Important and salient sensory stimuli occur with low probability and are rare, while high probability stimuli, occurring repeatedly, are usually of less importance and are ignored by an organism. Sensory cortical circuitry development is activity dependent and hence is based on the sensory environment to which an animal is exposed early during development. Particularly in the auditory system, altering the natural auditory environment during a specific period, the critical period, of early development can remarkably alter cortical circuitry and organization. A crucial player in development of cortical circuits is the subplate. Subplate neurons (SPNs), the first born cortical neurons, transient in nature, play an important role in sculpting thalamo-cortical inputs and hence functional cortical circuitry and organization. With a new auditory exposure paradigm before the established auditory critical period (before ear canal opening, ECO) using low probability salient/deviant stimuli in the early auditory environment, we show that the functional auditory cortical (ACX) responses are remarkably altered into adulthood, in a manner specific to the deviant or rare exposure stimulus. The observed plasticity is an outcome of the unique deviant detection properties we find of SPNs, before ECO, with strong selectivity to the rare stimulus. These ages are equivalent to gestational week 25 in humans, suggesting prenatal experience affecting sensory development. A computational network model derived from our experimental results, with spike timing dependent plasticity shows how such long term plasticity can occur. Further, theoretically, using mutual information maximization and sparse coding principles, we show that the outcome of early exposure with our exposure paradigm can be predicted theoretically. Our results thus suggest revision of the established timelines and concept of auditory critical period and may generalize to other sensory systems.
Sharba Bandyopadhyay did his BTech (1999) in Electronics and Electrical Communication Engineering, IIT Kharagpur, India. He then did his MSE (2001) and PhD (2007) in Biomedical Engineering from Johns Hopkins University, Baltimore, USA, respectively from the School of Engineering and School of Medicine. Sharba’s Master’s Thesis was on speech coding in the auditory nerve and his doctoral work was on spectral and temporal coding properties of neurons in the cochlear nucleus. Following his PhD he joined the Institute of Systems Research and Department of Biology at the University of Maryland, College Park, USA as a postdoctoral fellow and worked on the sound encoding properties of the auditory cortex and rapid and developmental plasticity in the auditory cortex. He later continued at UMD as Research faculty (2009-2012). At UMD Sharba worked on answering questions about auditory encoding and plasticity using in-vivo and in vitro 2-photon Ca imaging, 2-photon single neuron stimulation and electrophysiology. With a Wellcome Trust DBT Fellowship, Sharba moved to India to start his own lab. After short a stay at NBRC India, he moved to IIT Kharagpur and is an Assistant Professor in E&ECE from 2015. His research interests include developmental plasticity at the neuronal micro-circuit level and neurodevelopmental disorders. Other than research, Sharba also teaches Neuroscience to Engineering students and other Electrical Engineering and Electrical Communication courses.