Cognitive Performance, Hyperoxia, and Heart Rate Following Oxygen Administration in Healthy Young Adults
Abstract
It was recently established that supplemental oxygen administration significantly enhances memory formation in healthy young adults. In the present study, a double-blind, placebo-controled design was employed to assess the cognitive and physiological effects of subjects' inspiration of oxygen or air (control) prior to undergoing simple memory and reaction-time tasks. Arterial blood oxygen saturation and heart rate were monitored during each of six phases of the experiment, corresponding to baseline, gas inhalation, word presentation, reaction time, distractor and word recall, respectively. The results confirm that oxygen administration significantly enhances cognitive performance above that seen in the air inhalation condition. Subjects who received oxygen recalled more words and had faster reaction times. Moreover, compared to participants who inhaled air, they exhibited significant hyperoxia during gas administration, word presentation, and the reaction-time task, but not at other phases of the experiment. Compared to baseline, heart rate was significantly elevated during the word presentation, reaction-time, and distractor tasks in both the air and oxygen groups. In the oxygen group, significant correlations were found between changes in oxygen saturation and cognitive performance. In the air group, greater changes in heart rate were associated with more improved cognitive performance. These results are discussed in the context of cognitive demand and metabolic supply. It is suggested that under periods of cognitive demand a number of physiological responses are brought into play that serve to increase the delivery of metabolic substrates to active neural tissue. These mechanisms can be supplemented by increased availability of circulating blood oxygen, resulting in an augmentation of cognitive performance. Heart rate reactivity and the capacity for increased blood oxygen appear to be important physiological individual differences mediating these phenomena.

783
Physiology & Behavior, Vol. 67, No. 5, pp. 783–789, 1999
© 1999 Elsevier Science Inc.
Printed in the USA. All rights reserved
0031-9384/99/$–see front matter
PII S0031-9384(99)00183-3
Cognitive Performance, Hyperoxia, and
Heart Rate Following Oxygen
Administration in Healthy Young Adults
ANDREW B. SCHOLEY,*
1
MARK C. MOSS,* NICK NEAVE* AND KEITH WESNES†
*
Human Cognitive Neuroscience Unit, Division of Psychology, University of Northumbria,
Newcastle upon Tyne NE1 8ST, UK; and
†
CDR Ltd CDR House, Portman Road, Reading, RG30 1EA, UK
Received 8 June 1998; Revised 17 June 1999; Accepted 29 June 1999
SCHOLEY, A. B., M. C. MOSS, N. NEAVE AND K. WESNES.
Cognitive performance, hyperoxia, and heart rate fol-
lowing oxygen administration in healthy young adults.
PHYSIOL BEHAV
67
(5) 783–789, 1999.—It was recently established
that supplemental oxygen administration significantly enhances memory formation in healthy young adults. In the present
study, a double-blind, placebo-controled design was employed to assess the cognitive and physiological effects of subjects’ in-
spiration of oxygen or air (control) prior to undergoing simple memory and reaction-time tasks. Arterial blood oxygen satu-
ration and heart rate were monitored during each of six phases of the experiment, corresponding to baseline, gas inhalation,
word presentation, reaction time, distractor and word recall, respectively. The results confirm that oxygen administration sig-
nificantly enhances cognitive performance above that seen in the air inhalation condition. Subjects who received oxygen re-
called more words and had faster reaction times. Moreover, compared to participants who inhaled air, they exhibited signifi-
cant hyperoxia during gas administration, word presentation, and the reaction-time task, but not at other phases of the
experiment. Compared to baseline, heart rate was significantly elevated during the word presentation, reaction-time, and dis-
tractor tasks in both the air and oxygen groups. In the oxygen group, significant correlations were found between changes in
oxygen saturation and cognitive performance. In the air group, greater changes in heart rate were associated with more im-
proved cognitive performance. These results are discussed in the context of cognitive demand and metabolic supply. It is sug-
gested that under periods of cognitive demand a number of physiological responses are brought into play that serve to in-
crease the delivery of metabolic substrates to active neural tissue. These mechanisms can be supplemented by increased
availability of circulating blood oxygen, resulting in an augmentation of cognitive performance. Heart rate reactivity and the
capacity for increased blood oxygen appear to be important physiological individual differences mediating these phenomena.
© 1999 Elsevier Science Inc.
