Here's one way (there are almost certainly slicker ways!):
% Arbitrary data
x = 0:10:70;
y = [ 5 2 3 7 8 1 7 4];
% Labels
L1 = ["Sham" "Active"];
L2 = ["Theta" "Gamma"];
L3 = ["90-min" "1-week"];
% Positions for text
yp1 = -0.5*ones(size(x));
yp2 = 2*yp1;
yp3 = -1.5;
% Bar chart
bar(x,y)
set(gca,'Position',[0.13 0.2 0.775 0.775]); % Make space for labels
set(gca,'XTickLabel','') % Remove numbers
% Insert text labels
for i = 1:2:length(x)
text(x(i)-4, yp1(i), L1(1))
text(x(i+1)-4, yp1(i), L1(2))
end
for i = 1:4:length(x)
text(x(i), yp2(i), L2(1))
text(x(i+2), yp2(i), L2(2))
end
text(x(2), yp3, L3(1))
text(x(6), yp3, L3(2))
This resuts in:
