Quanta/analysls of synapti~: transmission at connections between neurons tn the CNS has provided mslghts concerning the structural constraints on transmitter release and postsynaptic responsiveness. However, it has proven difhcult in many cases to resolve the size and variabihty of a single quantum or to distinguish clear peaks in amphtude histograms of evoked responses, due m part to the superp0sition of background tnstrumental and biological notse. These

/imitations raise questions about recent attempts to use direct or indirect methods of quanta/analysis m order to distinEuish between pre-and postsynaptic/oct of the modifications underlyin E lonE-term potenttat/on, particularly since the interpretations are mode/-dependent and the statistical treatments and experimental techniques employed incorporate stmplifyin B assumptions not yet proven.

Until recently, attempts to gain insight into the question of the mechanism by which neurotransmitters are released and detected in the CNS have been confronted by a number of technical difficulties specific to central neurons and networks. However, the advent of patch-clamp techniques that considerably improve the signal-to-noise ratio has resulted in a renewed interest in how synapses work at the microscopic level. The expectation is that it may be possible to resolve elementary problems such as: is release quantal in a given system, and according to what model does it occur? A focus on quantal analysis has also been prompted by the fact that it is an irreplaceable tool for identifying the pre-or postsynaptic locus of changes in synaptic efficacy, the most dramatic being long-term potentiation (LTP).