Oxygen Hyperoxia Cognition Demand Heart rate Metabolism
THE brain is the most metabolically active organ in the body
(39). This metabolism consists almost exclusively of the oxy-
gen-dependent breakdown of glucose. Indeed, a number of
brain imaging techniques exploit the fact that there is en-
hanced uptake of glucose and oxygen into brain areas that are
differentially active, depending on the cognitive task involved
(18,33,35).
The availability of glucose and oxygen can affect cognitive
functioning. Reversible cognitive impairments are evident
during hypoglycaemia (16,17,41,46) and hypoxia (8,14,31).
Similarly, aging-related cognitive decline has been attributed
to the compromised delivery of oxygen and glucose through
the cerebral vasculature (11,14,40). It has also been demon-
strated that memory performance can be enhanced through
the administration of a glucose drink. The phenomenon is
more pronounced in the elderly (7,15), but has also been ob-
served in younger individuals (4,5,12). Elevated blood glucose
is also associated with improvement on a number of nonmne-
monic cognitive tasks particularly when such tasks require
“effortful” mental processing (10). Some of these studies sug-
gest that the magnitude of response to a glucose load in terms
of rising (4,7) or falling (5,32) blood glucose predicts the level
1
Requests for reprints should be addressed to A. B. Scholey, Human Cognitive Neuroscience Unit, Division of Psychology, University of
Northumbria, Newcastle upon Tyne NE1 8ST, UK.

784 SCHOLEY ET AL.
of cognitive performance [see Foster et al (12) for a recent cri-
tique of the area].
Previous work in our laboratory has established that, like
glucose, oxygen administration is capable of enhancing as-
pects of cognitive performance. Oxygen inspiration for 1 min
prior to presentation of a word list resulted in a significant in-
crease in number of words recalled 10 min or 24 h later (28).
Administration of oxygen immediately preceding recall did
not increase the number of items recalled, suggesting that
supplemental oxygen can affect memory formation but not re-
trieval. This interpretation was supported in a related study
where blood oxygen saturation was monitored constantly, and
oxygen administered at different time points relative to a sim-
ple word recall task (38). Word recall (tested 12 min following
presentation) was enhanced only when transient (2-min) oxy-
gen delivery, and consequent hyperoxia, occurred immedi-
ately before, immediately following, or 5–3 min prior to word
presentation. No effect was evidence when oxygen adminis-
tration occurred 10 min prior to, nor 5 min following, word
presentation nor immediately prior to word recall. We have
also assessed oxygen’s impact on performance of other cogni-
tive tasks (29). The overall finding was that cognitive perfor-
mance on computerized tests of various aspects of informa-
tion processing, including attention and verbal memory, were
selectively enhanced through supplemental oxygen adminis-
tration in a dose-dependent manner. Individual tasks were
differentially enhanced by various durations of the gas. Else-
where, oxygen (but not glucose) administration was found to
improve aspects of “everyday” memory, including shopping
list items and matching names to faces (48). It should also be
noted that not all cognitive measures are improved by oxygen.
Computerized tests of working memory were unaffected by
oxygen administration, although methodological factors may
account for this finding (29,38). Similarly, induced hyperoxia
improved neither forward nor backward digit span perfor-
mance (38), a result that is consistent with those reported for
glucose (13). Clearly, further research is required in which di-
rect comparisons are made between the cognitive effects of
glucose, oxygen, and their combination.
What of the relationship between glucose, oxygen, and cog-
nitive processing in the absence of a glucose or oxygen load?
The brain’s metabolism is altered in response to cognitive de-
mand (19), an effect mediated by a number of physiological
changes that may serve to increase the levels of glucose and
oxygen in the blood, and their delivery to task-sensitive neural
mechanisms. In a series of studies in the 1970s the Laceys dem-
onstrated that tasks requiring cognitive processing are associ-
ated with heart rate acceleration (21,22). In a more recent ex-
ample of the phenomenon, memory improvements during
muscle tension-induced arousal were accompanied by acceler-
ated heart rate (30). Similarly, both heart rate and oxygen con-
sumption were increased in subjects who played a video game
or performed complex mental arithmetic (42), and effortful in-
formation processing was shown to be associated with faster
and more shallow respiration (1,47). In a related study, in-
creased memory load (number of items) was accompanied by
accelerated heart rate, faster respiration rate, and greater vol-
ume of exhaled carbon dioxide, a direct indicator of oxygen
uptake (2). With respect to physical exercise, induced hyper-
oxia has been shown to increase subjects’ endurance time to
exhaustion by some 41% (34), an effect that was accompanied
by increased heart rate and oxygen uptake.
