The window of tolerance.

It’s a mild summer evening after work and you are swinging along in the arena practicing your dressage test for next weekend. Rhythm is good and your horse seems to be taking weight evenly on all four legs. It feels like the perfect time to head up the centre line.

You halt at X, take the reins in one hand, then find yourself clutching at some mane as the stable cat leaps up onto the post at E and your horse spins about her forelegs to fixate on what just happened.

As she snorts loudly at the cat, you regain your seat. “For goodness sakes, it’s just the cat” you say.

You draw your right rein outwards, keen to get back to the centreline and pick up where you left off, but nothing happens.

Now you get frustrated. Not only has your horse seen the cat a million times before, but she is now ignoring your turning aid.

You add some leg into the mix. A squeeze. A nudge. A tap. A few kicks. You ask harder and faster and still nothing. It’s like the light is on but no one is home. “Listen!” you say before turning your toes out for full spur effect.

Before you know it, you’re bolting back towards the arena gate picking up reins that didn’t seem nearly so long before. What on earth just happened?

One explanation is that the cat scared the horse. Others could be that your horse gave more attention to the cat than the rider. Your horse was deaf to the aids. Your horse should have known better. Your horse was being difficult.

With these interpretations in mind, you might decide you need to desensitise your horse to the cat and/or repeat stop and go transitions until you are satisfied that she has remembered what your rein and leg aids mean.

But that’s only going to fix one side of the picture – the external side where things happen to the horse. What about what’s going on internally, regarding your horse’s capacity to respond to and process the external world?


Horses, like humans, are mammals. We both have a mammalian nervous system and, one way to think through your horse’s unusual behaviour is to consider what we know about how human nervous systems perceive threats, danger and safety – a process known as neuroception.

When humans perceive danger, they often go into a state of hyperarousal such as screaming, crying, running, etc., or a state of hypoarousal which includes fainting, freezing or acute depression.

Our nervous system is hardwired to enter these states to help us survive. When we are in these states, we can’t control our behaviours and, depending on our prior experiences and present state of health, we may be more likely to go into or stay ‘stuck’ in them.

To return to our cat example, it is easy to become frustrated because your horse already knows your cat, but it is much more useful to think about our horse’s ‘window of tolerance’, a term coined by Dr Daniel Siegel.

The window of tolerance is a way to explain the horse's emotional comfort zone

The window of tolerance is a term coined by Dr Dan Siegel that is now widely used in all areas of mental health. When an individual is pushed out of their window of tolerance their ‘thinking’ brain stops functioning and their limbic system takes over. Before they can make sense of the situation, they need to
find their way back into their window of tolerance. Illustration by Cristina Wilkins, adapted from Equusoma’s Polyvagal Defense Hierarchy.

The window of tolerance

If we think of your horse grazing happily with a few other horses nearby, we can say that she is in her window of tolerance.

If something happens, she might take notice but then return to grazing, resting and digesting. This is a calm state of arousal. Arousal is not a bad thing. It is what keeps horses (and us) awake, aware, attentive, engaged, communicative and responsive to the environment.

Some horses have a wide window of tolerance. They seem able to absorb lots of external stimuli into their window.

Other horses seem to have a narrower window of tolerance. They don’t seem to be able to accommodate many external stimuli at all. Depending on what the stimulus is, even the slightest thing might make them spook, buck, bite, rear, kick bolt or freeze.

We tend to label horses with a wide window of tolerance ‘quiet’ and those with a narrow window of tolerance as ‘spooky’, but in reality, their window is never fixed. It is dynamic.

The window of tolerance changes in relation to other factors (such as different riders or even different times of day). It also changes over time and occasion.

The threshold

At the edge of the window is the horse’s threshold. That’s where we find the behaviours we know as fight, freeze and flight and it is in that exact order that the horse in our example reacted. Turning to face the cat was a fight (hyperarousal) response to the sudden jump that took the horse over threshold.

The rider’s additional stimulus of reins and legs pushed the horse even further into freeze (hypoarousal) which was then followed by flight (hyperarousal).

In both states of hypo and hyperarousal, mammals are incapable of communicating and responding (or learning). The rider’s aids thus became another stimulus that push the horse even more over threshold.

So, the cat in our example put our horse over threshold. That’s fairly clear. But why did the cat put our horse over threshold today when it doesn’t normally?

A horse's window of tolerance is dynamic, sometimes narrow, sometimes wider

The window of tolerance is never fixed, it’s dynamic. The narrower the window, the more ‘space’ the cat takes up when it appears, and the more chances the horse will be pushed over the threshold.

One way to think about this is to use the idea of a window of tolerance (and other mixed metaphors) where the horse’s nervous system is calmly aroused. If there is lots of free space in the window, the cat doesn’t take up much space.

The nervous system might be aroused momentarily (perhaps manifesting as a slight wobble off the centreline) but – assuming the stimulus is not too big or novel – the nervous system can respond to the shock of the cat’s jump, discharge that energy and fairly quickly return to a calm state of arousal.

