Scientists demystify secrets behind hallucinations
Posted on Friday, November 24, 2006 (EST)
Some may call it a figment of a person's imagination while others term
it as delirium, but now scientists carrying out brain scan research,
have found a compelling explanation for how the human mind conjures up
hallucinations.
London, Nov 24: Some may call it a figment of a person's imagination
while others term it as delirium, but now scientists carrying out
brain scan research, have found a compelling explanation for how the
human mind conjures up hallucinations.
They say that what we see is driven as much by what we expect to see
as by the patterns of light and colours picked up by our eyes.
This top-down, not bottom-up, picture of the way vision works could
explain bereavement hallucinations. Ten per cent of grieving people
believe they have caught sight of the dead person.
These hallucinations relate to higher cognitive functions of the
brain, some of which reside in the frontal cortex, the area of
decision-making.
In brain scan studies reported in the journal Science, Dr Christopher
Summerfield of Columbia University and colleagues in France and New
York asked volunteers to differentiate between houses and faces.
Signals in the frontal cortex became active whenever subjects expected
to see a face, irrespective of what the actual stimulus was. These
frontal regions appear to be active earlier than the parts of the
brain that process vision.
This backs a current theory, "predictive coding," which suggests the
brain has an expectation of what it will see, then compares this
template with information from the eyes to determine if it is indeed
seeing a face or something else.
When this process goes awry, hallucinations can occur, leading to
incidences of "paredolia," where healthy people report seeing faces in
the clouds, or on the Moon. (ANI)
