Feb 072010
 

Have you ever wondered how squirrels remember where they hid their food? Or how animals that migrate know the route to take each year? Or how birds living in large groups remember where their specific nest is among thousands? These are just some of the questions that spurred research into how the brain records information about the environment and the animal’s position in that environment. This work can help us to understand how feral horses find their way around their range and even how our domestic horses can find their way home if they escape or they end up without a rider.

Map and compass

Animal navigation is a complex process that we are only beginning to understand: first the animal determines its current location in relation to what he/she knows about and then chooses the appropriate direction of travel towards its destination. This is called the ‘map’ and ‘compass’ system (reviewed by Frost and Mouritsen, 2006). [N.B. for brevity I will use ‘she’ when referring to a horse]

Horses that live in large areas naturally ‘home range’- they move to different parts of their range as the seasons affect the available resources. Homing can be defined as navigation within near- to medium- distance unfamiliar space (reviewed in Frost and Mouritsen, 2006). Herds use the same routes every year and the alpha mare, who will have made the journey many times before, leads the movement of the herd within its home-range. So, how does the alpha mare know where to go?

Making maps

Since the 1970s, researchers have been studying the cellular mechanisms by which the processes of cognitive mapping, spatial learning and spatial memory occur. This just means studying at the level of cells how animals map their environment, learn about it and remember it.

Let’s consider the first time a horse moves to a new part of the herd’s home-range. When an animal is placed in a new environment, the brain processes sensory information about its surroundings – for horses, a great proportion of this information will be visual. Within minutes of experiencing the new ‘place’, about half of the million specialized brain cells called ‘place cells’ (first described by O’Keefe et al., 1971) in the part of the brain called the hippocampus are fired. The ‘view’ is split up into overlapping fields (‘place fields’) and each field is assigned a place cell. As the horse’s head moves into a place field, the cell assigned to that field fires and some cells stop firing, providing orientation in the field (reviewed in Rotenburg et al., 1996).

The place cells recording these overlapping fields are not actually next to each other – which is efficient because each place cell can be used in more than one spatial map. The hippocampus records the memory for several weeks and only if the information is to be retained does it move to the part of the brain where information is stored, the cerebral cortex (reviewed in Rotenburg et al., 1996). This mechanism has been proved for ‘near space’ navigation but is also relevant to longer distances because during a journey there will still be shorter-term destinations (e.g. resources along the way such as rivers to drink from).

Learning the route

Until 1996 scientists were not sure whether animals learn about their surroundings as a map or react automatically to various stimuli they come across. Two research groups helped to solve the mystery and significantly added to our understanding of cognitive mapping (Tsien et al. and Rotenburg et al. 1996). Both groups, using different methods, disrupted the way that connections between cells change in strength (called synaptic plasticity, which occurs during learning) and found that indeed, the animals were no longer able to navigate around their environments – spatial learning was affected. The involvement of synaptic plasticity shows the link between learning and spatial orientation so we now can hypothesize that animals, including horses, learn about their surroundings as a map rather than just reacting automatically to things in their environment.

Since this early work into place cells, two other types of brain cell have been discovered – head direction cells (HDCs) and grid cells. HDCs are those that fire when an animal orientates its head in a certain direction (Knierim et al., 1995). There are different HDCs for different head orientations and they are influenced by landmarks, and information concerning how the head moves.

Later, grid cells were discovered (Hafting et al. 2005). These are found in the part of the brain called the entorhinal cortex and fire strongly when an animal is in specific locations in an environment. Grid cells have multiple firing fields, which tesselate the environment in a hexagonal pattern. The grid cells are anchored to external landmarks, suggesting that grid cells may be part of a self-motion-based map of the environment. It has been suggested that grid cells add a ‘place code’ in the entorhinal cortex, providing associations between place and events (for example to associate a place with good resources) – needed for the formation of memories (Sargolini, 2006).

Finding the way

Exactly how animals navigate long distances is still being researched but there are some interesting concepts that are probably relevant to equine homing behaviour:

  1. Minimization of stimuli: We only pay attention to meaningful cues. In the same way that when asking for directions we don’t need to know the detail of who lives in all the houses you pass but just need to know where to turn right – or if you are looking for someone in a crowd who is meeting you at the airport you won’t notice the detail about the other people there – horses do not take note of all the cues in the environment, just the important ones (perhaps a big tree that is good for rubbing on or a sheltered site).
  2. Features theory: In the same way as above, we, and horses, can remember part of a route without having to remember everything about it.
  3. Context: In the same way that we might not recognize the postman out of his uniform if we see him in the supermarket there is a context-specific element to mapping.
  4. Landmarks: It is likely that horses use landmarks in recognizing their home range. The famous ethologist Tinbergen proved that animals use landmarks to find their nests. For example, if an insect’s nest is surrounded by a set formation of pine cones, the insect leaves home, you move the pine cones to a new location, the insect will return to the pine cones and not to the nest. Landmarks that horses might use could be trees, boulders, houses etc or could be patterns of smells.
  5. Prototype theory (Hernstein, 1976): if a route is followed many times then the ‘ideal’ will be remembered. For example, if you do the same journey to work every day you don’t remember the first time in particular, you only remember specific times if they were very good or bad. In the same way, if a foal takes a similar route many times she will only remember some of them.
  6. Central pattern generators (Randall et al. 1997): are sets of brain cells that activate cells resulting in movement according to pre-set patterns. When a horse sees a visual stimulus associated with its home range, central pattern generators could cause automatic walking behaviour towards that visual stimulus. Animals do form a ‘map’ as described above but there might be an element of automatic behaviour within that map.
  7. Time: Horses need to know when to move from one area at a particular time to get to the new area at the right time for plentiful resources. It is suggested that a ‘time tag’ could be added to the memory formation (e.g. when the trees are green, the journey should be started).

