Jiannis Taxidis

Research Interests:  My lab uses advanced calcium and voltage imaging techniques in vivo, combined with behavioral assays and computational modeling, to understand: (i) how neural circuits in the brain link sensory information across time and (ii)  store it as continuous memories and how this process goes awry in brain disorders associated with memory deficits, like Alzheimer’s disease or schizophrenia.

Appointments

Scientist, Program in Neurosciences & Mental Health, SickKids Research Institute
Assistant Professor, Department of Physiology, University of Toronto

Research Synopsis:

Keywords: Hippocampus, memory, calcium imaging, voltage imaging, optogenetics, behavioral tasks, computational neuroscience, modeling, neural networks

Detailed Description:
How does our brain turn our sequences of experiences into memory while also keeping track of their temporal relationships? Neuronal networks in the hippocampus (a brain region intricately related to memory formation) generate spiking sequences that encode sensory cues and link them by tiling the time gaps between them, forming trajectories in ‘memory space’ which track the passage of our experiences. During sleep, these sequences are reactivated, driving memory consolidation.

The overarching questions my lab seeks to answer are: 1) Which neuronal circuits and mechanisms control the formation and reactivation of such memory-encoding, multi-modal spiking sequences across time? 2) How are sensory and temporal representations shaped and influenced by learning of a context or by memory recall? 3) How are disrupted networks associated with memory deficits in brain disorders? Answering these questions is of utmost importance for understanding and treating human brain conditions associated with memory impairment. Given the complex anatomy of cortico-hippocampal circuits, we need to combine behavioral paradigms, experimental tools, computational models and complex mathematical analyses to fully understand such processes.

Research in our laboratory combines:
(i) in vivo calcium and voltage imaging and optogenetic/chemogenetic manipulations during complex behavioral assays
(ii) computational modeling of network interactions and oscillations.
We focus mainly on recording, manipulating and modeling activity from neural circuits in the hippocampus while mice learn and perform olfactory-driven behavioral tasks which involve memory mechanisms.

We design and execute complex experiments using cutting edge imaging methods, analyze collected data and build computer models of the suggested mechanisms that in turn inform the next experiments. This holistic Systems Neuroscience approach will allow us to understand how cortico-hippocampal networks encode incoming information and temporal associations, how this information is stored and consolidated as memory and how circuit alterations disturb these processes.

METHODS USED
Cell and tissue culture: Hippocampal neurons.

Procedures: Behavioral tests, two-photon calcium imaging, photostimulation, voltage imaging, optogenetics, chemogenetics, stereotaxic brain surgery

Computational modeling and advanced data analysis

EQUIPMENT USED

Two-photon calcium imaging microscope, single-photon voltage imaging microscope, optic fibers, mouse behavioral apparatus, olfactometer.

PRESENT TRAINEES

Recent Publications

Taxidis J., Pnevmatikakis E., Dorian C.C., Mylavarapu A.L., Arora J.S., Samadian K.D., Hoffberg E.A., Golshani P. Differential emergence and stability of sensory and temporal representations in context-specific hippocampal sequences. Neuron. 108: 984-998, 2020.

*Lazaro M.T., *Taxidis J., Shuman T., Bachmutsky I., Ikrar I., Ikrar T., Santos R., Marcello G.M., Mylavarapu A., Chandra S., Foreman A., Goli R., Tran D., Sharma N., Azhdam M., Dong H., Choe K.Y., Peñagarikano O., Masmanidis M., Racz B., Xu X., Geschwid D., Golshani P. Reduced prefrontal synaptic connectivity and disturbed oscillatory population dynamics in the CNTNAP2 model of autism. Cell Reports, 27: 2567–2578, 2019. * Equal contribution.

Giovannucci A., Friedrich F., Gunn P., Kalfon J., Brown B.L., Koay S.A., Taxidis J., Najafi F., Gauthier J.L., Zhou P., Khakh B.S., Tank D.W., Chklovskii D.B., Pnevmatikakis E. CaImAn an open source tool for scalable calcium imaging data analysis. Elife 8: e38173, 2019.

Taxidis J., Anastassiou C.A., Diba K., Koch C. Local field potentials encode place cell ensemble activation during hippocampal sharp wave-ripples, Neuron, 87: 590- 604, 2015.

Taxidis J., Mizuseki K., Mason R., Owen M.R. Influence of slow oscillation on hippocampal activity and ripples through cortico-hippocampal synaptic interactions, analyzed by a cortical- CA3-CA1 network model, Frontiers in Computational Neuroscience, 7: 1-19, 2013.

Taxidis J., Coombes S., Mason R., Owen M.R. Modeling sharp wave-ripple complexes through a CA3-CA1 network model with chemical synapses, Hippocampus, 22: 995-1017, 2012.