This study investigated the differences between past and future temporal discounting in terms of neural activity in relation to temporal distance. Results show that brain regions are engaged differently in past and future temporal discounting. This is likely because past temporal discounting requires memory reconstruction, whereas future temporal discounting requires the processing of uncertainty about the future. In past temporal discounting, neural activity differed only when preferences were made between rewards received one hour prior and rewards received further in the (...) past. The peak amplitudes of P2 and P3 varied as the temporal distance increased from 2 weeks to 50 years. In future temporal discounting, neural activity differed only when preferences were evaluated between two delayed rewards. The delay conditions and had a significant influence on P2 and N2. Findings indicate the existence of different decision-making systems operating in past and future temporal discounting. (shrink)