Discharge characteristics of motor units during long contractions

Michael Pascoe, M.S.

Background

• Motor unit

• Functional quantum of the neuromuscular system

• Comprises an alpha MN, its axon, and all the muscle fibers it innervates

Research Questions

•How long can a human voluntarily activate a motor unit?

•How does the discharge behavior change with time?

Surface EMG

Abduction force

Fine wire SMU

Spike2 - Sample Data

100 s

0.75 V

1 V

5 %MVC

0.75 V

sEMG

Force

iEMG

MU

Flowchart

Interspike Intervals

Motor Unit Discharge Times

Filter Out Long Intervals (> 250 ms)

Filter Out Short Intervals (< 10 ms)

Divide Into 5 Equal Duration Epochs

Calculate Discharge Characteristics

Spike2 Data

SpikeStats.txt

mu_anal_longdur.m

Input

Epoch Boundaries

100 s

0.75 V

1 V

5 %MVC

0.75 V

sEMG

Force

iEMG

MU

epoch(1) epoch(2) epoch(3) epoch(4) epoch(5)

first spike last spike

Creating Equal Duration Epochsfor i = 1:length(dis) if (dis(i) < epoch1_end) epoch(1).values(j) = dis(i); j=j+1; elseif (dis(i) > epoch1_end & dis(i) < epoch2_end) epoch(2).values(k)=dis(i); k=k+1; elseif (dis(i) > epoch2_end & dis(i) < epoch3_end) epoch(3).values(l)=dis(i); l=l+1; elseif (dis(i) > epoch3_end & dis(i) < epoch4_end) epoch(4).values(m)=dis(i); m=m+1; elseif (dis(i) > epoch4_end & dis(i) <= dis(end)) epoch(5).values(n)=dis(i); n=n+1; endend

Create interspike intervals% Determine interspike interval in seconds isi(i).values = diff(epoch(i).values);

% Remove ISIs greater than 0.25 or less than 0.01 s (<4 or >100pps) isi(i).values = isi(i).values(find(isi(i).values<0.25 & isi(i).values>0.01)); sizeisifilt(i).values = size(isi(i).values);

Filter interspike intervals

Discharge Characteristics

• Mean discharge rate

• Standard deviation of discharge rate

• Coefficient of variation for discharge rate

• Standard error of the mean of discharge rate

• Mean interspike interval

• Standard deviation of interspike interval

• Coefficient of variation for interspike interval

Stein et al. Nat Rev Neurosci 2005, 6: 389-397

Output

Output

• A single text file (one trial)

• Subject initials and date preserved

• _SpikeStats.txt in place of _Times.txt

• Column headers in first row

• Output variable values in five rows

Output

Output

Trial Name Mean DR (pps-direct) Mean DR (pps-estimate) SD DR (pps) SEM DR (pps) CV DR (pps) Mean ISI (ms) SD ISI (ms) CV ISI (%) Start time (s) End time (s) Train Duration (s) Impulses (No.) ISIs (No.) ISIs <10ms ISIs >250ms ISIs removed

BKB_(11_21_2007)_Times 11.24653 11.228448 0.825317 0.825317 7.350231 89.059501 21.935176 24.629799 698.31423 753.63023 55.30595 622 621 0 0 0

10.682879 10.664742 0.797252 0.797252 7.475587 93.766922 22.891283 24.412963 753.63023 808.94623 55.13495 589 588 0 0 0

11.581364 11.722199 0.748408 0.748408 6.384536 85.308229 18.64768 21.859181 808.94623 864.26223 55.17485 639 638 0 2 2

9.844349 10.698871 1.000401 1.000401 9.350527 93.467804 28.586902 30.584759 864.26223 919.57823 55.15855 543 542 0 13 13

9.934456 10.455567 1.093795 1.093795 14.913897 92.346243 55.07046 40.389043 919.57823 974.89423 55.18775 39 38 0 46 46

ValidationEpoch(5) MATLAB Spike2

MeanDR (pps) 7.334067 7.33Std Dev DR (pps) 1.093795 1.09

CV DR (%) 14.913897 14.91

Mean ISI (ms) 136.35 136.35Std Dev ISI (ms) 55.07046 55.07

CV ISI (%) 40.389043 40.39

Start Time (s) 919.57823 919.578End Time (s) 974.89423 974.894Train Dur (s) 55.18775 55.188

No. Impulses 39 39No. ISIs 38 38

ISIs < 10 ms 0 0ISIs > 250 ms 46 46

In the near future...

•Analysis of surface EMG

•Analysis of index finger abduction force

•Distribution statistics for discharge times