Introduction Mount Elbrus, the highest mountain in Europe, is

Brain Products Press Release
July 2012, Volume 43
IN THE FOCUS
On the MOVE with Brain Products – recording EEGs at the rooftop of Europe
by Simon Brezovar*, Jurij Dreo*
* Laboratory for Cognitive Neuroscience, Department of Neurology, University Medical Center Ljubljana, Slovenia
Introduction
Mount Elbrus, the highest mountain in Europe, is located in
the Western Caucasus mountain range. Many Europeans are
not familiar with Mt. Elbrus, and the belief that Mt. Blanc is
the highest European mountain is still per vasive. But since
geographically the whole surface of Elbrus is situated on
Caucasus’s north side, Elbrus is rightfully called the rooftop
of Europe. With 5642 metres it dwarfs neighbouring mountains
Fig. 1: Mount Elbrus
by more than 1000 metres. Together with our colleague Iztok
Cukjati we decided to organize a research expedition to Mt.
Elbrus to study the effects of prolonged high altitude exposure
on human physiology, especially on the human brain.
High altitude physiology
While the fraction of oxygen in the atmosphere remains fairly
constant up to the outer troposphere limit (approx. 15000 m),
the partial O2 pressure decreases exponentially with altitude.
This leads to a reduction of inspired and alveolar oxygen
pressure, associated with a decreased oxygen concentration
in the blood (hypoxaemia). Hyper ventilation may then occur
causing a drop in carbon dioxide levels (hypocapnia) (ViruesOrtega et al., 2006). These physiological changes can lead
to acute altitude sickness and in severe cases also to high
altitude pulmonar y and/or brain edema. Climbers and travellers
who are exposed to high altitude environments report
numerous cognitive deficits which can persist for more than a
year. Problems with memor y, word recall, attention, decision
making, problem solving are reported in literature (ViruesOrtega et al., 2004). Although anecdotal evidence on cognitive
changes due to high altitude exposure is common, actual
experimental data are quite rare.
High altitude and visual attention: out of the lab and
into the field
The objective of our research expedition was to study the
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influence of high altitude hypoxia on behavioural and
electrophysiological markers of visual attention. Our initial
plan was to record participants at three time-points: just before
the expedition (baseline), just after the expedition (acute
changes) and then one month after the expedition (chronic
changes). Even up to three months before the expedition we
were still unclear how it would be possible for us to record
EEGs on the mountain. While we were vaguely aware of certain
commercial portable EEG devices we were sure that our
budget could not cover these. We contacted Brain Products
to ask for their assistance and due to the interesting nature
of our proposed EEG experiment they graciously offered to
lend us their newest portable wireless EEG system – the
BrainVision MOVE. The long-battery life of the BrainAmps
together with the freedom of movement and ease of set-up
that the wireless MOVE add-on brings was exactly what we
needed. We visited Brain Products HQ near Munich and after a
very warm reception we received the necessary equipment.
Bottom-up and top-down mechanisms of visual attention
Our first measurements took place a few days before the
expedition. Subjects had to perform visual tasks that permit
discrimination between two systems of visual attention: topdown and bottom-up control (Li et al., 2010). Top-down control
regulates the relative signal strength of different information
channels based on immediate goals and past experience.
Bottom-up control acts automatically to enhance responses
to biologically salient stimuli. While bottom-up attention
seems reflexive and automatic, top-down attention appears
effortful, slow, and context-dependent (e.g. on the number of
distractors). Participants were first shown a triangle, and then
an array of four triangles, one of which (the target) was identical
to the previous sample triangle. They were asked to decide as
quickly as possible which side of the screen the target was on,
(Figure 2). In the bottom-up (pop-out) condition, the colour and
orientation of the three distractors differed from that of the
Fig. 2: Visual attention task
target. In the top-down (search) condition, however, only the
orientation of the distractors differed from that of the target.
In addition to the visual attention task we also performed
a standard checker-board pattern-reversal visual evoked
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potential (PRVEP) task as a reference for the effects of
hypoxia on earlier stages of visual processing.
High altitude EEG recordings: keeping a stiff upper lip
It would be ideal to perform the high-altitude recording as high
as possible. But since mountain weather is extremely unstable
and access to electricity is limited we decided to conduct all
measurements at the “Barrel huts camp” located at 3900 m
(Figure 3) where we were assured that participants could be
seated
comfortably
and mains power was
available. After three
days of acclimatization
at 3400 m we made our
final ascent to the Barrel
huts camp. But we found
there was no electricity,
due to “problems with
terrorists”, as we were
told.
A
pylon
had
reportedly been mined,
cutting the power supply
Fig. 3: Barrel huts camp
to the camp. This meant
that we had to curtail our ambitious recording schedule. The
limiting factor proved to be one of our older laptops and not
the BrainAmps, which have up to 30 hours of runtime with
the PowerPack. We therefore decided to record just the
PRVEP task on the slopes of Mt. Elbrus.
Measurements were performed 3 days after our arrival at
the Barrel huts. Subject preparation was of course more
difficult than in the lab, where ever ything is to hand and it
is not -20°C. But since ever yone was highly motivated there
were few problems (Figure 4). The equipment functioned
perfectly even in the harsh mountain environment. Moreover,
as luck would have it, the laptop batter y lasted until a few
seconds after the last subject completed the PRVEP task.
Fig. 4: A climber before EEG recording
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July 2012, Volume 43
Curiosity about the results was naturally great but for the next
two days our attention was fully focused on the final ascent. On
2 May at 1 pm we were standing on the rooftop of Europe with an
appropriate banner in our hands (Figure 5).
Fig. 5: Simon Brezovar on Elbrus
Final results
All EEG analyses were performed with BrainVision Analyzer 2.
First we addressed the question of whether PRVEP latencies
and amplitudes were affected by high altitude exposure
and whether they returned to their starting values after the
expedition. While PRVEP amplitudes were not significantly
influenced by the climb, the latencies of some components,
especially N1 (N100) and P1 (P100) were increased at high
altitude (Figure 6). The N1 component peaked some 10 ms
(8 ms – 14 ms) later in comparison to baseline. The P1 peak
was prolonged for about 8 ms (6 ms – 12 ms). These differences
were consistent across all subjects and highly significant
(p < .01) even with our small sample of 6 subjects. In both
cases the peak latencies returned to their initial states one
week after descent. These findings were independent of
Fig. 6: PRVEP results
Brain Products Press Release
July 2012, Volume 43
electrode position but more pronounced with smaller checkerboard squares (15 arc minutes) than with large ones (1 arc
degree) which could indicate that the processing of more
complex visual stimuli is affected to a greater degree than the
processing of simpler stimuli.
Figure 7 (Visual attention task results, topographies show
times of individual peak P3 amplitudes, time in ms after
display of triangle array is indicated) shows peak
topographies of the P3 (P300) ERP for the visual search and
pop-out condition for each individual. In four individuals
(subjects 1 - 4) the P3 is, somewhat counter-intuitively,
increased after the expedition. In subjects 5 and 6 the P3
was reduced after descent. These results are consistent
across both tasks. Due to the small sample size it is hard
to draw reliable conclusions about the nature of these
differential P3 changes under hypoxic conditions but they
may point to different coping mechanisms present in each
individual. We will be able to expand on these preliminary
findings after our next expedition to Muztagh Ata (7546 m)
which will take place from 3 - 27 August 2012. Our goal is
to connect individual ERP results with other psychological
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Fig. 7: Visual attention task results
or physiological variables to try and improve our
understanding of the dynamics of the P3 response to hypoxic
conditions.