In a recent address to RIN Dr Kate Jeffery of the Institute of Behavioural Neuroscience at University College London described a very complete structure for understanding animal navigation. See http://animalnav.org/2014/10/navigation-networks-in-the-brain/
We at www.animalnav.org have been struggling with exactly these concerns.
Prof Jeffery postulates that you need four things to create a navigation system
- A compass so that you know how to orientate yourself in your map (representation of the world)
- A position estimate: where am I?
- Something to measure your distance run (odemeter)
- A representation of your target: where am I going?
There has been a lot of work especially in Germany (Wiltschko et al) on how the world’s magnetic field enables animals to navigate. The Wiltschko have particularly studied homing Pigeons. Recently David Keays at Vienna University has demolished the idea that pigeons have a magnetic sensor in their beaks: he dissected some pigeons and found the postulated magnetite sensor array was not in the beak at all. However, dowsers know that you can find North without any magnetic sensors so magnetic sensors are not necessary in order to find North. I mention dowsing as, just like animal navigation, no-one knows how it works, but this facility clearly works so is bound up in the mystery of how the brain operates.
Prof Jeffery’s idea that knowing how to orientate your map (we use North), is interesting as this puts several things in perspective. People who are good at navigating in the Northern Hemisphere are very often useless in southern and vice versa. This suggests that their maps are disorientated. The direction of the sun seems to be crucial to this too.
There are a lot of experiments “proving” that changing magnetic fields (using an adjustable Helmoltz coil for instance) leads to changes in behaviour and that some animals can be trained to seek food by changing magnetic gradients in a study box. (C Mora et al).
If the primary role of the magnet field is to orientate the animal’s navigational map then, if there is an absence of other clues, we could expect the animals to learn to use magnetic cues to orientate. Navigation is difficult so that animals use a number of cues to navigate by. If you take away all the navigational clues, except one, then the animal will respond by using that one in isolation but this does not mean that the navigation in the experiment is a good indicator of how navigation works in true life.
What is quite clear is that navigation is very difficult and that we all use as many inputs as possible to navigate by and that the inputs at the beginning of the journey (setting out) are not the same as the hippocampus mediated navigation around your neighbourhood.
From this we deduct that you need to know your orientation to make your internal map operate and that there are many inputs helping with navigation.
Having orientated you need to be able to identify your target (home or whatever). Often when you start a journey you are outside your memorised hippocampus grid and will need to set out in a roughly correct direction to get to your hippocampus mapped neighbourhood when you can locate your position in this grid so compute your direction based on your mapped (hippocampus) memory.
However many animals migrate over huge expanses of sea such as the bar tailed godwit navigating from Alaska to New Zealand each year across the Pacific Ocean. We also have the conundrum of the fledgling cuckoo navigating to it winter grounds in Africa as it leaves the nest in Europe, all by itself with no guides.
For all of this I think you need to have a vision of your destination. Quantum Physics propose extraordinary things. For instance it describes “entanglement” the ability of one electron to act in total harmony with another instantly at the other end of the universe. Einstein called this spooky action at a distance.
Since then, we have more discoveries in Quantum mechanics whereby total entanglement is not required to deliver perfectly good information transfer. Vlatko Vedral suggests that, from a Quantum point of view, that the cosmos is a giant computer that holds all the information that has ever existed. Many people have discussed the fact that seemingly the conscious interacts with this database. For instance a dowser asks for different things that he wants to dowse for, for instance a drain, or an electric cable and the dowser only finds what he is searching for to the exclusion of all the others. This means their conscious, or intent, seems to search the something we might call “The Universal Information Field” and find what is wanted.
If you can tolerate the idea of an Universal Information Field, you immediately have a way of asking for and being delivered an answer to the question: “where am I going”. Having asked, all you need to do is follow the way shown to you. Dowsers can follow invisible tracks easily, they just feel the correct route.
It is important to remember that most migratory birds going to and from Britain cross the sea at night and seem to be able to know the right direction to go. Navigating at night even on overcast skies mean that these birds must use dead reckoning (path integration) to carry out their migrations
They gain altitude at dawn which is navigationally completely correct as this gives them the chance to see further to check where they are and make adjustments from what they can see such as the coast ahead (landmarks).
But animals must register not only direction but, “how far have I gone?” For this you need an odometer. I think that birds unconsciously count their wing beats, some say they judge speed using their nostrils as a Pitot head. For other animals it can be footsteps etc, others yet suggest that they can feel the Doppler beat of their trajectory over the gravitational field.
For dead reckoning you need a gyro to record all the changes of direction. You need to add together distance run and changes in direction and you have a navigational system. There are lots of tiny gyros made for things such as cameras. It seems obvious that nature has mastered that too and provided us with one
We believe that the Pineal gland in Animals and/or the whirring gyrations of ATP (especially in insects) provide just the gyro that is required.
The Pineal is interesting as it sits low down in the brain just on top of the oldest part of the brain the Cerebellum surrounded by the Hippocampus. There is only one Pineal gland whereas most of the body has two paired organs. The shape of the Pineal is just right to be a gyro. Experiments in Pigeons show that when the Pineal is calcified (this happens with ageing) it no longer works properly and pigeons with calcified Pineal glands cannot navigate.
Professor Jeffery and her team at UCL in London have spent a great deal of time looking into the brain to understand how navigation might work. Her colleagues have decided that the Hippocampus is key to navigation and mediates memory too. If you cannot remember landmarks you get lost.
“Hippocampus navigation” is based on learnt landmarks. There a place cells that fire at known landmarks. There are also links to cells that know your heading –which way are you facing.
The important thing is that as in all animal navigation you use as much information as you can from all sources to complete your journey.
Initially you need a “Sense of Direction” so you know where you need to head. It looks as if people with a great sense of direction are good at dead reckoning (path integration). As people get older this sense gets worse –is it calcification of the Pineal?
We know that older people with the onset of Alzheimer’s get lost as they fail to recognise the key landmarks that drive hippocampus navigation.
External sources such as light form the moon or sun as also used, for instance dung beetles must go in a straight line away from the dung. Research shows that the light of the moon helps them keep direction.
Racing Pigeons are released hundreds of miles further away than the nearest landmark to their lofts. They must use a sense of direction to get themselves into their memorised Hippocampus map to find their way home.
But how does a fledgling cuckoo know how to fly to the Congo when it takes to the air for the first time? This is not a learnt response as there is no-one to teach it. The route is not straight (a bearing) it also includes preferred stopping (refuelling) points. Could the cuckoo genetic makeup point it towards picking up and following cuckoo imprinted routes (just like a dowser can find imprinted tracks left by animals).
The difficulty is that Science likes to isolate phenomena in order to measure and deduct. Isolation means switching off a whole range of sensors that are integrated into a whole navigational system. For instance the problem of accurate navigation as sea was solved by making accurate clocks (chronometers), having accurate navigational tables and accurate sextants. All three were needed, none by itself is enough.
Our difficulty is to work out how we can deliver an explanation of how navigation works as it relies on so many things integrated to make the whole.
The rats in the experiments at UCL live in cage so that the Hippocampus style of navigation is of course the one they use.
It looks as if we are approaching a framework in which to describe animal navigation. The problem is to provide one that is credible. We need to cover the fact that it looks as if different skills and approaches are needed for different parts of the journey. We also need to think about how navigation is achieved for different species.
© Richard Nissen December 2014