In resting subjects, the usual responses to induced hyper-
oxia include heart rate deceleration (6,9,23). This finding, and
the possibility that increased heart rate may serve to deliver
higher levels of metabolic substrates to active neural mecha-
nisms, suggests that increased heart rate associated with cog-
nitive processing may be of a lesser magnitude in hyperoxic
individuals. We are not aware of any study in which the inter-
action between induced hyperoxia, cognitive processing, and
heart rate has been studied.
The aims of this study were twofold. First, we wished to
further examine whether, following oxygen administration,
blood oxygen levels are indeed higher during memory forma-
tion and a reaction time task—two measures that are known
to be sensitive to oxygen-associated improvements (29). Sec-
ond, we were particularly interested in exploring the rela-
tionship between blood oxygen levels and heart rate during
information processing. These issues were addressed by moni-
toring subjects’ arterial hemoglobin oxygen saturation and
heart rate during a word memory and a simple reaction-time
task following inspiration of oxygen or air.
METHOD
Subjects
Twenty-one female and 11 male volunteers (mean age
21.06 years) took part in the study. This sample size was se-
lected on the basis of previous results (28,29,38), and allowed
a between-subjects design to be utilized. Prior to their partici-
pation in the experiment each subject signed an informed
consent form that had been approved by the Divisional Ethics
Board.
Cognitive Measures
Word recall and Simple Reaction-Time tasks, drawn from
the Cognitive Drug Research Ltd computerized assessment
battery (44,45), were run on an Elonex 386 personal com-
puter. Word presentation consisted of 15 two-syllable words
being presented sequentially on the screen for 1 s each, with
an interstimulus interval of 1 s. In the recall phase, subjects
were instructed to write down as many of the words as possi-
ble. In the Simple Reaction-Time task subjects were required
to press a response button as quickly as possible following
each (random interval) presentation of the word “YES” on
the computer screen.
Physiological Measures
Arterial hemoglobin oxygen saturation (%) and heart rate
(beats per minute) data were sampled automatically at 30-s
intervals using a N100-P hand-held pulse oximeter (Nellcor
Puritan Bennet, Coventry, UK) according to the manufac-
turer’s instructions. These data were collected throughout the
experiment, with each reading representing a “snapshot” of
the two measures at that time point.
Gas Administration
Gas delivery was achieved using the following assembly,
arranged so that neither experimenter nor subject were aware
of whether oxygen or air was being administered. Cylinders
containing medical quality compressed air and oxygen, re-
spectively, were purchased from British Oxygen Company,
Guilford, UK. Attached to each cylinder was a full-nose regu-
lator and an air flow meter; these were both set to simulta-
neously deliver the gases at a rate of 8 liters per min. Each
subject inspired one of the gases (depending on their experi-
mental condition) for 70 s via a hand-held face mask. This was
attached by tubing to one arm of a three-way “Y”-junction,

HYPEROXIA, HEART RATE, AND COGNITIVE PERFORMANCE 785
the other two branches of which were connected by tubes to
the oxygen and air sources, respectively. The assembly was ar-
ranged such that the gas source for each gas delivery session
was hidden from both subject and experimenter. Situated on
these tubes, adjacent to the Y-junction, were valves that were
closed off, thus preventing the gases from entering the piping
to which the face mask was attached. Following allocation to
experimental condition, one of the valves (which were labeled
by code) was opened, causing oxygen or air to be fed into the
face mask for inspiration.
Procedure
Subjects were tested individually following a placebo-con-
trolled double-blind design. Upon entering the laboratory,
each subject was randomly assigned to one of the two coded
conditions representing oxygen and air. They were familiar-
ized with the use of the face mask, and the oximeter probe
was placed on the index finger of their nondominant hand.
