Local contribution to the somatosensory evoked potentials in rat’s thalamus

Abstract

Local Field Potential (LFP), despite its name, often reflects remote activity. Depending on the orientation and synchrony of their sources, both oscillations and more complex waves may passively spread in brain tissue over long distances and be falsely interpreted as local activity at the recording site. Here, we study the contribution of local and distant currents to LFP recorded from rat thalamic nuclei and barrel cortex activated by whisker stimulation. We reconstructed the current sources using dense multichannel recordings and a model-based kernel Current Source Density (kCSD) method. We show that the evoked potential wave seen in the thalamic nuclei around 7-15 ms post-stimulus has a substantial negative component reaching from cortex. This component can be analytically removed and truly local thalamic LFP, with purely thalamic contributions, can be recovered reliably using kCSD. In particular, concurrent recordings from the cortex are not essential for reliable thalamic CSD estimation. Proposed framework can be used to analyse LFP from other brain areas and has consequences for general LFP interpretation and analysis.