-
Here are two images of a house.
-
There’s one obvious difference,
-
but to this patient, P.S.,
-
they looked completely identical.
-
P.S. had suffered a stroke that
damaged the right side of her brain,
-
leaving her unaware of everything
on her left side.
-
But though she could discern no difference
between the houses,
-
when researchers asked her
which she would prefer to live in,
-
she chose the house that wasn’t burning—
-
not once, but again and again.
-
P.S.’s brain was still processing
information
-
from her whole field of vision.
-
She could see both images
-
and tell the difference between them,
-
she just didn’t know it.
-
If someone threw a ball at her left side,
-
she might duck.
-
But she wouldn’t have any
awareness of the ball,
-
or any idea why she ducked.
-
P.S.’s condition,
-
known as hemispatial neglect,
-
reveals an important distinction between
the brain’s processing of information
-
and our experience of that processing.
-
That experience is what
we call consciousness.
-
We are conscious of both the external
world and our internal selves—
-
we are aware of an image
-
in much the same way we are aware of
ourselves looking at an image,
-
or our inner thoughts and emotions.
-
But where does consciousness come from?
-
Scientists, theologians, and philosophers
-
have been trying to get to the bottom of
this question for centuries—
-
without reaching any consensus.
-
One recent theory is that
-
consciousness is the brain’s imperfect
picture of its own activity.
-
To understand this theory,
-
it helps to have a clear idea
-
of one important way the brain processes
information from our senses.
-
Based on sensory input,
-
it builds models,
-
which are continuously updating,
simplified descriptions
-
of objects and events in the world.
-
Everything we know is based
on these models.
-
They never capture every detail of
the things they describe,
-
just enough for the brain to determine
appropriate responses.
-
For instance, one model built deep
into the visual system
-
codes white light as brightness
without color.
-
In reality,
-
white light includes wavelengths
-
that correspond to all the
different colors we can see.
-
Our perception of white light is wrong
and oversimplified,
-
but good enough for us to function.
-
Likewise, the brain’s model of the
physical body
-
keeps track of the configuration
of our limbs,
-
but not of individual cells
or even muscles,
-
because that level of information
isn’t needed to plan movement.
-
If it didn’t have the model keeping track
of the body’s size, shape,
-
and how it is moving at any moment,
-
we would quickly injure ourselves.
-
The brain also needs models of itself.
-
For example,
-
the brain has the ability to pay attention
to specific objects and events.
-
It also controls that focus,
-
shifting it from one thing to another,
-
internal and external,
-
according to our needs.
-
Without the ability to direct our focus,
-
we wouldn’t be able to assess threats,
finish a meal, or function at all.
-
To control focus effectively,
-
the brain has to construct a model
of its own attention.
-
With 86 billion neurons constantly
interacting with each other,
-
there’s no way the brain’s model of its
own information processing
-
can be perfectly self-descriptive.
-
But like the model of the body,
-
or our conception of white light,
-
it doesn’t have to be.
-
Our certainty that we have a
metaphysical, subjective experience
-
may come from one of the brain’s models,
-
a cut-corner description of what it means
to process information
-
in a focused and deep manner.
-
Scientists have already begun trying
to figure out
-
how the brain creates that self model.
-
MRI studies are a promising avenue
for pinpointing the networks involved.
-
These studies compare patterns
of neural activation
-
when someone is and isn’t conscious
of a sensory stimulus, like an image.
-
The results show that the areas needed
for visual processing
-
are activated whether or not the
participant is aware of the image,
-
but a whole additional network lights up
-
only when they are conscious
of seeing the image.
-
Patients with hemispatial neglect,
like P.S.,
-
typically have damage to one particular
part of this network.
-
More extensive damage to the network
can sometimes lead to a vegetative state,
-
with no sign of consciousness.
-
Evidence like this brings us closer
to understanding
-
how consciousness is built into the brain,
-
but there’s still much more to learn.
-
For instance,
-
the way neurons in the networks
related to consciousness
-
compute specific pieces of information
-
is outside the scope of our
current technology.
-
As we approach questions of consciousness
with science,
-
we’ll open new lines of inquiry
into human identity.