Cognitive Aspects: How People Perceive, Memorize, Think and Talk About Landmarks - Landmarks: GIScience for Intelligent Services - page 59

3.3.1 The Brain

The hippocampus is the region in the brain that has a central role in encoding and
retrieving information for behavior guided by memory, not only for spatial behavior
but for a range of different behaviors. However, just as the hippocampus is not solely
occupied with spatial memory and abilities it is also not the only region in the brain
involved in spatial memory and abilities. This makes mental spatial representations
and reasoning one of the more complex areas for neuroscience to understand.
Adding to the challenge, neuroscience can only rely on indirect (non-invasive)
observations on humans. Recent technology such as functional magnetic resonance
imaging (fMRI) is observing oxygen levels in blood, which may be correlated with
cell activity but must not be identified with it. Patients with brain lesions provide
further, but also indirect insight into the working of the brain [ 36 , 181 ] . Whether
cell activity of rodents, observed by invasive procedures, can be taken to explain
human capacities is open for debate. Furthermore, several types of brain cells seem
to be involved in mental spatial representations. With one of them, grid cells ,being
discovered only less than a decade ago [ 59 ] , it may be no surprise that there is still
uncertainty and speculation about the mechanics of mental spatial representations
[ 46 , 174 ] .
Very early, and based on behavioral experiments with rats, Tolman established
facts for a direct spatial representation in animals' long-term memory:

We assert that the central office itself is far more like a map control room than it is like an
old-fashioned telephone exchange. The stimuli, which are allowed in, are not connected by
just simple one-to-one switches to the outgoing responses. Rather, the incoming impulses
are usually worked over and elaborated in the central control room into a tentative,
cognitive-like map of the environment ( [ 216 ] , p. 192).

Some 30 years later O'Keefe discovered place cells in the hippocampus of rodents.
These cells fire when a rat returns to a place it had visited before [ 158 ] . The topic he
wrote with Nadel [ 159 ] still suggested the existence of a cognitive map .Itwastoo
tempting to believe that the brain stores the experiences at particular locations in a
map-like fashion. By now, however, it has become clear that place cells are not the
only cells involved in mental spatial representations (e.g., [ 173 ] ), and that spatial
abilities are formed by complex interactions between various regions in the brain.
Place cells, or fields of place cells, show firing patterns depending on location.
But how does a rodent's brain know? In principle there are two ways for an animal to
locate itself: One by path integration, i.e., sensorimotor stimulations, and the other
by perception of external cues. Since place cells fire even when an animal moves in
the dark, current thinking is that hippocampal representations are primarily driven
by path integration. Since path integration is accumulating uncertainty over time,
external cues may help to stabilize the localization, but are clearly second order.
In contrast, head direction cells , monitoring the direction of the face, have been
shown to be sensitive to visual external cues [ 209 , 210 ] . This is no surprise since
stationary visual external cues provide a stable reference frame for turning the head.
However, head direction cells also operate in the absence of light, supported by