There are two different ways to deal with behavioral problems. One is to de-sensitize and the other is to counter condition. Usually, the hardest part of tackling a behavior is knowing which one to choose. De-sensitization is used to change an unwanted behavior that is still developing, in other words, the horse is still being sensitized; and counter conditioning is used when an unwanted behavior is learned and is now classically conditioned.
So now we need to understand the difference between sensitisation of behaviours and classically conditioned behaviours, then we can begin to understand the physiological difference (neural connections that are part of the learning) which will then allow us to better understand why one method works better on each problem.
A classically conditioned behaviour ALWAYS happens
A classically conditioned behaviour ALWAYS happens. The intensity of the reaction is unlikely to change. So if you have a horse that ALWAYS has an issue about trailer loading and the intensity of the reaction to not go on the trailer is as bad as it can get, this is a classically conditioned response.
If the refusal to load is only sometimes, or the reaction is sometimes worse than others, this is still in the sensitisation stage. So the horse is effectively still learning about the cue (trailer) and the consequences (confinement, isolation, going somewhere stressful etc). At this stage, most people will get out the whips and lunge lines etc and try to make the horse load, and in fact this just confirms to the horse that the trailer is bad and bad things happen when this cue (trailer) arrives. So the neural pathways for “trailer = negative emotion” are firmed up a bit more so getting closer and closer to it becoming an automatic (classically conditioned) reaction, i.e. always happens.
Once neural pathways are laid
Once neural pathways are laid, they don’t go away or change, it is the strength of the pathway that changes depending on how often it is used. So if you think about riding a bike. If you haven’t done it for 20 years, you CAN get back on and ride. You won’t be as good at it as you were 20 years ago but the neural pathways that you strengthened when you learned to ride a bike are still there 20 years later, they are just not a strong as they used to be and you need to practice to get them to work automatically again.
The same recall of habit can happen with classically conditioned negative emotional reactions (Conditioned emotional response or CER) in animals (including humans). For recall of CERs, the process is called spontaneous recovery. It is thought that because negative reactions are usually lifesaving reactions, the wiring with them is so much easier to firm up again that 1 episode of spontaneous recovery can cause a CER to re-emerge (or spontaneously recover) and stay for a long time. With sensitisation, if the horse gets a big enough fright/shock, the learning stage about the negative reactions can be totally by-passed and the reaction can immediately be as bad as it can get and therefore is a CER (classically conditioned response). So it seems these connections in the negative pathway are pretty firm once they are made….which makes perfect sense if you are a flight animal.
Generalisation
The other thing to remember as well is that once a negative emotion about something is learned, that can very easily be generalised to similar objects. So with the trailer example, if it is the small space the horse does not like, you might start to find narrow doorways become an issue. Or the generalization can be to other objects in the environment at the same time as the trailer is present. It might be something like a bucket, the people who are trying to load the horse, the equipment used to get the horse in the trailer….and this can include the feed scoop and the feed itself, etc.
The reason for this is that now two fear neural pathways are being triggered and being strengthened at the same time. What is then believed to happen is that when one fires, it is now so closely linked to the other, that it triggers the other one, so you end up with the spooky horse.
Smells and Memories
An example of this is, if you have a smell that reminds you of something bad, you don’t have to experience the bad thing to experience the feeling of fear (or whatever the emotion is) to experience/remember that emotion. The smell has been so closely linked neurologically to the original cue that it is enough to trigger your memory of the bad thing and thus the negative emotion that went with it. Firming up of neural pathways is called long term potentiation (learning) and when another pathway is being firmed as a result of another one being triggered, this is associative learning (or long term potentiation).