Summary

When a horse is moving within her home range or being ridden out on a hack, she is learning about the environment – including about information about landmarks and features – such as areas that are sheltered or particularly good grazing areas. If the horse is wild, feral or kept almost naturally in a herd, as a foal she will follow the group to different resources at different times of the year. She will remember (via prototype theory above) the ideal situation with respect to, for example, crossing a river.

Physiologically, as the foal enters new environment, place cells will be fired within the place field, and when she orientates her head in a certain position, the corresponding head direction cells will fire, influenced by landmarks and information about the position of her head during orientation. When she is in some specific locations within her home range, grid cells will fire, to add the place coding to the memory associated with the event (good areas for food, for example).

Although further research is needed into how place cells, head direction cells and grid cells work together in determining orientation in space and in navigation, we are on the way to an improved understanding of the complex mechanism of homing behaviour.

By Suzanne Rogers

www.learningaboutanimals.co.uk

© Learning About Animals 2009

(Enjoyed this article? Then please donate a little to The Equine Independent to keep us writing. You can donate via paypal to mail@theequineindependent.com – Many thanksm Emma Lethbridge -editior)

References:

Frost, B.J. and Mouritsen, H. (2006) The neural mechanisms of long distance animal navigation. Current Opinion in Neurobiology 16, 481-488

Hafting et al. (2005) Microstructure of a spatial map in the entorhinal cortex. Nature 436, 801-806

Herrnstein, R. J., Loveland, D. H., & Cable, C. (1976). Natural concepts in pigeons Journal of Experimental Psychology: Animal Behavior Processes, 2, 285-302

Knierim, J. (1995) Place cells, head direction cells, and learning landmark stability. J. Neuroscience 15, 1645-1659

Liang, K.C. et al. (1994) Involvement of hippocampal NMDA and AMPA receptors in acquisition, formation and retrieval of spatial memory in the Morris water maze. Chin. J. Physiol. 37, 201-212

O’Keefe, J. and Dostrovsky, J. (1971) The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat. Brain Research 34, pp. 171–175

Rotenburg et al. (1996) Mice Expressing Activated CaMKII Lack Low Frequency LTP and Do Not Form Stable Place Cells in the CA1 Region of the Hippocampus. Cell Vol. 87, Pp. 1351-1361

Sargolini F, et al. (2006) Conjunctive representation of position, direction, and velocity in entorhinal cortex. Science 312, 758-62

Tinbergen, N. (1951) The study of instinct. Clarendon Press, Oxford.

Jan 292010
 

Once upon a time, a horse owner said to an alternative therapist: “Thanks very much for treating Billy last week. He was much more relaxed than usual in the stable that night, and he went really well when I rode him the next day – more forward going, more supple and more willing than usual. I’d like you to come and do him again”.

Very satisfactory for all concerned. The horse was going well, the owner was happy and the therapist had a new client. Except for one thing – the therapist hadn’t treated Billy last week. She’d gone to the yard as requested and met not the owner but the groom, who through a misunderstanding had asked her to treat another horse. The owner, not knowing this, had ridden Billy the next day and had attributed her good ride to the treatment she thought the horse had had the day before.

Now this alternative therapist had an enquiring and scientific mind and decided to conduct an experiment. She asked a friend of hers whether she could give the friend’s horse a free session of her therapy. She didn’t want the friend to watch what she did, but she did want the friend to give her feedback afterwards. And she didn’t do anything to the horse at all. While the friend thought she was doing the treatment, she was actually sitting in the manger reading a book and the horse was eating his hay. When the therapist later asked the friend what had happened, she was not altogether surprised to hear a tale about a very relaxed horse who “went so much better than usual when I rode him the next day”.

Unlike most stories that begin ‘once upon a time’, this one is true. It illustrates very nicely the danger of attributing a change in our horse’s behaviour or performance to something we have just done. Or, as in this case, that we think we have done.

