Cross-channel correlations in tetrode recordings: implications for spike-sorting

We are exploring new methods of spike detection to improve spike-sorting in tetrode recordings. Based on our observation that the four channels of the tetrode carry highly correlated signals, we propose the use of a hyperellipsoidal thresholding surface in the 4-dimensional space of the signal values to detect spikes. This surface is determined by the cross-channel covariance matrix and provides a better approximation of the equiprobable surface of the noise amplitude distribution compared to the traditionally used hypercubical thresholding surface. This spike detection procedure greatly improves Rebrik, Wright, & Miller. Cross channel correlations in tetrode recordings. Page 2 of 8 the separation of signal clusters from the noise cluster around the origin. We have extended these approaches to automatic spike-sorting in both amplitude and full waveform spaces.