If the horse came into the arena with a wide window of tolerance, the stimulus of the cat’s jump may not have put the horse even close to threshold. If the horse came into the arena already with a narrowed window of tolerance, the cat was literally the final straw that took the horse over threshold.

A different perspective

Now, this gives us a very different perspective on the horse that appeared to make a big and unnecessary deal over the stable cat. The horse’s uncharacteristic reaction tells us that she was not coping as well as we had thought. It tells us that she was either close to threshold and/or her window of tolerance was narrowed.

Worse still, your horse may have been in a ‘faux’ window of tolerance where to human eyes, she was coping well but really she was only managing her behavioural reactions.

Your horse’s non-response to the aids tells us, not only that the nervous system was activated, but that she was physically incapable of interpreting your signals (being either hyper or hypo-aroused).

You can say that your horse’s ‘social engagement system was offline’ in the same way that you would not expect to have a thoughtful conversation with an arachnophobe in the presence of a huntsman spider. If you just kept talking louder and louder to get their attention, you shouldn’t be surprised if they ignored you, walked off or became aggressive towards you.

In short, the horse was not being stupid, ignorant, willful or difficult. The horse was having a difficult time. If she did indeed “know better”, she was physiologically incapable of doing any better due to being over threshold and in a hypo-/hyper-aroused nervous system state.

Another way to look at the horse's emotions in the window of tolerance is to think of them as 'ripples'

A different way to visualise the window of tolerance is like ripples. Provided the ripples stay within the tolerance band, the horse can manage his or her reactions to stimuli.

More options

This knowledge widens our options from simply desensitising the horse to the cat whilst sensitising her to the aids (remembering that, in our example, she is normally responsive to them).

Instead of focusing all our attention on what made your horse go over threshold, we can think about what may have compromised, narrowed or otherwise taken up space in her window of tolerance.

Stimulus stacking

There are some obvious things that horse people are typically good at noticing such as the weather (a windy day), a horse leaving or entering the property, a change of routine, feed or a digestive upset.

Sometimes it’s all of the above and, when the nervous system doesn’t have a chance to reset back into a calm state of arousal between stimuli, we can have a case of ‘stimulus stacking’. Each stimulus brings the horse cumulatively closer and closer to threshold until the slightest thing tips them into hyper- (fight, flight) or hypo-arousal (freeze).

We also experience times where hyper or hypo arousal seem to occur for no apparent reason. The days when your horse does something completely “out of the blue”. However, these may have been days when you weren’t noticing everything you could have.

Maybe there are signs you routinely ignore and narrow your horse’s window of tolerance over time (girthiness is a common example).

Sometimes, we humans are just too busy or preoccupied to notice some of the equine body language that reveals our horses’ nervous states and how close they may be tracking to threshold.

You might want to think back to the mounting block when your horse braced her back as you got on, and then back to the way she moved sideways as you put the saddle on her back, and back further, to the tie-up rail when you had to force the bit in her mouth, or even further back to the paddock where you blocked her from walking away so you could get the halter on quickly…

That’s when you might realise that you never allowed time for you horse’s nervous system to recover before you proceeded with what you wanted to do.

You just kept on despite your horse’s attempts at communicating that she was not feeling OK. Whilst your horse didn’t seem to go over threshold at each of those points, you were effectively stimulus stacking.

You might even realise it wasn’t just the halter, the bridle, or the saddle but you too who was a stimulus that together made the cat in the arena too much to bear on that one ‘freak’ occasion.

It doesn’t matter if the horse has seen the cat, been caught, haltered, bridled, saddled and mounted a million times before. Everything that happens creates a ripple that impacts the horse’s nervous system and influences their window of tolerance. If you don’t let the ripple settle and deactivate, you will end up (sooner or later) creating waves.

The more I engage with the science of the mammalian nervous system and think through metaphors of windows and thresholds (and ripples), the more I realise that, no matter how quiet or how slow we are, we are probably being louder and faster than our horses would wish.

It really doesn’t take long to stop, breathe, go slow, take a step back or wait until we sense a deactivation in the nervous system. In fact, that is precisely how we can help our horses to widen their window of tolerance, be less likely to go over threshold and if they do – more likely to deactivate and return to a state of calm arousal.

Next, read about growing your horse’s window of tolerance.

Further reading:

The Developing Mind, Third Edition: How Relationships and the Brain Interact to Shape Who We Are, by Daniel Siegel. On Amazon:

Language Signs and Calming Signals of Horses: Recognition and Application by Rachael Draiisma. On Amazon:

Equusoma and Equusoma resources


Neuroception is a term coined by Dr Stephen Porges

The ‘Faux window of tolerance’ concept was developed by Dr Kathy Kain and Dr Stephen Terrell

This article was published in Horses and People March-April 2020 magazine.