快猫短视频

DOES the winter weather get you down? Everybody tends to get a bit gloomy
when the days are short and the weather is cold and grey. But for some people,
the winter blues have a more serious and debilitating edge. As the nights draw
in, people with seasonal affective disorder, or SAD, begin to feel depressed and
sluggish, their thoughts clouded and slow. Their appetite for sex plummets,
replaced by a craving for sweets, bread and other carbohydrates. SAD people go
to bed early, rise late, and even begin to put on weight, rather like bears
getting ready to hibernate.

Not getting enough daylight and sunshine seems to be a major factor
underlying seasonal depression, but beyond that its cause is still a mystery.
Most people with the condition can get some relief through a daily dose of
bright artificial light. Yet, even with light therapy, many people with SAD
never feel as well as they do in the summer. And nobody knows why.

Perhaps, says Teodor Postolache, it would all get better if they just stopped
to smell the roses.

Postolache, a practising psychiatrist in Washington DC who works with many
SAD patients, has some intriguing new evidence that odours play a role in
seasonal depression. According to his studies, people with SAD have a more acute
sense of smell than people who do not suffer from seasonal depression. This
opens up the possibility that the scent of the seasons鈥攁s well as the
length of day鈥攑lays a role in seasonal mood shifts, and raises hopes that
adding stimulating odours to light treatment will give people with seasonal
depression a higher, more lasting lift鈥攁 kind of aromatherapy for the
winter blues.

For most animals, seasonality is the rule. At the bottom of it all is the
timing of reproduction: when to make babies so that they have the greatest
chance of survival. Even for humans there are scores of epidemiological studies
that suggest some kind of seasonal influence. Suicide, birth rate, homicide,
bulimia, and even the onset of warfare show seasonal trends.

In the industrialised world, bright indoor lighting and controllable heating
and cooling have largely insulated people from the influence of the outside
environment. This makes it difficult to discover how strongly seasonal patterns
are influenced by biological rhythms. All the same, such seasonal trends have
fuelled scientific curiosity about the possible influence of the environment on
our moods and behaviour.

Winter blues

And then there is SAD. A 1989 survey conducted by NIH researchers in
Montgomery County, Maryland鈥攏ear where Postolache does his
research鈥攆ound that about 4 per cent of the population suffers the
full-blown symptoms of SAD, including severe and persistent depression in the
winter. An additional 10 per cent experience a milder form known as the 鈥渨inter
blues鈥�, in which symptoms are not severe enough to require psychiatric
treatment. Elsewhere, the numbers change, depending on latitude.

Mild or severe, some of the fundamental signs of SAD鈥攕uch as torpor,
weight gain and reduced sex drive鈥攔esemble the kind of seasonal changes
that occur in many animals. The resemblance has led some researchers to wonder
if SAD is a form of seasonality gone awry. 鈥淚t kind of suggests that what we鈥檙e
calling a depression probably originates in some kind of seasonal biology gone
to an extreme, a caricature of seasonality that might have been important at one
time in human history,鈥� says Thomas Wehr, who heads the Clinical Psychobiology
branch at the National Institute of Mental Health, near Washington DC.

Wehr notes that in the past seasonal swings in conception rates were much
more marked than they are in the West today. 鈥淲hat seasonality we have has been
blunted a great deal,鈥� he says, 鈥渂ut given that we have so altered our
environment, why are there still some people that are so exquisitely sensitive
to changes in seasons?鈥�

Postolache was already on the scent of seasonal depression as a resident at
the Beth Israel Medical Center in New York City in the early 1990s. Two cases
had caught his attention. One was a woman who noted a connection between her
mood and the pungent odour of rotten leaves on the thawing ground in Central
Park. 鈥淎s soon as she smelt that, then she knew that she was going to improve,鈥�
Postolache says. The other case was a woman who reported that in the fall, when
she started to sink into her seasonal depression, she noticed that she could
barely detect her husband鈥檚 body odour after he returned from the gym. But in
the spring, as her depression lifted, she would suddenly begin to notice the
odour again.

In 1996, Postolache began a research fellowship at the NIH, joining Wehr and
Norman Rosenthal who were members of the team that first identified SAD. Here
Postolache started digging deeper into the animal research on seasonality. In
many cases, he discovered that when it comes to seasonal behaviour there is a
link between smell and vision. For example, laboratory rats don鈥檛 normally
respond to changing day length. But researchers in the early 1980s found that
they could 鈥渦nmask鈥� seasonality by severing the connection between the rats鈥�
olfactory nerves and the rest of the brain. The rats would begin to respond to
the length of the day.

Putting together the animal studies and his own work with patients,
Postolache came up with two possible roles that olfaction might play in SAD. One
was suggested by the case of the woman who couldn鈥檛 smell her husband as well in
the winter. Along with her seasonal mood shift and accompanying symptoms, her
sense of smell also appeared to shut down. This seemed reminiscent of the
seasonal pattern in some animals, in which the sense of smell declines along
with the urge to reproduce. An alternative scenario, suggested by the case of
the woman who perked up when she smelled leaves, would be that something in the
environment鈥攑erhaps a scent of spring鈥攈elped to nudge her seasonal
rhythm back into summer mode, lifting the depression.

In winter, several factors conspire to deprive people of olfactory
stimulation. 鈥淭he floral and leafy odours are not there,鈥� Postolache says. 鈥淥n
top of that, humidity is reduced, especially in buildings because of heating,
and we know that humidity is important in olfaction. Also, upper respiratory
infections are more frequent.鈥� Either way, whether because of some sort of
seasonal decrease in the sense of smell or an oversensitivity to the deprivation
of summer scents, perhaps these patients responded rather like the rats, where a
loss of olfactory information made them more sensitive to the length of day.

To test his patients鈥� sense of smell, Postolache teamed up with Richard Doty,
director of the Smell and Taste Center at the University of Pennsylvania in
Philadelphia. Doty and his colleagues developed two smell tests that are now
widely used. To measure olfactory acuity, they ask people to sniff different
concentrations of phenylethyl alcohol (PEA), a substance that has the scent of
roses. The second test, known as the University of Pennsylvania smell
identification test (UPSIT), is a 鈥渟cratch and sniff鈥� test that measures the
ability to identify particular scents.

Previous research by Dan Oren at the NIH found that people with SAD and
normal controls performed equally well in the UPSIT test. Postolache decided to
repeat Oren鈥檚 work, but with a couple of twists. First, he would measure
people鈥檚 overall sensitivity, using the PEA test, and then he would administer
the UPSIT separately to each nostril.

Other researchers have shown that the two nostrils can analyse scents
differently
(快猫短视频, 6 November, p 6).
Olfactory sensors in the
right nostril send messages to the right side of the brain, and vice versa, and
some research suggests that olfactory sensations are processed more on the right
side of the brain than the left. Emotion and mood also seem to tie in more
strongly with activity on the right side of the brain. For depression, results
are mixed: some studies find differences in activity on the right and left sides
of the depressed brain, while others find none. Even so, Postolache reasoned
that if there were a link between seasonal depression and olfaction,
discriminating between the right and left nostrils might increase the chance of
detecting it.

Postolache and Doty administered the tests in winter to a 24 people diagnosed
with seasonal depression and 24 control subjects. Postolache was expecting to
find a diminished sense of smell in people with SAD, and that this would be
somewhat improved by light treatment. But to his surprise, he didn鈥檛 pick up any
difference in the ability to detect PEA between the SAD cases and the
controls.

But the researchers did not come away empty-handed. In the second part of the
study, Postolache discovered that the more depressed the patients felt, the less
accurate they were at identifying odours presented to the right nostril. At
first glance, this finding seems to be consistent with the right-brain bias in
olfactory processing. But more importantly, it seemed to suggest that olfaction
may be connected in some complex manner in the brain to seasonal emotional
rhythms.

Next, Postolache decided to test how people with SAD fared in olfactory tests
in summer as well as winter. Perhaps, he reasoned, a difference would show up
across the seasons. This time, he tested each nostril鈥檚 sensitivity in the PEA
test, as well as in the discrimination test. Sure enough a difference in acuity
did show up, but the results weren鈥檛 quite what he expected. Overall, the SAD
patients had a more acute sense of smell than the controls. The effect seemed to
manifest itself almost exclusively in the summertime, although Postolache says
he now needs to test a larger group of SAD patients to confirm this
summer-winter difference.

It is not clear yet whether this finding can explain the olfactory oddities
Postolache has observed. Did the woman who seemed to awaken from her winter
depression when she smelt rotting leaves get a lift because of a more powerful
sense of smell, or was it just a coincidence that she noticed the smell of
leaves as her depression was lifting? Postolache has information on only a few
dozen SAD cases, which isn鈥檛 enough to answer questions like this. However,
linking olfaction to seasonality in humans is itself an important step, because
it opens up a new way of understanding the underlying biology of seasonality in
humans.

Past experiments with hamsters, which are strongly seasonal, suggest one
intriguing possibility. As the days grow shorter, hamsters build nests. Finally,
when winter arrives, they hibernate. But remove their olfactory bulbs, where
sensory nerves from the nose converge in the brain, and this seasonal behaviour
largely shuts down. Postolache鈥檚 findings may show the mirror image of this
relationship. 鈥淢aybe during evolution we lost some genes, which resulted in some
loss of both seasonality and olfactory ability,鈥� he says. 鈥淚鈥檓 just speculating,
of course, but maybe those people that are seasonal also preserved an increased
olfactory acuity.鈥� This could explain his tentative finding that SAD sufferers
have a more acute summertime sense of smell.

Speculation aside, Postolache鈥檚 findings could have implications for the
treatment of SAD. Postolache has done a small pilot study on the effect of
particular odours. He asked a group of patients to sniff a series of 15 odours
over a 45-minute period, and then estimate their level of depression before and
after. After sniffing, some of the patients reported that they experienced a
noticeable lift. Some even said that their craving for carbohydrates鈥攁 key
symptom of SAD鈥攁bated somewhat. And the effect appeared to persist into
the next day.

As Postolache himself emphasises, the results are very preliminary. He is not
advising people with SAD to run out to the nearest aromatherapy shop. But he
does want to find out whether combining light therapy with sniffing appropriate
odours will work better than light alone.

Baby-making mode

A study on seasonality in lemurs has spurred Postolache to try an entirely
different approach to treating SAD with smell鈥攖his time without light
therapy. Researchers from the Laboratory of General Ecology in Brunoy, France,
exposed male lemurs to shorter days in the lab. This caused their testosterone
levels to fall, so the animals became less socially active and less likely to
mate. Then they exposed females to longer periods of daylight, putting them into
spring baby-making mode. Remarkably, just allowing the males to smell the
female鈥檚 urine was enough to raise their testosterone levels and reactivate
their social behaviours, including the urge to fight other males for dominance.
Something in the odour had triggered the seasonal transformation.

Postolache was intrigued, and now he wants to see if something similar might
happen in people. He is beginning a study of olfaction and SAD in men鈥攖his
time in collaboration with Alexander Neumeister, a psychiatrist at the Vienna
General Hospital in Austria. One of the most common symptoms in men with SAD is
loss of sex drive. So three times a day, the men recruited for the study will
sniff a nasal spray of a compound that researchers believe is a human pheromone.
The study will look not only at the compound鈥檚 effect on sex drive, but also at
mood in general.

This should help to tackle the fundamental question that Postolache is trying
to answer: do smells help to regulate seasonal emotional rhythms in humans? It鈥檚
a hard case to make, he says. 鈥淪ome people believe we are not seasonal at all.
They believe that the most important thing is our social life, rather than the
environment. There is this idea that seasonality, in humans, is vestigial.鈥�

But then, as Rosenthal points out, the idea that light could make a
difference in the way people felt once seemed ridiculous. 鈥淧eople once thought
that light did nothing more than just enable us to see,鈥� he says, 鈥渁nd then we
found out that light does all kinds of things besides help us to see. Now here
we are with smell. Sure, it tells us whether the food smells bad or good, or
whether the flower is nice or not, but maybe it does other things, too.鈥