As a systems-level neurophysiologist, my recent research has focused on basic questions investigating how the cortex integrates information from more than one sense (e.g., sight and hearing), as well as on clinically-relevant questions as to how the cortex adapts to hearing loss and its perceptual implications.
Simply by considering our own daily experiences, we become keenly aware that the processing of information from each of our senses does not occur solely in isolation; rather, our brains naturally merge information from our different senses to provide us with a more complete sensory experience. In species ranging from mice to humans, there exist functionally-specialized regions of the cortex that are populated by neurons capable of processing multisensory information. Using in vivo extracellular electrophysiological recording techniques in animal models, I have investigated how information from the different senses can be integrated at the level of single neurons in the cortex (e.g., how neurons change their firing patterns when presented visual stimuli in combination with auditory and/or tactile cues). Future studies will record neural activity in awake-behaving rodents to determine how information processing in multisensory cortical circuits translates into behavioral outcomes.
Cortical Plasticity Following Hearing Loss:
How does the brain adapt (or mal-adapt) when it is deprived one of its senses? My previous research using animal models has shown that partial hearing loss, which denies the auditory system the full spectrum of sounds normally accessible from the environment, causes a dramatic increase in the proportion of neurons in the auditory cortex that respond to visual and tactile stimuli. Future studies will determine the consequences of this “crossmodal plasticity” on auditory- and multisensory behavioral tasks. Ultimately, rehabilitative therapies aimed at restoring hearing may be complicated by factors involving such crossmodal plasticity.
Tinnitus and Its Risk Factors:
It is well known that excessive exposure to loud noise can result in permanent hearing loss. A common corollary to this noise-induced hearing loss is tinnitus, the subjective perception of a phantom sound which is often described as a “ringing in the ears.” For ~10% of the general population, tinnitus is a constant disturbance that can lead to sleep problems, difficulty concentrating and, in some cases, severe forms of depression, all of which can negatively affect one’s quality of life. Unfortunately for tinnitus sufferers, a lack of understanding of the brain changes responsible for the phantom perception has hindered efforts to devise effective treatment. Using electrophysiological recordings in a rodent model, my ongoing research seeks to determine how aberrant cortical plasticity contributes to tinnitus. Additional studies are devoted to identifying risk factors that may increase one’s susceptibility to developing chronic tinnitus following loud noise exposure.
Undergraduate and potential graduate students with a background in Neuroscience, Physiology, Engineering, Psychology, or Computer Science are invited to inquire about possible research opportunities.
• Meredith MA, Keniston LP and Allman BL (2012) Multisensory dysfunction accompanies crossmodal plasticity following adult hearing impairment. Neuroscience. 214:136-148.
• Meredith MA and Allman BL (2012) Early hearing-impairment results in crossmodal reorganization of ferret core auditory cortex. Neural Plasticity. 2012(601591):1-13.
• Lobarinas E, Hayes SH and Allman BL (2012) The gap-startle paradigm for tinnitus screening in animal models: limitations and optimization. Hearing Research. E-pub ahead of print. PMID: 22728305.
• Stolzberg D, Salvi RJ and Allman BL (2012) Salicylate toxicity model of tinnitus. Frontiers in Systems Neuroscience. 6(28):1-12.
• Stolzberg D, Chrostowski M, Salvi RJ and Allman BL (2012) Intracortical circuits amplify sound-evoked activity in primary auditory cortex following systemic injection of salicylate in the rat. Journal of Neurophysiology. 108:200-214.
• Stolzberg D, Chen GD, Allman BL and Salvi RJ (2011) Salicylate-induced peripheral auditory changes and tonotopic reorganization of auditory cortex. Neuroscience. 180:157-164.
Sun W, Tang L and Allman BL (2011) Environmental noise affects auditory temporal processing development and NMDA-2B receptor expression in auditory cortex. Behavioral Brain Research. 218:15-20.
• Allman BL and Meredith MA (2009) Not just for bimodal neurons anymore: The contribution of unimodal neurons to cortical multisensory processing. Brain Topography. 21:157-167.
• Allman BL, Keniston LP and Meredith MA (2009) Adult-deafness induces somatosensory conversion of ferret auditory cortex. Proceedings of the National Academy of Sciences, USA. 106:5925-5930.
Allman BL, Keniston LP and Meredith MA (2008) Subthreshold auditory inputs to extrastriate visual neurons are responsive to parametric changes in stimulus quality: Sensory-specific versus non-specific coding. Brain Research. 1242: 95-101.
• Allman BL, Bittencourt-Navarrete RE, Keniston LP, Medina AE, Wang MY and Meredith MA (2008)
Do cross-modal projections always result in multisensory integration? Cerebral Cortex. 18:2066-2076.
• Allman BL and Meredith MA (2007) Multisensory processing in "unimodal" neurons: cross-modal subthreshold auditory effects in cat extrastriate visual cortex. Journal of Neurophysiology. 98:545-549.