Larry Cahill and his colleagues at the University of California, Irvine,
showed two sets of films鈥攐ne containing disturbing scenes of violence and
animal mutilation, the other with emotionally neutral content鈥攖o eight
young men. The researchers mapped the activity of the subjects鈥� brains using
positron emission tomography (PET), which measures metabolic activity in the
brain by recording variations in blood flow. Three weeks later, they tested how
well the people remembered scenes from the films.

Not surprisingly, the volunteers recalled more about the emotionally charged
images than they did about the blander ones鈥攂ut the PET scans also
revealed a probable reason why. The scientists found that the more an emotional
scene activated one particular region of the brain鈥攖he right half of a
part of the midbrain known as the amygdala鈥攖he more likely the subjects
were to remember the scene.

By contrast, there was no correlation between right amygdala activity and
recall of scenes that were not so emotionally charged (Proceedings of the
National Academy of Sciences, vol 93, p 8016).

Neuroscientists have had earlier hints that the amygdala may be involved in
memory for emotional events. One patient with a damaged amygdala was unable to
recognise fear on the faces of people in photographs (New 女生小视频,
Science, 17 December 1994, p 20). Another patient who suffered from a rare
inherited disease which damaged his amygdala proved unable to recall
emotionally
arousing events with any more clarity than more mundane ones.

The new study, however, provides the first direct link between amygdala
activity during an emotional situation and later recall, as well as
locating the
activity on the right side of the amygdala. 鈥淭his is the first study to show a
relationship between a healthy human amygdala and long-term memory associated
with emotional events,鈥� says Cahill. 鈥淚t strongly suggests that the amygdala is
crucial for emotional memory.鈥�

Sitting in the midbrain, the amygdala is ideally situated to be wired
to both
the input of the senses and the motor responses of the body. It is already
thought to be responsible for split-second, reflex responses to danger, and the
link to emotional memory adds another string to its bow.

These two functions鈥攕toring emotional memory and triggering rapid
response to sensory input鈥攎ay combine to useful effect. We may use the
amygdala as a repository for emotional lessons which we can draw on without
thinking so we can act rapidly in emergencies.

John Badding and his colleagues at Pennsylvania State University in
University Park persuaded potassium and nickel to react with each other by
forcing them together at more than 300 times atmospheric pressure and more than
2000 掳C.

At normal pressures, potassium鈥攁 member of the group of elements known
as alkali metals鈥攄oes not react with nickel, which is a member of a
different group of elements, known as transition metals. The fact that
they bond
means that potassium, too, is behaving like a transition metal, says Badding
(Science, vol 273, p 95).

Chemists explain the properties of the transition metals in terms of their
electronic structure: they form bonds by using the electrons that occupy an
orbit shaped like a clover leaf, known as a d orbital. With alkali
metals, the single electron that is responsible for most of their reactions
occupies a spherical s orbital.

Alkali metals do not react with transition metals at atmospheric pressure
because their size and electronic structures are incompatible. But under huge
pressure, a potassium atom shrinks to one-fifth its usual volume and one of its
electrons moves into a d orbital, allowing it to form a bond with a
nickel atom.鈥滻 think that when you change the chemistry of the potassium
to that
of a transition metal d element, you鈥檝e pretty much got a new
别濒别尘别苍迟,鈥�
says Badding. Not everyone agrees, however. Michael Mingos at Imperial College,
London, says that all elements behave differently under extreme conditions.
Hydrogen, for example, has been shown to have metallic properties.

女生小视频s conventionally define an element by the number of protons in its
nucleus. By this definition, Badding鈥檚 鈥減ressurised鈥� potassium is not a new
element. In practice, however, an atom鈥檚 electronic structure determines how it
reacts with other atoms.