Trouble adding TRUE parameter for next/previous posts

I am currently upgrading my theme (iA3) to a new version and am trying to redo a few customizations that were done for me to the old version.

I would like the next and previous links on a page to only show posts within the same category ‘portfolio’.

I have done some searching and found this code:

<?php next_post_link('%link', 'Next post in category', TRUE); ?>

But I can’t sort out where the TRUE parameter goes in the code below as it is formatted differently. Nothing seems to work.

<ul>
 <?php if(get_previous_post()): ?>

<li><?php previous_post_link('%link', __('? Previous', 'ia3')); ?></li>
<?php else: ?>

<li><?php _e('? Previous', 'ia3'); ?></li>
<?php endif; ?>

<?php edit_post_link(__('Edit', 'ia3'), '<li>', '</li>'); ?>

<?php if(get_next_post()): ?>

<li><?php next_post_link('%link',  __('Next ?', 'ia3')); ?></li>
<?php else: ?>

<li><?php _e('Next ?', 'ia3'); ?></li>
<?php endif; ?>
</ul>

Any ideas where I would add the ‘TRUE’ parameter to this new code so only posts from the same category show when clicking next or previous?

I appreciate anyone that has read this far and any help you can provide.