The start of each subjects’ data collection (time zero) was syn-
chronized with switching on the pulse oximeter. Four readings
were taken to establish baseline levels of oxygen saturation
and heart rate. Oxygen/air delivery began 2 min 20 s following
the start of the experiment, and ended immediately following
the oximeter data output at 3 min 30 s. Word presentation be-
gan at 3 min 55 s, encompassing two oximeter readings, and
was followed at 4 min 55 s by the Simple Reaction-Time task,
that terminating at 7 min 15 s (during which time five oxime-
try readings were collected). Between 7 min 25 s and 9 min 15 s
subjects underwent a distractor task in which they were in-
structed to count out loud backwards in threes from one thou-
sand (this phase encompassed five oximetry readings). At 9
min 25 s subjects were instructed to write down as many of the
words as they could remember (five oximetry readings were
collected during this phase). The experimental session termi-
nated with the final pulse oximeter output at 11 min and 30 s.
Prior to debriefing, subjects were asked to indicate which gas
they thought they had received by responding “oxygen,”
“air,” or “don’t know.”
Statistics
Word recall and Simple Reaction-Time data were ana-
lyzed by independent sample
t
-test. Oxygen saturation and
heart rate data were investigated statistically by analyses of
variance (ANOVA).
Any relationship between physiological measures and cog-
nitive performance were further explored using Pearson mo-
ment-product correlations. Mean baseline hemoglobin satura-
tion and mean baseline heart rate were each compared to
reaction time scores and word recall scores, separately for the
air group and the oxygen group. The change in each of the
two physiological measures during the experiment were also
compared to cognitive scores: mean baseline oxygen level and
mean baseline heart rate were subtracted from the mean oxy-
gen level and mean heart rate, respectively, for each of the
three experimental phases involving cognitive processing (i.e.,
word presentation, reaction time, and word recall). Each of
the resulting six measures were compared to both number of
words recalled and reaction time, separately for the air group
and the oxygen group, again using Pearson moment-product
correlations.
The responses as to which condition subjects believed they
had been in were subjected to a
x
2
contingency test.
RESULTS
Cognitive Measures
There was a significant effect of experimental condition on
both word recall,
t
(30)
5
2.127,
p
,
0.05, and reaction time,
t
(30)
5
1.975,
p
,
0.05 (see Fig. 1). Subjects who received ox-
ygen recalled more words than those who received air (means
5
6.219 and 4.688, respectively). Simple Reaction Time was
faster in the oxygen condition than the air condition (means
5
237.461 and 256.050 ms, respectively).
Physiological Measures
Mean levels of arterial oxygen saturation and heart rate
over the duration of the experiment are plotted in Fig. 2a and
b, respectively. For the purpose of statistical analyses data
were collapsed into six categories representing the mean heart
rate or oxygen saturation for each phase of the experiment;
baseline, gas administration, word presentation, reaction
time, distractor, and recall.
There was a significant condition
3
phase of experiment
interaction,
F
(1, 5)
5
17.356,
p
,
0.0001, with simple main ef-
fects analysis revealing a significant elevation of blood oxygen
saturation in the oxygen compared to the air condition, during
gas administration,
F
(1, 45)
5
12.901,
p
,
0.005, and word
presentation,
F
(1, 45)
5
21.228,
p
,
0.0001. There was also a
significant main effect of phase of experiment on blood oxy-
gen saturation,
F
(1, 5)
5
34.083,
p
,
0.0001. With the excep-
FIG. 1. The effect of oxygen administration on (a) word recall, and
(b) simple reaction time. Error bars depict standard errors (*p , 0.05;
compared to air condition).

786 SCHOLEY ET AL.
tion of the difference between mean values obtained during
the baseline and the distractor phase (which was not signifi-
cant), oxygen saturation in each phase was significantly differ-
ent to that in every other phase.
Comparisons of overall mean oxygen saturation did not
show a significant difference between groups during the Sim-
ple Reaction Time task. However, an ANOVA performed on
the five individual oximeter readings during the reaction time
task revealed that there was a significant condition
3
time in-
teraction,
F
(1, 4)
5
3.676,
p
,
0.01, and a significant main ef-
fect of time point,
F
(1, 4)
5
12.162,
p
,
0.0001. Subjects who
received oxygen had significantly higher blood oxygen satura-
tion. Examination of the data suggests that this effect was
masked in the overall means analysis due to decaying oxygen
levels during the Simple Reaction Time task (see Fig. 2a).
