Thanos Siapas

Professor of Computation and Neural Systems
B.S., Massachusetts Institute of Technology, 1990; M.S., 1992; Ph.D., 1996. Assistant Professor, Caltech, 2002-08; Bren Scholar 2003-08; Associate Professor, 2008-10; Professor, 2010-.

Research Summary

Our research focuses on the study of information processing across networks of neurons, with emphasis on the neuronal mechanisms that underlie learning and memory formation. By recording the simultaneous activity of large numbers of neurons in freely behaving animals, we study the structure of the interactions between the hippocampus and neocortical brain areas and the role of these interactions in learning and memory.       

The hippocampus is a brain structure that has long been known to be critical for the formation of new memories. This hippocampal involvement is temporary as memories are gradually established in neocortical stores through the process of memory consolidation and their retrieval becomes independent of the hippocampus. During consolidation recently learned information is progressively integrated into cortical networks through the interactions between cortical and hippocampal circuits.

The direct experimental investigation of these interactions has been difficult since, until recently, simultaneous chronic recordings from large numbers of well-isolated single neurons were not technically feasible. These experiments became possible with the development of multi-electrode recording techniques.  Using these techniques we record the simultaneous activity of large numbers of cortical and hippocampal cells during the acquisition and performance of memory tasks, as well as during the sleep periods preceding and following experience. Our research efforts focus on analyzing the structure of cortico-hippocampal interactions in the different brain states and on characterizing how this structure is modulated by behavior; how it evolves throughout the learning process; and what it reflects about the intrinsic organization of memory processing at the level of networks of neurons. In addition, we combine two-photon imaging and whole-cell recordings in order to characterize the contributions of different neuronal cell types to circuit dynamics.

A significant focus of our current efforts also involves the development of novel technologies for monitoring and manipulating brain activity.  Our experimental work is complemented by theoretical studies of network models and the development tools for the analysis of multi-neuronal data.

Selected Awards: 
Vannevar Bush Faculty Fellow
NIH Director's Pioneer Award
McKnight Scholar
Alfred P. Sloan Fellow
Bren Scholar
James S. McDonnell Foundation 21st Century Science Initiative Award
Selected Publications 

Shan K.Q., Lubenov E.V., Siapas A.G., "Model-based spike sorting with a mixture of drifting t-distributions", Journal of Neuroscience Methods 288 : 82-98 (2017).

Hulse B.K., Lubenov E.V., Siapas A.G., "Brain state dependence of hippocampal subthreshold activity in awake mice", Cell Reports 18 (1): 136-147 (2017).

Rios G., Lubenov E.V., Chi D., Roukes M.L., Siapas A.G., "Nanofabricated Neural Probes for Dense 3-D Recordings of Brain Activity", Nano Lett. 16(11), 6857-6862, (2016).

Shan K.Q. , Lubenov E.V., Papadopoulou M., Siapas A.G., "Spatial tuning and brain state account for dorsal hippocampal CA1 activity in a non-spatial learning task", eLife 2016; 5:e14321.

Hulse B.K., Moreaux L.C., Lubenov E.V., Siapas A.G., "Membrane Potential Dynamics of CA1 Pyramidal Neurons during Hippocampal Ripples in Awake Mice", Neuron 89: 800-813 (2016).

Sauerbrei B.A., Lubenov E.V., Siapas A.G., "Structured Variability in Purkinje Cell Activity during Locomotion", Neuron 87: 840-852 (2015).

Lubenov E.V., Siapas A.G., "Hippocampal Theta Oscillations are Traveling Waves", Nature 459:  534-539 (2009). 

Wierzynski C.M., Lubenov E.V., Gu M., Siapas A.G., "State-dependent spike timing relationships between hippocampal and prefrontal circuits during sleep", Neuron 61: 587-596 (2009).  

Lubenov E.V., Siapas A.G., "Decoupling through synchrony in neuronal circuits with propagation delays", Neuron 58: 118-131 (2008).

Siapas A.G., Lubenov E.V., Wilson M.A., "Prefrontal phase locking to hippocampal theta oscillations", Neuron 46(1):141-151 (2005).

Siapas A.G., Wilson M.A., "Coordinated interactions between hippocampal ripples and cortical spindles during slow-wave sleep", Neuron 21(5):1123-1128 (1998). 


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