation at a distance
Followed by gradual approach with the option to step away
Building familiarity before confinement
Only later expecting full loading and duration
Flooding overwhelms capacity. Systematic exposure expands it.
Avoidance does not build resilience.
Nor does force.
Individual Differences Matter
Not all horses have the same window.
Baseline arousal and window width are influenced by:
Temperament
Genetic factors
Breed selection history
Early life experience
Accumulated stress and trauma
Two horses can face the same task with very different nervous system demands. This is not weakness. It is biology.
The Role of Pain, Body State, and Social Context
Nervous system responses do not occur in isolation.
Pain, discomfort, gastric health, saddle fit, dental issues, and musculoskeletal strain all narrow the window, often dramatically.
Equally important:
Herd dynamics
Social rank pressure
Resource competition
Isolation or instability
A horse may be regulated alone and dysregulated in a group, or vice versa. This reflects context-specific nervous system load, not inconsistency.
A Note on Polyvagal Nuance
The autonomic nervous system is not a simple three-state ladder.
Mixed states are common:
Freeze often involves sympathetic activation layered over dorsal vagal suppression. Horses may oscillate rapidly between states
Regulation is dynamic, not static. The window of tolerance is a map, not the territory.
Why This Framework Matters
This lens allows us to:
Distinguish compliance from capacity
Reduce misinterpretation of behaviour
Make training more ethical and effective
Honour the horse’s lived experience
A horse can perform while dysregulated. A horse can stand still while terrified. Behaviour alone is not proof of wellbeing.
When we work with the nervous system rather than against it, learning becomes safer, clearer, and more sustainable.
Not because the horse must comply. But because the horse can participate.
Note for clarity and authorship
This piece reflects original work developed within The Whole Horse Journey, shaped through our own observation, applied practice, study, and lived experience working with horses and their humans.
It synthesizes established concepts from neuroscience, learning theory, stress physiology, and polyvagal-informed perspectives as they relate to equine behaviour and welfare, interpreted through our specific lens and field experience.
While similar themes may be discussed by other practitioners or disciplines, this article is not copied from, paraphrased from, or derived from any single individual, framework, or publication. Overlapping conclusions reflect shared underlying science rather than shared authorship.
This work represents an integrative, practice-based contribution to ongoing conversations around nervous-system-informed horsemanship.
Further Reading:
Siegel, D. The Developing Mind
Porges, S. The Polyvagal Theory
McGreevy & McLean – Equitation
