PSYC 311 Chapter Notes - Chapter 13.3: Dentate Gyrus, Visual Learning, Two-Streams Hypothesis
9 Jun 2016
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Long frequency stimulation of the synaptic inputs to a cell can decrease, rather than increase, their strength. This phenomenon is known as long-term depression (ltd) and also plays a role in learning: apparently, neural circuits that contain memories are established by strengthening some synapses and weakening others. Stimulation frequencies of above 10hz cause ltp, but lower frequencies cause ltd: both effects are blocked by ap5 which inhibits ndma receptors, and thus the activation of nmda receptors is required for both effects. Studies have demonstrated associative long-term depression, which is produced when synaptic inputs are activated at the same time that the postsynaptic membrane is weakly depolarized or hyperpolarized. Ltp occurs in many other brain areas beyond the hippocampal formation. In some, but not all, of these regions, ltp is initiated by stimulation of ndma receptors: for example, this does not seem to be the case in field ca3 which contains very few.
