How to remove letters outside a contour shape in tikz

Question

I wish to remove parts of the letter outside the contour that forms the shape of the brain below.

\documentclass[10pt]{standalone}
\usepackage{pgf,tikz}
\usepackage{libertine}

\begin{document}

 \begin{tikzpicture}

 \draw(11.61697,6.215) node {\scalebox{13.6}{\color{purple!77}math} \scalebox{6.915}{\color{gray}\&} };
 \draw(11.7,3) node {\scalebox{14.7}{\color{gray} physics}};
 \draw(10.7,.32) node {\scalebox{8.59}{\color{cyan!96}MATTER}};


 \draw[ line width=1.2mm] plot [smooth,tension=.6] coordinates { (11.611676609979014,-1.1158187173456824)  
    (12.557159646551849,-0.845680706896301)  
    (13.603944437043202,-0.6768444503654376)  
    (14.397474842738259,-0.42359006556914264)  
    (15.258539751045662,-0.1703356807728476)  
    (16.27155729023084,-0.10280117816050227) 
    (17.16638944984442,-0.20410293207902028) 
    (18.07810523511108,-0.13656842946667494)  
    (18.922286517765396,0.25175496055431074)  
    (19.445678913011072,1.2141216227802318)  
    (19.51321341562342,2.277790038924671)  
    (18.82098476384688,3.5778292142123185)  
    (18.230057865988858,4.371359619907376)  
    (17.740432722049352,4.793450261234534)  
    (17.520945588559233,5.418144410398729) 
    (16.778066059823434,5.840235051725887)  
    (16.305324541537015,6.38051107262465)  
    (15.579328638454303,6.6675327087271175)  
    (14.566311099269123,7.089623350054276)  
    (13.51952630877777,7.342877734850571) 
    (12.50650876959259,7.477946740075262)  
    (11.594792984325927,7.477946740075262)  
    (10.649309947753093,7.410412237462917)  
    (9.602525157261741,7.224692355278967)  
    (8.623274869382733,7.055856098748103)  
    (7.863511714993848,6.785718088298722)  
    (6.884261427114841,6.5493473291555135) 
    (5.9050111392358335,5.87400230303206)  
    (5.195898861806207,5.36749353343947)  
    (4.554321086988926,4.371359619907376)  
    (4.250415825233373,3.999919855539477)  
    (3.9465105634778186,3.6622473424777504)  
    (3.7945579326000414,3.0206695676604696)  
    (3.8452088095593004,2.3284409158839297)  
    (3.980277814783991,1.7712812693320807) 
    (4.047812317396336,1.3998415049641815) 
    (4.2166485739272,1.0115181149431958)  
    (4.3686012048049765,0.7413801044938144)  
    (4.571204712642013,0.23487133490122442) 
    (4.959528102662999,-0.1703356807728476)  
    (5.398502369643244,-0.47424094252840165)  
    (6.006312893154352,-0.5755426964469197) 
    (6.61412341666546,-0.5248918194876606)  
    (7.25570119148274,-0.47424094252840165)  
    (7.812860838034589,-0.6937280760185239)  
    (8.150533351096316,-1.1327023429987686)  
    (8.707692997648165,-1.5716766099790134)  
    (9.315503521159274,-1.8924654973876538)  
    (10.,-2.) 
    (10.919447958202474,-1.605443861285186) (11.611676609979014,-1.1158187173456824) };

 \end{tikzpicture}

\end{document}

Answer 1

As pointed out by Symbol 1, you can use \clip for that. A slight subtlety is that clip cannot be used with other options. So you need to use the path twice. There are many possibilities to handle this, one of them is to use the use path trick which allows one to recycle paths. Other minor points are that you were passing options to plot which should be put into the path, and that you need to add the nodes after the clip. Of course, I will be happy to remove this if Symbol 1 posts an answer.

\documentclass[10pt]{standalone}
\usepackage{tikz}
\usepackage{libertine}
\makeatletter % from https://tex.stackexchange.com/a/127045/121799
\tikzset{use path/.code=\tikz@addmode{\pgfsyssoftpath@setcurrentpath#1}}
\makeatother

\begin{document}

\begin{tikzpicture}
 \draw[line width=1.2mm, color=blue, fill=gray!20,save path=\pathA] plot [smooth,tension=.6] coordinates { (11.611676609979014,-1.1158187173456824)  
    (12.557159646551849,-0.845680706896301)  
    (13.603944437043202,-0.6768444503654376)  
    (14.397474842738259,-0.42359006556914264)  
    (15.258539751045662,-0.1703356807728476)  
    (16.27155729023084,-0.10280117816050227) 
    (17.16638944984442,-0.20410293207902028) 
    (18.07810523511108,-0.13656842946667494)  
    (18.922286517765396,0.25175496055431074)  
    (19.445678913011072,1.2141216227802318)  
    (19.51321341562342,2.277790038924671)  
    (18.82098476384688,3.5778292142123185)  
    (18.230057865988858,4.371359619907376)  
    (17.740432722049352,4.793450261234534)  
    (17.520945588559233,5.418144410398729) 
    (16.778066059823434,5.840235051725887)  
    (16.305324541537015,6.38051107262465)  
    (15.579328638454303,6.6675327087271175)  
    (14.566311099269123,7.089623350054276)  
    (13.51952630877777,7.342877734850571) 
    (12.50650876959259,7.477946740075262)  
    (11.594792984325927,7.477946740075262)  
    (10.649309947753093,7.410412237462917)  
    (9.602525157261741,7.224692355278967)  
    (8.623274869382733,7.055856098748103)  
    (7.863511714993848,6.785718088298722)  
    (6.884261427114841,6.5493473291555135) 
    (5.9050111392358335,5.87400230303206)  
    (5.195898861806207,5.36749353343947)  
    (4.554321086988926,4.371359619907376)  
    (4.250415825233373,3.999919855539477)  
    (3.9465105634778186,3.6622473424777504)  
    (3.7945579326000414,3.0206695676604696)  
    (3.8452088095593004,2.3284409158839297)  
    (3.980277814783991,1.7712812693320807) 
    (4.047812317396336,1.3998415049641815) 
    (4.2166485739272,1.0115181149431958)  
    (4.3686012048049765,0.7413801044938144)  
    (4.571204712642013,0.23487133490122442) 
    (4.959528102662999,-0.1703356807728476)  
    (5.398502369643244,-0.47424094252840165)  
    (6.006312893154352,-0.5755426964469197) 
    (6.61412341666546,-0.5248918194876606)  
    (7.25570119148274,-0.47424094252840165)  
    (7.812860838034589,-0.6937280760185239)  
    (8.150533351096316,-1.1327023429987686)  
    (8.707692997648165,-1.5716766099790134)  
    (9.315503521159274,-1.8924654973876538)  
    (10.,-2.) 
    (10.919447958202474,-1.605443861285186) (11.611676609979014,-1.1158187173456824) };
   \clip[use path=\pathA];
   \draw(11.61697,6.215) node {\scalebox{13.6}{\color{purple!77}math} \scalebox{6.915}{\color{gray}\&} };
   \draw(11.7,3) node {\scalebox{14.7}{\color{gray} physics}};
   \draw(10.7,.32) node {\scalebox{8.59}{\color{cyan!96}MATTER}};

 \end{tikzpicture}

\end{document}