Sadegh Nabavi, Niels Andersen and Nathalie Krauth publish a review article in Current Opinion in Neurobiology
The title of the review is: Hebbian plasticity in vivo: relevance and induction.
As an introduction for the review the authors writes:
Nineteen years ago, Charles Stevens posed a million-dollar question: Are long-term potentiation (LTP) and long-term depression (LTD) the cellular mechanisms underlying memory formation ? Ever since, there have been numerous attempts to prove, and occasionally disprove, the concept. It started by detecting synaptic potentiation after animals learned a task  and more recently it was demonstrated, that a fear memory can be inactivated and reactivated simply by inducing well-established LTD and LTP protocols [3•]. These protocols are successful at inducing plasticity in vivo. They do, however, rely on highly synchronized activation of many pre-synaptic and postsynaptic neurons, a phenomenon rarely observed in vivo. This raises the question: how is plasticity induced in a physiological condition? This question is the main subject of our mini-review. Due to limited space, we have given emphasis to works published in the last two years on LTP/LTD in associative forms of learning and memory. For a broader overview on cellular and molecular mechanisms of memory formation and consolidation we refer our readers to excellent recent reviews.