Synaptic potentials can be recorded by

Potential" refers to electrical potential, or voltage, and paicularly to voltage recorded with a microelectrode embedded within neuronal tissue, typically in the brain of an anesthetized animal or within a thin slice of brain tissue maintained in vitro. The electrical activities in the neurons are rapid being measured in milliseconds, and the voltage changes are too small measured in millivolts.........the microelectrode has a tip diameter of less thanone mirometer .....hence it is used to measure the synaptic potential. Ref guyton and hall textbook of medical physiology 12/e p58