|
BCM theory, BCM synaptic modification, or the BCM rule, named for Elie Bienenstock, Leon Cooper, and Paul Munro, is a physical theory of learning in the visual cortex developed in 1981. Due to its successful experimental predictions, the theory is arguably the most accurate model of synaptic plasticity to date. "The BCM model proposes a sliding threshold for Long-term potentiation or Long-term depression induction and states that synaptic plasticity is stabilized by a dynamic adaptation of the time-averaged postsynaptic activity. According to the BCM model, reducing the postsynaptic activity decreases the LTP threshold and increases the LTD threshold. The opposite applies to the increase in postsynaptic activity."〔Bologna, M., Agostino, R., Gregori, B., Belvisi, D., Manfredi, M., & Berardelli, A. (2010). Metaplasticity of the human trigeminal blink reflex M. Bologna et al. Metaplasticity of the blink reflex. European Journal of Neuroscience, 32(10), 1707-1714. .〕 == Development == In 1949, Donald Hebb proposed a working mechanism for memory and computational adaption in the brain now called Hebbian learning, or the maxim that ''cells that fire together, wire together''. This law formed the basis of the brain as the modern neural network, theoretically capable of Turing complete computational complexity, and thus became a standard materialist model for the mind. However, Hebb's rule has problems, namely that it has no mechanism for connections to get weaker and no upper bound for how strong they can get. In other words, the model is unstable, both theoretically and computationally. Later modifications gradually improved Hebb's rule, normalizing it and allowing for decay of synapses, where no activity or unsynchronized activity between neurons results in a loss of connection strength. New biological evidence brought this activity to a peak in the 1970s, where theorists formalized various approximations in the theory, such as the use of firing frequency instead of potential in determining neuron excitation, and the assumption of ideal and, more importantly, linear synaptic integration of signals. That is, there is no unexpected behavior in the adding of input currents to determine whether or not a cell will fire. These approximations resulted in the basic form of BCM below in 1979, but the final step came in the form of mathematical analysis to prove stability and computational analysis to prove applicability, culminating in Bienenstock, Cooper, and Munro's 1982 paper. Since then, experiments have shown evidence for BCM behavior in both the visual cortex and the hippocampus, the latter of which plays an important role in the formation and storage of memories. Both of these areas are well-studied experimentally, but both theory and experiment have yet to establish conclusive synaptic behavior in other areas of the brain. Furthermore, a biological mechanism for synaptic plasticity in BCM has yet to be established. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「BCM theory」の詳細全文を読む スポンサード リンク
|