Spectral modulation of LFP activity in M1 during dexterous finger movements

Abstract

Recent studies have shown that cortical local field potentials (LFP) contain information about planning or executing hand movement. While earlier research has looked at gross motor movements, we investigate the spectral modulation of LFP activity and its dependence on recording location during dexterous motor actions. In this study, we recorded LFP activity from the primary motor cortex of a primate as it performed a fine finger manipulation task involving different switches. The event-related spectral perturbations (ERSP) in four different frequency bands were considered for the analysis; 4 Hz, 6-15 Hz, 17-40 Hz and 75-170 Hz. LFPs recorded from electrodes in the hand area showed the largest change in ERSP for the highest frequency band (75-170 Hz) (p 0.05), while LFPs recorded from electrodes placed more medially in the arm area showed the largest change in ERSP for the lowest frequency band (4 Hz) (p 0.05). Furthermore, the spectral information from the <4 Hz and 75-150 Hz frequency bands was used to successfully decode the three dexterous grasp movements with an average accuracy of up to 81%. Although previous research has shown that multi-unit neuronal activity can be used to decode fine motor movements, these results demonstrate that LFP activity can also be used to decode dexterous motor tasks. This has implications for future neuroprosthetic devices due to the robustness of LFP signals for chronic recording.

Fig. 1.

A rhesus monkey was instructed to reach to and operate one of three switch targets (vertical toggle switch, pushbutton switch, horizontal toggle switch) in one of three spatial locations (centered around the primate’s right shoulder).

Fig. 2.

Four microelectrode arrays were implanted in M1, contralateral to the hand performing the movement (center image). a-d) Four plots corresponding to log ERSP activity from a single channel in each array. Four distinct frequency bands are highlighted: <4 Hz, 6–15 Hz, 17–40 Hz and 75–170 Hz. The solid and dotted traces are the ERSP values 500 ms and 10 ms before switch closure. The frequency axis is shown in log scale to facilitate visualization of ERSP change in the lower frequency bands. For clarity, data is not shown around 60 Hz. Trace (a) shows activity from an array placed laterally in the hand area, while trace (d) shows activity from an array placed medially in the arm area.

Fig. 3.

The temporal evolution of ERSP change from baseline of the electrode in Fig. 2a (averaged across all frequencies in each frequency band and all trials) for each switch task. The dotted line shows the time of switch closure. The net ERSP activity from 50 ms before to 20 ms after switch closure was used to decode the movement type using an ANN classifier.

Fig. 4.

Average decoding accuracy using spectral feature sets from each of the four frequency bands, as well as the raw LFP signal. The highest decoding accuracy was achieved using only spectral information in the <4 Hz and 75–170 Hz bands.