Keep the handles to the axes you create:
axs(1) = subplot(1,2,1);
axs(2) = subplot(1,2,2);
Then make the axes you want to plot on the current axes before plotting:
for i1 = 1:17,
g = randn(1);
if g > 0
axes(axs(2))
plot(randn(1,23),'linewidth',2,'color',rand(1,3))
hold on
else
axes(axs(1))
plot(randn(1,23),'linewidth',1,'color',rand(1,3))
hold on
end
end
HTH