Ph.D., University of Texas, Austin
Synaptic Transmission and Neural Circuits
We are interested in determining the criteria that sensory nuclei use to decide which incoming stimulus to enhance and which to suppress, and how a neural network maximizes the information between the input (e.g. an auditory stimulus) and the output (the neural response). The number of neurons activated by an input, the balance between excitation and inhibition, and intrinsic membrane properties and local circuitry, limit the amount of information that can be conveyed by the network about the input, and the maximization of the output becomes a complex task.
Our laboratory focuses primarily on the inferior colliculus, an auditory midbrain nucleus. The organization of the inferior colliculus and its importance to auditory function make it an excellent model system to address the functional importance of intrinsic membrane properties, synaptic transmission and network organization in controlling excitability. In particular, we are examining the characteristics of inputs and how they change with stimulus strength and frequency, and the role of voltage-gated ion channels and local circuitry in shaping neuronal responses to changing inputs.
To understand how the inferior colliculus functions, we examine the constraints imposed on response patterns by a basic circuit defined in terms of cell types and connections. Important elements of the circuit include 1) parallel excitatory and inhibitory inputs to the central nucleus of the inferior colliculus; 2) local circuitry contained within single (iso-frequency) laminae of the central nucleus; 3) inter-laminar circuitry (cross-frequency connections) within one colliculus, and 4) commissural connections between the two colliculi.
E. Gaier, R. Rodriguiz, X-M. Ma, S. Sivaramakrishnan, D. Bousquet-Moore, W. C. Wetsel, E. Eipper, R. Mains (2010). Haploinsufficiency in peptidylglycine alpha-amidating monooxygenase leads to altered synaptic transmission in the amygdala and impaired emotional responses. J. Neuroscience. Oct 13; 30(41):13656-69.
L. Chandrasekaran, Y. Xiao, S. Sivaramakrishnan* (2013). Functional architecture of the inferior colliculus revealed with voltage-sensitive dyes. Front Neural Circuits. 7: 41.
S. Sivaramakrishnan*, J. T. Sanchez, C. A. Grimsley. (2013). High concentrations of divalent cations isolate monosynaptic inputs from local circuits in the auditory midbrain. Front Neural Circuits. 7:175.
C. A. Grimsley, J. T. Sanchez and S. Sivaramakrishnan* (2013). Midbrain local circuits shape sound intensity codes. Front Neural Circuits. 7:174.
C.A. Grimsley, S. Sivaramakrishnan* (2014). Postnatal developmental changes in the medial nucleus of the trapezoid body in a mouse model of auditory pathology. Neuroscience Letters. 559: 152-157.
Ying Li, Robert A. Davey, Shobhana Sivaramakrishnan*, William P. Lynch* (2014). Postinhibitory rebound neurons and networks are disrupted in retrovirus-induced spongiform neurodegeneration. J. Neurophysiology. August 1, 2014: 683-704. DOI: 10.1152/jn.00227.2014.
*Equal contribution as heads of laboratories
L. Chandrasekaran, Y. Xiao, S. Sivaramakrishnan* (2013). Functional architecture of the inferior colliculus revealed with voltage-sensitive dyes. Front Neural Circuits. 7: 41. Cited as top performing article in Frontiers in Neuroscience, February 2014.
L. Chandrasekaran, Y. Xiao, S. Sivaramakrishnan* (2013). Functional architecture of the inferior colliculus revealed with voltage-sensitive dyes. Front Neural Circuits. 7: 41. Cited as special interest to the drug development sector and advancement in medicine. Global Medical Discoveries, June 2013.