While extracellular electrical recordings are the work horse in in vivo electrophysiology, the interpretation of such recordings is not trivial. The recorded extracellular potentials in general stem from a complicated sum of contributions from all transmembrane currents of the neurons in the vicinity of the electrode contact. The high-frequency part of the recorded signal contains information about action-potential firing (spikes), and the signal can often be sorted into spiking contributions from Individual neurons surrounding the electrode. The interpretation of the low-frequency part of the low-frequency part, the local field potential (LFP), is more challenging as thousands of neurons in general will contribute to the measured signal (Lindén et al., Neuron, 2011). To take full advantage of the new generation of silicon-based multielectrodes recording LFPs from tens, hundreds or even thousands of contact positions simultaneously, we thus need to develop new data analysis methods (Einevoll et al., Nat Rev Neurosci, 2013).

From volume conduction theory it follows that the extracellular potentials can be calculated by adding contributions from the transmembrane currents around the electrode contact, and a forward-modeling scheme for calculating the extracellular potential generated from activity in biophysically detailed neuron models has been developed. In the seminar I will discuss results from our group where this scheme has been used to explore the neural activity underlying LFPs and to develop new analysis methods for the signal.