Cortical Information Processing: Crowd Coding and Circuits

1. In vivo imaging of cortical organization and plasticity
 
The cortex is a laminated structure that is thought to underlie sequential information processing. Sensory input enters layer 4 (L4) from which activity quickly spreads to superficial layers 2/3 (L2/3) and deep layers 5/6 (L5/6).
Using 2-photon imaging we are investigating the functional architecture of the auditory cortex. Our work already identified the functional micro-architecture of the superficial layers of the auditory cortex (A1) and showed that the representation of sound frequency changes between layer 4 and layer 2/3 (Bandyopadhyay et al Nature Neuroscience 2010, Winkowski & Kanold 2013). Receptive field properties of neurons can rapidly and adaptively be reshaped when an animal is engaged in a behavioral task, indicating that encoding of stimuli is dependent on task- or context-dependent state. One source of task-dependent signals are frontal areas and we showed using 2-photon imaging that the functional responses in A1 can change rapidly when such areas are engaged (Winkowski et al. 2013).
 
Thus sensory responses under behavioral conditions depend on ongoing, i.e. spontaneous cortical activity, as well as the state and behavioral context of the animal.Responses also depend on ongoing cortical dynamics in a lamina-dependent fashion. However, we do not know how neuronal circuits shape these emergent dynamics within and between laminae, and we do not know which neurons encode which aspect of a sensory stimulus. In a collaborative project, together with Dr. Dietmar Plenz (NIMH) and Dr. Wolfgang Losert (UMd Physics), funded by the NIH BRAIN initiative we use in vivo 2-photon imaging and stimulation technology that allows rapid imaging and stimulation in multiple focal planes and by developing new computational and analysis techniques based on dynamic systems and graph theoretic measures to extract network dynamics at the single neuron and population level. We use these new techniques to investigate the 3D single cell and population activity patterns in the auditory cortex in mice and identify  the influence of single neurons relative to the synergistic influence of specific groups of neurons (the crowd) on network dynamics and ultimately behavior of the animal.
 

2. In vitro studies of cortical micro-circuits

To understand how neurons are wired up we need to reveal their connections with each other. To do this we use in vitro single and 2-photon photostimulation, coupled with patch clamp recordings and 2-photon imaging. Photostimulation allows us to selectively stimulate neurons and we can then observe which other neurons are responding. Thus we essentially can create input and output connection maps of targeted neurons. By performing these studies across layers and across ages we aim to assemble a wiring diagram of the adult and developing brain. Our work already identified the micro-circuitry of L2/3 of auditory cortex (Watkins et al. 2014) and how it can change (Meng et al. 2015).
 
Patrick Kanold
Department of Biology