The brain exists in an exquisite balance between excitation and inhibition, and disruptions in this balance underlie a wide range of brain disorders. Recent work has found that artificially inhibiting inhibitory neurons leads to a paradoxical effect: an increase in their activity. However, the circuit mechanism of this paradoxical effect is unknown, and it is unclear whether it is utilised in cognitive state-specific computations. This project will address these unknowns by combining three cutting-edge approaches. First, we will use state-of-the-art computational models capable of making experimental predictions, developed by the Sadeh lab. Second, we will measure simultaneous activity from multiple inhibitory cell classes while perturbing one cell class, an approach pioneered by the Khan lab. Third, we will use advanced holographic optogenetic simulations for modifying the activity of specific groups of neurons, or ‘playing patterns into neurons’.
The student will learn the following techniques and skills, all of which are currently used in the Khan lab: in-vivo 2-photon calcium imaging, holographic 2-photon optogenetic stimulation, mouse cranial window surgical implants, viral vector injections, mouse behaviour. These will be used to address the following overarching aim: To uncover the microcircuit basis of paradoxical effects in the mouse cortex and determine how this circuit is modulated under distinct cognitive states. This work will be highly relevant to cognitive symptoms in conditions such as schizophrenia and ASD.
In Year 1, the student will learn the core methodology of the project: in-vivo 2-photon calcium imaging in behaving mice. PV cells will be optogenetically activated during recordings. The same neurons will then be identified post-hoc using the in-situ gene labelling approach HCR, providing cell class information. In year 2 the student will establish holographic stimulation of individual PV cells, and later, groups of 3 to 10 PV cells, in varying spatio-temporal patterns. This will map out the conditions in which the paradoxical effect happens under two different cognitive states. Year 3 will see close collaboration with the Sadeh lab to develop an experiment-theory-experiment pipeline. This will produce unprecedented circuit models of inhibition in two cognitive states. In year 4 we will extend this approach to SOM cells, and optionally VIP cells.
Rotation: The student will learn to stimulate single PV cells while measuring the activity of multiple pyramidal, SOM and VIP neurons using 2-photon imaging. Given time, multiple PV cell stimulations will be attempted and used to build a model of PV-PV interactions.
