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: spm_gx_state_fmri.m
    path of file: ./repos/spm
    
    the code of the file until where you have to start completion: function [y] = spm_gx_state_fmri(x,u,P,M)
% Simulated BOLD response and copied state vector
% FORMAT [y] = spm_gx_state_fmri(x,u,P,M)
% y          - BOLD response and copied state vector
%
% x          - state vector     (see spm_fx_fmri)
% P          - Parameter vector (see spm_fx_fmri)

    
function [y] = spm_gx_state_fmri(x,u,P,M)
% Simulated BOLD response and copied state vector
% FORMAT [y] = spm_gx_state_fmri(x,u,P,M)
% y          - BOLD response and copied state vector
%
% x          - state vector     (see spm_fx_fmri)
% P          - Parameter vector (see spm_fx_fmri)
% M          - model specification structure (see spm_nlsi)
%
% The `copied state vector' passes the first hidden variable in each region
% to the output variable y, so that 'neural activities' can be plotted 
% by spm_dcm_generate.m
%
% See spm_fx_fmri.m and spm_dcm_generate.m
%__________________________________________________________________________
 
% Will Penny
% Copyright (C) 2011-2022 Wellcome Centre for Human Neuroimaging


y = spm_gx_fmri(x,u,P,M);

% Copy first hidden state (neural activity) from each region
nregions = size(x,1);
for i=1:nregions
    y = [y;x(i,1)];
end