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Abstract
Objective. Local field potentials (LFPs) that carry information about the subject's motor intention have the potential to serve as a complement or alternative to spike signals for brain–machine interfaces (BMIs). The goal of this study is to assess the utility of LFPs for BMIs by characterizing the largely unknown information coding properties of multichannel LFPs. Approach. Two monkeys were implanted, each with a 16-channel electrode array, in the parietal reach region where both LFPs and spikes are known to encode the subject's intended reach target. We examined how multichannel LFPs recorded during a reach task jointly carry reach target information, and compared the LFP performance to simultaneously recorded multichannel spikes. Main Results. LFPs yielded a higher number of channels that were informative about reach targets than spikes. Single channel LFPs provided more accurate target information than single channel spikes. However, LFPs showed significantly larger signal and noise correlations across channels than spikes. Reach target decoders performed worse when using multichannel LFPs than multichannel spikes. The underperformance of multichannel LFPs was mostly due to their larger noise correlation because noise de-correlated multichannel LFPs produced a decoding accuracy comparable to multichannel spikes. Despite the high noise correlation, decoders using LFPs in addition to spikes outperformed decoders using only spikes. Significance. These results demonstrate that multichannel LFPs could effectively complement spikes for BMI applications by yielding more informative channels. The utility of multichannel LFPs may be further augmented if their high noise correlation can be taken into account by decoders.
Highlights
An electrical signal sensed by a microelectrode inserted in the extracellular matrix of the cortex is typically decomposed into action potentials and local field potentials (LFPs)
The underperformance of multichannel LFPs was mostly due to their larger noise correlation because noise de-correlated multichannel LFPs produced a decoding accuracy comparable to multichannel spikes
Despite the high noise correlation, decoders using LFPs in addition to spikes outperformed decoders using only spikes. These results demonstrate that multichannel LFPs could effectively complement spikes for brainmachine interfaces (BMIs) applications by yielding more informative channels
Summary
An electrical signal sensed by a microelectrode inserted in the extracellular matrix of the cortex is typically decomposed into action potentials and local field potentials (LFPs). The LFP is a low-pass filtered signal, cut off at 300 Hz or less, and largely reflects the sum of slow local synaptic currents in thousands of neurons surrounding the electrode tip (Mitzdorf, 1985; Poulet and Petersen, 2008). Both spikes and LFPs can carry important information about movements such as reach target location, hand kinematics, hand grasp type, reach onset time, and electromyograms (EMGs) of arm muscles Probable causes are neuro-degeneration following post-surgical glial scar formation near the electrodes, changes of the electrode location by uncontrolled physical perturbations including cardiac and respiratory pulsations, mechanical movement of the subject, and migration of neural tissue (Santhanam et al, 2007; Dickey et al, 2009; McConnell et al, 2009)
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