How to interpret the values of the mixed effects model?

Good afternoon, please tell me how to interpret the results of the table, I processed an experiment related to mental calculations using a mixed effects model (conditions in the photo : subtraction of examples presented in text form) The data are presented for a group of 10 people, I UNDERSTAND CORRECTLY THAT THETA is the size of the amplitude of the hemodynamic response, WHY SUCH A LARGE REACTION and HOW TO INTERPRET NEGATIVE VALUES