With respect to heart rate, there was a significant main ef-
fect of phase of experiment,
F
(1, 5)
5
17.392,
p
,
0.0001, but
no significant main effect of condition, or phase
3
condition
interaction. In fact, the two experimental groups’ heart rates
were very similar in response to each experimental phase (see
Fig. 2b). ANOVAs performed on heart rate using the experi-
mental phase as a repeated-measures variable revealed that
this difference was due to increased heart rate, compared to
baseline, during word presentation, the reaction-time task,
and the distractor task (
p
,
0.01 in each case). These signifi-
cant differences were maintained when the oxygen and air
groups’ data were analyzed separately.
Effect of Oxygen Saturation Changes and Heart Rate Changes
on Cognitive Measures
There were a number of significant correlations between
physiological measures and cognitive performance.
For the oxygen group, there was a significant negative cor-
relation between baseline blood oxygen saturation and num-
ber of words recalled,
r
(14)
5
2
0.653,
p
,
0.01. Subjects with
lower baseline oxygen levels recalled more words. There were
several significant correlations between cognitive perfor-
mance and changes in physiological responses relative to
baseline. For the oxygen-breathing group, there was a signifi-
cant correlation between the change in oxygen level from
baseline to word presentation phase and the number of words
recalled,
r
(14)
5
2
0.631,
p
,
0.01. Greater magnitude of
change in oxygen levels was associated with higher word re-
call. For the oxygen group, there was also a significant corre-
lation between the change in oxygen level from baseline to re-
action time phase and reaction time,
r
(14)
5
0.684,
p
,
0.01,
suggesting that lower differences in oxygen levels were re-
lated to faster reaction times.
For the air-breathing group there was a significant positive
correlation between change in heart rate from baseline to
word presentation phase and recall score,
r
(14)
5
0.550,
p
,
0.05, subjects whose heart rate increased more during word
presentation had a higher recall score. There was also a signif-
icant negative correlation between change in heart rate from
baseline to word recall phase and reaction time score,
r
(14)
5
2
0.551,
p
,
0.05.
Subjective Condition Responses
There were no significant differences between subjects’ re-
sponses as to which gas condition they thought they had been
in and those expected by chance,
x
2
(2)
5
3.436,
p
5
0.179 (see
Table 1). This suggests that the cognitive enhancing effects of
oxygen cannot be attributed to subjective expectancy based
on some nonspecific oxygen-induced state.
DISCUSSION
The results of this study confirm that oxygen administra-
tion results in improved cognitive performance, including
memory formation and reaction time (28,29,38). Moreover,
the oxygen-induced hyperoxia measured during word presen-
tation and the reaction time task supports the hypothesis that
elevated circulating blood oxygen may be utilized by task-sen-
sitive neural substrates during periods of cognitive processing.
There were significant correlations between cognitive perfor-
mance and changes in individuals’ oxyhemoglobin levels for
the oxygen group, and between cognitive performance and
heart rate changes in the air group. These latter findings sug-
gest that the capacity to carry further oxygen and heart rate
FIG. 2. (a) Blood hemoglobin oxygen saturation (%), and (b) heart
rate (beats per minute) during experimental phases. Shaded bars
indicate the various phases of the experiment (see text for details).
TABLE 1
NUMBER OF SUBJECTS IN EACH EXPERIMENTAL
CONDITION INDICATING WHICH GAS THEY BELIEVED
THEY HAD INSPIRED
Condition Indicated by Subject
Experimental Condition Air Oxygen Don’t Know
Air (
n
5
16) 8 7 1
Oxygen (
n
5
16) 5 6 5

HYPEROXIA, HEART RATE, AND COGNITIVE PERFORMANCE 787
reactivity are both important physiological individual differ-
ences mediating cognitive performance. Subjects’ responses
as to which gas they believed they had inhaled were not signif-
icantly different to chance levels. This suggests that the cogni-
tive enhancement observed following oxygen administration
cannot be attributed to some subjective state following hyper-
oxia (an issue that could be further explored by obtaining sub-
jects’ confidence ratings for their perceived condition and ex-
amining the relationship between this, their actual condition,
and their cognitive performance). This latter results also sup-
ports previous findings where mood was unaffected by oxygen
administration (28).
Differences in blood oxygen saturation between experi-
mental groups were found only in the gas administration,
word presentation, and Simple Reaction-Time phases of the
experiment. In the case of the recall task, this result is consis-
tent with earlier findings from our laboratory, and suggests
that hyperoxia improves memory consolidation but not re-
trieval (28,38). We would tentatively suggest that such data
support the idea that target material is encoded more deeply
under conditions of hyperoxia. In the present study, and pre-
viously (38), there were differences in the hyperoxic state of
subjects between encoding and retrieval of target material.
