Rama Ratnam, Ph.D.
Assistant Professor of Systems & Computational Neuroscience
Office: BSE 2.402
Phone: (210) 458-7489
Rama.Ratnam@utsa.edu
Ph.D., University of Illinois at Urbana-Champaign, Illinois, U.S.A.
B. Tech., Indian Institute of Technology, Delhi, India.
Research Interests
Sensory neurobiology, Neuroethology, Auditory processing, Electrosensory processing.
Our senses tell us what is happening in the world around us. They help us to locate and identify objects in the environment and to orient and navigate effectively. But, how does the brain perform the complex calculations that give us a coherent percept of the world? This question is the focus of our lab. We investigate this question in two sensory modalities: auditory processing in frogs and toads, and active electrosensory processing in weakly electric fish. Our research program is broad and uses a mix of theory and experiments to understand these modalities. We are interested in 1) the signals that originate from the environment, 2) how they are transformed into an internal neural representation, 3) the computational mechanisms that group and segregate distinct signal sources and suppress noise, and 4) how the information comes together to give us a coherent perception of the world around us.
In auditory processing, the research is directed towards understanding how a frog can identify and select a mate calling in a dense and noisy frog chorus. A frog chorus is a dense mix of calling individuals from many different species, each trying to attract a female. The female has to listen carefully and select the call of a preferred conspecific male, locate him and then move towards him. In the process she has to ignore other sounds, including those originating from wind, rain and other animals, and cope with echoes and reverberation that distort the mating call and make it unrecognizable. The research is directed towards understanding the acoustics of the frog's environment via field recordings, in vivo single neuron electrophysiology to understand the neural representation of sounds patterns, and computational studies into the extraction of sound patterns embedded in noise. The broader goal is to understand how the brain extracts vocal communication signals (including speech), particularly when they are corrupted by noise and are degraded by the environment.
The electrosensory system of weakly electric fish is another area of research that provides insights into how the sensory system copes with noise while extracting a signal of interest. This fish generates a weak electric field (order of millivolts) around itself using an electric organ embedded in the tail. When small prey (water fleas) move into the field, they cause local field distortions that are sensed via receptors embedded in the skin. These distortions are extremely weak (order of microvolts) and barely noticeable in the background field activity, but the fish appears to catch prey with little difficulty. The research examines the pattern of neural activity in the afferents that transmit the distortion to the brain, and asks a simple question: How does the fish detect this barely noticeable distortion in its field? This research combines electrophysiology and statistical decision theory to answer the question, and provides insights into principles that govern the detection and identification of behaviorally relevant signals in the brain.
Recent Publications
Ratnam R, Jones DL, Wheeler BC, O'Brien WD Jr, Lansing CR, Feng AS. Blind estimation of reverberation time. J Acoust Soc Am. 2003 Nov;114(5):2877-92.
Goense JB, Ratnam R. Continuous detection of weak sensory signals in afferent spike trains: the role of anti-correlated interspike intervals in detection performance. J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2003 Oct;189(10):741-59.
Feng AS, Ratnam R. Neural basis of hearing in real-world situations. Annu Rev Psychol. 2000;51:699-725.
Ratnam R, Nelson ME. Nonrenewal statistics of electrosensory afferent spike trains: implications for the detection of weak sensory signals. J Neurosci. 2000 Sep 1;20(17):6672-83.