Science News - February 25, 2012

of sounds that were more evocative to people (such as a howling dog to dog-lovers) had a stronger effect on the brain.

These findings suggest that the path from the outside world to the brain’s inner experience is not a straight line. Scientists don’t yet know all the stops along that path, or which are most important (although candidates for such stops have been identified, such as a cortical wrinkle called the superior temporal sulcus).

What is now clear is that the brain is
not a stimulus-driven robot that directly
translates the outer world into a con-
scious experience. “What we’re conscious
of is what the brain makes us be conscious
of,” Meyer says. “While the images we
experience may be influenced to a certain
degree by information that’s incoming,
we need to get away from the idea that
they reflect exactly what’s out there.”
In the absence of incoming signals, bits
of memories tucked away can be enough
for a brain to get started with. That ability
is on display every time someone imag-
ines anything or dreams. A person sitting
in a silent dark room can vividly picture
mom’s face, even if she is thousands of
miles away. And dreams can be incred-
ibly vivid even when they
aren’t linked to sensory
inputs. “That tells us that
your brain, in the absence
of any outside input, can
generate this movie that
appears totally realistic to
you,” Meyer says.

In the Jan. 27 Science, Meyer proposed that, more generally, all conscious experiences could be thought of as what

Nobel laureate and neuroscientist Gerald Edelman calls a “remembered present.” From tiny slivers of sensations, scraps of memories and flashes of emotion, the mind makes something much bigger. In the blink of an eye, the brain creates the entire world. s

plex areas: places in the cortex where memories, skills and thoughts reside. When these signals then travel back to the simpler cortical regions, conscious experience emerges, proposes cognitive neuroscientist Kaspar Meyer of the University of Southern California in Los Angeles.

Perhaps the best evidence for Meyer’s idea comes from his work on how a small bit of information that stimulates one sense can generate a sensation elsewhere. While watching video clips of someone handling a ball of yarn, volunteers’ brains filled in a sort of “mind’s touch,” re-creating the sensation of the soft yarn, Meyer and colleagues reported last year in Cerebral Cortex.

A similar effect showed up for vision and hearing. Watching silent movies that are suggestive of a noise — a crowing rooster or a finger hitting a piano key — spurred a person to have the experience of hearing that noise, the team reported in 2010. What’s more, videos

A silent video of a finger
striking a piano key
(still, shown) triggered
activity in people’s
auditory cortex, and the
sensation of sound.

Superior
temporal
sulcus
Auditory cortex
Thalamic region
Visual
cortex

Sensory links The journey that a visual input takes to the thalamus and then the visual cortex, which includes V1, is well understood. But some researchers think that to reach awareness inputs also need to go to a more sophisticated spot in the brain, such as the superior temporal sulcus, and then travel to more basic regions that deal with a speci;c sense, say the auditory cortex.

leagues last year at the annual meeting of the Society for Neuroscience. In this experiment, electrodes measured V1 nerve cell activity as monkeys either perceived or didn’t perceive an object, while either paying or not paying attention.

With fMRI studies and electrode studies in agreement, the results suggest that visual signals from the outside world don’t break into consciousness as soon as they reach V1. The same may be true for corresponding early cortical stops for auditory, touch and other kinds of sensory input.

“The separation of attention and consciousness is a beautiful example to show that you can make progress on this difficult mind-body problem,” Koch says. What’s more, the split calls for a careful examination of earlier studies to make sure attention wasn’t behind any results that were attributed to consciousness, he and Tsuchiya write in the February Trends in Cognitive Sciences.