If you have the Signal Processing Toolbox, try PYULEAR, PBURG, PCOV, PMCOV. Those will give you a periodogram for a given time slice.
You can either call it once per time slice, or if you'd like to do it all in one shot, you can give it a column for each estimate. Something like this pseudo-code:
function pburgspectrogram(x, order, nwin, noverlap, nfft, Fs)
% x - the input signal
% order - the model order
% nwin - the number of samples for any one given estimate
% noverlap - the number of overlapping samples between windows
% nfft - how many points you want for the FFT.
% Fs - sample rate of signal
nx = length(x);
ncol = fix((nx-noverlap)/(nwin-noverlap));
coloffsets = (0:(ncol-1))*(nwin-noverlap);
rowindices = (1:nwin)';
xin = x(rowindices+coloffsets);
T = (coloffsets+(nwin/2)')/Fs;
[Pxx,F] = pburg(xin,order,nfft,Fs);
imagesc(T, F, 10*log10(abs(Pxx)+eps));
set(gca,'YDir','normal');
xlabel('Time');
ylabel('Frequency');
colorbar;
Example
load mtlb
pburgspectrogram(mtlb, 6, 128, 120, 128, Fs);