This begs the question as to whether the possibility of “state
dependency”—a phenomenon whereby learned material is
more readily assessed at retrieval when the subjective state at
encoding is reinstated during retrieval—may further increase
hyperoxia-associated mnemonic improvement. Our labora-
tory is presently investigating this possibility.
There were a number of significant correlations that were
specific to the air-breathing group and the oxygen group, re-
spectively. Although caution should be taken in interpreting
these data—corrections for multiple comparisons were not
considered to be appropriate in such exploratory analyses—it
is interesting to speculate on their possible relationship to
cognitive performance. Comparisons between individual
mean blood oxygen saturation and cognitive performance re-
vealed a significant negative correlation between baseline
blood oxygen saturation and word recall scores. This may re-
flect the fact that oxygen’s cognitively enhancing effect may
be relatively more pronounced where there is greater poten-
tial for increasing blood oxygen saturation. There was no such
correlation for the air-breathing group; therefore, the effect is
not due to lower baseline levels per se. The interpretation is
supported by the positive correlation, in the oxygen group
only, between the relative changes in blood oxygen saturation
during the word presentation phase and the number of words
recalled, a result that is consistent with reports of a positive
relationship between rising blood glucose levels and cognitive
performance (4,7). Again, this suggests that a higher capacity
for increasing blood oxygen levels is associated with a greater
amount of cognitive enhancement. Less clear is the meaning
of the significant positive correlation, in the oxygen group, be-
tween the change from baseline to reaction-time oxygen satu-
ration and reaction-time scores. A similar relationship has
been reported for falling glucose levels and reaction times (5),
although the same study found that falling blood glucose was
associated with improved word recall. The reason that in-
creased oxygen levels are associated with better encoding but
slower reaction times may be due to the relationship between
task order, and oxygen delivery and uptake. Increased levels
of circulating blood oxygen may be available to neural pro-
cesses involved in encoding target material. In the case of re-
action times, hyperoxia is already decaying at this phase of the
experiment (see Fig. 2a), and increased uptake of oxygen, re-
flected by an accelerated decay in the blood, may be associ-
ated with improved reaction time. This possibility could be
tested through reversing the task order to determine whether
the pattern of the relationships between rising and falling ox-
ygen levels and individual task performance were reversed
(indeed, given the transient nature of hyperoxia, future stud-
ies may usefully be directed at examining these effects using
different task orders in relation to oxygen delivery). The fall
in blood oxygen to below baseline levels for both groups dur-
ing word recall may also be related to this phenomenon. It is
interesting to note the apparent rise in heart rate during the
distractor task followed by a fall during word recall (Fig. 2b).
It is possible that, in the absence of an increased heart rate
during word recall, there is an uptake of oxygen over and
above that maintained by baseline heart rate. Clearly, the re-
lationship between rising and falling blood oxygen (and glu-
cose) levels in response to cognitive processing requires fur-
ther exploration. In particular, the relationship between
hyperoxia and glucose levels has received scant attention,
comeasurement of the two indices during cognitive process-
ing would provide useful information about this issue.
Significant heart rate acceleration occurred during word
presentation and the reaction-time phases of the experiment
in both the air- and oxygen-breathing groups. Accelerated
heart rate was also observed during the distractor, a mathe-
matical task where subjects may have felt that their perfor-
mance was being monitored (because no performance mea-
sures were actually taken here, we cannot rule out the
possibility that some subjects surreptitiously rehearsed the
words during this phase of the experiment). These findings
support the hypothesis that effortful information processing is
accompanied by an increase in autonomic activity. Our labo-
ratory is currently investigating the extent to which the level
of effort involved in task performance interacts with changes
in heart rate, glucose levels, and oxygen levels (both in the
presence and absence of a glucose/oxygen load).
