While for regular product attributes like manufacturer, name, color, you can choose to include or exclude from search.
For product categories is not possible.
So if I go to the table "catalogsearch_fulltext", I see all the product attributes I decided to index for searches divided by | . Example:
Anai-751|Anais Lingerie|Anais Lingerie|Anais Lingerie|Anais Lingerie|Anais Lingerie|anais - aura body black|anais - aura body black|anais - aura body black-NERO-S|anais - aura body black-NERO-XL|anais - aura body black-NERO-L|1
How can I add also product categories to that column ? So when magento searches using fulltext can also use product categories names as search indexes.