Columns

// Custom columns
    function custom_columns($args) {
        $args = array('cb' => '<input type="checkbox" />', 'title' => __('Title'), 'thumbnail' => __('Thumbnail'), 'author' => __('Author'), 'categories' => __('Categories'), 'tags' => __('Tags'), 'date' => __('Date'));
        return $args;
    }
    add_filter('manage_edit-slides_columns', 'custom_columns');

    // Image column
    function image_column($args, $post_id) {
        switch($args) {
            case 'thumbnail':
                echo the_post_thumbnail('admin-thumbnail');
            break;
        }
    }
    add_action('manage_slides_posts_custom_column', 'image_column', 10, 2);