Despite no significant differences in heart rate between
the air- and oxygen-breathing groups, there were significant
correlations between heart rate changes and cognitive perfor-
mance when individual mean heart rates were analyzed for
the air-breathing group. There was a significant positive cor-
relation between the relative change in heart rate during
word presentation and the number of words recalled. We
would tentatively suggest that this is part of a physiological
response to increased neural activity that results in the in-
creased delivery of oxygen for energetic processes. The same
relationship was not observed in the oxygen group where the
demand for increased oxygen may have been reduced due to
increased availability of circulating oxygen following gas in-
spiration. Finally, in the air-breathing group only, there was a
significant negative correlation between the change in heart
rate relative to baseline in the recall phase and reaction-time
scores. The reason for this relationship is unclear, although
there was a similar (not significant) trend with respect to
change in heart rate from baseline to word presentation phase
and reaction times (
r
5
2
457, 0.1
.
p
.
0.05). It is possible
that subjects whose heart rate is more responsive to cognitive
processing may perform better.
We would suggest that the increased heart rate during cog-
nitive processing facilitates the delivery of metabolic sub-
strates to the brain; these are then utilized by neural mecha-
nisms underpinning cognitive performance. The results of this
study suggest that mental effort results in increased metabolic
activity (heart rate). For example, it is evident that heart rates
during the reaction time task are raised less than during either

788 SCHOLEY ET AL.
word presentation or word recall (Fig. 2b). It seems likely that
a cognitive load of a simple reaction time task is less than that
of a memory task. It would appear that the effectiveness of
this process on information processing may be related to indi-
vidual physiological sensitivity to cognitive demand. Induced
hyperoxia seems to supplement this process, thereby improv-
ing cognitive performance. This (unknown) demand-related
mechanism may also override the decreased heart rate, which
is among the usual physiological responses to hyperoxia, al-
though recent evidence suggests that this slowing stabilizes to
a steady state only after some 5 min of continuous hyperoxia
(23). Clearly, this issue requires further investigation.
The mechanism by which oxygen improves cognitive per-
formance remains unknown. In the case of cognitive-enhanc-
ing agents (so-called “smart drugs”), a number of authors
have suggested that improved cognitive performance is medi-
ated via liberation of glucose stores and the increased synthe-
sis of acetylcholine [e.g. (43)]. Although the same model
would account for oxygen’s effects on some measures of cog-
nitive function, it is unlikely that the cholinergic system fulfills
the role of being the necessary, sufficient, and exclusive medi-
ator of such phenomena. Although turnover of both oxygen
and glucose would lead to increased synthesis of acetylcholine
via a side branch of the glycolytic pathway, it seems equally
probable that the increased availability of metabolic sub-
strates, possibly leading to increased synthesis of adenosine
triphosphate (the universal cellular “energy currency”), per se
may account for their performance-enhancing properties (28).
It should also be noted that the temporal relationship be-
tween oxygen (or glucose) administration and improved cog-
nitive performance are not similar to those observed for
cholinergic drugs (12,36,38). Additionally, we have some pre-
liminary evidence that certain aspects of cognitive perfor-
mance are very differently effected by oxygen when com-
pared with the cholinergic agonist nicotine (37). It may also
be relevant that a number of putative cognitive enhancers are
reported to have their effects through mechanisms including
increased blood flow, glucose metabolism, and cerebral blood
oxygenation (26,27). Future research should also be directed
at delineating the brain areas mediating hyperoxia-associated
cognitive enhancement.
There has been debate over the past decade as to the
whether increased neural activity relies on oxidative metabo-
lism (3). Early studies, using simultaneous oxygenation mea-
surement with positron emission tomography, found an insig-
nificant rise in oxygen uptake in active brain areas (13).
However, the development of functional magnetic resonance
imaging, and more sophisticated techniques for monitoring
blood oxygen fractions, has generated results that are consis-
tent with the proposal that there is a substantial increase in ox-
ygen utilization in active neural tissue (25). The evidence pre-
sented here provides behavioral support for the latter model.
The results of the present study mirror those from studies
of low oxygen levels where hypoxic individuals show deficits
in reaction time (24,31) and free recall (8). It is possible that
cognitive performance is related to a continuum of blood oxy-
genation ranging from hypoxia, through normoxia, to hyper-
oxia. It is commonly accepted that the brain has evolved to
function optimally. However, results from our laboratory and
studies elsewhere of hyperglycaemia-associated cognitive im-
provement lead to the somewhat paradoxical conclusion that
cognitive performance may be physiologically resource lim-
ited. This concept has previously been described in terms of
information-processing resources, where “mental effort” de-
scribes the level of such resources required to maintain task
performance (20). There is now ample evidence to suggest
that such mental effort is also a reflection of the availability of
metabolic resources drawn upon during task performance, an
effect supported by brain imaging studies during differing
mental loads (19). Such an intuitively pleasing model makes a
number of specific predictions about the relationship between
cognitive demand, availability of oxygen and glucose, and task
performance; for example, that tasks requiring higher mental
effort should be more susceptible to the enhancing effects of
oxygen administration. Our laboratory is currently investigat-
ing these matters.
