The Bernstein Center for Computational Neuroscience Freiburg

Announcement for the next
BCCN Seminar

Dr. Arvind Kumar

Brown University, USA

W(H)AT is the relationship between the LFP and spikes in cortex?

Tuesday, December 11th, 2007


Lecture Hall (ground floor)
BCCN building
Hansastraße 9A
79104 Freiburg

Extracellular signals recorded in the brain are composed of very high frequency components (i.e. spikes) and low frequency components which are refered to as the local-field-potentials (LFP). While the origin of spikes is well understood there is very little known about the origin of LFP. Although LFP is considered to be either neural output (spikes) or neural input (synaptic currents), there is still no conclusive evidence to support either theory. This lack of understanding about LFP is surprising since, as with spike-trains, LFP is an informative signal about neural activity. Furthermore, the recording stability and continous nature of LFP provide certain advantages over discrete spike trains for understanding and decoding neural activity. Our understanding of LFP would greatly improve if we could relate it to spiking activity, since the mechanisms of spike generation are well understood. Earlier attempts to relate LFP to spikes were primarily based on reverse correlation and spike triggered averaging. However, since spike trains are binary they only reveal information about the average LFP associated with a spike, and thus the spike rate cannot be determined from LFP. Here, we introduce the concept of cortical blips which are derived from fluctuations in LFP. Cortical blips allow us to isolate average waveforms for various fluctuation amplitudes in LFP. Blip wave amplitude triggered (WAT) averaging reveals a threshold linear relationship between LFP amplitude and spike rate. This relationship between LFP and spikes suggests a reevaluation of the established theories on LFP generation. Additionally, this threshold linear relationship implies that we should reinterpret numerous experiments (such as those studying synaptic plasticity in vivo) which have drawn certain conclusions from LFP signal.

The talk is open to the public. Guests are cordially invited!