Dr. Ranjan Batra

Ranjan Batra, Ph.D.

Associate Professor of Anatomy
Department of Anatomy
The University of Mississippi Medical Center
2500 North State Street
Jackson, Mississippi 39216-4505 

Office Telephone: 601-984-1652
                  601-984-1640
Department FAX:   601-984-1655
: rbatra@anatomy.umsmed.edu
EDUCATION
B.Sc.(Biophysics), University of Guelph, Ontario, 1976
Ph.D., Institute for Sensory Research, College of Engineering, Syracuse University, 1983

RESEARCH INTERESTS
Structure and Function of the Auditory Pathways

CURRENT RESEARCH
Binaural Processing

Our brains face a unique challenge when trying to determine the source of a sound, as compared to determining the source of a light or an object touching our bodies. The sensory receptors in the eye and the skin are organized according to the location of objects we see and feel, and this image is transmitted to the brain. The receptors for sound, however, are not organized by location. These receptors lie in the inner ear, and are organized by frequency. Consequently, the location of a sound has to be computed neurally within the brain. Decoding the location of a sound along the azimuthal, or horizontal, direction requires both ears and involves interpreting subtle binaural cues. These cues are the differences in the intensity of a sound at the two ears, and the differences in its time of arrival. The latter, the interaural temporal differences, are especially fine, and amount to a difference of a few hundred microseconds when a sound is directly opposite one ear. This is less than the time for a single action potential to occur!

The timing differences that are important are not those that occur at the start of a sound, but rather the ongoing difference in the time of arrival of the pattern of the sound. Traditionally, it was believed that timing differences were only important when the frequency of the sound was low, and auditory neurons could respond in synchrony with the pressure variations at the ear. Now it is known that high-frequency sounds with a relatively slowly varying envelope can also generate interaural timing cues that can be detected.

Because the localization of sounds must involve computations within the brain, it is likely to be vulnerable to anesthesia. Despite this, most studies that have examined the neural basis of sound localization have used anesthetized animals. I pioneered the use of an unanesthetized animal-the rabbit-in studying the neural basis of sound localization. My research has yielded three general findings. First, there appear to be at least two, and maybe three, systems for conveying timing information up the brainstem. In one, neurons discharge maximally at a particular delay, while in the second, neurons are maximally suppressed at particular delay. These neurons would discharge maximally or be maximally suppressed by sounds at a given location. A third pathway seems to be specialized for encoding interaural timing in transient sounds. Second, the sensitivity of neurons to timing cues in the envelopes of high-frequency sounds can be as precise as their sensitivity to timing cues in low-frequency sounds. Third, the precision of tuning to a particular interaural delay increases at higher stations in the auditory pathway. All of this means that determining the location of a sound appears to involve parallel neural processing at several levels of the brain.

©2001, Copyright R. Batra


PUBLICATIONS
  1. Batra, R. 2006. Responses of neurons in the ventral nucleus of the lateral lemniscus to sinusoidally amplitude modulated tones. Journal of Neurophysiology 96: 2388-2398.
  2. Kuwada, S., D. C. Fitzpatrick, R. Batra and E.-M. Ostapoff. 2006. Sensitivity to interaural time differences in the dorsal nucleus of the lateral lemniscus of the unanesthetized rabbit: comparison with other structures. Journal of Neurophysiology 95: 1309–1322.
  3. Batra, R. and T. C. T. Yin. 2004. Cross-correlation by neurons of the medial superior olive: a reexamination. Journal of the Association for Research in Otolaryngology 5: 238-252.
  4. Batra, R. 2003. Inferior Colliculus. In: "Encyclopedia of the Neurological Sciences," (J. C. Masdeu, M. Aminoff and R. B. Daroff, eds.), Academic Press, San Diego,
  5. Oliver, D. L., G. E. Beckius, D. C. Bishop, W. C. Loftus and R. Batra. 2003. Topography of interaural temporal disparity coding in projections of medial superior olive to inferior colliculus. Journal of Neuroscience 23: 7438 –7449.
  6. Batra, R. and D. C. Fitzpatrick. 2002. Processing of interaural temporal disparities in the medial division of the ventral nucleus of the lateral lemniscus. Journal of Neurophysiology 88: 666-675.
  7. Batra, R. and D. C. Fitzpatrick. 2002. Monaural and binaural processing in the ventral nucleus of the lateral lemniscus: a major source of inhibition to the inferior colliculus. Hearing Research 168: 90-97.
  8. Fitzpatrick, D. C., S. Kuwada and R. Batra. 2002. Transformations in processing interaural time differences between the superior olivary complex and inferior colliculus: beyond the Jeffress model. Hearing Research 168: 79-89.
  9. Fitzpatrick, D. C., S. Kuwada and R. Batra. 2000. Neural sensitivity to interaural time differences: beyond the Jeffress model. Journal of Neuroscience 20: 1605-1615.
  10. Batra, R. and D. C. Fitzpatrick. 1999. Discharge patterns of neurons in the ventral nucleus of the lateral lemniscus of the unanesthetized rabbit. Journal of Neurophysiology 82: 1097-1113.
  11. Beckius, G. E., R. Batra and D. L. Oliver. 1999. Axons from anteroventral cochlear nucleus that terminate in medial superior olive of cat: observations related to delay lines. Journal of Neuroscience 19: 3146-3161.
  12. Fitzpatrick, D. C., S. Kuwada, D. O. Kim, K. Parham and R. Batra. 1999. Responses of neurons to click-pairs as simulated echoes: auditory nerve to auditory cortex. Journal of the Acoustical Society of America 106: 3460-3472.
  13. Kuwada, S. and R. Batra. 1999. Coding of sound envelopes by inhibitory rebound in neurons of the superior olivary complex in the unanesthetized rabbit. Journal of Neuroscience 19: 2273-2287.
  14. Batra, R. and D. C. Fitzpatrick. 1997. Neurons sensitive to interaural temporal disparities in the medial part of the ventral nucleus of the lateral lemniscus. Journal of Neurophysiology 78: 511-515.
  15. Batra, R., S. Kuwada and D. C. Fitzpatrick. 1997. Sensitivity to interaural temporal disparities of low- and high-frequency neurons in the superior olivary complex: II. Coincidence detection. Journal of Neurophysiology 78: 1237-1247.
  16. Batra, R., S. Kuwada and D. C. Fitzpatrick. 1997. Sensitivity to interaural temporal disparities of low- and high-frequency neurons in the superior olivary complex: I. Heterogeneity of responses. Journal of Neurophysiology 78: 1222-1236.
  17. Fitzpatrick, D. C., R. Batra, T. R. Stanford and S. Kuwada. 1997. A neuronal population code for sound localization. Nature 388: 871-874.
  18. Kuwada, S., R. Batra and D. C. Fitzpatrick. 1997. Neural processing of binaural temporal cues. In: "Binaural and Spatial Hearing in Real and Virtual Environments," (R. H. Gilke and T. R. Anderson, eds.), Lawrence Erlbaum Associates, Mahwah, NJ, pp. 399-425.
  19. Kuwada, S., R. Batra, T. C. T. Yin, D. L. Oliver, L. B. Haberly and T. R. Stanford. 1997. Intracellular recordings in response to monaural and binaural stimulation of neurons in the inferior colliculus of the cat. Journal of Neuroscience 17: 7565-7581.
  20. Fitzpatrick, D. C., S. Kuwada, R. Batra and C. Trahiotis. 1995. Neural responses to simple simulated echoes in the auditory brainstem of the unanesthetized rabbit. Journal of Neurophysiology 74: 2469-2486.
  21. Feng, J. J., S. Kuwada, E.-M. Ostapoff, R. Batra and D. K. Morest. 1994. A physiological and structural study of neuron types in the cochlear nucleus. I. Intracellular responses to acoustic stimulation and current injection. Journal of Comparative Neurology 346: 1-18.
  22. Batra, R. 1993. Interaural temporal coding of complex high-frequency sounds: a transformation in the inferior colliculus? In: "Sensory Research: Multimodal Perspective," (R. T. Verrillo, eds.), Lawrence Erlbaum Assoc. Inc., Hillsdale, NJ, pp. 141-50.
  23. Batra, R., S. Kuwada and T. S. Stanford. 1993. High-frequency neurons in the inferior colliculus that are sensitive to interaural delays of amplitude-modulated tones: evidence for dual binaural influences. Journal of Neurophysiology 70: 64-80.
  24. Stanford, T. R., S. Kuwada and R. Batra. 1992. A comparison of the interaural time sensitivity of neurons in the inferior colliculus and thalamus of the unanesthetized rabbit. Journal of Neuroscience 12: 3200-3216.
  25. Batra, R., S. Kuwada and T. R. Stanford. 1989. Temporal coding of envelopes and their interaural delays in the inferior colliculus of the unanesthetized rabbit. Journal of Neurophysiology 61: 257-268.
  26. Kuwada, S., R. Batra and T. R. Stanford. 1989. Monaural and binaural response properties of neurons in the inferior colliculus of the rabbit: effects of sodium pentobarbital. Journal of Neurophysiology 61: 269-282.
  27. Kuwada, S., T. R. Stanford and R. Batra. 1987. Interaural phase sensitive units in the inferior colliculus of the unanesthetized rabbit. Effects of changing frequency. Journal of Neurophysiology 57: 1338-1360.
  28. Batra, R., S. Kuwada and V. L. Maher. 1986. The frequency-following response to continuous tones in humans. Hearing Research 21: 167-177.
  29. Kuwada, S., R. Batra and V. L. Maher. 1986. Scalp potentials of normal and hearing-impaired subjects in response to sinusoidally amplitude-modulated tones. Hearing Research 21: 179-192.
TEACHING

Medical Gross Anatomy
Fall quarter: M, T, Th, F: 1:00-5:00 PM

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