State-dependent and cell-type-specific information processing in auditory cortex

"When we are paying attention to music, we can clearly perceive it. When we sleep, however, our perception is significantly diminished. But why? As this simple example, we can perceive exactly same sounds differently depending on our behavioural conditions (e.g., wakefulness vs sleep). But we really don't know exactly how this happens in our brain.

The key is an internal state of our brain. Intriguingly, even when we sleep, our brain is still active: our brain is never at rest. But the pattern of brain activity during sleep is different from it in paying attention to sounds. Thus, such brain states must be a key to solve the mystery. Our proposed research concerns how our brain processes sounds depending on different brain states.

We will study this at cellular resolution. The neocortex is the brain structure that is highly evolved in the mammals, in particular humans. While millions of neurons are communicating each other, there are many different types of neurons, like our social networks. In the neocortex, neurons form an organised layer structure and in every single layer there are different types of neurons. One of the biggest mysteries in contemporary brain sciences is why they are so diverse. Our proposed research also concerns such neuronal diversity.

Given these two contexts (brain states and neuronal diversity), we will ask how different brain states affect auditory processing in a part of the neocortex, called auditory cortex, and how diverse neurons process sound signals differently. We will address these questions, combining two advanced technologies (called massively parallel neural recording and optogenetics).

Our proposed research will advance our understanding of how we (do not) hear sounds and how the brain works. These efforts will eventually create new opportunities to develop the treatment of hearing disorders and brain diseases."

"In systems neuroscience, one of the fundamental issues is how the global brain state shapes sensory processing. Cortical state varies from moment to moment, affecting the way that sensory information is transformed from the thalamus through cortical circuits. However, little is known about how cortical states affect temporal tuning in the auditory cortex across cortical layers despite the fact that temporal processing is critical for speech recognition and that the neocortical laminar structure is one of the most prominent anatomical features in the mammalian brain.
Recording neural population activity from both the primary auditory cortex (AC) and medial geniculate body (MGB) simultaneously with electrical stimulations of the basal forebrain (BF) in rats, we have discovered that although the reduction in response variability is inherited subcortically, state-dependent improvement of temporal tuning emerges within the cortex. This finding sheds light on the importance of state-dependent intracortical processing in hearing."