Help with chi-square statistics with a dataset

Hi everyone,

I have a vector containing the numbers of same modality links between the neuron and its 5 closest other neurons for 41 neurons. lets call this vector X. Now I want to see with a Chi-square test whether neurons are clustered by modality or not. So the expected value is equal to the distribution of the 2 modalities of neurons in the sample. The observed value is the Value of X(i) where i is the neuron number (1:41). I already computed a new vector with for every neuron the (O-E)^2/E values, but I don't know how to go from there. - Do I have to use chi2pdf - Or chi2cdf and if so, - what should I use as X, - how do I plot it?

 I have tried so much but can't figure it out.

Thanks in advance!

Jesper