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- "In the present study, SpO 2 during the 0-back task phase (cognitive processing phase) was increased compared with that during the control phase. This agrees with the results of previous studies [8,11,13,16171822,23], where oxygen requirements increased during cognitive processing. There was an interaction effect between oxygen concentration and phase because of the lower increase rate of SpO 2 from control phase to 0-back task phase at 92% oxygen compared with 21% oxygen. "
[Show abstract] [Hide abstract] ABSTRACT: The present study addressed how 92% oxygen administration affects cognitive performance, blood oxygen saturation (SpO2), and heart rate (HR) of intellectually and developmentally disabled people. Seven males (28.9 ± 1.8 years) and seven females (34.4 ± 8.3 years) with intellectual and developmental disabilities (disabled level 2.1 ± 0.5) completed an experiment consisting a 0-back task with normal air (21% oxygen) administered in one run and hyperoxic air (92% oxygen) administered in the other run. The experimental sequence in each run consisted of a 1-min adaptation phase, 2-min control phase, and 2-min 0-back task phase, where SpO2 and HR were gauged for each phase. The administration of 92% oxygen increased 0-back task performance of intellectually and developmentally disabled people, in association with increased SpO2 and decreased HR. Our results demonstrate that sufficient oxygen supply subserving cognitive functions, even as a short-term effect, could increase cognitive ability for the intellectually and developmentally disabled people. It is concluded that enriched oxygen can positively affect, at least in the short-term, the working memory of those with intellectual and developmental disability.- "Chronic brain hypoxia might especially cause ischemia or microinfarcts in the cortex, eventually resulting in cortical thinning. Previous studies suggested that cortical ischemia or microinfarcts are associated with brain atrophy and cognitive deficits (Stuss et al., 1997; Scholey et al., 1999; Shah et al., 2012). Alternatively, chronic brain hypoxia might induce amyloidogenic processing, which in turn leads to brain atrophy (Manley et al., 2001; Bazan et al., 2002; Li et al., 2009; de Souza et al., 2011; Wang et al., 2011; Zlokovic, 2011; Chetelat et al., 2012). "
[Show abstract] [Hide abstract] ABSTRACT: Decreased hemoglobin levels increase the risk of developing dementia among the elderly. However, the underlying mechanisms that link decreased hemoglobin levels to incident dementia still remain unclear, possibly due to the fact that few studies have reported on the relationship between low hemoglobin levels and neuroimaging markers. We, therefore, investigated the relationships between decreased hemoglobin levels, cerebral small-vessel disease (CSVD), and cortical atrophy in cognitively healthy women and men. Cognitively normal women (n = 1,022) and men (n = 1,018) who underwent medical check-ups and magnetic resonance imaging (MRI) were enrolled at a health promotion center. We measured hemoglobin levels, white matter hyperintensities (WMH) scales, lacunes, and microbleeds. Cortical thickness was automatically measured using surface based methods. Multivariate regression analyses were performed after controlling for possible confounders. Decreased hemoglobin levels were not associated with the presence of WMH, lacunes, or microbleeds in women and men. Among women, decreased hemoglobin levels were associated with decreased cortical thickness in the frontal (Estimates, 95% confidence interval, -0.007, (-0.013, -0.001)), temporal (-0.010, (-0.018, -0.002)), parietal (-0.009, (-0.015, -0.003)), and occipital regions (-0.011, (-0.019, -0.003)). Among men, however, no associations were observed between hemoglobin levels and cortical thickness. Our findings suggested that decreased hemoglobin levels affected cortical atrophy, but not increased CSVD, among women, although the association is modest. Given the paucity of modifiable risk factors for age-related cognitive decline, our results have important public health implications.- "In the oxygen group, significant correlations were found between changes in oxygen saturation and cognitive performance. In the air group, greater changes in heart rate were associated with more improved cognitive performance [64]. These findings suggest that during times of cognitive demand availability of metabolic resources impact on cognitive functioning. "
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