Did you try just a brute force approach? Untested code (because you forgot to actually attach your variable in a mat file).
[rows, columns] = size(spikes);
numElements = zeros(rows, columns);
for col = 1 : columns
for row = 1 : rows
thisCellsContents = spikes(row, col);
numElements(row, col) = numel(thisCellsContents);
end
end
mostElements = max(numElements(:));
% Find out what row and column it appears at (may be more than 1 cell).
[maxRowIndexes, maxColIndexes] = numElements == mostElements;
It's straightforward and intuitive. But I'm sure someone will come up with a shorter but more cryptic way of using cellfun() if you'd rather do it that way.
