We use optogenetic tools (such as two-photon imaging of genetically encoded neuronal activity reporters or light-gated neuronal activity switches) coupled with electrophysiological measurements (extracellular and intracellular recordings) to study how sensory systems encode information from the environment, how these inputs are processed at different junctions or synapses of the underlying neuronal circuits and how these representations change with the state of the system and its circuits.
The broad scope of this effort is observing how perceptions arise.
The world outside us is flooded with information and our sensory systems are dedicated to perceive different bits of this information and process it in a form that’s understandable by our brain. Useful information must be extracted and the rest ignored.
For instance, even as one skims through this page, while the eyes read the letters, the ears tune to the track on the ipod, the nose smells the wires burning in the next room (hopefully not!) and the reader debates between a coffee and finishing the contents of this window. Each sensory system thus receives vastly different nature of stimuli and requires processing them differently, all at the same time.
The structure of any such system and the nature of information processing within it are defined by the activities of individual neurons that make it up, and the way they are wired up together.
To understand any brain area or neuro-circuit, we broadly address the following questions:
1) What are the inputs and how are they represented?
2) What kinds of operations are performed on these inputs as they are transferred among the members of the circuit?
3) How are these operations implemented in terms of the local connectivity, as well as feedback from other brain areas?
4) What role does the circuit play in enforcing particular behaviors?
The olfactory system, particularly the olfactory bulb, in rodents provides us with an ideal substrate to answer these questions, given its well-defined circuitry and multi-layered organization.
Rodents, being nocturnal animals, depend heavily on olfaction for survival - finding food, mates, avoiding predators and more. Airborne chemicals or odors are translated into neuronal signals by specific receptors in the nose and sent first to the bulb and then to higher centers in the brain (olfactory cortex). The bulb thus being the relay center provides the opportunity to study both the nature of the inputs it receives, and the nature of output it sends to the brain and the computations that allow for this input-output transformation.
Technological advances in multi-photon imaging, the explosion of numerous genetically encoded reporters of neuronal activity coupled with electrophysiological measurements and opto-genetic tools now enable us to monitor and alter patterns of activity with unprecedented synaptic resolution, while the animals perform various olfactory tasks.