Stanton P K, Sejnowski T J
Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218.
Nature. 1989 May 18;339(6221):215-8. doi: 10.1038/339215a0.
A brief, high-frequency activation of excitatory synapses in the hippocampus produces a long-lasting increase in synaptic strengths called long-term potentiation (LTP). A test input, which by itself does not have a long-lasting effect on synaptic strengths, can be potentiated through association when it is activated at the same time as a separate conditioning input. Neural network modelling studies have also predicted that synaptic strengths should be weakened when test and conditioning inputs are anti-correlated. Evidence for such heterosynaptic depression in the hippocampus has been found for inputs that are inactive or weakly active during the stimulation of a conditioning input, but this depression does not depend on any pattern of test input activity and does not seem to last as long as LTP. We report here an associative long-term depression (LTD) in field CA1 that is produced when a low-frequency test input is negatively correlated in time with a high-frequency conditioning input. LTD of synaptic strength is also produced by activating presynaptic terminals while a postsynaptic neuron is hyperpolarized. This confirms theoretical predictions that the mechanism for associative LTD is homosynaptic and follows a hebbian covariance rule.
海马体中兴奋性突触的短暂高频激活会产生一种被称为长时程增强（LTP）的突触强度持久增加。一个单独的测试输入本身对突触强度没有持久影响，但当它与另一个单独的条件输入同时被激活时，通过关联作用可得到增强。神经网络建模研究还预测，当测试输入与条件输入呈反相关时，突触强度应会减弱。在海马体中，已发现对于在条件输入刺激期间不活跃或弱活跃的输入存在这种异突触抑制的证据，但这种抑制并不依赖于测试输入活动的任何模式，而且似乎不像LTP那样持久。我们在此报告，当低频测试输入在时间上与高频条件输入呈负相关时，在CA1区会产生一种联合性长时程抑制（LTD）。突触强度的LTD也可通过在突触后神经元超极化时激活突触前终末产生。这证实了理论预测，即联合性LTD的机制是同突触的，并遵循赫布共变规则。
