Figure 8. Increased footshock intensity increased conditioned freezing in adult rats.

Footshock intensity was increased for conditioning of adult rats to produce greater conditioned freezing levels during testing that were equivalent to adolescent conditioned freezing (0.1 mA above threshold intensity). (A) A small increase (0.1 mA) of footshock intensity did not have a significant effect on acquisition of fear conditioning. (B) There was no significant effect of the small increase of footshock intensity on freezing during the last conditioning trial. (C) Use of suprathreshold footshock intensity caused an increase of conditioned freezing in adult rats measured during fear testing, compared to threshold footshock intensity. (D) There was significantly greater conditioned freezing during the initial testing phase and late testing phase (E) when a suprathreshold footshock was used, compared to a threshold footshock intensity. (F) Suprathreshold footshock intensity led to conditioned freezing in adult rats that was similar to the conditioned freezing of adolescent rats at the threshold intensity. (G) There was no significant difference in the initial conditioned freezing during testing between adult rats conditioned with the suprathreshold intensity and adolescent rats conditioned with the threshold intensity. (H) However, there was greater conditioned freezing during the later phase in adult rats conditioned with suprathreshold footshock compared to adolescent rats conditioned with threshold footshock intensity. Black represents groups using threshold footshock intensity (adolescents or adults), grey represents groups using suprathreshold footshock intensity. *p < 0.05, **p < 0.01 compared between threshold and suprathreshold non-restraint groups.