Variations in Clustering of Multielectrode Local Field Potentials in the Motor Cortex of Macaque Monkeys during a Reach-and-Grasp Task

Examples of spectrograms of the LFP activity, during different sessions, aligned at Pellet drop (Time = 0; Pellet drop served as the GO cue) averaged across all trials and electrodes for the indicated movement type (ipsilateral or contralateral) and brain area of the session.

Illustration of hierarchical clustering technique. a, LFP spectral power at 2.5 Hz (scale on the right) for all the electrodes from a single trial of Monkey M. Each horizontal line corresponds to the LFP spectral power of one recorded electrode for the entire trial. The trial epochs are indicated by vertical black lines. b, Dendrogram obtained by using hierarchical clustering on the data of a. The dashed black vertical line indicates a distance of 150 (a.u.). This line was used as the point at which cluster numbers were counted. c, Data of spectrogram in a reorganized to follow the dendrogram presented in b. The clustering algorithms was applied to the entire trial and led to the clustering of information from electrodes with correlated spectral power.

a, b, Heatmap of the average absolute pairwise correlation of LFP spectral power between electrodes at different frequencies during each phase of the movement for one trial of Monkeys S and M. c, Average absolute pairwise correlation of spectral power for the delta band for all the trials in one session for Monkey S under different trial conditions. Error bars indicate the variance between trials. d, Average of the absolute pairwise correlation in the delta band for all trials and sessions performed by the two monkeys (two sessions per monkey). Note that this included different pointing conditions. Error bars indicate the variance between trials.

Clustering of the activity in delta band recorded from all the electrodes during one trial of Monkey M. As in Figure 3, each line shows activity recorded from one electrode during the trial. The area of origin of the electrode is color coded by the column on the left of each graph (color legend on the left). It is to be noted that clusters are not restricted to a particular area of the motor cortex and contain LFPs from different regions. The black lines indicate the timing of the task epochs. a, b, are from two different sessions of Monkey M.

Average normalized cluster number in the delta band as a function of task epochs. Clusters were found using correlations. a, b, For all the trials of the same task conditions for Monkey M. There are trials from two sessions presented. c, d, For all the trials of the same task conditions for Monkey S (over two sessions). e, For all the trials of both sessions of both monkeys. In this case, the average normalized cluster number for each task epoch is the average of the values from the five subperiods. Error bars indicate the variance.