The conscious perception of sound consists of specialized neurons in the brain

A new study co-led by researchers at the French Human Brain Project reveals how conscious listening produces a collection of neurons in the brain that produce specific sounds
.
While awake, hundreds or thousands of nerve cells can coordinate to form these specific sound patterns
at the same time.
Under anesthesia, the brain's response to auditory stimuli can still be observed, but it is indistinguishable
from spontaneous brain activity.
The study, which combines in vivo experiments and computational models, was published in Nature Neuroscience
.

Even when we are unconscious, the constant activity in the brain is combined with sensory perception to respond to and process
stimuli.
However, it's unclear whether this joint activity processes each stimulus differently or whether the same underlying dynamics are at work
.
Distinguishing neuronal activity in conscious perception remains a complex problem
compared to unconscious states.

The study, conducted by researchers Alain Destexhe (Institute of Neuroscience at the University of Saclay in Paris) and Brice Bathellier (Pasteur Institute of Hearing, Paris), now has a new understanding
of how the brain responds to sound in these states.

The scientists found that when sound is consciously perceived, the cerebral cortex organizes itself in specific collections of neurons, producing "creative" patterns
of activity.
When the brain perceives auditory stimuli under anesthesia, a collection of hundreds of neurons also appears, but only in the awake and conscious state do specific neurons appear and are associated with
specific sounds.

The researchers used an optical recording technique, calcium imaging combined with multiphoton microscopy, to track the activity
of nearly 1,000 neurons in the mice's auditory cortex during awake and anesthetized states.

To interpret the observed data, the team modeled different hypotheses about what determines the groups
of neurons that are activated.
This analysis showed that the likelihood of a neuron becoming part of a sound response under anesthesia is largely influenced by its likelihood of being part of spontaneous activity, reducing the freedom to encode actual sound information
.
In the waking state, the two possibilities are more independent, opening up greater possibilities
for encoding information in different ways.

Under anesthesia, the cerebral cortex responds to auditory stimuli, but this response evokes collections
of neurons that already exist in spontaneous activity without stimulation.
If the stimulus is perceived while awake, the auditory cortex produces new combinations that target each sound
.
By using auditory input fiber imaging techniques, the researchers also showed that the new combination was created
entirely at the cortical level.

"Compared to unconscious states, the cerebral cortex is more creative when awake and creates new patterns
of neuronal activity when it responds to each sound.
This creativity seems to be an important association of
sensory perception.
”

Awake perception is associated with dedicated neuronal assemblies in the cerebral cortex