ABSTRACT
The previous chapter focused on the biophysics of generation of spikes, the extracellular signature of action potentials, representing the output of the computation done by individual neurons. In this chapter, we focus on the generation of local eld potentials (LFPs), which in contrast appears to predominantly reect the synaptic inputs to the neurons. The measurement of LFPs, which we here dene as the low-frequency part of the electrical potential recorded by an extracellular electrode inserted into the brain, is among the oldest techniques for studying neural activity. Already in 1875, Richard Caton could report that he had measured electrical signals from the cortical surface of living animals (Caton 1875), 50 years before the rst EEG was recorded (Berger 1929). As the LFP stems from activity in populations of neurons around the electrode, the signal is not straightforward to interpret. Early investigators thus focused on the high-frequency part of the signal, the multi-unit activity (MUA), which contains information about the ring of action potentials of a handful of the surrounding neurons (Adrian and Moruzzi 1939). The interest in the LFP signal revived in the 1950s with the introduction of current-source density (CSD) analysis of multiple LFP recordings across well-organized layered neural structures such as cortex, cerebellum, and hippocampus (Pitts 1952).
