Next Post and Previous Post navigate only in same category

I have already read up on it and tried numerous times and I just can't get it to work. I have already read: http://codex.wordpress.org/Function_Reference/previous_post_link but everytime i try i just get errors or it doesn't work at all. Here is what my code looks like:

<div class="nav-previous">
<?php next_post_link( '%link', '<span class="meta-nav">' . _x( '←', 'Previous post link', 'thirdstyle' ) . '</span> %title' ); ?></div>

<div class="nav-next">
<?php previous_post_link( '%link', '%title <span class="meta-nav">' . _x( '→', 'Next post link', 'thirdstyle' ) . '</span>' ); ?></div>

I just want it so that the Previous post and Next Post links only navigate to posts with-in the same category of the current post.

I hope someone can help me out!

 

<?php next_post_link('format', 'link', 'in_same_cat', 'excluded_categories'); ?>

You would write "TRUE" in place of the "in_same_cat" text.