You might suspect that I enjoyed telling this story because I am highly sceptical of alternative therapies, and you would be right. However, that isn’t really the point here. The therapy in question, unlike many, actually had some biological plausibility: it was a manipulative technique that many people find relaxing and invigorating, and it is not beyond the bounds of possibility to suppose that horses might also get at least temporary benefits. The point is that the intervention (or non-intervention) could have been anything: a veterinary treatment; a new feed or feed supplement; a new saddle or bridle; a visit from the farrier or equine dentist – you name it. The only necessity was for the owner to believe that any improvement in the horse’s behaviour following the intervention must have been a result of that intervention. As we have seen, the intervention didn’t even have to happen. All that was required was for the owner to want to make that connection.

The fact is that a horse will vary from day to day in how lively, enthusiastic, supple or willing he feels and there can be many reasons for this: working hard the day before, a slip in the field, more time than usual in the stable, the weather, the time of day, his social relationships and the amount of sleep he’s had, to name only a few of the possibilities. It is just unfortunate that we, with our pattern-recognising, all-too-human brains, are likely to come to the wrong conclusions about the reasons why, because of what we want to believe. If we have given the horse something we believe will improve his performance – and especially if we’ve paid a lot of money for it – we are likely to think that any subsequent improvement in performance is a result of what we did. As you can see, the fact that a change in behaviour followed an intervention does not prove that the intervention caused the change, and this is where science comes in.

Science is just a way of testing things. It’s not esoteric or mysterious. All you do in essence is ask a question, test it and then come to a conclusion. Imagine you own a nervous horse who is reluctant to eat from a bucket in the stable. Your bucket is black. You wonder whether the colour of the bucket makes any difference. So you go round the yard and borrow as many different-coloured buckets as you can. Each day you give your horse his feed in one of them (including the original black one), and record something like the time he takes to start or finish the feed, or the number of times he knocks the bucket over: something you can put a number to. Then once you have tested them all several times over several weeks, you compare the results from the coloured buckets with those from the original black bucket. You’ve used the scientific method to test whether bucket colour makes a difference to the time it takes your horse to eat a feed. You have results that you can use. If the horse eats best from a blue bucket you’ve solved your original problem. If you find no difference, you’ve still got a result. Now it’s time for a new idea: what else might make my horse reluctant to eat? This is how we make progress in science.

Unscientific ideas tend to start with the conclusion. You have the same horse with the same problem, but rather than doing the experiment, you just go out and buy him a yellow bucket because you believe that according to ancient Chinese philosophy, yellow is the colour associated with comfort, security and eating. The first problem with this approach is all the untested assumptions it makes: that the Chinese philosophy makes sense; that horses see the same colours in the same way that we do; that they respond psychologically to colours in the same way that we do and so on. The second problem is the likelihood that having bought the bucket you will then go on to notice all its positive effects while ignoring any negative ones, thereby reinforcing your original decision. And whether the results are good or bad, you have no idea whether the bucket really made any difference, because you haven’t done anything to find out. You haven’t compared buckets of different colours before making a decision: you’ve started with the decision.

What if you then wanted to start a business selling buckets for nervous horses? The person who found out that her horse preferred the blue bucket would have to do a more careful experiment to see whether her results were likely to hold true for all nervous horses, not just her own. She would need to try harder to avoid having her results affected by human errors such as wishful thinking, existing beliefs and her expectations, or by variation due to age, sex or breed among the horses, and would need to show that the positive results for say blue buckets were more than she would expect purely by chance. She would need to know whether the results made sense in relation to what is already known about horse biology, such as whether horses can actually distinguish blue from other colours. I won’t go into details, but the scientific method includes techniques to deal with all of these, helping to make a study as objective as it can possibly be. This person could then use her evidence to advertise her buckets: “Blue buckets decrease eating problems for 96% of nervous horses”, if that was what she found. The person who began with the assumption that yellow buckets were the ones to use, however, would have to convince other people to accept her beliefs without any evidence, and so would probably rely almost entirely on testimonials from satisfied customers. You might have thought that was fair enough, before you read the story above and discovered how easy it is to be led astray.

So, if you wanted a bucket for your own picky anxious horses, which bucket-seller would you choose? The person who sold blue buckets because she had done the experiment on lots of horses and discovered that most of them ate best out of blue ones, or the person who sold auspicious Chinese yellow buckets because she believed them to be effective? Sure, this is a trivial example, but horse owners make almost daily choices on behalf of their animals, and some of these choices could have large effects on their horses’ health, soundness and sanity, not to mention their own bank balances. Much of what we are offered has never been properly tested to see whether it is safe and effective. Wouldn’t it be better to buy from someone who had done the work and testing before putting the product on sale? Some things have been tested, and have been shown to be ineffective, but they are still for sale. Wouldn’t you like to be able to tell which these are, before you spend your money? That’s why we need science.

Note to readers: I’m well aware that it is not always easy to tell the difference between what is supported by science and what is not, so I intend to write more about this in my next article.

By Alison Averis

(Enjoyed this article? Then please donate a little to The Equine Independent to keep us writing. You can donate via paypal to mail@theequineindependent.com – Many thanks (Emma Lethbridge -editior))