How to Call Categorys Subcategory in Particular Category.   Create CMS Block in Magento. Here call your brand.phtml file. Like Below Code.

After this call this block in Category.
And Put Below Code in brand.phtml file.
$category = Mage::getSingleton('catalog/layer')->getCurrentCategory();
$categories = $category->getCollection()
        ->addAttributeToSelect(array('name', 'thumbnail'))
        ->addAttributeToFilter('is_active', 1)
<div class="item">
<ul class="subcategories">
    <?php foreach ($categories as $category): ?>
        <li class="brands">
            <a href="<?php echo $category->getUrl() ?>"><img src="<?php echo Mage::getBaseUrl('media') . 'catalog' . DS . 'category' . DS . $category->getThumbnail() ?>" width="200" height="200" alt="<?php echo $this->htmlEscape($category->getName()) ?>" />
                <h2 class="product-name"><?php echo $category->getName() ?></h2>
      <?php endforeach; ?>
<div class="clear"></div>

  After this you see your Categorys Subcategories name and image Display in your category.