visual_mu_synch {motoRneuron}

Determination of Motor Unit Synchronization by Visual Inspection of Cross Correlation Histogram

Description

Calculates the time-domain synchronization indices CIS, k', k'-1, S, E, SI (detailed below) between two motor unit discharge trains based on a visual determination of peaks in the cumulative sum graph configured from the cross correlation histogram. Function calls dygraphs (allows zooming) to present the normalized cumulative sum. User is prompted to input the left and right boundaries (time points in seconds) of peak seen as a dramatic slope increase in the cumulative sum graph around 0. If no peak is detected, a default +/- 5 ms is used.

Dygraphs package is leveraged in this function to plot the cumulative sum graph in Rstudio's viewer. This allows for interactions within the graph, specifically zoom and unzoom.

Usage

visual_mu_synch(motor_unit_1, motor_unit_2, order = 1, binwidth =
 0.001, get_data = T, plot = F)

Arguments

motor_unit_1, motor_unit_2

Numeric vectors of strictly increasing numbers denoting sequential discharge times (in seconds) of a motor unit or neuron or any strictly increasing point process.

order

Numeric as a positive integer for the number of forward and backward orders for calculating recurrence times. Default = 1.

binwidth

Numeric as a positive for the bin allocation size for computational histogram. Default = 0.001 sec or 1 ms.

get_data

T/F logical for outputting motor unit data. Default is TRUE.

plot

T/F logical for outputting the cross correlation histogram. Default is FALSE.

Value

A list of lists containing motor unit data (the names of each discharge train used, number of discharges, the interspike intervals (ISI), mean ISI, and the recurrence times associated with each order) and synchronization indices. CIS = frequency of synchronized discharges. k' = ratio of total discharges in peak to expected discharges in peak. k'-1 = ratio of synchronized discharges to expected discharges in peak. S = ratio of synchronized discharges to total number of discharges of both motor units. E = ratio of synchronized discharges to non-synchronized discharges. SI = ratio of synchronized discharges to reference motor unit discharges.

References

Nordstrom, M.A., Fuglevand, A.J., Enoka, R.M. (1992) Estimating the Strength of Common Input to Human Motoneurons from the Cross-Correlogram. Journal of Physiology 453, pp. 547-574

Examples

  
  x <- c(0.035, 0.115, 0.183, 0.250, 0.306, 0.377, 0.455, 0.512, 0.577,
  0.656, 0.739, 0.821, 0.866, 0.950, 1.014, 1.085, 1.153, 1.213, 1.279,
  1.355, 1.431, 1.482, 1.551, 1.631, 1.692, 1.749, 1.832, 1.897, 1.964,
  2.106, 2.149, 2.229, 2.302, 2.384, 2.420, 2.505, 2.592, 2.644, 2.722,
  2.801, 2.870, 2.926, 3.011, 3.098, 2.030, 3.183, 3.252, 3.319, 3.395,
  3.469, 3.560, 3.589, 3.666, 3.744, 3.828, 3.876, 3.943, 4.020, 4.104)
  x <- sort(x)
  y <- sort(jitter(x))
  y <- round(y, digits = 3)
  visual_mu_synch(x, y, order = 1, binwidth = 0.001, get_data = TRUE,
  plot = FALSE)