The ability to project the self forward in time to pre-experience personal events is referred to as episodic future thinking. Different theories have been proposed to try to explain the neurocognitive mechanisms underlying episodic future thinking. In this paper we focus on studies concerning the episodic prospection capacity in cognitive aging and in neurodegenerative diseases such as Alzheimer's disease and semantic dementia. Older adults usually produce fewer episodic details than young adults when recalling past events and when imagining future events. Patients with early to moderate Alzheimer's disease have impaired capacity in the generation of episodic details for retrieved past events and imagined future events. Similarly patients with early to moderate semantic dementia have difficulties in episodic future thinking whereas they succeed to retrieve episodic past events. These patterns are discussed with regard to the respective role of the episodic and personal semantic representations in future personal thoughts as a function of temporal distance by purposing a new neurocognitive model (TEDIFT).