When we refer to something "in the head," we typically mean it's a mental or emotional construct. There are several synonyms for this phrase, depending on the context. For example, "in the mind" refers to something that's being thought about or imagined, whether true or not. "In the psyche" also implies something internal, but with a greater emphasis on the unconscious or subconscious aspects of the self. "In the brain" is a more scientific term that suggests biological processes, such as cognition or memory. Finally, "in one's thoughts" is a more general phrase that doesn't specify where the thoughts are coming from.