Fig. 2: Overtraining leads to impaired extinction (Ext-RP) and persistent avoidance.

a Rats conditioned for 8d or 20d were presented with tones in the absence of shock over 4 days, with a Plexiglas barrier inserted to block access to the platform (Ext-RP). Initially, both groups showed equivalent freezing, but extinction of freezing was impaired in the 20d group, as was extinction of suppression of bar pressing (inset). Rats in the 20d group were also impaired in their extinction of press suppression during the pre-tone period. b One day following Ext-RP training, rats were tested with the barrier removed (Test 1). The 20d group showed excessive avoidance compared to the 8d group, during both the pre-tone and tone periods, but there was no group difference in freezing. c The 20d group also showed elevated anxiety, as indicated by reduced time spent in the open arms of an elevated plus maze (EPM). d, e Distribution of avoidance values (time on platform) during Test 1. Rats showing more than 70% time on platform were classified as persistent (P), whereas those showing less than 70% were classified as non-persistence (NP). 8d group: n = 38; 20d group: n = 40. For EPM, 8d group: n = 20; 20d group: n = 14. Ext-RP data shown as blocks of three trials, whereas Test 1 data shown as single trial. All data are mean ± SEM. *p < 0.05, **p < 0.01.