You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: read_spike6mat_header.m
    path of file: ./repos/spm12/external/fieldtrip/fileio/private
    
    the code of the file until where you have to start completion: function header = read_spike6mat_header(filename)

% read_spike6mat_header() - read Matlab files exported from Spike 6
%
% Usage:
%   >> header = read_spike6mat_header(filename);
%
% Inputs:
%   filename - [string] file name
%
% Outputs:
%   header   - FILEIO toolbox type structure
% _______________________________________________________________________

    
function header = read_spike6mat_header(filename)

% read_spike6mat_header() - read Matlab files exported from Spike 6
%
% Usage:
%   >> header = read_spike6mat_header(filename);
%
% Inputs:
%   filename - [string] file name
%
% Outputs:
%   header   - FILEIO toolbox type structure
% _______________________________________________________________________
% Copyright (C) 2008 Institute of Neurology, UCL
% Vladimir Litvak

if nargin < 1
  help read_spike6mat_header;
  return;
end