The Chicago Medical School (CMS) of the Rosalind Franklin University of Medicine and Science (RFUMS) have announced that Assistant Professor of Cell Biology and Anatomy, Athanasios Tzounopoulos, has uncovered novel forms of synaptic plasticity that occur at the very first step in the processing of sound in the central nervous system. His findings are released in Neuron.
“The ability to observe synaptic plasticity and uncover its cellular mechanisms at such an early, relatively unprocessed stage allows us to study the role of these mechanisms in sensory processing,” said Professor Tzounopoulos. “Our findings also show that the brain is able to change itself as a result of previous experience at places where processing is much simpler and better understood. This new capability could have a significant impact on our understanding and cures for disorders caused by neural plasticity-like mechanisms,” he added.
These findings may be relevant for understanding the mechanisms of human tinnitus. Tinnitus is the perception of ringing, buzzing, roaring, or other noises in the ears or head – when there is no external source of the noise. It is estimated that more than 50 million Americans experience tinnitus to some degree. Of these, about 12 million have tinnitus severe enough to seek medical attention. Many learn to ignore the sounds and experience no major effects. However, about two million patients are so seriously debilitated that they cannot function normally, finding it difficult to hear, work or sleep. Though research is providing more evidence for the causes and treatments of tinnitus, there is no real understanding of the biological bases of tinnitus, nor are there any treatments that help most sufferers. Recent studies point to the central nervous system as the site for the maintenance of tinnitus. Moreover, animal models of tinnitus indicate a role for the dorsal cochlear nucleus (DCN, an auditory brainstem nucleus), the brain area where Professor Tzounopoulos performed his studies.
“It is quite possible that transient exposure to intense sound might induce long-term changes in the balance of excitation and inhibition in the DCN, through the mechanisms described in our recent findings. Our studies, by providing a detailed understanding on how this plasticity is induced, expressed, and modulated at the cellular level may ultimately lead to treatments for tinnitus” said Professor Tzounopoulos.
According to these recent findings, newly formed hypotheses suggest that concerted operation of different forms of synaptic plasticity gate sensory activation of the DCN and can lead to activity-dependent modulation of timing precision. Timing is an important feature in the brain and especially in the auditory system. Many neurons in the auditory system are known for their ability to fire action potentials that occur in a precise temporal relationship to the stimulus (phase locking). Activity-dependent modulation of spike timing precision through these mechanisms is a new concept that may allow sensory systems to adapt to different patterns of sensory activity and to properly integrate and encode varying sensory stimuli.
Recent studies have shown that more robust and faithful brainstem timing encoding is observed in trained individuals (musicians) compared to untrained individuals (non-musicians). While these types of learning phenomena have been attributed to cortical plasticity until now, our studies suggest that the brainstem itself has the mechanisms and the capability to support such learning. Similar studies have established that brainstem timing precision serves as a reliable marker of individuals with learning disabilities. Faulty mechanisms of neural timing at the brainstem may be the biological basis of malfunction in children with learning disabilities. “Therefore, elucidation of mechanisms underlying synaptic plasticity and timing precision in the brainstem may provide the cellular basis for these learning disabilities,” said Professor Tzounopoulos.
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