Network with cell assembly in TikZ

network.tex

\documentclass{standalone}
 
\usepackage{tikz,graphicx}
\usepackage{sfmath}
\usepackage{xifthen}
\renewcommand\familydefault\sfdefault

\usetikzlibrary{calc,fadings,decorations.pathreplacing}

\begin{document}
\begin{tikzpicture}[thick]
   \pgfmathsetmacro{\n}{10}  % sets number of units -1
   \pgfmathsetmacro{\r}{1.5} % sets radius
   \pgfmathsetmacro{\e}{0.5} % sets sparseness
   \pgfmathsetmacro{\s}{12346} % sets random seed
   \definecolor{patterncolor}{RGB}{0,0,0} % assembly color

   \coordinate (center) at (0,0);

   \foreach \i in {0,1,...,\n}{% This one doesn't matter
		% with the front lipids visible
		% top layer
		\pgfmathsetmacro{\dx}{rand*0.1}% A random variance in the x coordinate
		\pgfmathsetmacro{\dy}{rand*0.1}% A random variance in the y coordinate,

		\ifthenelse{ \isodd{\i} }{
			\node[circle,draw,patterncolor,fill] (neuron\i) at ($({\r*sin(\i*360/(\n+1))},{\r*cos(\i*360/(\n+1))})+(center)$) {} ;
		}{
			\node[circle,draw,lightgray,fill] (neuron\i) at ($({\r*sin(\i*360/(\n+1))},{\r*cos(\i*360/(\n+1))})+(center)$) {} ;
		}
   }

  \pgfmathsetseed{\s} % set random seed
  \foreach \source in {0,...,\n}
	\foreach \dest in {0,...,\n} {
		\pgfmathparse{rnd}
		\pgfmathsetmacro{\foobar}{\pgfmathresult}
		\ifthenelse{\lengthtest{\foobar pt<\e pt}}{
			\ifthenelse{\equal{\source}{\dest}}{
			}{
				%\ifthenelse{\isin{\source}{13578} \AND \isin{\dest}{13578}}{
				\ifthenelse{ \isodd{\source} \AND \isodd{\dest} }{
				%\ifthenelse{\source<5 \AND \dest<5}{
					\draw[->,patterncolor,thick] (neuron\source) to (neuron\dest);
				}{
					\draw[->,lightgray] (neuron\source) to (neuron\dest);
				}
			}
		}{}
	}

 \end{tikzpicture}
\end{document}