by Jonathan Smith
On the 19th December in the Royal Society, the British Neuroscience Association (BNA) held a special Christmas symposium on the subject of the neuroscience of navigation, featuring topics ranging from ants and bird flocks to computer simulations for rodents! After these exciting talks, a concluding session of wine and mince pies went down a treat!
Not being overly familiar with
the area around Pall Mall, I was forced to put my own neglected navigation
skills to the test in order to arrive at the prestigious venue, the Royal
Society, in time for the introduction by Professor David Nutt who is the
current president of the BNA. In the introduction, he explained some of the
background of research into navigation and outlined some of the latest
developments that were being made by researchers. These covered a wide range of
life, embarking from more basic organisms like the ant, passing through flocks
of birds, crossing the development of navigation in mammals, traversing the
fields of mammalian cognitive maps and arriving at the age-related changes in
human navigation. Here, I try to summarise some of the fascinating
presentations which deserve much more than a single article to review!
The first speaker, Dr Paul Graham
from the University of Sussex, talked about the humble ant. Ants need to find
food. They also must know where their own nest is in order to transport the
food back home. But how do they remember where it is? In a series of
experiments on the Australian desert ant, Dr Graham’s team worked out that
these ants use visual panoramic cues to encode the locations of the nest and of
food sources. Not only that, but they quickly set up a route between the two
locations that becomes hard-wired and idiosyncratic, just like a human
travelling the same route to work and back. That way, it seems that ants do not
have a cognitive map of the area around the nest, but instead store information
of food sources in relation to familiar cues (e.g. the location of the nest).
It is thought that this system could even be the origin of our spatial
cognition!
Dr Laura Biro from the University
of Oxford presented her research into flock navigation. The research began with
studies of individual pigeons establishing routes and expanded into simulating
the flight paths of over 10 pigeons! How do these flocks decide which route to
take? Firstly, individual pigeons develop idiosyncratic routes, similar to
those in ants, that are based on visual landmarks. If you train two individuals
with different routes and release them as a travelling pair, the results vary
from either bird compromising its own route to them falling out and going their
separate ways! Clearly there are complex leadership issues at work here. In
flocks of more than two pigeons, there is a definite leader whose route is
followed by the rest. This leader is not always at the top of the pecking order
in social issues, but may possibly be the most efficient navigator of the
flock.
But how do the flock decide who
is the leader? This is a complex decision-making process that Biro et al have
made strides in simulating. It may be that there is a hierarchy of each pigeon
asserting its dominance over another in a similar fashion to winning Wimbledon
- the champion proves that he plays better than the runner up and all of the
runner up’s previous opponents. There is still much work to be done. Biro et al
are currently working on good simulations for flocks of thousands such as those
of starlings that form incredible shapes in the sky!
We then moved on to mammals. Next to present was Dr Emma Wood from the University of Edinburgh who dealt with the subject of encoding an intended destination into a memory. Firstly, mammals have neurons that fire only when the organism is in a specific location in an environment. These are called “place cells” and it is thought that these help to encode our location in space. There are also many types of these place cells e.g. some that fire at a boundary and others that fire when the mammals are travelling to an intended destination, called goal-dependent place cells.
Wood et al found through many behavioural experiments that these goal-dependent place cells were more active when the animal (in this case, a rat) was strategically planning to run to an area containing a reward. Additionally, through further experiments, they found that instead of mainly encoding the location of the destination, the goal-dependent place cells principally encoded the route to the destination. From this, a pattern is emerging that remembering routes is easier for an organism than just remembering locations and recalculating the route every time!
Dr Francesca Cacucci from
University College London then talked about her research into the development
of spatial cognition in rats. After birth, a rat takes roughly three weeks to
develop skills needed for exploration of its surroundings. Interestingly, at
approximately 19 days after birth, rats shift from being couch potatoes to
intrepid explorers practically overnight! Cacucci et al think that somewhere in
this transition the capacity for encoding spatial maps is developed. Rats are
able to perform spatial memory tasks after around 20 days of age. This is
largely dependent on a brain region called the hippocampus, so the implication
is that the hippocampus is sufficiently developed to encode spatial maps. As
navigation and memory uses many other navigational functions such as
orientation, distance and boundaries, place cells (encoding the rat’s current
location) in the hippocampus must be connected with orientational cells called
head direction cells, map-encoding cells called grid cells and
boundary-encoding cells called boundary vector cells. Work by Cacucci et al
shows that these are not all connected before 20 days of age and could be the
reason why spatial memory and exploration only kicks in at this age.
Dr Carlo De Lillo from the
University of Leicester made a presentation based on searching systems in
space. This was based on the concept that when making an efficient search of
objects in an area, you can either form a structured way of searching them e.g.
from left to right, depend on simply remembering which objects you have already
visited or a bit of both. Experiments investigating how efficiently different
species searched a set of objects in a room found that in comparison with rats,
four-year-old children and capuchin monkeys made the most structured searches. Other
experiments by De Lillo et al showed that humans in fact use structured
searching as a complement to memory retention much more than other species. Put
another way, it is like someone is searching through boxes and doesn’t have to
remember exactly which boxes he has searched because he is working through them
from left to right. This research could lead to many new tests of memory and
executive function that could help in the diagnosis of conditions such as
dementia and schizophrenia.
Next to present was Dr Jan Wiener from the University of Bournemouth.
His research consisted of giving human participants the task of navigating a
virtual maze with a set route and then retracing and rejoining the route from
unfamiliar directions. Egocentric navigation is the strategy of recalling a
route and exploring until your surroundings resemble this route. On the other
hand, allocentric navigation involves being able to consider the spatial map
independently from your own location and is needed for retracing a route and
rejoining it. Experiments by Wiener et al on younger and older participants
indicate that as we age, we become less able to use allocentric navigation than
younger people and use egocentric navigation more and more, even when it fails
to help us navigate well. Don’t panic just yet though - this ageing effect can
be reduced by regular training!
The final speaker that day was
Professor John O’Keefe from University College London who discovered
hippocampal place cells in 1971 and was a member of the BNA in its infancy as a
pub meet up! He outlined his most recent research into virtual reality for
rodents. In order to generate a virtual reality for mice, his group set up a
floating ball on which the animal is placed. Two screens project a scene which
the mouse can move in while walking on this ball, similar to a hamster ball
except with a virtual backdrop! O’Keefe et al found that a virtual scene
resulted in similar amounts of place cell activity to an actual environment.
Additionally, the team found that passively moving the mouse through the scene
resulted in much less place cell activity, suggesting that place cell activity
is largely based on active movement through a location. O’Keefe hopes now to
expand the experiments to record hundreds of place cells in future as a better
measure of encoding location.Overall, the day was fascinating to attend and the discussions afterwards were very engaging. I benefited from the presentations as a way of glimpsing the world of neuroscience outside of my own studies to get the bigger picture of our progress. Oh, and the mince pies and wine afterwards didn't hurt either!
